Skeletons in confusion: a review of astrophorid sponges with (dicho-) calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida) Author Van Soest, Rob W. M. Author Beglinger, Elly J. Author De Voogd, Nicole J. text ZooKeys 2010 68 1 88 http://dx.doi.org/10.3897/zookeys.68.729 journal article http://dx.doi.org/10.3897/zookeys.68.729 1313-2970-68-1 Dercitus Stoeba sibogae sp. n. Figs 22 A-D Material examined. Holotype ZMA Por. 02220, Indonesia, Papua, 32 m, 1.7083°S; 130.7916°E, coll. Siboga Exped. Stat. 164, dredge, 20 August 1899. Description. Thin leathery-rubbery encrustation (Fig. 22A) cementing coral rubble and filling crevices in coral material. Colour (alcohol) pale orange brown. Surface smooth, not encrusted, no oscules apparent; interiorly with a different more mushy texture. Size 2.5 x2x 0.5 cm. Skeleton: an ectosomal crust of microscleres overlying a mixture of microscleres and dichocalthrops embedded in largely organic choanosome with relatively low spicule density. Spicules: dichocalthrops, sanidasters and compressed fat sanidasters. Dichocalthrops (Fig. 22B) relatively small and delicate, with curved pointed deuterocladi; protocladi, rather uniform in length, more variable in thickness, 24 -26.5- 30 x 5 -8.0- 11 µm ; deuterocladi variable in length, 12 -26.1- 39 x 3 -5.6- 9 µm ; rhabd short and pointed, 36-75 x 6-9 µm ; cladome 75 -101.1- 144 µm . Sanidasters in two categories, long-and-thin (Fig. 22C) and short-compressed (Fig. 22D); the latter are ovoid, not compressed to the extent that they form asters. Thin sanidasters, 12 -13.9- 16 x 1.5 -2.05- 3 µm , short-compressed sanidasters 7 -11.0- 13 x 4.5 -5.6- 7.5 µm . Figure 22. Dercitus (Halinastra) sibogae sp. n., holotype ZMA Por. 02220, from Indonesia, Papua, A habit B various dichocalthrops C sanidasters D compressed sanidasters. Etymology. Named after the Dutch naval vessel HMS 'Siboga' which was instrumental to the 1899-1900 collection of a rich deep sea fauna from South East Asian waters. Habitat. Dredged from a sandy bottom with small limestone rubble and shells. Distribution. Known only from the type locality in Eastern Indonesia. Remarks. The present specimen was identified by Maurice Burton (who provisionally identified a large part of the Siboga sponge collection) as Stoeba extensa , but habit and colour differ from that of Dendy's species, whereas the spicules are significantly smaller. Stoeba extensa has a dense mass of dichocalthrops but also calthrops which are absent from the present new species. The density of megascleres is also much different. The dichocalthrops appear similar to those of Dercitus (Stoeba) occultus (see above), and also the colour matches. However, that species has an endolithic growth form and the sanidasters are apparently not divisable in two shapes. The membership of Halinastra of this species rests on the differentiation of the sanidasters into two shapes, but proper pseudasters are not found. If the spicular variation of Dercitus (Stoeba) occultus and Dercitus (Halinastra) sibogae sp. n. will be demonstrated to overlap in a future study it might turn out the two are conspecific, but for the time being the emphasis is put on the differences. Nominal Dercitus and Stoeba species excluded from the genus