Heterogorgia abdita sp. nov. is a newly identified mesophotic octocoral species collected at Tigre shoal off Santa Elena Peninsula (Pacific Costa Rica). The new species is described based on distinctive morphological characters that classify it within the genus Heterogorgia. It is characterised by its conspicuous small branching colony with prominent calyces and thin branches. While its scleroma aligns with the genus, the presence of club-like spindles is notable, as these have previously been observed only in the sole Atlantic Heterogorgia species. This study enhances our understanding of the intriguing genus Heterogorgia and contributes to the knowledge of octocoral biodiversity within the Área de Conservación Guanacaste north Pacific Costa Rica and the broader marine biodiversity of the eastern tropical Pacific.

Two new species of the cheilostomate bryozoan genus Stylopoma are described from Brazil-Stylopoma anacarolinae sp. nov. and Stylopoma priscilae sp. nov. Stylopoma anacarolinae sp. nov. exhibits zooids with single or paired small avicularia and an orifice with a U-shaped sinus, in contrast to the long avicularia and orifice with a teardrop-shaped sinus of Stylopoma priscilae sp. nov. In addition to taxonomic description, a revised comparative table of living species worldwide is provided.

Hammerhead sharks (Family Sphyrnidae) comprise a monophyletic Miocene radiation of carcharhiniform sharks characterized by their laterally expanded and dorsoventrally compressed head ('cephalofoil'). The bonnethead shark (Sphyrna tiburo) is currently described as a single amphi-American hammerhead species composed of the subspecies Sphyrna tiburo tiburo in the Western Atlantic Ocean (WA) and S. tiburo vespertina in the Eastern Pacific Ocean (EP). Variation in mitochondrial DNA and cephalofoil shape suggest a species complex, with S. tiburo occurring in the U.S., Mexico, and Bahamas; S. aff. tiburo occurring from Belize to Brazil; and S. vespertina occurring in the EP. Morphometric, meristic, and genetic variation was used to resolve the bonnethead shark complex in the Western Atlantic. Twenty-three specimens (12 S. aff. tiburo from Belize and 11 S. tiburo from U.S.) were subject to sixty-one morphometric measurements and three meristic characters (counts of the number of precaudal vertebrae, lower and upper rows of functional teeth). An allometric formula was used to standardize any effect caused by differences in size of the individuals and data were analyzed with univariate and multivariate statistics. Sphyrna aff. tiburo and S. tiburo have non-overlapping vertebral counts (80-83 and 71-74 respectively) but no morphometric differences were detected. Although not captured in morphometric analysis, the cephalofoil of S. aff. tiburo has a more pointed anterior margin than S. tiburo that together with lobule shaped posterior margins gives the cephalofoil a distinctive shovel-shaped appearance. Concatenated mitochondrial sequences and 12 nuclear microsatellite markers clearly separated S. aff. tiburo and S. tiburo. We conclude that this complex comprises two species in the Western Atlantic, S. tiburo and S. alleni sp. nov., and we provide a description of the latter, which is distinguished by precaudal vertebral counts (80-83), a shovel-shaped cephalofoil with rounded posterior margins, and robust differences in mitochondrial and nuclear genetic markers. We suggest nuclear genetic and meristic examination of EP bonnetheads is needed to update the taxonomical status and redescribe S. vespertina.

