Paleogeographical and paleoenvironmental significance of ostracodes from the Pennsylvanian Nagaiwa Formation, northeast Japan

Abstract

The Early Pennsylvanian Nagaiwa Formation contains fossils such as corals, fusulinids, and ostracodes, and its age and depositional environments have been determined by fusulinids and sedimentology. In this study, I describe the ostracode assemblages from the Nagaiwa Formation. Moreover, I provide a reconstruction of the paleogeography of northeastern Japan during the Early Pennsylvanian by comparing this ostracode assemblage with assemblages from other regions during the same period. Thirty ostracode species, including 12 genera, have been identified, most of which are endemic species and 10 of which are new: Jordanites michinokuensis n. sp., Thuringobolbina ikeyai n. sp., Aechmina iwatensis n. sp., Pseudobythocypris asiatica n. sp., P. zipangu n. sp., P. siveteri n. sp., Platyrhomboides tohokuensis n. sp., P. japonica n. sp., Healdia ofunatensis n. sp., and H. rikutyuensis n. sp. Two of these species are also found in central Japan. The ostracodes from the Nagaiwa Formation are unique when compared with any other similarly aged assemblages.

UUID: http://zoobank.org/c43f0787-4bb6-45d1-9c12-54a747c0b040

Introduction

Several attempts have been made to reconstruct the paleogeographic position of Japan in the Paleozoic. Tazawa (2004) mentioned that Japan originated in a subduction zone of the eastern margin of North China during the Early Ordovician, and the position did not change until the late Permian–Late Jurassic. On the other hand, Ehiro (2001) considered Japan as located near South China from the early Paleozoic to the middle Permian or Mesozoic as a “microcontinent.” Isozaki et al. (2010) applied age estimation methods using detrital zircons in Paleozoic sedimentary rocks from Japan, compared various zircon ages from adjacent areas and considered the paleogeographic position of Japan. The typical peaks of zircon ages from the Paleozoic of Japan indicate that it originated as arcs outboard from South China (Isozaki et al., 2011). With further data from zircon ages, Isozaki et al. (2014) proposed “Greater South China,” which expands from the South China craton to the South Kitakami belt of Japan, via the East China Sea. He also explained that the similarity of brachiopod assemblages between Japan and Northeast China can be explained by the northward extension of Greater South China where Northeast Japan is located (Isozaki, 2019). Recently, Wakita et al. (2021) collected detrital zircon ages and examined igneous rocks in the West Pacific region. They concluded that Japan initially was situated on the continental margin of Gondwana during the early–middle Paleozoic; then, with the break-up of the Gondwana margin, South China and the Japan arc were separated from Gondwana during the Late Devonian–Carboniferous. Williams et al. (2014) cautioned that consideration of life strategy and facies control should be factored in when drawing biogeographical conclusions from Japanese lower and middle Paleozoic faunas. They noted widely divergent signals from different groups as evidence for this caution.

Ostracodes are small crustaceans (usually <1 mm) that bear a bivalved calcitic shell. Among them, myodocope ostracodes are benthic or planktonic, and podocope ostracodes are benthic or nectobenthic. Here, I examined podocopes because Recent species are demonstrably useful for defining biogeographical regions (Titterton and Whatley, 1988; Tanaka, 2008) and therefore they are important taxa for reconstructing paleogeography (Schallreuter and Siverter, 1985; Williams et al., 2003; Perrier and Siveter, 2014; Tanaka et al., 2019; but see Pour et al., 2011; Mohibullah et al., 2012). In Japan, some Paleozoic ostracodes were described from Southwest Japan (Kuwano, 1987; Tanaka et al., 2012, 2013, 2018, 2019; Stocker et al., 2016; Siveter et al., 2018). However, little is known about Paleozoic ostracodes from Northeast Japan, and all the existing works were written before the 1970s using optical photographs only (Ishizaki, 1963, 1964a, b, 1967, 1968). This study aims to describe the ostracodes from the Pennsylvanian Nagaiwa Formation that previously were studied by Ishizaki (1963, 1964b) and consider the paleogeographic position of Japan during the Pennsylvanian based on the ostracode assemblages.

Geological setting

The geology of Japan is subdivided into Southwest Japan and Northeast Japan by a large structural lineament “Fossa Magna” (Koto, 1888) (Fig. 1.1). In Northeast Japan, the South Kitakami belt is composed of Ordovician ultramafic, igneous, and metamorphic rocks, Silurian/Devonian igneous rocks, and Paleozoic–Mesozoic sedimentary rocks (Isozaki, et al., 2010; Kawamura et al., 2013). Carboniferous strata are sporadically distributed in the northern part of Nagaiwa, ~15 km NNW of Ofunato City, Iwate Prefecture, Japan (Fig. 1.2).

Figure 1. Locality map of the Nagaiwa Formation. (1) Northeast Japan (NE Japan) and Southwest Japan (SW Japan) are geologically divided by Fossa Magna. Rectangular box shows area in Figure 1.2. (2) Magnified map of South Kitakami belt showing Paleozoic and Mesozoic (Triassic/Jurassic) rocks that are sporadically distributed and deformed by many faults (map based on Isozaki et al., 2010, and Kawamura et al., 2013). (3) Detailed geological map of the study area and sample locality. The geological map, sample locality, and each number of sample locality is based on Kobayashi (1973). White circle shows that ostracodes were recovered, shaded circles show that there were no ostracodes. Abbreviation: Fm., Formation; No., Number.

The Nagaiwa Formation unconformably overlies the Mississippian Onimaru Formation and is unconformably covered by the lower Permian Sakamotozawa Formation (Kobayashi, 1973). According to Kobayashi (1973), the Nagaiwa Formation is subdivided into Lowermost, Lower, Middle, and Upper members. The Lowermost Member consists of sandstone, mudstone, and no fossils. The Lower Member is composed of mudstone and black to gray massive limestone. The mudstone contains a sponge genus, Chaetetes, and the limestone contains many fossils such as fusulinids, crinoids, calcareous algae, bryozoans, corals, and small foraminifers. The Upper Member mainly consists of non-fossiliferous limestone, mudstone, and chert (Kobayashi, 1973). The Middle Member, which is formed of dark-gray to gray massive limestone and mudstone, contains many crinoids and fusulinids; sometimes, gastropods and small foraminifers occur in the limestone, which contains siliceous nodules. Based on the fusulinid biostratigraphy, the Lowermost and Lower members are comparable to the Millerella Zone, and the Middle and Upper members correspond with the Profusulinella Zone, showing that the Nagaiwa Formation was deposited during the early Bashkirian to early Moscovian (Kobayashi, 1973).

Materials and methods

Based on the lithologic character and reports of the fossils collected by Kobayashi (1973), I collected eight fossiliferous localities from the Nagaiwa area, Ofunato City, Iwate Prefecture, Northeast Japan (Figs. 1.3, 2). Approximately 2 kg of limestone rocks were collected from each sample locality. Among them, one sample was from the Lower Member at sample locality No. 25 of Kobayashi (1973), which is dark gray massive limestone; three samples (Loc. 38, 37, 53 of Kobayashi, 1973) were recovered from the Middle Member and consisted of dark gray massive limestone; and four samples (Loc. 46, 47, 56, 58 of Kobayashi, 1973) of light gray dolomitic limestone and some altered mudstones were collected from the Upper Member. The rocks were split into ~2–4 cm³, washed with running water, placed on a 16-mesh (1 mm) sieve attached to a 235-mesh (63 μm) sieve, and arranged in a bucket where the upper sieves were filled with 5% acetic acid. After two weeks, the sieves were picked up and rinsed in water inside a large bucket to remove the acid from residue. The residue was collected into a beaker and dried in an oven at 60°C for one day. The ostracode specimens were picked under a binocular microscope (Olympus SZH10) at ×20 magnification and stored in faunal slides.

Figure 2. Column of the Nagaiwa Formation, fusulinid biostratigraphy, and each horizon of sample locality and number of sample localities (altered Kobayashi, 1973). Abbreviations: E, Early; Eosch., Eoschubertella; Fm., Formation; L., Lower; LMM, Lowermost Member; Parast., Parastaffella; Pss., Pseudostafella.

Repositories and institutional abbreviations

Ishizaki's type specimens have been deposited in the Institute of Geology and Paleontology, Tohoku University, Sendai, Miyagi, Japan (IGPS-number); Jiang et al.'s (1995) types have been deposited in the Xinjiang Petroleum Administration Bureau (Xj-number). All figured specimens reported here have been preserved in the collection of the Tohoku University Museum (IGPS-number).

Systematic paleontology

The terminology of Paleozoic ostracodes follows Vannier et al., 1989.

Class Ostracoda Latreille, 1802
Subclass Podocopida Sars, 1866
Order Beyrichiocopida Pokorný, 1954
Suborder Beyrichicopina Scott, 1961
Superfamily Paraparchitoidea Scott, 1959
Family Paraparchitidae Scott, 1959
Genus Samarella Polenova, 1952

Type species

Samarella crassa Polenova, 1952 (VNIGRI Z5-116), from the upper part of the Givetian Stage of the central Devonian field, Samarkaya Luka (Syzran), Penza region (Yulovo-Ishim), Russia, by original description.

Samarella hataii Ishizaki, 1964
Figure 3.1–3.5

1964b

Samarella hataii, Ishizaki, p. 37, pl. 1, figs. 10a–c.

1977

Samarella ? hataii; Hanai et al., p. 15.

Figure 3. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–5) A carapace of Samarella hataii Ishizaki, 1964b, IGPS-112670; (1) left lateral view, (2) right lateral view, (3) dorsal view, (4) ventral view, (5) anterior view. (6–10) A right valve of Kirkbyella sp. 1, IGPS-112671; (6) outer lateral view, (7) inner lateral view, (8) dorsal view, (9) ventral view, (10) anterior view. (11–15) A right valve of Kirkbyella sp. 2, IGPS-112673; (11) external view, (12) internal view, (13) ventral view, (14) dorsal view, (15) anterior oblique view. (16–18) A right valve of Kirkbyella sp. 3, IGPS-112674; (16) external view, (17) internal view, (18) dorsal view. (19, 20) A left valve of Kirkbyella sp. 1, IGPS-112672; (19) outer lateral view, (20) inner lateral view. (21–24) A right valve of Kirkbyella sp. 4, IGPS-112675; (21) external lateral view, (22) internal view, (23) dorsal view, (24) anterior view. Scale bar = 200 μm.

Holotype

Holotype, a carapace IGPS-78405; type locality: Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian to Moscovian.

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One carapace, length = 640 μm, height = 308 μm, IGPS-112670.

