Astroceramus Fisher 1906

Astroceramus Fisher 1906: 1056; 1911: 172 (in key); 1919: 309; Döderlein 1924: 60; Macan 1938: 388; H.L. Clark 1941: 45; Halpern 1970: 140; Clark & Downey 1992: 230; A.M. Clark 1993: 243; McKnight 2006: 88; Kogure & Tachikawa 2009:77.

Diagnosis. Abactinal plates polygonal in outline, abutted, no surficial granules, surface smooth, bare. Crystalline nodules embedded in surface of abactinal plates. Marginal plates large, blocky, quadrate in outline, surface with coarse, surficial granules. Superomarginal plates abutted over midline variably from base of arm to paired distal penultimate plates. Actinal surface variably covered by coarse granules to bare. One to many large, thick subambulacral spines present in most species. Pedicellariae present or absent.

Comments. Astroceramus is a widely occurring goniasterid present in the Atlantic (one species), the Pacific (five species), and Indian oceans (historically two with two new species described below). Astroceramus specimens are present in several Indo-Pacific deep-sea collections (Mah unpublished data) suggesting that it is much more widely occurring than prior occurrences have suggested. Two tropical Pacific species have been recently been described, Astroceramus boninensis from the Ogasawara Islands in Japan by Kogure and Tachigawa (2009) and Astroceramus eldredgei from the Hawaiian Islands by Mah (2015). Mah (2015) also presented in situ observations of Astroceramus feeding.

Although four species are identified from the Indian Ocean, they appear to form two distinct clusters based on their location and characters. Astroceramus species in the more northern Indian Ocean, Astroceramus fisheri (Off southern India and Indonesia) and Astroceramus cadessus (Maldives) display superomarginal plates abutted over the midline for most of the arm distance and with a more weakly stellate shape (R/r=2.2–2.9). The second cluster, including Astroceramus eleaumei n. sp. and Astroceramus kintana n. sp., posses abactinal plates which extend along the proximal 50–70% of the arm distance, more elongate arms with a more stellate body form (R/r=2.2–4.1). Further comparative and phylogeographic work for these and other Indo-Pacific species remains to be done.