Deep-sea decapods sampled or observed with a manned submersible at the Rio Grande Rise (SW Atlantic), including the first record of four species from this region

The Rio Grande Rise (RGR) is a volcanic topographic structure of the Southwest Atlantic basin that rises over 3000 m from the seafloor and is located half way between the Brazilian continental margin (similar to 30A degrees S latitude) and the Mid-Atlantic Ridge. Previous records of decapods at the RGR are uncertain or non-existent. The observations and material examined here were collected by the manned submersible Shinkai 6500 during two dives to the plateau of the RGR main topographic feature, known as Alpha. Additional records were determined by analysing high-definition photos and videos obtained by the Shinkai 6500. Five species of deep-sea decapods were found: a Solenoceridae, Hymenopenaeus debilis Smith, 1882 previously sampled at the Brazilian slope; a Nematocarcinidae, Nematocarcinus parvus Burukovsky, 2000 previously unknown from the Atlantic Ocean; a Parapaguridae, Strobopagurus gracilipes (Milne-Edwards, 1891); a rare Palinuridae, Projasus parkeri (Stebbing, 1902); and the brachyuran Chaceon sanctaehelenae Manning & Holthuis, 1989 that were never sampled in the western Atlantic Ocean. The results show that the RGR decapod fauna is rare, unknown and, in its great majority, distinct, at the species level, from that found at the South American slope. At the genus and family levels, however, we can observe similarities between the RGR decapod fauna and that recorded on the South American slope. Unique exploration initiatives such as this can improve significantly the knowledge on western Atlantic deep-sea biodiversity and contribute to the understanding of deep-sea biogeography.