Remarks

Ishizaki (1964b) placed this species into the genus Samarella with some doubt because the adductorial sulcus (S2) is present in the left valve but is missing from the right valve. Hanai et al. (1977) mentioned that the generic identification is questionable. The present study revealed there is no S2 in both valves, showing that Ishizaki's described S2 is the result of compression by fossilization, as he mentioned in the comments on the genus. Furthermore, the right valve overlaps the left valve in the dorsal area, and the left valve overlaps the right valve in the ventral area, which is the definition of the genus Samarella (Polenova, 1952). Samarella hataii is similar to Shivaella suppetia Sohn, 1971, from the Late Mississippian Platy Limestone Member of the Alapah Limestone, Little Chander Lake, Brooks Range, Alaska, USA, in sharing a widely arched umbo with that taxon, but it differs in that it has a widely arched anterior and ventral margins, an acute posterior margin, and no dorsal spine.

Suborder Palaeocopina Henningsmoen, 1953
Superfamily Kirkbyoidea Ulrich and Bassler, 1906
Family Kirkbyidae Ulrich and Bassler, 1906
Genus Kirkbyella Coryell and Booth, 1933

Type species

Kirkbyella typa Coryell and Booth, 1933 (Columbia University Paleo. Coll. Cat. No. 27545) from the Pennsylvanian Wayland Shale Member of the Graham Formation, Texas, USA, by original description.

Kirkbyella sp. 1
Figure 3.6–3.10, 3.19, 3.20

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Materials

A right valve, length = 541 μm, height = 406 μm, IGPS-112671; a left valve, height = 332 μm, IGPS-112672.

Remarks

Kirkbyella sp. 1 is similar to Kirkbyella typa Coryell and Booth, 1933, from the Pennsylvanian Wayland Shale Member of the Graham Formation, Texas, USA; it has a broad bend terminating in a knob-like structure, but K. sp. 1 differs from K. typa in that it has a straight dorsal margin, develops a narrow carina, and has an obliquely extending S2. This species is similar to Kirkbyella pterygia Jiang in Jiang et al., 1995, from the Pennsylvanian Shiqiantan Formation, northern slope of Bogduo Mountain, Xinjiang, China, in that it has a broad bend terminating in a knob-like structure, but it differs in that it has a smooth surface, broadly arched ventral margin, and obliquely extending S2. Kirkbyella sp. 1 is similar to K. sp. of Jiang et al. (1995), discovered from the Pennsylvanian Dongtujinhe Formation in the Boluohuolo Mountain, Wenquan area, Xinjiang, China, in that it has a smooth surface; however, K. sp. 1 is distinguished by the presence of an obliquely extending S2, a broadly arched ventral margin, and the broad bend terminating in a knob-like structure.

Kirkbyella sp. 2
Figure 3.11–3.15

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Materials

A right valve, length = 541 μm, height = 431 μm, IGPS-112673.

Remarks

Kirkbyella sp. 2 is similar to Kirkbyella typa of Coryell and Booth (1933) from the Pennsylvanian Wayland Shale Member of the Graham Formation, Texas, USA, with an undulated dorsal margin, but K. sp. 2 differs from K. typa in that it has an obliquely extending S2, fine reticulation, and a narrowly convex anterior margin. This species is also similar to Kirkbyella pterygia Jiang in Jiang et al., 1995, from the Pennsylvanian Shiqiantan Formation, northern slope of Bogduo Mountain, Xinjiang, China, in that it has a broad bend terminating in a knob-like structure, but it differs in that it has fine reticulation, a sub-parallelogram lateral outline, and an obliquely extending S2. Kirkbyella sp. 2 is similar to K. sp. of Jiang et al. (1995) discovered in the Pennsylvanian Dongtujinhe Formation in the Boluohuolo Mountain, Wenquan area, Xinjiang, China, in that it has a broad bend terminating in a knob-like structure; however, K. sp. 2 is distinguished by the presence of an obliquely extending S2, a sub-parallelogram lateral outline, and a fine reticulated surface.

Kirkbyella sp. 3
Figure 3.16–3.18

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Materials

A right valve, length = 652 μm, height = 357 μm, IGPS-112674.

Remarks

Kirkbyella sp. 3 has ornamentation that is similar to Kirkbyella sp. 2 from the same locality, but K. sp. 3 differs from K. sp. 2 in its longer and flatter lateral outline. This species is also similar to Kirkbyella pterygia Jiang in Jiang et al., 1995, from the Pennsylvanian Shiqiantan Formation, northern slope of Bogduo Mountain, Xinjiang, China, in that it has a broad bend terminating in a knob-like structure, but it differs in having a fine reticulation, a sub-parallelogram lateral outline, and an obliquely extending S2. Kirkbyella sp. 3 is similar to K. sp. of Jiang et al. (1995) discovered in the Pennsylvanian Dongtujinhe Formation in the Boluohuolo Mountain, Wenquan area, Xinjiang, China, in having a broad bend terminating in a knob-like structure; however, K. sp. 3 is distinguished by the presence of an obliquely extending S2, a sub-parallelogram lateral outline, and a finely reticulated surface.

Kirkbyella sp. 4
Figure 3.21–3.24

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Material

One right valve, length = 529 μm, height = 369 μm, IGPS-112675.

Remarks

Kirkbyella sp. 4 resembles Kirkbyella typa Coryell and Booth, 1933, from the Pennsylvanian Wayland Shale, Texas, USA, in that it has a straight but slightly posteriorly elongate S2. Kirkbyella. sp. 4 differs from K. typa in that it has a higher and shorter lateral outline, a straight dorsal margin, and finer ornamentation. Kirkbyella sp. 4 is also similar to Kirkbyella pterygia Jiang in Jiang et al., 1995, from the Pennsylvanian Dongtujinhe Formation at Boluohuolo Mountain, Wenquan area, Xinjiang, China, in that it has a prominent tubercle at the end of the ventral ridge. Kirkbyella sp. 4 differs from K. pterygia in that it has finer ornamentation, a wider flat area along the anterior margin, and a 4:3 length-height ratio in lateral view.

Genus Kirkbya Jones, 1859

Type species

Dithyrocaris permiana Jones, 1850 (type specimen was not designated), from the Permian limestone of Byer's Quarry northeast England, UK, by original description. Topotype specimens (PM OS 7305–7307) have been deposited in The Natural History Museum, London.

Kirkbya nipponica Ishizaki, 1964
Figure 4.1–4.4

1964b

Kirkbya nipponica Ishizaki, p. 32, pl. 1, figs. 3a, b.

1977

Kirkbya? nipponica; Hanai et al., p. 9.

Figure 4. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1, 2) A left valve of Kirkbya nipponica Ishizaki, 1964b, IGPS-112676; (1) external view, (2) internal view; (3, 4) a right valve of Kirkbya nipponica Ishizaki, 1964b, IGPS-112677; (3) external view, (4) ventral view. (5) Kirkbya nagaiwensis Ishizaki, 1964b, external view of right valve, IGPS-112678. (6, 7) A right valve of Kirkbya sp., IGPS-112682; (6) external view, (7) ventral view. (8–13) Deformed specimens of Kirkbya sarusawensis Ishizaki, 1968; (8) lateral view of left valve and (9) its ventral view, IGPS-112679; (10) lateral view of right valve and (11) its ventral view, IGPS-112680, (12) lateral view of juvenile specimen and (13) its ventral view, IGPS-112681. Scale bar = 400 μm.

Types

Holotype, one right valve IGPS-78392; paratype, one left valve IGPS-78398; type locality: Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Occurrence

Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One left valve, length = 1560 μm, height = 920 μm, IGPS-112676; one right valve, length = 1540 μm, height = 840 μm, IGPS-112677.

Remarks

Ishizaki (1964b) placed this species in the genus Kirkbya. Hanai et al. (1977) regarded the generic identification as questionable because of the poor preservation of the type specimen. I extracted this species from Loc. 46 of Kobayashi (1973), but many fossil specimens from this locality were deformed by diagenesis. However, present materials show a posterior shoulder and a more acutely curved posterior cardinal angle than anterior ones, and these characteristics are diagnostic of Kirkbya. Kirkbya nipponica is similar to Kirkbya parva Buschmina, 1975, from the Mississippian of Kamenka Creek, Kolyma, Far East Russia, but K. nipponica differs from K. parva in that it has an acutely curved posterior cardinal angle, a prominent shoulder, and a more rounded lateral outline. Kirkbya nipponica Ishizaki, 1964b, is similar to Kirkbya sp. of Ishizaki (1967) from the early Permian Tassobe Formation, South Kitakami Massif, Northeast Japan, by having a straight dorsal margin, but it differs in that it has a prominent anterior shoulder, an acutely curved posterior cardinal angle, and prominent rims.

Kirkbya nagaiwensis Ishizaki, 1964
Figure 4.5

1964b

Kirkbya nagaiwensis Ishizaki, p. 33, pl. 1, figs. 5a, b.

1977

Kirkbya nagaiwensis; Hanai et al., p. 8.

Holotype

Holotype, one carapace, IGPS-78400; type locality: Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Occurrence

Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One right valve, length = 1580 μm, height = 580 μm, IGPS-112678.

Remarks

Specimens from this locality were deformed by diagenesis. However, present materials show an elongated lateral outline similar to the type specimen of Ishizaki (1964b). Kirkbya nagaiwensis is similar to Kirkbya punctata Kellett, 1933, from the Pennsylvanian Stanton Limestone, Kansas, USA, in its elongated lateral outline, but it differs in that it has a prominent rim, a rather flat shoulder, and coarser ventral reticulation. Kirkbya nagaiwensis Ishizaki, 1964b, is similar to Kirkbya inornatum Roth, 1929, from the Carboniferous Wapanucka Limestone Pontotoc County, Oklahoma, USA, in its slightly sinuate ventral margin, but it differs in its reticulation, an acutely curved posterior cardinal angle, and prominent rims. Kirkbya nagaiwensis is also similar to Kirkbya jolliffana Bradfield, 1935, from the Carboniferous Dornick Hills Formation, northwest of Berwyn, Oklahoma, USA, in its elongated lateral outline, but it differs in having a prominent inner rim (marginal ridge), coarser reticulation, and no nodes on the dorsal area.

Kirkbya sarusawensis Ishizaki, 1968
Figure 4.8–4.13

1968

Kirkbya sarusawensis Ishizaki, p. 13, pl. 1, fig. 7.

1977

Kirkbya sarusawensis; Hanai et al., p. 9.

1995

Kirkbya vivata Jiang in Jiang et al., p. 106, pl. 97, figs. 16, 17.

