The genus Branchamphinome Hartman, 1967 is a moderately understood genus of Amphinomidae that differs morphologically from most other genera in the form of its chevron-shaped caruncle and the presence of branchiae from chaetiger 1. Branchamphinome is presently represented by two deep-water species: B. antarctica, described from the Southern Ocean and B. islandica, from Iceland. We describe a new species of Branchamphinome from shallow South-west Atlantic waters, coast of Brazil. The new taxon revealed the surprising presence of notopodial hooks in chaetiger 1, which was subsequently also found to be present in the lectotype of B. antarctica. Both the genus and Hartman's species are emended to include this morphological feature. Historically, the presence of notopodial hooks has long been considered a diagnostic character for the genus Paramphinome, particularly when distinguishing Paramphinome from Linopherus. Branchamphinome tropicalis sp. nov. was found inhabiting sand sediments at depths of 150 m and temperatures of 16–20°C. Branchamphinome tropicalis sp. nov. differs from its congeners by its characteristic and highly developed pigmentation pattern, shape of the caruncle, branchiae and disposition of prostomial eyes. This is the first report of this genus from shallow tropical waters.

Six nephtyid species were identified from samples collected off the west coast of Saudi Arabia. Two of these species had been previously reported for the Red Sea (Inermonephtys aff. inermis, Nephtys palatii), three are new records (Aglaophamus lobatus, A. cf. verrilli, Micronephthys stammeri) and one is new to science (Inermonephtys aramco). Inermonephtys aramco was collected in the southern region of the Red Sea at depths between 60 and 83 m. It is characterized by the presence of branchiae from chaetiger 15 or 16, well-developed parapodial prechaetal lamellae, broadly rounded notopodial postchaetal lamellae and rudimentary neuropodial postchaetal lamellae. The species Nephtys palatii is transferred to the genus Micronephthys. Based on the current finding, the previously known bathymetric range of Micronephthys stammeri is extended from 4–7 to 17 m, and occurrence depths for N. palatii are given for the first time (4–90 m). Full descriptions are included for all species except M. stammeri. An identification key for all the species known to occur in the Red Sea is provided.

This study recognizes six species of onuphid polychaetes associated with the Cymodocea nodosa meadows of the Canary Islands. Of these, three species of the genus Aponuphis, A. bilineata, A. brementi and A. ornata have been previously reported from the eastern North Atlantic, whilst A. willsiei was only known from the western Mediterranean Sea. We describe two new species: Onuphis erici sp. nov. and Kinbergonuphis sanmartini sp. nov., of which the latter represents the first discovery of the genus Kinbergonuphis in the eastern North Atlantic Ocean. Furthermore, we present brief notes on their ontogeny and ecology and remarks on the presence and microstructure of lateral organs observed in one of the new species.

Cirrophorus nikebianchii sp. nov. is described from brackish-water and organically enriched marine environments of the Mediterranean Sea. The new species is characterized by a very small prostomial antenna and a high number of branchiae pairs. A phylogenetic analysis carried out through the use of three molecular markers (16S rRNA, 18S rRNA and COI) supports the distinction between C. nikebianchii and C. furcatus, a closely related species with which it has been misidentified. Preliminary results obtained show that the genera Cirrophorus and Paradoneis are not reciprocally monophyletic, with uncertain relationships with the remaining genera of Paraonidae. This outcome suggests that the evolutionary history of Paraonidae is less straightforward than previously supposed. Moreover, the uncertainty about the taxonomic status of Paraonides neapolitana, type species of the genus Paraonides, makes the revamping of the taxonomy of Paraonidae more challenging. Awaiting support from studies including more species, and based on morphological and genetic data as well, we suggest to provisionally maintain the current use of Cirrophorus and Paradoneis, and to assign to Paraonella the species traditionally assigned to Paraonides.

