Published online by Cambridge University Press: 24 April 2020
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).