2016

Kirkbya sarusawensis; Stocker et al., p. 101, fig. 4a, d, g.

Holotype

Holotype, one right valve IGPS-78410; type locality: west of Nanatsumori and 1 km north of Sarusawa, Daito Town, Iwate Prefecture, Northeast Japan, the Mississippian Takezawa Formation.

Occurrence

Mississippian Takezawa Formation, Daito Town, Iwate Prefecture, Northeast Japan; Pennsylvanian Azigan Formation, Kunlun Mountain, Xinjiang, China; Pennsylvanian (middle Moscovian) Ichinotani Formation, Mizuboradani Valley, Takayama City, Gifu Prefecture, central Japan; Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One deformed left valve, IGPS-112679; one deformed right valve, IGPS-112680; one deformed juvenile valve, IGPS-112681.

Remarks

Ishizaki (1968) described this species as new based on its slightly dorsally protruded anterior lobe. Specimens from this locality were deformed by diagenesis. However, these specimens show the anterior lobe lower than the posterior lobe, as opposed to the opposite in Ishizaki's (1968) description. Kirkbya sarusawensis Ishizaki, 1968, is similar to Kirkbya knuepferi Kozur, 1985, from the late Permian Nagyvisnyó Formation, Mihalovits Steinbruch, north Hungary, in its less protruded anterior lobe, but it differs in that it has coarse reticulation, a prominent posterior lobe, and a widely arched velate ridge. Kirkbya sarusawensis is also similar to Kirkbya clarocarinata (Knight, 1928a) figured by Zhang and Liang (1987) from the Pennsylvanian Taiyuan Formation, Xingyang, Henan, South China, in its less protruded anterior lobe, but it differs in that it has an evenly arched velate ridge, a knob-like posterior lobe, and no smooth antero-dorsal area.

Kirkbya sp.
Figure 4.6, 4.7

Occurrence

Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One right valve, length = 1620 μm, height = 900 μm, IGPS-112682.

Remarks

Kirkbya sp. resembles Kirkbya nipponica Ishizaki, 1964b, in its similar lateral outline and prominent rims, but it differs in having a coarser reticulation, a less prominent posterior shoulder, and an anterior lobe.

Order Hollinocopida Henningsmoen, 1965
Suborder Hollinocopina Swartz, 1936
Superfamily Hollinoidea Swartz, 1936
Family Hollinellidae Bless and Jordan, 1971
Genus Jordanites Bless, 1967

Type species

Jordanites rawihinggili Bless, 1967 (Geologisch & Mineralogisch Instituut of the Rijksuniversiteit of Leiden, No. Fe361-1) from the Westphalian D (Pennsylvanian) of the Coal-mine, Mosquitera, Asturias, Spain, by original description.

Jordanites modica (Jiang in Jiang et al., 1995)
Figures 5, 6

1964b

Hollinella tingi; Ishizaki, p. 30, pl. 1, fig. 1.

1977

Hollinella (Hollinella) tingi; Hanai et al., p. 7.

1995

Hollinella modica Jiang in Jiang et al., p. 96, pl. 96, figs. 12–17.

Figure 5. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–4) A female carapace of Jordanites modica (Jiang in Jiang et al., 1995), IGPS-112683; (1) left lateral view, (2) right lateral view, (3) dorsal view, (4) ventral view; (5–7) a female left valve of Jordanites modica (Jiang in Jiang et al., 1995), IGPS-112684; (5) external view, (6) internal view, (7) anterior view; (8–12) a male carapace of Jordanites modica (Jiang in Jiang et al., 1995), IGPS-112685; (8) left lateral view, (9) right lateral view, (10) dorsal view, (11) ventral view, (12) anterior view; (13, 14) a juvenile carapace of Jordanites modica (Jiang in Jiang et al., 1995), IGPS-112686; (13) left lateral view, (14) right lateral view; (15–17) a juvenile carapace of Jordanites modica (Jiang in Jiang et al., 1995), IGPS-112687; (15) left lateral view, (16) right lateral view, (17) ventral view. Scale bar = 200 μm.

Figure 6. Ontogenetic change of length/height of Jordanites modica (Jiang in Jiang et al., 1995).

Types

Holotype, a complete carapace Xj-1817; paratypes, three carapaces Xj-1819, Xj-1820a, 1820b; type locality: Pennsylvanian Kalawuyi Formation, Tarim Basin, Xinjiang, China.

Occurrence

Pennsylvanian Kalawuyi Formation, Tarim Basin, Xinjiang, China; Locality 36 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

One female carapace, length = 689 μm, height = 455 μm, IGPS-112683; one female left valve, length = 639 μm, height = 480 μm, IGPS-112684; one male carapace, length = 589 μm, height = 455 μm, IGPS-112685; two juvenile carapaces, length = 529 μm, height = 394 μm, IGPS-112686, length = 517 μm, height = 369 μm, IGPS-112687.

Remarks

The figured specimens in this study have a fused lobe 1 (L1) and lobe 2 (L2), large lobe 3 (L3), and inconspicuous lobe 4 (L4), which is consistent with the generic character of Jordanites designated by Bless (1967). Ishizaki (1964b) identified the specimens from the Nagaiwa Formation as Hollinella tingi Patte, 1935, from the Permian of southeastern China, as a result of its outline and ornamentation, but it differs in that it has a straight dorsal margin, rounded lateral outline, fused L1 and L2, and a widely arched anterior margin. Jordanites modica (Jiang in Jiang et al., 1995) is similar to Jordanites rawihinggili Bless, 1967, from the Pennsylvanian of Asturias, northwestern Spain, in its sub-quadrate lateral outline, but it differs in that it has ornamentation, a prominent L3, and an acutely arched posterior margin. Jordanites modica is also similar to Jordanites cristinae (Bless, 1967) of Asturias, northwestern Spain, in its acutely arched posterior margin, but it differs in that it has a dorsally protruded L3, a dorsally inflated L1, and a more inflated carapace. Jordanites modica (Jiang, 1995) is somewhat similar to Jordanites henanensis Zhang in Zhang and Liang, 1991, from the Pennsylvanian Taiyuan Formation, Xingyang, Henan, South China, in its prominent L3, but it differs in that it has a subquadrate lateral outline, surface ornamentation, and a prominent L1. Jordanites modica (Jiang in Jiang et al., 1995) is similar to Jordanites reticularis Błaszyk and Natusiewicz, 1973, from Mississippian samples from a borehole, northwestern Poland, in its sub-quadrate lateral outline, but it differs in that it has a prominent L3, no reticulation, and an acutely arched posterior margin.

Jordanites michinokuensis new species
Figures 7.16–7.23, 8, 9.1–9.4

Types

Holotype, a female left valve IGPS-112688; paratype, a male left valve IGPS-112691; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 7. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–5) A right valve of Thuringobolbina sp., IGPS-112695; (1) right external view, (2) internal view, (3) ventral view, (4) dorsal view, (5) posterior view. (6, 7) A female left valve of Thuringobolbina ikeyai n. sp., IGPS-112693 (holotype); (6) external lateral view, (7) internal view; (8) an external view of left valve of male Thuringobolbina ikeyai n. sp., IGPS-112694 (paratype). (9, 10) A female carapace of Aechmina iwatensis n. sp., IGPS-112696 (holotype); (9) right side view, (10) posterior view; (11, 12) a male carapace of Aechmina iwatensis n. sp., IGPS-112697 (paratype); (11) right lateral view, (12) dorsal view; (13) a male right valve of Aechmina iwatensis n. sp., IGPS-112698 (paratype); (14, 15) a juvenile carapace of Aechmina iwatensis n. sp., IGPS-112699 (paratype); (14) right lateral view, (15) anterior view. (16–20) A female left valve of Jordanites michinokuensis n. sp., IGPS-112688 (holotype); (16) external lateral view, (17) internal view, (18) ventral view, (19) dorsal view, (20) posterior view; (21) a male right valve of Jordanites michinokuensis n. sp., IGPS-112689 (paratype); (22, 23) a male left valve of Jordanites michinokuensis n. sp., IGPS-112690 (paratype); (22) external lateral view, (23) internal view. (24, 25) A carapace of Jordanites sp., IGPS-112692; (24) left lateral view, (25) right lateral view. Scale bar = 400 μm for (1–15) and 200 μm for (16–25).

Figure 8. Ontogenetic change of length/height of Jordanites michinokuensis n. sp.

Figure 9. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–4) A male left valve of Jordanites michinokuensis n. sp., IGPS-112691 (paratype); (1) external lateral view, (2) internal view, (3) dorsal view, (4) posterior view. (5–8) A right valve of Punctoprimitia tomokoae (Ishizaki, 1964b), IGPS-112700; (5) external lateral view, (6) internal view, (7) anterior view, (8) dorsal view. (9–13) A male right valve of Punctoprimitia tumida (Ishizaki, 1964b), IGPS-112701; (9) external lateral view, (10) internal view, (11) dorsal view, (12) ventral view, (13) anterior view; (14–16) a male left valve of Punctoprimitia tumida (Ishizaki, 1964b), IGPS-112702; (14) external lateral view, (15) internal view, (16) ventral view; (17, 18) a female right valve of Punctoprimitia tumida (Ishizaki, 1964b), IGPS-112703; (17) external view, (18) ventral view; (19–22) a female left valve of Punctoprimitia tumida (Ishizaki, 1964b), IGPS-112704; (19) external lateral view, (20) ventral view, (21) dorsal view, (22) posterior view. Scale bar = 200 μm.

Diagnosis

Valve sub-quadrate; dorsal margin slightly concave, anterior margin narrowly arched, posterior margin broadly arched in female, narrowly arched in male; smooth surface with straight adductorial sulcus (S2) extending obliquely from one third border of dorsal margin to median area; a broad bend running from mid-anterior area to mid-ventral area.

Occurrence

Only known from the type locality.

Description

Prominent dimorphism. In external lateral view, valve sub-quadrate; dorsal margin slightly concave, anterior margin narrowly arched, ventral margin broadly convex, posterior margin broadly arched in female, narrowly arched in male; smooth surface with straight adductorial sulcus (S2) extending obliquely from one third border of dorsal margin to median area; fused lobe 1 (L1) and lobe 2 (L2), indistinct lobe 3 (L3) and lobe 4 (L4); in female, a broad bend running from mid-anterior area to middle mid-ventral area. In internal lateral view, narrow contact margin, two prominent depressions corresponding to L1 and L3. In dorsal and ventral views, valve half-moon outline, deep S2 in dorsal view, prominent bend parallel to ventral margin.

Etymology

“Michinoku” is an ancient word for northeastern Japan.