Two new species of Cossura Webster & Benedict, 1887 were found in material collected during sampling from the terminal lobes of the Congo deep-sea fan. They were described using light and scanning electron microscopy. Cossura platypus sp. nov. has 15–17 thoracic chaetigers, a prostomium longer than it is wide, with a widely rounded anterior margin, an abruptly expanded posterior prostomial ring the same length as the peristomium, without a mid-ventral notch, a branchial filament attached to the midlength of chaetiger 3, and a pygidium with three anal cirri. Cossura platypus sp. nov. is similar to C. brunnea Fauchald, 1972 but differs in the shape of the prostomium, which is widely rounded anteriorly in C. platypus sp. nov. and is broadly triangular in C. brunnea; furthermore, C. platypus sp. nov.is uniformly pale, whereas C. brunnea has dark pigmentation. Cossura candida Hartman, 1955 differs from C. platypus sp. nov. in the conical shape of the prostomium and 24–35 thoracic chaetigers. Cossura flabelligera sp. nov. has 16–19 thoracic chaetigers, a conical prostomium, and a branchial filament arising from the posterior part of chaetiger 2; the entire body, including the chaetae, is covered by a thick mucous sheath similar to the tunic of flabelligerids. Cossura flabelligera sp. nov. resembles C. longocirrata Webster & Benedict, 1887 in the position of the branchial filament, the shape of the prostomium, and the number of thoracic chaetigers; it differs in having a thick mucous sheath. This character seems to be unique for the Cossuridae.

Among the polychaetes, the family Cirratulidae is one of the most challenging taxonomically because most of the currently used diagnostic characters change during ontogeny. It is therefore necessary to use a combination of characters to make an accurate identification. The present work is the first of a planned revision of the genus Cirratulus from coastal zones of Argentina. The examined material came from the two largest natural history museums of the country, and showed several morphotypes. Some specimens corresponded to described species, but others were undoubtedly undescribed. Among the previously known Cirratulidae, Cirratulus jucundus (Kinberg, 1866) and Cirratulus patagonicus (Kinberg, 1866), formerly distributed for Antarctica are now also present in coastal continental areas of Argentina. The new species Cirratulus mianzanii sp. nov. is described from subtidal areas off Peninsula Valdés, Patagonia. This species is distinguished from its congeners by the segmental origin of both tentacular filaments and first pair of branchiae in the junction between the peristomium and first chaetiger. Branchiae arise some distance from the notopodium but not at the dorsal midline of the body. Ventral groove present along the body, with a fine dark midline. Capillary chaetae are serrate seen under an optical microscope, and the segmental origin of neuro- and notopodial spines is different from other species of the genus.

The new species Abarenicola wellsi n. sp. from the Falkland Islands is described along with a re-description of Abarenicola brevior n. stat. with which it had previously been confused. The two species are distinguished using both morphological and molecular techniques, new characters are described and previously recognized characters are clarified, all of which support the assignment of species status as opposed to subspecies. Both species are part of the Abarenicola assimilis ‘group’ within which all taxa were originally described as subspecies. The group as a whole is re-evaluated and all members are elevated from subspecies to species status based mainly on the new characters of shape, distribution and pigmentation of the proboscidial papillae. The group now consists of six species: Abarenicola assimilis n. stat., A. brevior n. stat., Abarenicola devia n. stat., Abarenicola haswelli n. stat., Abarenicola insularum n. stat. and A. wellsi n. sp.

