First record of Hyalascus (Hexactinellida: Rossellidae) from the Indian Ocean, with description of a new species from a volcanic seamount in the Andaman Sea

摘要

A new species of Hyalascus is described from the submarine volcanic crater seamount of Andaman Back-arc Basin, Indian Ocean. The genus was previously known in the Pacific Ocean only. Hyalascus was established by Ijima in 1896 for a sponge from SagamiBay (Japan). The genus comprised eight doubtless species until now: H. baculifer (Schulze, 1886); H. stellatus (Schulze, 1886); H. sagamiensis Ijima, 1896; H. giganteus Ijima, 1898; H. similis Ijima, 1904; H. attenuatus Okada, 1932; H, anisoactinus Tabachnick & Levi, 2004; and H. pinulohexactinus Tabachnick & Levi, 2004; all occurring in the Pacific Ocean only. Hyalascus hodgsonii Kirkpatrick, 1907 from the Antarctic Ocean appears to be a doubtful representative of the genus due to the presence of two types of microdiscohexasters; one with numerous secondary rays, and another possessing a reduced number of these rays.