Materials

A female left valve, length = 788 μm, height = 431 μm, IGPS-112688 (holotype); a male left valve, length = 689 μm, height = 369 μm, IGPS-112691 (paratype).

Remarks

The genus Jordanites is quite similar to the Hollinella (Bless, 1968), but the two genera are distinguished, respectively, by L1 and L2 being fused or not (Bless, 1968; Crasquin et al., 2018). Hollinella samarensis Polenova, 1952, from the late Givetian, Russian Platform, has fused L1 and L2, and therefore this species is re-designated as Jordanites samarensis (Polenova, 1952) n. comb. in this study. Jordanites michinokuensis n. sp. is similar to J. samarensis (Polenova, 1952) n. comb. from the Russian Platform in its widely convex ventral margin, but it differs in having a slightly concaved dorsal margin, narrowly arched posterior margin, and indistinct L3. This species is also similar to Jordanites krasnodonensis Fohrer in Fohrer et al., 2007, from the middle Moscovian (Pennsylvanian) of the Donets Basin, Ukraine, in its indistinct L1, but it differs in that it has an elongate lateral outline, obliquely extending S2, and no postero-ventral spine.

Jordanites sp.
Figure 7.24, 7.25

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Material

One carapace, length = 874 μm, height = 505 μm, IGPS-112692.

Remarks

Jordanites sp. is similar to J. samarensis (Polenova, 1952) n. comb. from the Russian Platform in its widely arched posterior margin, but it differs in that it has an antero-ventrally protruded anterior margin, less prominent L3, and indistinct L1.

Family Hollinidae Swartz, 1936
Genus Thuringobolbina Zagora, 1967

Type species

Thuringobolbina thuringica Zagora, 1967 (?Geological Institute of the University of Jena, Org.-Nr.: P1028, however, the specimen has not been discovered in the collections yet, as noted by Groos-Uffenorde et al., 2022) from the Borehole Beulwitz 12, depth 137–139 m, middle part of the tentaculate nodular limestone (Early Devonian), Thuringia, Germany, by original description.

Thuringobolbina ikeyai new species
Figure 7.6–7.8

Types

Holotype, a female left valve, length = 1046 μm, height = 603 μm, IGPS-112693; paratype, a male left valve, length = 984 μm, height = 468 μm, IGPS-112694; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Valve oblate pentagonal outline; dorsal margin slightly sinuate, anterior margin widely arched; long spatula-shaped antero-ventral structure, short fin-shaped postero-ventral projection; surface ornamented by short spines, indistinct adductorial sulcus (S2) with small pit at central area.

Occurrence

Only the type locality.

Description

Prominent dimorphism, female more inflated than male. In external lateral view, valve oblate pentagonal outline; dorsal margin slightly sinuate, anterior margin widely arched, ventral margin broadly convex, postero-ventral straight, postero-dorsal margin convex; anterior and posterior cardinal angle equal; horn-like antero-cardinal spine, long spatula-shaped antero-ventral structure curved postero-ventrally, short fin-shaped postero-ventral projection extending postero-ventrally, triangular protrusion on postero-dorsal margin, several spines developed from mid-anterior margin to posterior margin; surface ornamented by short spines, indistinct adductorial sulcus (S2) with small pit in central area. In internal lateral view, narrow contact margin.

Etymology

In honor of Emeritus Professor Noriyuki Ikeya (Shizuoka University) who was the author's supervisor.

Materials

A female left valve IGPS-112693 (holotype), a male left valve IGPS-112694 (paratype).

Remarks

Thuringobolbina ikeyai n. sp. is similar to Thuringobolbina sibirica Melnikova, 2000, from the Middle Ordovician sediments from the Nizhnyaya Taimyra River, northern Taimyr Peninsula, Russia, in its anterior cardinal spine and antero-ventral projection, but it differs in that it has a spine, widely arched anterior margin, and sinuate dorsal margin. This species is also similar to Thuringobolbina? blessi Becker and Sánchez de Posada, 1977, from the Early Devonian Moniello Formation, Asturias, northern Spain, in its antero-ventral projection, but it differs in that it has a short postero-ventral projection, postero-dorsal triangle projection, and indistinct S2. Thuringobolbina ikeyai n. sp. is similar to Thuringobolbina? australis Shallreuter, 1988, from the Devonian of New South Wales, Australia, in its anterior cardinal spine and antero-ventral projection, but it differs in that it is ornamented by spines, possesses no ventral spine, and has a sinuate dorsal margin.

Thuringobolbina sp.
Figure 7.1–7.5

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Material

One right valve, length =1157 μm, height = 578 μm, IGPS-112695.

Remarks

Thuringobolbina sp. resembles Thuringobolbina? blessi Becker and Sánchez de Posada, 1977, from the Early Devonian Moniello Formation, Asturias, northern Spain, in its oblate pentagonal lateral outline, but it differs in that it has a hook-like projection at the antero-ventral and postero-ventral areas, an obtuse posterior cardinal angle, and a long spine at the postero-ventral end. Thuringobolbina sp. is also similar to Thuringobolbina? australis Shallreuter, 1988, from the Devonian of New South Wales, Australia, in its widely arched ventral margin, but it differs in that it has surface ornamentation, no ventral spine, and a sinuate dorsal margin.

Suborder Binodicopina Schallreuter, 1972
Family Aechminidae Bouček, 1936
Genus Aechmina Jones and Holl, 1869

Type species

Aechmina cuspidata Jones and Holl, 1869 (a type specimen was not designated and subsequently was assigned by Kempf, 1986) from the Wenlock limestone of Croft's Quarry near West Malvern, England, UK, by original description. After that, A. cuspidata from the Lower Elton Formation, Gorstian Stage from Wenlock Edge, Shropshire, England, was deposited in The Natural History Museum, London (specimen No. PM OS 6640) by Professor David Siveter (University of Leicester) in 1984; this specimen in considered to be the primary reference specimen.

Aechmina iwatensis new species
Figure 7.9–7.15

?1987 Aechmina sp. C Adachi, p. 4, fig. 2.

Types

Holotype, a female carapace IGPS-112696; paratypes, a male carapace IGPS-112697, a male right valve IGPS-112698, a juvenile carapace IGPS-112699; type locality: Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Carapace sub-ovate; dorsal margin straight, anterior margin widely arched toward mid-anterior, ventral margin slightly sinuate in male, straight in female, posterior margin narrowly arched at one-third height; prominent dorsal lobe backwardly truncated at one-third from anterior end. In dorsal view, left lobe located anteriorly.

Occurrence

Upper Member of the Ichinotani Formation, Mizuyagadani-Valley, Fukuji District, central Japan, Pennsylvanian; Locality 46 of Kobayashi (1973) from Upper Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Description

Prominent dimorphism. In lateral view, carapace subovate; dorsal margin straight, anterior margin widely arched toward mid-anterior, ventral margin slightly sinuate in long form, straight in female, posterior margin narrowly arched at one-third height, anterior and posterior cardinal angles are equal in female, larger anterior cardinal angle in male; prominent dorsal lobe backwardly truncated at one-third from anterior end. In posterior view, left dorsal lobe is higher than right dorsal lobe. In dorsal view, left lobe is located anteriorly.

Etymology

The species is named after Iwate Prefecture, the local name according to the type locality.

Material

A carapace, length = 755 μm, height = 706 μm, IGPS-112696 (holotype), a long form carapace, length = 891 μm, height = 529 μm, IGPS-112697 (paratype), a long form right valve, length = 843 μm, height = 491 μm, IGPS-112698 (paratype), a juvenile carapace, length = 397 μm, height = 509 μm, IGPS-112699 (paratype).

Remarks

Aechmina iwatensis n. sp. is similar to Aechmina akumame Stocker et al., 2016, from the middle Moscovian (Pennsylvanian) Ichinotani Formation, Fukuji, central Japan; it has a straight dorsal margin, but A. iwatensis n. sp. differs from A. akumame in that it has a sinuate or straight ventral margin, narrowly arched posterior margin, and backwardly truncated dorsal lobe. Aechmina iwatensis n. sp. probably was assigned to Aechmina sp. C of Adachi (1987) from the Pennsylvanian Ichinotani Formation based on the position of the dorsal knob, although Adachi (1987) only showed the species with a simple illustration. This species is similar to Aechmina tianshanensis Jiang in Jiang et al., 1995, from the Pennsylvanian Dongtujinhe Formation, Xinjiang, China, in its spineless dorsal lobe, but it differs in its straight or sinuate ventral margin, a narrowly arched posterior margin, and a backwardly truncated dorsal lobe. Aechmina iwatensis n. sp. is also similar to Aechmina sp.? of Dewey (1983) from the “Middle” Carboniferous of the Port au Port Peninsula, western Newfoundland, Canada, in its backwardly truncated dorsal lobe, but it differs in having a straight dorsal margin, a sinuate or straight ventral margin, and lack of a small knob-like swelling in front of the dorsal lobe. This species is also similar to Aechmina sp. A of Becker and Sánchez de Posada (1977) from the Early Devonian Moniello Formation, Asturias, northern Spain, in its backwardly truncated dorsal lobe, but differs in that it has a shorter dorsal lobe, a dorsal lobe projected at one-third from the anterior end, and a straight or sinuate ventral margin. Aechmina iwatensis n. sp. is similar to Aechmina serrata (Stewart, 1936) from the Middle Devonian Silica Shale Formation, Ohio, USA, in its straight dorsal margin, but it differs in that it has a sinuate or straight ventral margin, narrowly arched posterior margin, and has a short dorsal lobe.

Order Platycopida Sars, 1866
Suborder Kloedenellocopina Scott, 1961
Superfamily Kloedenelloidea Ulrich and Bassler, 1908
Family Kloedenellidae Ulrich and Bassler, 1908
Genus Punctoprimitia Stewart and Hendrix, 1945

Type species

Haploprimitia simplex Stewart, 1936 (Ohio State University, no. 18172) from the Middle Devonian, Blue Shale (Zone 1) of Silica Shale in the quarry at Silica, Ohio, USA, by original description.

Punctoprimitia tomokoae (Ishizaki, 1964)
Figure 9.5–9.8

1964b

Glyptopleurina tomokoae Ishizaki, p. 34, pl. 1, figs. 6a, b, text-fig. 2.

1968

Glyptopleurina cf. tomokoae; Ishizaki, p. 15, pl. 1, fig. 8.

1977

Glyptopleurina tomokoae; Hanai et al., p. 14.

Types

Holotype, an adult right valve IGPS-78393; paratype, a left valve IGPS-78403; type locality: Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Material

One right valve, length = 775 μm, height = 369 μm, IGPS-112700.