The definitions of terebellid genera have caused considerable confusion. Some genera, such as Pista Malmgren, 1866, are clearly not monophyletic and the need to revise them is widely accepted. A phylogenetic analysis of genus level morphological characters within the Axionice/Pista complex and other Terebellidae with large lateral lobes revealed two well defined groups; these differed in the arrangement of different forms of lateral lobes on segments 1–3, the shape of the branchiae, structure of the ventral pads and, if present, the origin of the manubrium on the uncini. One of the groups includes the type species of Pista; the other includes the type species of Axionice and almost all the other genera whose taxonomic status is discussed in this paper (Betapista, Eupistella, Lanice, Loimia, Paraxionice) which we propose to treat as its junior synonyms. Three other genera – Lanicides, Lanicola and Scionella – did not fall within these two groups; they are accepted as distinct. A complete list of species of Axionice and Pista is provided; 39 species currently included in Pista should be moved to Axionice, thus Axionice includes at least 94 species. Many authors’ descriptions of the type species of Pista (Amphitrite cristata Müller, 1776) conflict with the original description. Amphitrite cristata s. str. has been described as a new species: Scionella lornensis Pearson, 1969 and the type species of a new genus: Pistella Hartmann-Schröder, 1996. Scionella lornensis is here considered a junior synonym of Amphitrite cristata. Redescriptions of the type species of Axionice and Pista are provided.

A new species of Terebellidae, Loimia ramzega sp. nov., has been identified from North Brittany beaches (English Channel). This new species is characterized by its gigantic size (max 650 mm, live), two pairs of lateral lappets on segments 1 and 3; first pair more ventral, second pair more developed and lateral but oblique, with wavy edge. Nine ventral pads from segment 2 (fused on segments 2 and 3), first three pads swollen, next ones subsequently decreasing in size. Three types of notochaetae, asymmetrically bilimbate, symmetrically bilimbate and capillary. Uncini pectinate with 6 teeth (some with 5 teeth) slightly decreasing in size, in one vertical row. Pygidium with about 14 long conical marginal papillae surrounding anus.

During several sampling periods in the Northern Adriatic Sea (Mediterranean) from 2003–2010, one species of Pista and one of Pistella were found. They were initially identified as Pista cf. lornensis (Pearson, 1969), but detailed examination revealed the presence of two new species, one belonging to the genus Pistella Hartmann-Schröder, 1996, P. rovignensis sp. nov. and one belonging to the genus Pista, P. adriatica sp. nov. These two species differ from each other in the structure of the branchiae, shape of lateral lobes and the structure of the anterior thoracic uncini. The two new species are compared with other species of Pistella and Pista currently known. The relationship of Pistella and Pista is confusing and a complete revision of the two genera is urgently needed together with other genera characterized by having long-handled thoracic uncini.

A new Spiogalea species is described from South-east Brazil. The specimens were collected in muddy bottoms during a large survey (15–3000 m) in southern Brazil. This genus comprised, up to now, only one species described from Capbreton Canyon (Bay of Biscay). The new species differs from the type-species, mostly in the morphology of the prostomial chitinous plate, a character restricted to the genus Spiogalea. With this new species, the generic diagnosis of the genus was amended.

Four species of Laonice (Annelida: Spionidae) were collected from the lower bathyal depths (3300–3700 m) in the Whittard Canyon, NE Atlantic. Two are herewith described as new species: Laonice whittardensis sp. nov. and Laonice natae sp. nov. The other two are Laonice blakei Sikorski & Jirkov, 1988 and Laonice magnacristata Maciolek, 2000. Laonice whittardensis has genital pouches appearing from chaetiger 3, prostomium free of peristomium and bidentate hooks. Laonice natae belongs to the subgenus Appelloefia nov. with prostomium distinct from the peristomium, more than two vertical rows of capillaries in several anterior chaetigers, genital pouches present on a limited number of segments or totally absent. However, the absence of pronounced anterior widening of the body together with anterior branchiae, which are remarkably (nearly twice) longer than the notopodial postchaetal lobes, the narrow lanceolate notopodial postchaetal lobes, the pronounced pointedness of all postchaetal lobes (both notopodial and neuropodial) in the anterior half of body at least, and absence of genital pouches and the size of the body all distinguish L. natae from other species belonging to this subgenus. An identification key to all nine known deep-water (>400 m depth) Laonice species in North Atlantic is given and four previously recognized sub-generic groups are formally named: Laonice, Sarsiana subgen. nov., Appelloefia subgen. nov., Norgensia subgen. nov.

