During our research programme about mussel spat in Amsa Bay, we found some specimens of Hesione sicula delle Chiaje, 1830 and noted as the first record for Mediterranean Moroccan coasts and for the Mediterranean coastlines of North Africa. Five specimens of this species were collected for the first time in the Amsa shellfish farm on October 30, 2021, and we provide some characteristics and illustrations for the species. This new record from the bay contributes to the Polychaeta list of North Africa and expands the geographical distribution range of species within the Mediterranean Sea.

The reproductive cycle of Marphysa sanguinea is described for a population at Mount Edgecombe, Plymouth, near the type location in Southwest England, using a data set obtained previously (October 1999 to September 2000). The species is iteroparous without schizogamy, spawning prior to October 1999 and during a short breeding season in 2000 from end August through September. The sexes are separate with a sex ratio of 1:1. Mature oocytes and spawned eggs are 215 μm in diameter and spermatozoa of the ectaqua sperm type. Mature gametes of both sexes are discharged through paired coelomoducts, and the diploid chromosome number is 28. Proliferation of new coelomic gametes from paired gonads began within a month of spawning and continued for 8–9 months but ovulation was suppressed in June and July. Attempts to undertake fertilisation using spawned oocytes and active spermatozoa were unsuccessful. The size of discharged oocytes suggests a short pelagic larval duration of a few days. This is the first publication about the reproduction of this species, and our results suggest that M. sanguinea is restricted to intertidal areas in SW England, NW France and southern North Sea. The highly synchronised pattern of reproduction observed is not compatible with a quasi-cosmopolitan species range indicating that this species has been mistakenly reported from around the world. Future studies of the genus should combine rigorous taxonomy with observations of reproduction to facilitate comparison among Marphysa spp.

Shovelhead worms are common polychaetes around the British Isles and have been recorded in numerous ecological surveys. Yet, understanding of their habitat conditions is poor, based heavily on visual observations of sediments from historical records. In this study, the drivers of abundance and geographical distribution of two morphologically and behaviourally diverse species Magelona alleni and Magelona minuta are investigated by reanalysing sediment characteristics and depths from museum marine monitoring surveys. Although both species are historically associated with muddy sediments, the records herein suggest that M. alleni occurs in an extensive range of sediments, but is more abundant at localities with more than 25% sand. In comparison, M. minuta shows a negative linear relationship between grain diameter and abundance, corroborating previous work that the species is abundant in fine-grained mud. The depth records show that while M. alleni predominates below 60 m, M. minuta is a distinct offshore species. These differences may be attributed to the interspecific variation in morphology and motility between the species: M. alleni is stout and tube-dwelling, while M. minuta is fragile, small, and fairly motile. To corroborate these findings, sediment grains from tubes of M. alleni were classified using the Udden–Wentworth grain size scale and suggest sand is the key component for tube construction. Overall, this study highlights that sediment parameters for M. alleni have been misinterpreted and generalised in historical records, emphasising the importance of quantitative sediment analysis in defining the habitat of Magelona.

Polychaetes from tropical ecosystems of the eastern Pacific have been poorly studied; thus, the aim of this study was to analyse their taxonomic composition in the southern Mexican Pacific shelf and to examine their biogeographic affinities. A total of 3741 specimens from 82 species, 52 genera, and 27 families were identified from 38 stations at 42–109 m depth. The Sedentaria group was more diverse (40 species, 48.8%) and abundant (1753 ind., 46.9%) compared to the Errantia (36 species, 43.9%; 346 ind., 9.2%) and the Basal Annelida groups (6 species, 7.3%; 1642 ind., 43.9%). The families Onuphidae (14 spp.), Spionidae (8 spp.), and Paraonidae (8 spp.) were the most diverse. The Amphinomidae and Spionidae accounted for 72.6% of the fauna; the remarkably high abundance of both families together is unusual in the tropical eastern Pacific. The polychaete species had high biogeographic affinities with the Mexican tropical Pacific ecoregion (45.1%), which has tropical conditions, and the Cortezian (29.3%), which has warm-temperate characteristics. Twelve amphiamerican species and ten with worldwide distribution were found. The tropical eastern Pacific is one of the world regions with the lowest number of polychaete records, thus underlining the importance of the taxonomic and biogeographic information provided here. The sampling effort should increase, since the non-parametric estimators indicated that 116–138 species were expected, instead of the 82 species actually found.

Pisione Grube, 1857 was considered rare animals, but its numbers have increased in recent decades. New species have been described, mainly from the Indo-Pacific region. In this study, we described Pisione balasubramaniani sp. nov., from Tamil Nadu, southeastern coast of India. The new species resembles other species in the ‘remota complex’ in the shape of the copulatory organs, elongated ventral cirri on the first segment and a short dorsal cirrus on the second segment. It can be distinguished from members of this group by having protruding notoacicula from the anteriormost to the very last chaetigers, three pairs of copulatory organs on chaetigers 15–17 and variances in the morphology of the copulatory organ. We also provide an updated comparison between all known species of Pisione based on key morphological characters. We also present a discussion of species of this genus in India and nearby regions.

