The detailed study of arm ossicles, particularly the lateral arm plates, is providing valuable information in the elucidation of ophiuroid taxonomy. The present study describes in detail 16 species of brittle stars from Araçá Bay, Brazil. This information is used to construct the first interactive electronic key, providing a valuable resource for a broad range of researchers. Brittle stars families were divided into three groups based on their spatial distribution: i) infaunal species of intertidal and shallow subtidal belonging to Amphiuridae and Ophiactidae, ii) epizoic species belonging to Amphiuridae, Ophiactidae, and Ophiotrichidae and, iii) epifaunal species of the subtidal belonging to Ophiodermatidae and Hemieuryalidae. In the global context of recent revisions of ophiuroid taxonomy, the present work provides additional characters for use in future phylogenetic studies.

<p>Este guia ilustrado apresenta 57 espécies de Echinodermata Bruguière, 1791 [ex Klein, 1734] registradas na porção sul do Embaiamento Sul Brasileiro (ESB), incluindo o litoral sul do Estado de São Paulo, todo o litoral do Paraná e norte de Santa Catarina. O guia destina-se a pesquisadores e estudantes que atuam ou gostariam de atuar com o grupo e serve de auxílio na identificação em campo e laboratório. Apresentamos uma caracterização do filo Echinodermata, uma breve descrição da área de estudo, técnicas de coleta e preservação dos exemplares. Para cada classe, são apresentadas caracterizações com as principais estruturas morfológicas de importância taxonômica, seguida das diagnoses das espécies registradas na ESB. Dentro de cada classe, as espécies foram organizadas por família e depois alfabeticamente de acordo com o gênero e a espécie. Para cada espécie foram incluídas fotos, diagnoses, distribuição geográfica e hábitat quando disponíveis em literatura. Esse trabalho é o primeiro guia ilustrado de equinodermos no Brasil e complementa de forma consistente o conhecimento da biodiversidade do grupo, gerando subsídios para futuras intervenções, tomadas de decisões e manutenção da diversidade deste incrível grupo de animais marinhos.</p><p><strong>Palavras chave</strong>: Equinodermos, sul do Brasil, diversidade, Sudoeste Atlântico, Taxonomia.</p>

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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).

We re-describe and confirm the validity of Ophiothrix trindadensis Tommasi, 1970 (Echinodermata: Ophiuroidea). This is a native species from Brazil, however it lacked a type series deposited in scientific collections. The recognition of O. trindadensis was made possible using integrative taxonomy applied to many specimens from the type locality (Trindade Island) as well as from different locations along the Brazilian coast (Araçá Bay and Estuarine Complex of Paranaguá). Initially, 835 specimens were studied and divided into four candidate species (CS) inferred from external morphological characters. Afterwards, the CSs were compared using integrative taxonomy based on external morphology, arm microstructures morphology (arm ossicle), morphometry, and molecular studies (fragments of the mitochondrial genes 16S and COI). Analyses indicated CS1 and CS2 as O. trindadensis, and CS3 as O. angulata, both valid species. CS4 remains O. cf. angulata as more data, including their ecology and physiology, are needed to be definitively clarified. Our integrative investigation using specimens from the type locality overcame the lack of type specimens and increased the reliable identification of O. trindadensis and O. angulata.