The brittle stars of the family Ophiocomidae inhabit shallow waters and coral reefs of tropical regions. The species of Ophiocoma are difficult to identify due to high morphological variation, especially when different stages of development are observed. Here, based on morphological analyses, two Brazilian morphotypes of Ophiocoma were studied and characterized, Ophiocoma sp. NB (Northeastern Brazil) and Ophiocoma sp. TMV (Trindade and Martin Vaz Archipelago), and subsequently thoroughly analysed to confirm whether they were the same species or not. After the morphological studies, including external morphology, morphometry and microstructural characters, and analysis of molecular data, involving the 16S gene, it was concluded that Ophiocoma sp. NB and Ophiocoma sp. TMV do not correspond to the same species, the first being identified as Ophiocoma echinata (Lamarck, 1816) and the latter being a new species. This new species is characterized by two tentacle scales on the first arm segment and then one on all following segments, and the dorsalmost arm spines are robust and rounded, as wide as long or almost as wide as long.

The genera Ophiophragmus and Amphiodia are amphiurids that are considered taxonomically difficult due to their great resemblance, few diagnostic characters and synonymy problems. Our aim is to redescribe the species using scanning electron microscopy and morphometry of diagnostic structures, and to provide new information for the identification of these Ophiuroidea. Five Amphiodia spp. and six Ophiophragmus spp. recorded in Brazil were rigorously redescribed. The descriptions include new diagnostic characters derived from external morphology, arm microstructures and morphometry. We also provided comparative analyses of species with shared characters such as Amphiodia riisei and Amphiodia trychna. The geographic and bathymetric distributions of the studied species were updated, and new records are provided. All the information presented may be used in taxonomic, ecological and phylogenetic studies, helping to fill gaps in the knowledge of the biodiversity, ecology and evolution of these Ophiuroidea. Conclusively, all the tools applied here assisted in the identification of genera and species and could be useful in other taxonomic studies of Echinodermata.

Since 2012, when Ophiothela was first described in the Atlantic, there has been no consensus regarding its identification. It has been described as O. mirabilis, O. cf. mirabilis, O. danae, or only Ophiothela sp. In order to fill these gaps, our aim was to test if specimens from Brazil are Ophiothela mirabilis and/or Ophiothela danae. Syntypes from the Museum of Comparative Zoology and United States National Museum, Smithsonian Institution, were used. We examined species boundaries of the small six-rayed brittle star Ophiothela using independent character sets utilizing morphology (external morphology and morphometry) and molecular data (16S and COI). Concordance was found between the analyses indicating that Ophiothela sp. from Brazil (BR), Ophiothela mirabilis and Ophiothela danae are closely related. We suggest that O. danae should be considered as a junior synonym of O. mirabilis. A detailed description of O. mirabilis BR is presented using external morphology and microstructural ossicles (arm plates, vertebra, dental and oral plates). This description includes new diagnostic features, particularly regarding its microstructures: (i) transspondylous articulation (first record in Ophiotrichidae); (ii) eight smooth knobs on the dorsal surface of the vertebrae (to date only in Ophiothela); (iii) vertebrae with distal keel divided into two separate end processes matching the two large dorsal grooves proximally (first time in the literature); and (iv) an opening on both sides of the oral plate (as seen in other fissiparous species Ophiactis savignyi and Ophiocomella ophiactoides).

The first record of the ophiuroid family Ophiohelidae from the Mediterranean Sea is reported. It consists of the description of the new record of Ophiomyces grandis from the Mallorca Channel seamounts in the Balearic Islands, western Mediterranean, where it shows high abundances. We present both the morphological description of the individuals collected and, for the first time, the cytochrome oxidase subunit I (COI) sequence of this species. The morphological traits of our specimens match the available descriptions of O. grandis. On the other hand, molecular analyses show a large genetic distance between O. grandis and Ophiomyces delata, the two species being very similar morphologically. Despite the high abundances of O. grandis reported here, previous surveys in the Mallorca Channel seamounts using ROV did not detect it, emphasizing the importance of beam trawl sampling to improving the biodiversity description of these geomorphological sea bottom features.

In this study, we present descriptions, illustrations, comments, and bathymetric and geographic distributions of the brittle star species related to the estuary region of Camamu Bay, located in the State of Bahia, Brazil. The brittle star fauna lives on biological substrates, sand bottoms, mud and rubble in the Camamu Bay and comprises 12 species divided into five families. Almost all of them are common in the tropical and subtropical fauna of the regions of shallow water. Ophiophragmus filograneus is reported for the first time in Bahia, and nine other species are recorded for the first time in Camamu Bay: Amphipholis januarii, Amphipholis squamata, Ophiophragmus filograneus, Ophiostigma isocanthum, Ophioderma cinerea, Ophioderma januarii, Ophiactis lymani, Ophiactis savignyi and Ophiocoma echinata. The results suggest that the ophiuroid assemblages are strongly affected by marine currents as well as by different kinds of bottom substrate.

Aspects of the distribution and ecology of ophiuroids from shallow waters off Maceió, State of Alagoas in north-eastern Brazil were characterized. The ophiuroid fauna comprised 16 species in nine genera and seven families, including three endemic species from Brazil, Ophiocnida loveni, Ophiactis brasiliensis and Amphiura kinbergi, and also four new records for the coastal reef system off north-eastern Brazil. On coral reefs 15 species were found and Ophiothrix angulata was the most abundant species. The sandstone reefs presented six species with dominance to Ophioderma appressa. Four of these species were associated with the fouling community on piers. Ophioderma appressa and Ophioderma cinerea were common in the intertidal zone on the reef edges and tide pools on coral reefs. The results demonstrated the presence of a large number of Ophiuroidea species in the shallow waters of Maceió, and expanded their distributions to the State of Alagoas and the reef systems of north-eastern Brazil.