(Fig. 21 A – C)
Sphaeroturia bitentaculata Ludwig, 1893: 184; 1894: 141, pl. 12, figs 16 – 17, pl. 14, figs 5 – 14. Ypsilothuria bitentaculata attenuata Perrier 1886: Massin, 1996: 44, figs 1 & 2.
Ypsilothuria bitentaculata: Massin & Hendrix, 2011: 422, fig. 7 (synonymy and records before 2011)
Material examined. Non-type material: IE-2007-757 (1 specimen, sampled between Majunga and Cape Saint André); IE-2007-758 (1 specimen, sampled between Majunga and Cape Saint André); IE-2007-762 (1 specimen, sampled in front of Nazendry Bay); IE-2007-765 (2 specimens, sampled in front of Majunga); IE-2007-784 (1 specimen, sampled between Majunga and Cape Saint André); IE-2007-786 (1 specimen, sampled in front of Nazendry Bay); IE-2007-789 (1 specimen, sampled in front of Majumga); IE-2007-780 (5 specimens, sampled in front of Nazendry Bay); IE-2007-792 (2 specimens, sampled between Majunga and Cape Saint André); IE-2007- 795 (1 specimen, sampled between Majunga and Cape Saint André); IE-2007-797 (2 specimens, sampled between Majunga and Cape Saint André); IE-2007-811 (3 specimens, sampled in front of Mahajamba Bay); IE-2007-815 (1 specimen, sampled between Majunga and Cape Saint André); IE-2007-821 (2 specimens, sampled in front of Nazendry Bay).
Remarks. Ypsilothuria is thought to contain only two species: Y. talismani Heding, 1942, which is soft bodied, and Y. bitentaculata (Ludwig, 1893) which is ‘hard as a little echinoid’ according to Heding (1942). The specimens here under study clearly also have the ‘hard’ aspect of Y. bitentaculata (fig. 21A,B). Heding (1942) recognized two subspecies in the latter species: the cosmopolitan Y. bitentaculata attenuata R. Perrier, 1886 and the North Atlantic Y. bitentaculata virginiensis Heding, 1942. For Y. bitentaculata attenuata, Heding (1942) states that it is closely related to the bitentaculata from the Indo-Pacific which he described earlier (Ludwig & Heding, 1935; see also Heding, 1942: textfig 27, 2) based on material collected in the Zanzibar Channel. Our specimens fit well with those descriptions because their body wall thecal plates vary in length between 1500 – 3000 mm (fig. 21C). This is also more or less in agreement with the measurements (scales can exceed 2 mm in length) that Cherbonnier & Féral (1981) provide. On the other hand our specimens differ from other descriptions of Y. bitentaculata from the Indo- Pacific in that their thecal plates are more than twice as long (e.g. Pawson, 1965 reports on an average length of 1200 mm; Thandar (1999) gives a range between 900 and 1270 mm) or from the Mediterranean (Massin, 1996; mean length of plates 1000 mm), in that they often carry two spires, and in that these spires are, with a length up to 1100 mm, considerably higher then those reported by Ludwig (1894) (500 – 580 mm high), Pawson (1965) (500 mm high), Thandar (1999) (500 mm high), Cherbonnier and Féral (1981) (100 mm high) and Massin (1996) (400 – 500 mm high).
Given these differences we were tempted to erect a new species for our material. We however refrained from doing so until the material collected earlier in the Zanzibar Channel could also be studied.