Alien polychaetes belonging to the genus Marenzelleria were recorded from the mouth of the Don River and Taganrog Bay in the Sea of Azov in February–March 2014. Morphological characteristics varied greatly and matched those of two species: M. neglecta and M. arctia. Some individuals did not match the descriptions of both species. A genetic study using different sequences (primarily COI, but also 16S, 28S, cytb and nuclear histone 3a) showed that only M. neglecta was present despite some morphological mismatches. A morphological description of the species according to the new data is presented, together with a revised table of variability of the key numeric characters. Since 2014, Marenzelleria has spread swiftly and become dominant in a considerable part of the Taganrog Bay, making up to 91% of the total abundance/biomass (6800 ind. m−2 and 31.2 g m−2, respectively). Monodominant sites were also present. Its occurrence is 100% in recent surveys. Such a sharp increase seems to be due to a lack of detritophages in the bay; this is supported by the fact that M. neglecta has not formed its specific assemblage. The community structure, if M. neglecta is excluded, is equal to that before the invasion. In the Sea of Azov itself, M. neglecta is not as abundant, but occurs up to the Strait of Kertch and at some sites in the Black Sea. Its spread further into the Black Sea seems possible, as well as into the Caspian Sea via the Volga-Don Canal.

The Mediterranean fan worm, Sabella spallanzanii (Gmelin, 1791), is a highly invasive pest species introduced to Australia and New Zealand, with the ability to alter marine ecosystems by outcompeting native species for food and space. Sabella spallanzanii has been established in southern Australia for decades, but was discovered in Botany Bay (NSW, eastern Australia) in 2013. In New Zealand, S. spallanzanii was first detected in March 2008. Using cytochrome c oxidase subunit 1 (COI) sequences, we investigate the phylogeography of the Australian and New Zealand populations of S. spallanzanii, including the possible origins of the recent incursions in both countries. Australian and New Zealand S. spallanzanii show minimal genetic diversity (0.2% divergence) and were dominated by two main haplotypes suggesting a commonality. Our molecular data are insufficient by themselves to identify fine-scale invasion pathways in antipodean S. spallanzanii, but the similar, minimal haplotype diversity in combination with well-constrained field survey data suggests that the New Zealand incursion originated from southern Australia, rather than as a new incursion from the Mediterranean Sea. This highlights the importance of ongoing marine biosecurity surveillance and monitoring as well as improvements to biosecurity protocols for international and domestic vessels. The origin of the eastern Australian (Botany Bay) incursion is plausibly derived from either southern Australia or as a ‘return’ from New Zealand, and requires further, more detailed investigation.

A temporal analysis of the benthic polychaete community and its relationship with environmental variables was conducted by comparing coastal sediment samples collected in three separate sampling events between 1998 and 2013 from the southern end of the Southern California Bight (SCB). Environmental variables indicated a spatio-temporal increase of the sand fraction in sediment composition. Station stratification by depth from shallow to deep, and a reduction of trace metal enrichment (Co, Cr, Cu, Mn, Ni, Pb and Zn) was also found. There was a notable change in polychaete family composition due to high abundances and frequency of Spionidae, Chaetopteridae and Phyllodocidae in 2013, especially close to the Binational wastewater treatment plant discharge. An increase in polychaete abundance, richness and diversity was indicative of a probable relationship with regional weather conditions (El Niño-Southern Oscillation and recent drought events during sampling) along with local anthropogenic discharges of wastewater treatment plants in the area.

