Abstract
Chionelasmus darwini (Pilsbry, 1907) was first collected at 417 to 430m depth near Kauai, Hawaiian Islands. Pilsbry (1911) subsequently recognized that it was distinct from Catophragmus s. s. and proposed the subgenus Chionelasmus to accommodate it. Nilsson-Cantell (1928) elevated Chionelasmus to full generic rank based on a complete specimen collected from 526m depth off Port Mathurin, Rodrigues Island in the western Indian Ocean, largely because the wall turned out to be composed of six rather than eight plates. These two specimens plus 11 specimens from the Hawaiian Islands and three specimens from Madagascar contained in the Benthic Invertebrate Collection of Scripps Institution of Oceanography, and one from the Kermadec Islands of the South Pacific (Foster 1981), were utilized in the present study. The morphology of the scutum and tergum and the ontogenetic development of the third and fourth whorls of basal imbricating plates in the Pacific and Indian Ocean populations are different, and therefore a new subspecies, Chionelasmus darwini cantelli, is proposed for the latter.