A new species belonging to the genus Trophoniella Hartman, 1959 (Polychaeta: Flabelligeridae) was described from the coastal area of Civitavecchia (Northern Tyrrhenian Sea). The species was collected in gravelly coarse sands from Posidonia oceanica beds at around 7 m depth. Trophoniella cucullata sp. nov. clearly differs from all other congeners species primarily by the distribution of the sediment grains on the body and by the starting point of the anchylosed neurohooks. Diagnostic morphological traits for the identification of the species are discussed. The description of Trophoniella cucullata sp. nov. in the same P. oceanica biocenosis where other species have been recently reported in the Northern Tyrrhenian Sea, testifies to the role of this marine phanerogam as a biodiversity hotspot.

The present study reports polychaetes that bore into limestone rocks along the east coast of the Aegean Sea (eastern Mediterranean). Rock materials were collected at two depth intervals (0–5 and 5–10 m) at 15 stations in four localities of Ildırı Bay. A total of 276 specimens belonging to 12 species and four families (Eunicidae, Spionidae, Cirratulidae and Sabellidae) were recorded. Specimens belonging to Dodecaceria and Pseudopotamilla were identified at the genus level, because they differ from described species, were few in number or were in poor condition. Dipolydora giardia is a new species to the marine fauna of Turkey. The most dominant and frequent family in the area was Eunicidae, followed by Spionidae. Lysidice ninetta and L. margaritacea comprised 59% of the total number of individuals. The number of species and individuals, and the diversity index did not change with regard to depth or locality. Two species assemblages were found in the area, mainly formed by Dipolydora and Lysidice species. The Lessepsian species, Palola valida, which is a new record for the Aegean Sea, occurred abundantly at the study sites, posing a risk of damage to limestone rocks in the Mediterranean Sea. The morphological features of the species identified at the generic level and the burrow structure of these species are presented. The burrow shapes of Palola siciliensis and P. valida were described for the first time in the present study; they constructed complicated galleries, including more than four entrances.

Morphological and genetic investigations have led to the identification of Spiophanes adriaticus sp. nov. (Polychaeta: Spionidae) from the North Adriatic Sea (Central Mediterranean). A total of 81 specimens were recorded along the sublittoral zone between 8 and 27.5 m of depth. This species differs from other congeners by having: two pairs of black eyes, a cirriform occipital antenna, dorsal ciliated organs as thin bands usually extending to chaetigers 11–12, dorsal ciliated crests from chaetiger 14–17, undulate glandular opening on chaetigers 5–7, unhooded hooks from the 15th chaetiger and Y shaped tubes. A detailed description and illustrations are provided for the new species. Through DNA barcoding results and comparison of DNA sequences of the new species with those of other congeners available in the GenBank database, the validity of the new finding was confirmed. Spiophanes adriaticus sp. nov. represents the eighth species of Spiophanes recorded for the Mediterranean Sea. A key for the identification of Mediterranean Spiophanes species is also provided.

The syllid genus Anguillosyllis is relatively rare and mainly restricted to deep waters. The phylogenetic position of the genus was only recently inferred, while its reproductive mode, an important trait in the classification of the Syllidae, remains unknown. We describe herein our finding of one specimen of Anguillosyllis lanai with fragile egg capsules dorsally attached to some parapodial lobes, the first observation to date providing information about reproductive aspects of animals of the genus, and discuss possible evolutionary and phylogenetic implications of this finding.

The present study is the first attempt to describe beta-diversity patterns in polychaetes of the Caribbean Sea, analysing depth changes in species composition of the Eunicida and Amphinomida inhabiting dead coral in Chinchorro Bank, southern Mexican Caribbean. In April 2008, dead coral fragments were collected by scuba diving in eight stations along two bathymetric gradients (4–9 m and 7–16.2 m depth); 755 individuals from 53 species of the families Amphinomidae, Dorvilleidae, Eunicidae, Lumbrineridae, Oenonidae and Onuphidae were identified. The highest number of species (32) and individuals (514) were found in the family Eunicidae. The Northern transect harboured 36 species, on average 18.75 ind. L−1, which decreased linearly with depth; the Central transect had 43 species, on average 19.01 ind. L−1, which increased at middle depths. The species inhabiting both these zones were moderately different (βsor = 0.603): 49.06% of the fauna occurred on both transects, but the components of beta-diversity, turnover and nestedness, displayed distinct patterns: in the Northern one replacement was the dominant factor (βsim = 0.3–1; βnes = 0–0.091), practically representing all faunal differences (βsor = 0.391–1); in the Central, dissimilarity due to nestedness increased (βnes = 0.031–0.829), mainly at the shallowest stations, but from 5 m depth, beta-diversity was almost completely explained by species replacement (βsim = 0.417–0.5; βnes = 0.031–0.318). Faunal differences were mostly related to higher abundances of Lysidice caribensis, Eunice goodei and Lumbrineris floridana in the Northern zone, and Lumbrineris perkinsi, Nicidion obtusa, Lysidice caribensis, Lumbrineris floridana, Lysidice unicornis and Eunice mutilata in the Central zone.