Remarks

Punctoprimitia tomokoae (Ishizaki, 1964b) is similar to Punctoprimitia simplex (Stewart, 1936) from the Middle Devonian Silica Shale Formation, Ohio, USA, in having a slit sulcus, but it differs in that it has an elongated lateral outline, concave dorsal margin, and obliquely extending S2. Punctoprimitia tomokoae is also similar to Punctoprimitia cf. P. simplex Becker and Sánchez de Posada, 1977, from the Early Devonian Moniello Formation, Asturias, northern Spain, in its elongated lateral outline, but it differs in that it has an acutely curved anterior margin, rather flat L2 and L3, and narrowly arched posterior margin.

Punctoprimitia tumida (Ishizaki, 1964)
Figure 9.9–9.22

1964b

Glyptopleurina tumida Ishizaki, p. 35, pl. 1, figs. 7a, b, text-fig. 3.

1977

Glyptopleurina tumida; Hanai et al., p. 14.

Types

Holotype, a right valve IGPS-78394; paratype, a right valve IGPS-78396; type locality: Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian to lower Moscovian.

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Materials

One male right valve, length = 640 μm, height = 468 μm, IGPS-112701; one male left valve, length = 602 μm, height = 480 μm, IGPS-112702; one female right valve, length = 578 μm, height = 492 μm, IGPS-112703; one female left valve, length = 603 μm, height = 480 μm, IGPS-112704.

Remarks

In the present study, I found a pair of right and left valves with dimorphism: the male is higher from lateral view and flatter from dorsal view than the female. Punctoprimitia tumida (Ishizaki, 1964b) is similar to Punctoprimitia simplex (Stewart, 1936) from the Middle Devonian Silica Shale Formation, Ohio, USA, in its rounded lateral outline, but it differs in that it has a narrow S2, an undulated dorsal margin, and an obliquely extending S2. Punctoprimitia tumida is also similar to Punctoprimitia cf. P. simplex Becker and Sánchez de Posada, 1977, from the Early Devonian Moniello Formation, Asturias, northern Spain, in its inflated L2 and L3, but it differs in that it has a higher lateral outline, a rather narrow S2, and a concave dorsal margin.

Punctoprimitia sp.
Figure 10.1–10.5

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 10. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–5) A right valve of Punctoprimitia sp., IGPS-112705; (1) external lateral view, (2) internal view, (3) anterior view, (4) dorsal view, (5) ventral view. (6–8) A carapace of Platyrhomboides tohokuensis n. sp., IGPS-112717 (holotype); (6) right lateral view, (7) left side view, (8) dorsal view. (9, 10) A left valve of Platyrhomboides japonica n. sp., IGPS-112718 (holotype); (9) external lateral view, (10) internal view; (11, 12) a right valve of Platyrhomboides japonica n. sp., IGPS-112719 (paratype); (11) external lateral view, (12) internal view; (13–16) a juvenile carapace of Platyrhomboides japonica n. sp., IGPS-112720 (paratype); (13) left lateral view, (14) right lateral view, (15) dorsal view, (16) posterior view. (17–20) A carapace of Waylandella sp., IGPS-112728; (17) right lateral view, (18) dorsal view, (19) ventral view, (20) anterior view. Scale bar = 200 μm.

Material

One right valve, length = 861 μm, height = 726 μm, IGPS-112705.

Remarks

Punctoprimitia sp. is similar to Punctoprimitia simplex (Stewart, 1936) from the Middle Devonian Silica Shale Formation, Ohio, USA; it has a distinct and deep S2, but P. sp. differs from P. simplex in that it has a rounded lateral outline, broadly arched anterior and posterior margins, and a flat postero-dorsal area. Punctoprimitia sp. is also similar to Punctoprimitia cf. P. simplex Becker and Sánchez de Posada, 1977, from the Early Devonian Moniello Formation, Asturias, northern Spain, with its flat postero-dorsal area, but it differs in that it has less inflated L2 and L3, a rather narrow S2, and a straight dorsal margin.

Order Podocopida Müller, 1894
Suborder Podocopina Sars, 1866
Superfamily Bairdioidea Sars, 1888
Family Bairdiocyprididae Shaver, 1961
Genus Pseudobythocypris Shaver, 1958

Type species

Bythocypris pediformis Knight, 1928b (type specimen was not designated) from the Pennsylvanian Henrietta Formation, eastern Missouri, USA, by original description. Shaver (1958) designated four hypotypes (U.S. National Museum 133377–133380) from the “metatype” slide of Knight (1928b).

Pseudobythocypris asiatica new species
Figures 11.1–11.8, 12

1995

Healdia lucida Jiang in Jiang et al., pl. 117, fig. 2.

Figure 11. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–4) A female carapace of Pseudobythocypris asiatica n. sp., IGPS-112706 (holotype); (1) left lateral view, (2) right lateral view, (3) ventral view, (4) anterior view; (5–8) a male carapace of Pseudobythocypris asiatica n. sp., IGPS-112707 (paratype); (5) left lateral view, (6) right lateral view, (7) ventral view, (8) anterior view. (9–12) A carapace of Healdia sp., IGPS-112727; (9) left lateral view, (10) right lateral view, (11) dorsal view, (12) posterior view. (13–16) A female carapace of Pseudobythocypris siveteri n. sp., IGPS-112708 (holotype); (13) left lateral view, (14) right lateral view, (15) dorsal view, (16) anterior view; (17–20) a male carapace of Pseudobythocypris siveteri n. sp., IGPS-112709 (paratype); (17) left lateral view, (18) right lateral view, (19) ventral view, (20) posterior view. (21–24) A female carapace of Pseudobythocypris zipangu n. sp., IGPS-112710 (holotype); (21) left lateral view, (22) right lateral view, (23) ventral view, (24) posterior view; (25–28) a male carapace of Pseudobythocypris zipangu n. sp., IGPS-112711 (paratype); (25) left lateral view, (26) right lateral view, (27) ventral view, (28) posterior view. Scale bar = 200 μm.

Figure 12. Ontogenetic change of length/height of Pseudobythocypris asiatica n. sp.

Types

Holotype, one female carapace, IGPS-112706; paratypes, a carapace Xj-2090, a male carapace IGPS-112707; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, lower Bashkirian–lower Moscovian.

Diagnosis

Carapace subovate; dorsal margin arched, anterior margin narrowly arched; longest at mid-height, highest slightly behind mid-length from anterior end. Prominent dimorphism: in lateral view, female more elongated than male; in dorsal and ventral views, posterior area of female more inflated than male; in anterior view, female is more rounded than male.

Occurrence

Pennsylvanian Tahaqi Formation, Kunlun Mountains, Xinjiang, China; locality 36 of Kobayashi (1973), upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Description

In lateral view, carapace subovate; dorsal margin arched, anterior margin narrowly arched, ventral margin slightly sinuate in right valve, straight in left valve, posterior margin narrowly arched; longest at mid-height, highest slightly behind mid-length from anterior end; left valve larger than right valve, overlap along anterior to lower half of posterior margin via ventral margin. In dorsal and ventral views, carapace fusiform. In anterior view, carapace ovate outline. Prominent dimorphism: in lateral view, female more elongated than male; in dorsal and ventral views, posterior area of female more inflated than male; in anterior view, female is more rounded than male.

Etymology

So named because the species has been reported only from Asia.

Materials

One male carapace, length = 566 μm, height = 332 μm, IGPS-112706 (holotype); one male carapace, length = 640 μm, height = 295 μm, IGPS-112707 (paratype); one possibly male carapace, Xj-2090 (paratype).

Remarks

Jiang in Jiang et al. (1995) described Healdia lucida from the Pennsylvanian Shiqiantan and Tahaqi formations, Xinjiang, China. He designated one carapace as holotype (Xj-2078) and three carapaces as paratypes (Xj-2078a, 8957, 2090). However, one paratype (Xj-2090) with a straight ventral margin is not Healdia lucida, because H. lucida was described as having a convex ventral margin (Xj-2078, 2078a, 8957).

Pseudobythocypris asiatica n. sp. is similar to Pseudobythocypris pediformis (Knight, 1928b) from the Pennsylvanian Henrietta Formation, eastern Missouri, USA, with that taxon sharing an arched dorsal margin, but it differs in that it has a narrowly arched (not protruded) posterior margin, is longest at mid-height, and has a more inflated carapace. This species is also similar to Pseudobythocypris parallela (Knight, 1928b) from the Pennsylvanian Henrietta Formation, eastern Missouri, USA, in its elongated lateral outline, but it differs in that its highest point is situated more backwardly from the anterior end, is longest at mid-height, and has a wider arched posterior margin. Pseudobythocypris asiatica n. sp. is similar to P. kellettae (Cordell, 1952) from the Pennsylvanian Bonner Spring Formation and the Canville Limestone from Missouri, USA, in its narrowly arched anterior margin, but it differs in its backwardly located highest point from the anterior end, longest point at mid-height, and a more inflated outline from dorsal view. This species is also similar to P. parallela (Knight, 1928b) of Glebovskaya (1939) from the Pennsylvanian–Permian of Vyarta, northern Ural, Russia, in its straight ventral margin, but it differs in that it has a narrowly arched posterior margin, is longest at mid-height, and has a more acutely arched dorsal margin. Pseudobythocypris asiatica n. sp. is similar to Healdianella darwinuloides Posner, 1951, from the Mississippian of the western part of the Moscow Basin in its overlapped left valve from posterior to anterior margin via ventral margin, but it differs in that it has a longer lateral outline, a highest point situated slightly behind mid-length from the anterior end, and a straight ventral margin in the left valve.

Pseudobythocypris siveteri new species
Figures 11.13–11.20, 13

Types

Holotype, one female carapace, IGPS-112708; paratype, one male carapace IGPS-112709; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 13. Ontogenetic change of length/height of Pseudobythocypris siveteri n. sp.

Diagnosis

Carapace sub-trapezoidal; anterior margin arched toward antero-ventral direction, posterior margin broadly arched toward postero-ventral direction, protruded two-thirds height from venter; longest at one-third height. In dorsal and ventral views, carapace bullet-shaped.

Occurrence

Only the type locality.

Description

In lateral view, carapace sub-trapezoidal; dorsal margin widely arched, anterior margin arched toward antero-ventral direction, protruded at mid-height from venter, ventral margin straight in left valve, concave at mid-length from anterior end in right valve, posterior margin broadly arched toward postero-ventral direction, protruded two-thirds height from venter; longest at one-third height, highest at mid-length from anterior end; left valve larger than right valve, overlap along all margins, typically prominent overlap at ventral margin. In dorsal and ventral views, carapace bullet-shaped. In posterior view, carapace ovate outline. Prominent dimorphism: in lateral view, female more rounded than male; in dorsal view, female more inflated than male.