During surveys worldwide, we collected adult and larval specimens of Pseudopolydora Czerniavsky, 1881 similar to P. achaeta Radashevsky & Hsieh, 2000 and P. rosebelae Radashevsky & Migotto, 2009 far from their type localities in Taiwan and Brazil, respectively. Analysis of sequence data of five gene fragments: mitochondrial COI and 16S rDNA, nuclear 18S rDNA and 28S rDNA, and Histone 3 (3114 bp in total) of individuals from Nha Trang Bay (Vietnam), São Paulo (Brazil), Florida (USA), and the Caribbean Sea (Martinique) confirmed their conspecificity with P. achaeta from Taiwan. Based on the morphology, we also report this species for the first time for the East Sea (South Korea) and provide new records for the north-western part of the Sea of Japan (Russia). The analysis also showed the conspecificity of worms from Vietnam with P. rosebelae from Brazil. Based on the morphology, we also report P. rosebelae for the first time for the Caribbean Sea (Belize), South China Sea (Thailand), and Hawaii. Developed pelagic larvae of P. achaeta and P. rosebelae from Nha Trang Bay are described and illustrated. A worm from the Great Barrier Reef (Queensland, Australia) earlier identified as P. cf. rosebelae, is referred to the new species Pseudopolydora nivea sp. nov. Following our earlier hypothesis about the origin of Pseudopolydora in the Indo-West Pacific Ocean, we explain the occurrence of these worms, including Pseudopolydora floridensis Delgado-Blas, 2008, on the Atlantic coasts of North and South America by unintentional transportation in ballast water, followed by successful invasions. We assume that the penetration of warm waters of the East China Sea through the Korea Strait and the warming of the waters of the Sea of Japan have led to the extension of the range of tropical-subtropical P. achaeta to the north-western part of the Sea of Japan.

Some of the most fascinating and poorly known animals on this planet are comb jellies of the phylum Ctenophora. About one-quarter of ctenophore richness is encompassed by the benthic species of the order Platyctenida, nearly all known from shallow waters. In this work, we integrate several systematic methods to elucidate an enigmatic genus, Tjalfiella, known previously only from deep waters near the western coastline of Greenland in the North Atlantic. For the first time, we employ microCT on museum specimens-one nearly 100 years old from the type locality of the only known species of the genus, T. tristoma-of extant ctenophores to visualize and compare their anatomy. With these data, we integrate in situ videography and genetic sequence data derived from newly collected deep sea specimens observed via NOAA Ship Okeanos Explorer in 2018 and 2022 at two distant localities in the North Atlantic, near North Carolina, USA, and the Azores, Portugal. The genetic data indicate that the newly collected specimens represent closely related but distinct species of Tjalfiella. However, neither can be named at this time because neither one could be definitively differentiated from T. tristoma, given that microCT and in situ imagery reveal striking morphological similarities and only variation in color and host preference. Despite the lack of new species descriptions, this work characterizes both the morphology and genetics of the benthic ctenophore genus Tjalfiella and specimens representing species within it, advancing our understanding of a rarely observed component of the deep-sea fauna.

Currently, Leodice has 34 species recorded worldwide. Among these, seven species are known along the Brazilian coast. This study is based on material collected during the Marine Algae project conducted in 1981 along the Continental Shelf of the State of Paraíba, at depths of 10-35 m. In this study, we present three new records: L. pellucida comb. nov. for South America, L. marcusi for northeastern Brazil, and L. unifrons for the State of Paraiba. A new species of Leodice is described from the State of Paraiba, Northeast Brazil, Leodice ivanildae sp. nov. This taxonomic study increases the number of known species of Leodice to 37, with nine occurring in Brazil. Additionally, it expands the species of Leodice known from the State of Paraiba, Brazil, from two to six.

A taxonomic review of Aclis Lóven, 1846 from Brazil led to the discovery of ten species, five of them are new. Before this study, only four species were known from the area. Aclis sarissa Watson, 1881 is revised and reassessed regarding its shell variability. Aclis marplatensis (Castellanos & Landoni, 1984) comb. nov. is here revised and transferred to Aclis based on the presence of spiral keels and microscopic spiral striae on the teleoconch. Additional material of A. watsoni Barros, Lima & Francisco, 2007 is presented here. Aclis macrostoma Barros, Lima & Francisco, 2007 is still known only from the type series. The new species (Aclis pulchra sp. nov., Aclis costai sp. nov., Aclis anaglyptica sp. nov., Aclis corniculata sp. nov. and Aclis multicarinata sp. nov.) can be distinguished from other congeners mainly by the shape, size, sculpture, color pattern, and the presence or absence of an umbilicus. Besides these taxa, three morphotypes from Brazil might represent new species, but are not formally described due to the inadequate material. An overview of the remaining Aclis from the western Atlantic and Saint Helena, based on type material led to the following conclusions: Aclis dalli Bartsch, 1911, Aclis verrilli Bartsch, 1911, and Aclis fernandinae Dall, 1927 are revalidated; Aclis pendata Dall, 1927 is proposed as synonym of Aclis stilifer Dall, 1927; Aclis canaliculata (E.A. Smith, 1890) is reallocated in Aclis. Besides, some species, previously attributed to Aclis are removed from the genus, some of them being reallocated to other gastropod families.

