First record of Hyalascus (Hexactinellida: Rossellidae) from the Indian Ocean, with description of a new species from a volcanic seamount in the Andaman Sea Author Sautya, Sabyasachi Author Tabachnick, Konstantin R. Author Ingole, Baban text Zootaxa 2010 2667 64 68 journal article 10.5281/zenodo.276395 197eceef-ac41-4277-8bc8-5494d4596986 1175-5326 276395 Hyalascus andamanensis sp. nov. ( Figures 1–2 ) Material examined. Volcanic seamount, Andaman Back Arc Basin, Andaman Sea: R.V. ‘ SONNE ', stn. TVG- 9, 25 .XI.2007, 7 o56.036’ N 94o03.026’ E , 705 m . FIGURE 1. Hyalascus andamanensis sp. nov. : (A) upper part of type specimen with osculum and (B), its’ lateral view showing the basal broken part. FIGURE 2. Hyalascus andamanensis sp. nov. , spicules of the holotype. A, dermal stauractin. B, atrial hexactin. C, hypodermal pentactin. D, E, fragments of tangential rays of hypodermal pentactins. F, choanosomal diactin. G, oxyhexactin. H, oxyhemihexaster. I, oxyhexaster. J, K, microdiscohexasters. Holotype . NIO / BOD /3/2010, stored in alcohol. IORAS i1 , slide. Etymology. The species name is derived from its place of collection. Description. Body: The sponge has a white cylindrical body, about 13 mm long and 6 mm in diameter; the osculum is 4 × 3 mm in diameter, the walls are very thin 0.5– 1 mm . Prostalia lateralia are hypodermal pentactins which protrude at about 300 µm above the dermal surface ( Fig. 1 ). Spicules ( Fig. 2 ): The choanosomal skeleton is composed of diactins 700–3800 µm in length and 4–15 µm in diameter; they have rounded, rough outer ends and stout, smooth shafts. Hypodermal pentactins have orthotropal tangential rays about 800–1700 µm in length and 8–24 µm in diameter, the proximal ray is more than 1400 µm in length. Some of the tangential rays are smooth, the others have rough surface; the outer ends are conically pointed. Dermalia are stauractins, rarely tauactins and pentactins, sometimes they have 1–2 rudimental tubercles instead of the reduced rays. The rays of dermal stauractins are rough with rounded or conically pointed outer ends, have 59–111 µm in length (n=25, avg=93, std=12) with a diameter of about 5 µm. Atrialia are hexactins, their rays directed inside the atrial cavity are 67–215 µm in length (n=23, avg=161, std=36), tangential rays are 74–200 µm in length (n=24, avg=146, std=30), ray directed inside the body is 41– 207 µm in length (n=22, avg=138, std=36). The rays are 5–7 µm in diameter, their surface is rough and outer ends are rounded or conically pointed. Microscleres are oxyhexactins together with some oxyhemihexasters and oxyhexasters, and microdiscohexasters. Oxyhexactins are 67–141 µm in diameter (n=25, avg=103, std=3). Oxyhemihexasters and oxyhexasters are 74–141 µm in diameter (n=10, avg=98, std=20) with primary rosette 7–10 µm in diameter (in the latter). Microdiscohexasters are spherical, 18–25 µm in diameter (n=7, avg=22, std=3) with primary rosette 4–7 µm in diameter (n=7, avg=6, std=1). Remarks. Most species of Hyalascus have dermal spicules predominately in the form of pentactins: H. baculifer , H. giganteus , H. similis and H. stellatus . In one species, they are mostly hexactins: H. sagamiensis . Four species, including the new one, have mostly stauractins: H. andamanensis sp. nov. , H. anisoactinus , H. attenuatus and H. pinulohexactinus . The new species differs by the smallest size of microdiscohexasters, 18– 25 µm in diameter, while in all other species, these spicules are larger (25–72 µm in H. anisoactinus ; 25–65 µm in H. pinulohexactinus ) and even notably larger in some species (about 117 µm in H. baculifer and about 63 µm in H. stellatus ).