Etymology

In honor of Emeritus Professor David J. Siveter (University of Leicester) who is an excellent paleontologist and the author's supervisor.

Materials

One female carapace, length = 492 μm, height = 271 μm, IGPS-112708 (holotype); one male carapace, length = 468 μm, height = 234 μm, IGPS-112709 (paratype).

Remarks

Pseudobythocypris siveteri n. sp. is similar to P. phaseoella (Stover, 1956) from the Middle Devonian Windom Shale Member of the Moscow Formation from western New York, USA, in its antero-ventrally truncated anterior margin, but it differs in that it has a more inflated lateral outline, a widely arched dorsal margin, and bullet-shaped outline from the dorsal view. This species is also similar to Pseudobythocypris kellettae (Cordell, 1952) from the Pennsylvanian Galesburg Shale from Missouri, USA, in its overlapped left valve to right valve at the ventral margin, but it differs in that it has a shorter anterior margin, a protruded posterior margin at two-thirds height from venter, and a bullet-shaped outline from the dorsal view. Pseudobythocypris siveteri n. sp. is similar to P. pediformis (Knight, 1928b) from the Pennsylvanian upper Fort Scott Limestone of the Henrietta Formation, Missouri, USA, in its protruded anterior margin slightly below mid-height, but it differs in that it has broadly arched anterior and posterior margins, and a bullet-shaped outline from the dorsal view. Pseudobythocypris siveteri n. sp. is also similar to P. deesensis (Bradfield, 1935) of Shi (1987) from the Pennsylvanian Taiyuan Formation, Shanxi, China, in its antero-ventrally directed anterior margin, but it differs in that it has a widely arched posterior margin, more rounded lateral outline, and a bullet-shaped outline from the dorsal view.

Pseudobythocypris zipangu new species
 Figure 11.21–11.28

Types

Holotype, one female carapace, IGPS-112710; paratype, one male carapace IGPS-112711; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Dorsal margin widely arched, anterior margin equally arched, ventral margin sinuate, concave at one-third distance from anterior end, posterior margin unequally arched; longest at mid-height from venter, highest point slightly forward of mid-length from anterior end. Prominent dimorphism: in lateral view, female more rounded than male.

Occurrence

Only the type locality.

Description

In lateral view, carapace bean-shaped; dorsal margin widely arched, anterior margin equally arched between dorsal and ventral half, protruded anteriorly at mid-height, ventral margin sinuate, concave at one-third distance from anterior end, posterior margin unequally arched between ventral and dorsal margin, postero-ventral margin widely arched, postero-dorsal margin narrowly arched, protruded at one-third of height from venter; longest at mid-height from venter, highest point located slightly forward of mid-length from anterior end. Left valve larger than right valve, overlap along antero-dorsal to postero-dorsal margin via ventral margin. In dorsal and ventral views, carapace rice-shaped. In anterior view, carapace has ovate outline. Prominent dimorphism: in lateral view, female more rounded than male; in dorsal and ventral views, female more inflated than male.

Etymology

According to the book “The Travels of Marco Polo,” Zipangu is located off the east of China, and the palace was made of gold (Komroff, 2001); thus, Zipangu has been considered as Japan, and the palace has been thought to refer to the Chusonji Konjiki-do Temple in Iwate Prefecture (type locality of this species).

Materials

One female carapace, length = 480 μm, height = 320 μm, IGPS-112710 (holotype); one male carapace, length = 468 μm, height = 308 μm, IGPS-112711 (paratype).

Remarks

Pseudobythocypris zipangu n. sp. is similar to P. pecki (Cordell, 1952) from the Pennsylvanian Lawrence Formation from Missouri, USA, in its equally arched anterior margin, but it differs in that it has a protruded posterior margin at one-third height from venter, is longest at mid-height from venter, and does not have an overlapped left valve along dorsal margin of right valve. Pseudobythocypris zipangu n. sp. is also similar to Pseudobythocypris oblongata (Cordell, 1952) from the Pennsylvanian Muncie Creek Shale from Missouri, USA, in its bean-shaped lateral outline, but differs in that it has a sinuate ventral margin, a widely arched postero-ventral margin, and no overlap between left valve and right valve along the dorsal area. Pseudobythocypris zipangu n. sp. is similar to P. cytherellinoides (Kummerow, 1953) from the Early Devonian Zorgensis Limestone, Trautenstein, Germany, in its bean-shaped lateral outline; it differs in that the left valve overlaps the right valve at anterior and posterior areas, having a sinuate ventral margin, and has an acutely arched anterior margin. This new species is also similar to P. lucasensis (Stewart, 1936) from the Middle Devonian Silica Shale Formation, Ohio, USA, in its bean-shaped lateral outline, but it differs in that it has a widely arched dorsal margin, is highest near mid-length from anterior end and has an acutely arched dorso-posterior margin.

Family Bairdiidae Sars, 1888
Genus Bairdia McCoy, 1844

Type species

Bairdia curtus McCoy, 1844 (type specimen was not designated) from the Carboniferous of Ireland by original description. Sohn (1960) erected a new genus, Orthobairdia, and included B. curta McCoy, 1844, in the genus Orthobairdia. The type species of Orthobairdia is Orthobairdia cestriensis (Ulrich, 1891), and the lectotype (U.S. National Museum 41789) was designated by Sohn (1960) among Ulrich's 12 cotype specimens.

Bairdia hanaii Ishizaki, 1963
 Figure 14.17–14.19

1963

Bairdia hanaii Ishizaki, p. 165, pl. 4, figs. 1a, b.

1977

Bairdia hanaii; Hanai et al., p. 16.

Figure 14. Scanning electron micrographs of ostracodes from the Pennsylvanian Nagaiwa Formation. (1–3) A left valve of Healdia cf. H. simplex Roundy, 1926, IGPS-112722; (1) lateral view, (2) dorsal view, (3) anterior view; (4–7) a right valve of Healdia cf. H. simplex Roundy, 1926, IGPS-112721; (4) external lateral view, (5) dorsal view, (6) anterior view, (7) inner view. (8–12) A female carapace of Healdia ofunatensis n. sp., IGPS-112723 (holotype); (8) left lateral view, (9) right lateral view, (10) dorsal view, (11) ventral view, (12) anterior view; (13–16) a male carapace of Healdia ofunatensis n. sp., IGPS-112724 (paratype); (13) left lateral view, (14) right lateral view, (15) dorsal view, (16) anterior view. (17) A carapace in right lateral view of Bairdia hanaii Ishizaki, 1963, IGPS-112712; (18, 19) a carapace of Bairdia hanaii Ishizaki, 1963, IGPS-112713; (18) right lateral view, (19) ventral view. (20–22) Bairdia sp., (20) left lateral view of carapace IGPS-112714, (21) right lateral view of carapace IGPS-112715, (22) left valve IGPS-112716. (23, 24) A female carapace of Healdia rikutyuensis n. sp., IGPS-112725 (holotype); (23) left lateral view, (24) right lateral view; (25–27) a male carapace of Healdia rikutyuensis n. sp., IGPS-112726 (paratype); (25) left lateral view, (26) right lateral view, (27) dorsal view. Scale bar = 200 μm for (1–16, 20, 22–27). Scale bar = 400 μm for (17–19, 21).

Holotype

Holotype, right IGPS-78380; type locality: Nagaiwa, Hikoroichi Town, Ofunato City, Iwate Prefecture, Japan, the Pennsylvanian Nagaiwa Formation.

Occurrence

Pennsylvanian Nagaiwa Formation, Nagaiwa, Hikoroichi Town, Iwate Prefecture, Northeast Japan; Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Materials

Two carapaces, length = 2000 μm, height = 870 μm, IGPS-112712, length = 1410 μm, height = 500 μm, IGPS-112713.

Remarks

Bairdia hanaii Ishizaki, 1963, is similar to Bairdia aluca Kotschetkova, 1983, from the Pennsylvanian (Bashkirian) Akavasian Horizon, Chalyabinsk region, Kizil, southern Urals, Russia, in its elongated lateral outline, but it differs in that it has an acuminated dorsal margin, a longer posterior process, and a rightward bending posterior process in ventral view. Bairdia hanaii is also similar to Bairdia proxima Tkatscheva in Ivanova et al., 1975, from the Carboniferous deposits, western slope of the North Urals, Russia, in its less elongated lateral outline, but it differs in that it has a longer posterior process, a more antero-ventrally curved anterior margin, and an acuminated dorsal margin.

Bairdia sp.
Figure 14.20–14.22

Occurrence

Locality 46 of Kobayashi (1973), Upper Member of the Nagaiwa Formation, Nagaiwa, Japan.

Material

Two carapaces, length = 777 μm, height = 490 μm, IGPS-112714, length = 1250 μm, height = 783 μm, IGPS-112715; one left valve, length = 510 μm, height = 312 μm, IGPS-112716.

Remarks

Bairdia sp. is similar to Bairdia foveosa Jiang in Jiang et al., 1995, from the Pennsylvanian of Xinjiang, China, in sharing a widely arched anterior margin, but it differs in that it has a widely arched dorsal margin, a dorsally directed posterior end, and is longest at mid-height from anterior end. Bairdia sp. is similar to Bairdia auricula Knight, 1928b, from the Pennsylvanian Henrietta Formation, eastern Missouri, USA, in its straight ventral margin, but it differs in that it has widely arched anterior and dorsal margins, a narrower posterior margin, and a short posterior projection.

Family Beecherellidae Ulrich, 1894
Genus Platyrhomboides Harris, 1957

Type species

Platyrhomboides quadratus Harris, 1957 (Museum of Comparative Zoology at Harvard University No. 4648) from the Ordovician Bromide Formation, Bromide horizon, 15 feet below top of zone 10 of U.S. Highway, Simpson section, Oklahoma, USA, by original description.

Platyrhomboides tohokuensis new species
Figure 10.6–10.8

Holotype

Holotype, a carapace IGPS-112717: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Trowel-like carapace. In lateral view, trapezoidal outline; anterior margin protruded toward anterior, posterior margin protruded postero-ventrally, longest at one-fifth height from venter, highest point at two-thirds from anterior end.

Occurrence

Only the type locality.

Description

Trowel-like carapace. In lateral view, trapezoidal outline; dorsal margin straight, anterior margin protruded toward anterior, ventral margin widely arched or straight, posterior margin protruded postero-ventrally, longest at one-fifth height from venter, highest point at two-thirds from anterior end. In ventral view, carapace trowel-like outline, left valve larger than right valve.

