Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge

This report addresses sixty-two deep-sea pycnogonid specimens collected by the Southwest Indian Ocean Seamounts Expedition, November 7 to December 21, 2011 on-board the British research vessel R.S.S. James Cook (voyage numbers JC066, JC067). Pycnogonids were collected from four of six geological features sampled along the central section of the Southwest Indian Ridge (SWIR) in an area approximately 1500 km south-south east of Madagascar. Specimens were mostly gathered utilizing a remotely operated vehicle (ROV) and tethered video-sediment grab platforms. Additional specimens were gathered from sediment cores or hand-picked from whale bone and wood-fall experiment nets and mooring buoy ropes. Fifteen new species are described, illustrated and compared with their nearest relatives. Two previously described species belonging to the genera Colossendeis and Austrodecus are recorded. A specimen of Austrodecus bamberi represents the first record of the female and is the only species in the collection previously known from the SWIR. One species of Colossendeis remains unnamed pending further analysis. One subadult specimen of Sericosura showing strong morphological affinity with a specimen previously recorded from the Walvis Ridge remains undescribed pending availability of further material. One subadult specimen is tentatively assigned to Nymphon. Specimens are assigned to six families and eight genera. Colossendeis rostrata is synonymised with C. melancholicus. The methodology of counting palp segments in the genera Austrodecus and Rhynchothorax is reviewed.