Six benthic biotic indices (Shannon–Wiener H′log2, W-statistics, BOPA, BENTIX, AMBI and M-AMBI), based on different ecological principles, were applied to assess the health of variously disturbed tropical intertidal habitats of the Port Blair coastline. A total of 243 replicate samples were collected during the dry period (January, February and March) of 2014–2016. Temperature, salinity, dissolved oxygen, sediment pH, total organic matter content and texture were analysed. A high mean abundance of opportunistic species (Orbinia sp. 748, Capitella singularis 237 and Armandia sp. 114 ind. m−2) was observed at Phoenix Bay, a gradual decline in diversity at Junglighat and a comparatively high diversity and moderate biomass at Wandoor, reflecting a human pressure gradient. Results showed an annual decline of benthic quality from 2014 to 2016 (good to moderate). Overall BOPA failed to distinguish the magnitude of disturbances, while the rest of the indices classified the benthic quality from undisturbed/high (WD), slightly disturbed/good (JG), to moderately disturbed/moderate to poor (PB). The subjective analysis demonstrated that the urban centres corresponded to disturbed benthic communities of dominant first and second order opportunistic species, while sensitive (EGI) and indifferent (EGII) were associated with the least disturbed or undisturbed site. The study successfully demonstrated the performance of temperate indices in intertidal habitats against the mild organic enrichment. However, for an effective assessment, setting natural reference conditions and sampling in stable dry periods (strong seasonality in tropics) is desirable. In order to test the performance of biotic indices, a long-term monitoring approach of taking abiotic and biotic descriptors into account is recommended.

An increasing number of studies have forecast the potential responses of marine life to future climate change. This study predicts how the distributional range of temperate and tropical worm reefs (WRs) might respond to climate and environmental changes (CECs). Compared with current distributions, the tested hypotheses were: (i) under a low CO2 concentration and active atmospheric carbon capturing scenario (RCP2.6), both tropical and temperate WRs will maintain their current distributions and face only slight multi-directional biogeographic changes along the century; and (ii) under a high CO2 concentration scenario (RCP8.5) WRs will shift toward higher latitudes, with marked changes for tropical species and slight changes for temperate species, specifically at the end of the 21st century. The hypotheses were tested using species distribution modelling, and exploratory statistical analyses were performed to tune model settings. Under scenario RCP2.6, in the middle of the century, areas of suitable habitat are predicted to slightly increase for the temperate WRs and conversely contract for tropical WRs. At the end of the century, multi-directional shifts without range retraction were predicted for both species, but tropical WRs showed major changes in their distribution. Under scenario RCP8.5 and throughout the century, multi-directional shifts increased the areas of suitable habitat for temperate WRs, whereas tropical WRs experienced shifts toward high latitudes and significant retraction at low latitudes. Results indicate that biogeographic range shifts are idiosyncratic for temperate and tropical WRs depending on the CECs scenarios considered.

Spatial variations of polychaetes along the Baja California Peninsula continental shelf were analysed in two ways: (1) by evaluating the species richness and defining the faunal assemblages from local sampling, and (2) by characterizing the latitudinal variation of beta-diversity based on the distribution of all polychaetes reported up to now. Twenty-seven stations from three oceanographic expeditions were sampled, and 2858 individuals from 38 families and 231 species were identified. Polychaetes were abundant (mean = 37.5 ind 0.1 m−2) and diversified (mean = 15 species station−1). Differences in species composition defined seven faunal assemblages, but their number of species did not show significant latitudinal changes. The beta-diversity analysis was based on distribution data of 730 species from 47 families. The presence of a group of islands in the middle Gulf could have a negative effect on the species distribution, since the lowest values of β T-diversity (0.39) were found in the northern Gulf, but their species were different from those recorded in the central region. The wide variation in β T-diversity (0.5–0.87) showed latitudinal changes in the species composition, mainly in the Gulf mouth (0.86–0.87), which indicated that the fauna inside the Gulf was different from that inhabiting the Pacific coasts. The ICE and Chao2 estimators showed that the polychaetes in the study area are relatively well known (>80%), and that most species (415) have small distribution ranges. The effects of these infrequent species were similar at each latitudinal band, which suggested that the observed β T-diversity pattern could represent a suitable estimation.