Etymology

The provincial name where the type specimens were discovered.

Materials

A carapace, length = 566 μm, height = 271 μm, IGPS-112717 (holotype).

Remarks

The genus Platyrhomboides has been reported from Middle Ordovician–Late Devonian (Becker and Wang, 1992). This report provides the youngest fossil record of the genus, extending the geological time range into the Pennsylvanian. Platyrhomboides tohokuensis n. sp. is similar to Platyrhomboides quadratus Harris, 1957, from the Ordovician Bromide Formation, Simpson and West Spring Creek, Oklahoma, USA, in its quadrate lateral outline, but it differs in that it has trowel-like outline in ventral view, a slightly protruded anterior margin, and a widely arched dorsal margin in the left valve. This species is also similar to Platyrhomboides sp. A of Becker and Wang (1992) from the middle to late Silurian of Shaanxi Province, Inner Mongolia, China, in its straight dorsal margin in the right valve, but it differs in that it has a narrowly arched anterior margin, a widely arched ventral margin, and a shorter dorsal margin. Platyrhomboides tohokuensis n. sp. is similar to Platyrhomboides sp. C of Becker and Wang (1992) from the Lower Devonian (lower Emsian) in Guangxi, China, in its widely arched ventral margin, but it differs in that it has a protruded anterior margin, a straight dorsal margin in the left valve, and a lower posterior end than that of the anterior.

Platyrhomboides japonica new species
Figures 10.9–10.16

Types

Holotype, a left valve IGPS-112718; paratypes, a right valve IGPS-112719, a juvenile carapace IGPS-112720; type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Wheat-seed shaped carapace. In lateral view, dorsal margin widely arched in left valve, straight in right valve; anterior margin narrowly arched antero-dorsally, ventral margin widely arched or straight, posterior margin protruded postero-ventrally.

Occurrence

Only the type locality.

Description

Wheat-seed shaped carapace. In lateral view, oblong outline; dorsal margin widely arched in left valve, straight in right valve, anterior margin narrowly arched antero-dorsally, ventral margin widely arched or straight, posterior margin protruded postero-ventrally. In internal view, wide marginal border in right valve. In ventral view, carapace has ship-like outline, left valve larger than right valve. In posterior view, carapace has oblate outline.

Etymology

The name where the type specimens were discovered.

Materials

A left valve, length = 780 μm, height = 270 μm, IGPS-112718 (holotype), a right valve, length = 740 μm, height = 260 μm, IGPS-112719 (paratype), a juvenile carapace, length = 540 μm, height = 180 μm, IGPS-112720 (paratype).

Remarks

The genus Platyrhomboides has been reported from Middle Ordovician–Late Devonian (Becker and Wang, 1992). This report provides the youngest fossil record of the genus with P. tohokuensis n. sp. and extends the geological time range into the Pennsylvanian. Platyrhomboides japonica n. sp. is similar to Platyrhomboides quadratus Harris, 1957, from the Ordovician Bromide Formation, Simpson and West Spring Creek, Oklahoma, USA, in its straight or a widely arched ventral margin, but it differs in that it has a widely arched dorsal margin, slightly tapered anterior and posterior margins, and less prominent anterior and posterior cardinal angles. This species is also similar to Platyrhomboides sp. A of Becker and Wang (1992) from the middle to late Silurian of Shaanxi Province, Inner Mongolia, China, in its straight dorsal margin in right valve, but it differs in that it has narrowly arched anterior margin, broadly arched ventral margin, and less truncated posterior. Platyrhomboides japonica n. sp. is similar to Platyrhomboides sp. B of Becker and Wang (1992) from the Lower Devonian (lower Emsian) of the Guangxi, China, in its narrowly arched anterior margin, but it differs in that it has a widely arched or a straight ventral margin, a widely arched dorsal margin in the left valve, and a higher posterior end than that of the anterior.

Suborder Metacopina Sylvester-Bradley, 1961
Superfamily Healdioidea Harlton, 1933
Family Healdiidae Harlton, 1933
Genus Healdia Roundy, 1926

Type species

Healdia simplex Roundy, 1926 (type specimen was not designated) from the Mississippian Graham Formation, Stephens County, Texas, USA, by original description. Kellett (1935) designated the plesiotype (U.S. National Museum No. 90108) from the Middle Pennsylvanian Stanton Formation, Kansas, USA.

Healdia cf. H. simplex Roundy, 1926
Figures 14.1–14.7, 15

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 15. Ontogenetic change of length/height of Healdia cf. H. simplex Roundy, 1926.

Materials

One right valve, length = 456 μm, height = 258 μm, IGPS-112721; one left valve, length = 529 μm, height = 295 μm, IGPS-112722.

Remarks

Roundy (1926) described this species from the Pennsylvanian of Graham County, Texas, USA, but did not designate type specimens. Subsequently, in March 1935, Bradfield (1935) designated a plesiotype (Indiana University Paleontological Collections No.2098) of Healdia simplex using a complete carapace from the Pennsylvanian of the Ardmore Basin, Oklahoma, USA. Kellett (1935) designated plesiotypes (U.S. National Museum No. 90108) from the Middle Pennsylvanian Stanton Formation, Kansas, USA, on March 11, 1935. Since the publication date of Bradfield (1935) is not precisely known, it is not possible to determine whether or not of Kellett's (1935) plesiotypes have priority. Bradfield's (1935) plesiotype of H. simplex is similar to H. cf. H. simplex in its triangular lateral outline, but it differs in that it has its highest point slightly forward from the mid-length, a straight posterior half of the dorsal margin, and a more dorsally situated maximum length. Kellett's figured plesiotype (Kellett, 1935, pl. 16, fig. 2) of H. simplex of is similar to H. cf. H. simplex in its triangular lateral outline, but it differs in that it has its a straight ventral margin, a straight posterior half of the dorsal margin, and does not have an inflated valve.

Healdia cf. H. simplex is also similar to Healdia magna Jiang in Jiang et al., 1995, from the Pennsylvanian Shiqiantan Formation, Xinjiang, China, in its antero-ventrally protruded anterior margin, but it differs in that it has a longer lateral outline, an unequally arched posterior margin, and its highest point slightly forward of the mid-length from the anterior end. Healdia cf. H. simplex resembles Healdia askynensis Kotschetkova, 1983, from the Pennsylvanian (Bashkirian) Kizil Formation, southern Ural Mountains, Russia, in that it has a depressed postero-ventral area, but H. cf. H. simplex differs from H. askynensis in that its highest point is slightly forward of the mid-length from the anterior end, has a more rounded anterior margin, and has an elongated outline from the dorsal view.

Healdia ofunatensis new species
Figures 14.8–14.16, 16

Holotype

Holotype, one female carapace, IGPS-112723; paratype, one male carapace IGPS-112724, type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 16. Ontogenetic change of length/height of Healdia ofunatensis n. sp..

Diagnosis

Ovate carapace; dorsal margin symmetrically arched, ventral margin sinuate, concaved at mid-length from anterior end; longest at mid-height, highest at mid-length from anterior end; left valve larger than right valve, prominent overlap at ventral and postero-dorsal margins. Rice-shaped outline in dorsal view.

Occurrence

Only the type locality.

Description

In lateral view, ovate carapace; dorsal margin symmetrically arched, anterior margin widely arched toward antero-dorsal direction in left valve, tapered anteriorly in right valve, ventral margin sinuate, concave at mid-length from anterior end, posterior margin widely arched postero-dorsally or protruded at mid-height; longest at mid-height from venter, highest at mid-length from anterior end; left valve larger than right valve, overlap along entire margin, typically prominent overlap at ventral and postero-dorsal margins. In dorsal and ventral views, carapace rice-shaped. In posterior view, carapace has ovate outline. Prominent dimorphism: in lateral view, female more rounded than male; in dorsal view, female more inflated than male; in posterior view, female wider than male.

Etymology

Ofunato, the name of the city where the type specimens were discovered.

Materials

One female carapace, length = 505 μm, height = 332 μm, IGPS-112723 (holotype); one male carapace, length = 504 μm, height = 271 μm, IGPS-112724 (paratype).

Remarks

Healdia ofunatensis n. sp. is similar to Healdia humillis (Bradfield, 1935) from the Pennsylvanian of the Ardmore Basin, Oklahoma, USA., in its symmetrically arched dorsal margin, but it differs in that it has a sinuate ventral margin, its highest point at mid-height from venter, and prominent overlap at ventral and postero-dorsal margins. Healdia ofunatensis n. sp. is also similar to Healdia yiliensis Jiang in Jiang et al., 1995, from the Pennsylvanian Dongtujinhe Formation, Xinjiang, China, in its lateral outline, but it differs in that it has a protruded dorsal margin, a shorter ventral margin, and rice-shaped outline from dorsal view. Healdia ofunatensis n. sp. is also similar to Healdia ziganensis Kotschetkova, 1983, from the Pennsylvanian (Bashkirian) Tashasta horizon, southern Ural Mountains, Russia, in its symmetrically arched dorsal margin, but it differs in that it has a longer lateral outline, is longest at mid-height from venter, and has a sinuate ventral margin. This species is also similar to Healdia kashirica Kotschetkova, 1985, from the Pennsylvanian (Moscovian) Kashirian horizon, Korenevo Village, Moscow, Russia, in its symmetrically arched dorsal margin, but it differs in that it has a rounded lateral outline, tapered anterior margin in the right valve, and rice-shaped outline from dorsal view.

Healdia rikutyuensis new species
Figure 14.23–14.27

Holotype

Holotype, one female carapace, IGPS-112725; paratype, one male carapace IGPS-112726, type locality: Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Diagnosis

Carapace tetragonal outline; dorsal margin widely arched unequally, anterior margin tapered at one-third height from venter, ventral margin sinuate, posterior margin truncated at mid-height from venter; in dorsal and ventral views, carapace pear-shaped.

Occurrence

Only the type locality.

Description

Tetragonal outline in lateral view; dorsal margin widely arched unequally, shorter anterior and longer posterior, anterior margin tapered at one third height from venter, ventral margin sinuate, concave at mid-length from anterior end, posterior margin truncated at mid- height; longest at mid-height from anterior end, highest at one-third length from anterior end; left valve larger than right valve, overlap along entire margin, typically prominent overlap at dorsal and ventral margins; a prominent sulcus at postero-ventral area. In dorsal and ventral views, carapace pear-shaped. Prominent dimorphism: in lateral view, female more rounded than male.

Etymology

The species is named for Rikutyu, the previous name of Iwate Prefecture, acknowledging the type locality.