Many marine annelids are active tube builders. Several polychaete families make agglutinated tubes by fixing sediment particles with specific secretions from their epithelial glands. The fine structure of the tubes of six species of Maldanidae from five genera (Nicomache minor, N. lumbricalis, Maldane sarsi, Praxillella praetermissa, Axiothella catenata, Rhodine gracilior) was examined by scanning electron microscopy. These species exhibit different lifestyles. Nicomache minor and N. lumbricalis inhabit massive hard tubes attached to stones. Other species live in the sediment, Rhodine in rigid organic tubes, Praxillella, Axiothella and Maldane in sand or mud tubes. All the examined maldanid tubes have a similar basic structure. The inner sheath of the tubes is made of a hardened organic lining secreted by the worm. Fibres from the inner sheath fasten sediment particles of the agglutinated layer. In Nicomache the tube surface is covered with a fibrous outer layer. All tube layers contain variously arranged organic fibres, which form a 3D network in the agglutinated layer and fabric-like linings in the inner sheath and outer layer. The tubes of Maldanidae may be important for taxonomy, and useful for identification of fossils.

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.

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.

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.

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.

Reproduction in the shallow-water, sponge-dwelling, branching syllid Ramisyllis multicaudata exhibits several features unique among syllids and among annelids in general. We describe and illustrate the segmental asymmetry which intervenes between regions of symmetry, only found in branching annelids. We describe the morphology of the stolons and of the stolon stalks, which are unique to branching syllids but differ in detail from those of the other known branching syllid, Syllis ramosa. We also illustrate newly found paddle-shaped chaetae, which might indicate that these stolons do swim. We list the number of branch points and termini in an effort to gauge the extent of branching in a worm contained in a small sponge. The species appears to have separate sexes, but this cannot be proven. We compare R. multicaudata and S. ramosa as originally described and find new morphological differences between the branching syllid from Japan described as S. ramosa and R. multicaudata. We also compare the known stolons of branching syllids to those of other genera of the ‘ribbon clade’, a group including Trypanobia and Trypanosyllis, now known to be close relatives of R. multicaudata. Ramisyllis multicaudata is the first member of the ribbon clade, and one of few Syllinae, known to have sexually dimorphic stolons.

Larvae of ~100 species of benthic invertebrates were obtained from the vicinity of Tomales Bay and Dillon Beach, California, over a 6-year period (1971–1977). This study reports on larvae of 14 species in eight families of polychaetes: Micronereis nanaimoensis, Nereis vexillosa, Sthenelais fusca, Nephtys caecoides, Nephtys californiensis, Boccardia berkeleyorum, Polydora pygidialis, Polydora spongicola, Dipolydora cardalia, Mediomastus californiensis, Ampharete labrops, Phragmatopoma californica, Sabellaria cementarium and Pectinaria californiensis. Some species were cultured from embryos obtained from laboratory fertilizations or field-collected egg masses or capsules. Larvae of other species were obtained from meroplankton and some of these were cultured through metamorphosis. A summary table is presented documenting seasonal occurrence of 60 polychaete taxa in the meroplankton.

Among the polychaetes, the Syllidae comprise numerous species whose study over many years has benefitted from valuable revisions and descriptions of new species in Europe. This abundant literature proves very useful for revisiting the taxonomy and distribution of the Syllidae in the English Channel (EC), mainly as regards existing studies on coarse sediment communities in the eastern part of the Channel. This habitat is one of the most widespread in the EC and is known as favourable for the small polychaete fauna including Syllidae. A 2-year survey (winter and summer sampling periods) covering 19 stations, associated with the Branchiostoma lanceolatum coarse sand community offshore Dieppe-Le Tréport, led to the identification of 6537 individuals from 29 taxa including 27 species. Six fine sand stations were also sampled in which only 12 individuals were collected. Among these species, seven are new for the EC polychaete fauna and six others are observed for the first time in the eastern part of the EC. All the new species for the EC are warm temperate species previously only known south of the Bay of Biscay. The Syllidae list given in Dauvin et al. (2003) has been re-analysed and amended with our list and that of the Chausey Archipelago study (Olivier et al., 2012). To date, 91 Syllidae species have been recorded in the EC and are established mostly in coarse sediments.

Eggs of Marphysa gravelyi are spawned in gelatinous masses and the developing larvae are harboured in them until they are ready to undergo settlement. In order to understand the function of the jelly mass, morphometric, histochemical, biochemical and antimicrobial analyses were performed. The observations indicate the fibrous jelly mass is composed of carbohydrate, protein and lipid, and size is correlated to number of eggs present within. Extracts from the jelly mass of Marphysa gravelyi exhibit inhibitory activity against Escherichia coli, Vibrio vulnificus and Candida albicans but no activity was seen against seven other microorganisms tested. The results show that the function of the jelly mass is to nourish the developing embryos, protect against desiccation and predation from macrofauna, and most importantly prevent the dispersal of the juveniles from the desirable habitat.

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.