This work describes Bryozoa of the order Cheilostomata associated with polymetallic nodules collected by box-coring in the eastern part of the Russian exploration area of the Clarion-Clipperton Fracture Zone (CCFZ or CCZ) under contract to Yuzhmorgeologiya. Study of 569 cheilostome specimens from 4510-5280 m depth yielded 32 species (22 new) in 20 genera (3 new) and 14 families (1 new). For six species, the nomenclature was left open (genus only) owing to the paucity of defining characters. One species with a costate frontal shield, possibly belonging to the otherwise monotypic Polliciporidae, clearly represents a new genus, but was not named, as it comprises only an ancestrula, one fully formed daughter zooid and a zooid bud. Four of the species we detected are known from the deep sea beyond the CCZ; Columnella magna and Acanthodesiomorpha problematica occur not only elsewhere in the Pacific Ocean but also the Atlantic Ocean, while Smithsonius quadratus was first described from the Kuril-Kamchatka Trench, and the authors have unpublished records of Smithsonius candelabrum n. sp. from the Magellan Seamounts and the Louisville Ridge. These records give hope that other CCZ bryozoan taxa may also occur elsewhere, offsetting local extirpation through nodule mining. Almost 63% (20 species) of CCZ Cheilostomata have a flexibly erect colony attached by one or several rhizoids (and/or the ancestrula has a proximal cuticular stalk-like portion). Ten other species have fixed-erect rigid colonies; only two species are encrusting. If a 50 mm height or spread is taken as the lower limit defining a megafaunal organism, then only C. magna qualifies as megafaunal. If 20 mm is taken as the lower size limit (definitions vary), then nine other species have the potential to be recognized in ROV-obtained images. The completion of this monograph allows a summary of all bryozoan data for the Russian sector of the CCZ. Altogether, 52 species are known from this area, totalling 1002 specimens from 437 stations. The most abundant and most ubiquitous species was the cyclostome Pandanipora helix, comprising 230 specimens from 137 stations and accounting for almost 23% of all specimens collected. The next most abundant and ubiquitous species were the cheilostomes Aulopocella polymorpha (124 specimens, 105 stations) and Fulgurella marina (104 specimens, 92 stations). These three species accounted for almost 46% of all specimens collected. All other species yielded fewer than 45 specimens each from 33 or fewer stations. Twelve species were represented by a single colony. Although some ROV images from eastern sectors of the CCZ have been recognized as bryozoans and published as such, few have been studied systematically. Bryozoans have also been reported from seamounts, level-bottom rock flats, ridges and troughs in the CCZ, but their identities remain unknown. It is imperative that institutions seek the collaboration of taxonomists rather than allow material to languish unidentified in collections.

Ilyophis arx Robins, 1976 is redescribed based on the four type specimens from south of the Galapagos Islands and 21 additional specimens: 12 specimens from the western Clarion Clipperton Zone in the central Pacific Ocean, four specimens from the eastern Pacific Ocean, and five specimens from several localities in the central North Pacific Ocean. A new species, Ilyophis maclainei sp. nov., is described from the eastern North Atlantic. A taxonomic synopsis of the subfamily Ilyophinae is presented, and a key to the known species is provided.

A new species of Cyanea is described from trawl samples collected in the Gulf of Guinea during 2017 and 2019. The species is a member of the nozakii-group, possessing interrupted radial septa, and is characterised by, inter alia, deeper rhopalial than velar marginal clefts, a uniformly papillose exumbrella, up to 200 tentacles per tentacle cluster and a dense network of anastomosing canals in broadly quadratic lappets. The species can be distinguished genetically from its congeners at both ITS1 and COI (minimum of 14.4% intergroup variation) regions as confirmed by multiple phylogenies and K2P analyses. This is the first record of a nozakii-group member in the Atlantic Ocean and the first description of the genus Cyanea from the west coast of Africa and the tropical Atlantic Ocean.