Materials

One female carapace, length = 529 μm, height = 332 μm, IGPS-112725 (holotype); one male carapace, length = 529 μm, height = 295 μm, IGPS-112726 (paratype).

Remarks

Healdia rikutyuensis n. sp. is similar to Healdia magna Jiang in Jiang et al., 1995, from the Pennsylvanian Shiqiantan Formation, Bogduo Mountain, Xinjiang, China, in its truncated anterior margin, but it differs in that it has a tetragonal lateral outline, a widely arched dorsal margin, and a prominent sulcus at the postero-ventral area. Healdia rikutyuensis n. sp. is also similar to Healdia kashirica Kotschetkova, 1985, from the Pennsylvanian (Moscovian) Kashirian horizon, Korenevo Village, Moscow, Russia, in its truncated posterior margin at mid-height from venter, but it differs in that it has a tetragonal outline in lateral view, a sinuate ventral margin, and its highest point at one-third length from the anterior end. Healdia rikutyuensis n. sp. is similar to Healdia askynensis Kotschetkova, 1983, from the Pennsylvanian (Bashkirian) Kizil Formation, southern Ural Mountains, Russia, in its truncated anterior margin, but it differs in that it has a tetragonal lateral outline, its highest point at one-third length from the anterior end, and a depression at the postero-ventral area. This species is also similar to Healdia ovata Bradfield, 1935, from the Pennsylvanian Hoxbar Formation, Ardmore, Oklahoma, USA, in its left valve overlapping with the right valve along the dorsal and ventral margins, but it differs in that it has a trapezoidal lateral outline, a depression at the postero-ventral area, and a posterior margin truncated at mid-height from the venter.

Healdia sp.
Figures 11.9–11.12, 17

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Figure 17. Ontogenetic change of length/height of Healdia sp.

Material

One carapace, length = 492 μm, height = 308 μm, IGPS-112727.

Remarks

Healdia sp. resembles Healdia cara Bradfield, 1935, from the Pennsylvanian Deese? Formation, northeastern Ardmore, Oklahoma, USA, in its straight dorsal margin, but it differs in that it has a postero-dorsally protruded posterior margin, its highest point at two-thirds from the anterior end, and a widely arched anterior margin. This species is also similar to H. ovata Bradfield, 1935, from the Pennsylvanian Hoxbar Formation, Ardmore, Oklahoma, USA, in its straight ventral margin, but it differs in that it has an antero-ventrally protruded anterior margin, its highest point at two-thirds distance from the anterior end, and a postero-dorsally protruded posterior margin. Healdia sp. is similar to Healdia luculenta Jiang in Jiang et al., 1995, from the Pennsylvanian Xiaohaizi Formation, Xinjiang, China, in its arched dorsal margin, but it differs in that it has a postero-dorsally protruded posterior margin, its highest point at two-thirds from the anterior end, and a sinuate ventral margin.

Genus Waylandella Coryell and Billings, 1932

Type species

Waylandella spinosa Coryell and Billings, 1932 (Columbia University Paleontology Collection No. 25233) from the Wayland Shale, the uppermost member of the Graham Formation in North central Texas, USA, by original description.

Waylandella sp.
Figure 10.17–10.20

Occurrence

Locality 36 of Kobayashi (1973), Middle Member of the Nagaiwa Formation, Nagaiwa, Ofunato City, Iwate Prefecture, Northeast Japan, Bashkirian.

Material

One carapace, IGPS-112728.

Remarks

Waylandella sp. resembles Waylandella spinosa (Coryell and Billings, 1932) from the Pennsylvanian Wayland Shale, Texas, USA, in its antero-ventrally protruded anterior margin, but it differs in that it has an orthogonal posterior cardinal angle, its highest point at mid-length from the venter, and a longer lateral outline. Waylandella sp. is also similar to W. boleensis Jiang in Jiang et al., 1995, from the Pennsylvanian Dongtujinhe Formation, Xinjiang, China, in its elongate lateral outline, but it differs in that it has an antero-ventrally protruded anterior margin, widely arched dorsal margin, and a sinuate ventral margin. Waylandella sp. is similar to W. insolita Jiang in Jiang et al., 1995, from the Pennsylvanian of Xinjiang, China, in its narrowly arched anterior margin, but it differs in that it has an elongate lateral outline, its highest point at mid-length from the anterior end, and a sinuate ventral margin.

Results

Only two of the eight samples contained ostracodes, these being sample locality No. 36 (39°08′51.5′′N, 141°38′56.7′′E) from the Middle Member and sample locality No. 46 (39°09′00.8′′N, 141°38′52.7′′E) from the Upper Member. Furthermore, specimens from sample locality No. 46 were deformed due to diagenesis. Totals of 328 specimens and 16 specimens were extracted from No. 36 and No. 46, respectively (Table 1). Thirty ostracode species, including 12 genera, were identified (Table 1; Fig. 18), most of which were endemic species and 10 of which were new species. The details of each species are provided in the next section. Conodont elements that contain P₁ elements of Neognathodus spp. were recovered from localities No. 30 and No. 46, respectively (T. Maekawa, personal communication, March 23, 2022). Neognathodus is an index genus for the Bashkirian–Moscovian, and supports the determination of the age of the Nagaiwa Formation from fusulinids (Kobayashi, 1973).

Figure 18. Ostracode assemblages from two sample localities. White circles show that ostracodes were recovered (localities 36 and 46), shaded circles show that there were no ostracodes. Abbreviations: Fm., Formation; L., Lower.

Table 1. Ostracode species extracted from two sample localities (Loc. 36, Loc. 46) from the late Carboniferous Nagaiwa Formation, Northeast Japan. Each number shows number of specimens; white circles under C Japan (= central Japan) and Xinjiang indicate presence of the species.

Paleoecology of ostracodes from the Nagaiwa Formation

The assemblages from the Middle Member (No. 36) contained many ostracodes, including Samarella hataii, two Kirkbya species, three Jordanites species, two Thuringobolbina species, three Punctoprimitia species, three Pseudobythocypris species, two Platyphomboides species, four Healdia species, and one species of Weylandella. Based on a comparison with European assemblages, the ostracode fauna suggests a marine nearshore environment (Bless, 1983). Jordanites, Kirkbya, and Healdia, which have been reported from the Pennsylvanian paralytic coal basins of northern Spain, indicate marine nearshore to shallow offshore environments (Bless, 1983). In other localities, Samarella, Thuringobolbina, and Punctopurimitia have been reported from Ordovician (Russia) to Devonian (Russian Platform, northern Spain, Australia, and Ohio) sedimentary deposits. These genera, however, have not been reported previously from the Carboniferous. Thuringobolbina has been reported in non-polyzoan/sponge assemblages from the Devonian Receptaculites Limestone, New South Wales, Australia (Reynolds, 1978), where the depositional environment seems to be a fairly stable offshore shelf environment. Thuringobolbina has not been reported from other Carboniferous localities; thus, its microhabitat is uncertain.

Compared with ostracode species from the Middle Member, the Upper Member ostracodes are fewer and have low diversity (Fig. 18). Stocker et al. (2016) first reported a “Eiferian mega-assemblage” from central Japan (the Middle Moscovian Ichinotani Formation) composed of Amphissites, Kirkbya, Bairdia, Aechmina, and Healdia. The Eiferian mega-assemblage typically represents high-energy turbulent conditions in a shallow carbonate platform setting (Becker, 1971). In summary, the ostracode assemblages from the two sample localities of the Nagaiwa Formation indicate shallow marine conditions.

Paleogeography of the Pennsylvanian of Japan

Species of Hollinella and Jordanites were widely distributed during the Pennsylvanian in a limited range of marine-nearshore and shallow-offshore environments (Bless, 1983) as is the extant podocopid ostracode (Tanaka and Ikeya, 2002). Seventy-one Hollinella and Jordanites species have been reported from 31 localities in Pennsylvanian strata around the world (Table 2). Q-mode cluster analysis of these globally distributed hollinellid taxa connected by UPGMA (unweighted pair group method with arithmetic mean) using Jaccard coefficient in the software PAST (Hammer et al., 2001) showed that four Hollinellid associations could be recognized (Fig. 19): Association I was characterized by H. bassleri Knight, 1928a, at Locs. 16, 20; Association II consists of four localities (Locs. 8, 9, 11, 12) and was characterized by H. grahamensis (Harlton, 1927), H. shawnensis Kellett, 1929, and H. oklahomaensis (Harlton, 1928); Association III was characterized by H. plauta Kesling and Tabor, 1953, J. camochensis Sanchez de Posada, 1977, and J. cristinae from five localities (Locs. 7, 13, 15, 18, and 25); and Association IV consisted of two localities (Locs. 1, 5) and is characterized by J. modica.

Figure 19. Dendrogram of Q-mode cluster analysis of Hollinellid ostracodes from the Pennsylvanian of the world. Original data are from Table 2 and data matrix, both attached in Supplement 1. Roman numerals correspond to localities in Table 2. Italic number of each node shows the Bootstrap values (n = 1000).

Table 2. Hollinellid ostracodes from the Pennsylvanian. Location (Loc[s]) numbers correspond to those in Figure 12. Gray-shaded lines show the genus Jordanites.

Three associations (I–III) were distributed around the equatorial region of the Pangea paleocontinent, but association IV was distributed between the eastern part of North China and the South Kitakami belt (Fig. 20). Nine Jordanites species have been reported; with three species in two localities, and six confined to one locality (Fig. 20). Jordanites modica has been reported from Japan (Loc. 1 in Table 2, Fig. 20) and the Tarim Basin (Loc. 5 in Table 2, Fig. 20), but not reported from South China (Locs. 28–32). Jordanites camochensis was found in Spain (Loc. 18) and the Moscow Basin (Loc. 25), Jordanites cristinae has been reported from southern England (Loc. 15) and Spain (Loc. 18). These two species, J. camochensis and J. cristinae, occur in the eastern margin of the Pangea paleocontinent near the equator.

Figure 20. Paleogeographical distribution of shallow-marine Jordanites species during Pennsylvanian. Paleogeographic map is from Torsvik and Cocks (2017). Each Arabic numeral corresponds to the locality number in Table 2, and each Roman numeral (I–IV) shows Hollinellid association detected from Q-mode cluster analysis of Figure 19.

Conclusions

Thirty ostracode species, including 12 genera, have been identified from the Pennsylvanian Nagaiwa Formation, Northeast Japan. The ostracode assemblages from the Nagaiwa Formation indicate a shallow marine environment and are assigned to the Eiferian mega-assemblage which typically represents high-energy turbulent conditions in a shallow carbonate platform setting. The ostracodes from the Nagaiwa Formation show no clear affinities with any other comparably aged fauna.