Echinoderms of the mauritanian deep-sea waters

Abstract

Echinoderms are the most important taxa of megabenthic invertebrates on the Mauritanian deep-sea floor, both in density and biomass. The phylum is represented by approximately 82 species, Ophiuroidea and Asteroidea being the most diverse classes (25 and 23 species, respectively), followed by Holothuroidea and Echinoidea (19 and 12 species, respectively). Crinoidea is poorly represented by only three species. Holothuroidea (sea cucumbers) are, undoubtedly, the main component of deep Mauritanian echinoderms, accounting for 85.5% of numerical abundance and 96.0% of biomass. Species belonging to Echinothurioida are dominant among the sea urchins. The most common echinoderm species are Phormosoma placenta, Enypniastes eximia, Psilaster cassiope, Benthothuria funebris, Ophiernus alepidotus, Pseudarchaster gracilis gracilis and Ophiura flagellata. The Mauritanian echinoderm fauna are mostly composed of species with Atlantic distribution (80.5%) and a smaller group of wide distribution species (19.5%). Only three species, two sea stars and one ophiuroid, could be considered as endemic to Macaronesian African waters: Hymenaster roseus, Dyptaster mollis and Ophiothrix maculata. The bathymetric distribution of species and multivariate analysis clearly identify two main assemblages: the first groups the stations located on the deep shelf and upper slope (<400 m), and the second stations group located at greater depths along the continental slope.