Dercitus Stoeba exostoticus (Schmidt, 1868)

Van Soest, Rob W. M., Beglinger, Elly J. & De Voogd, Nicole J., 2010, Skeletons in confusion: a review of astrophorid sponges with (dicho-) calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida), ZooKeys 68, pp. 1-88 : 32-33

Dercitus Stoeba exostoticus (Schmidt, 1868) Figs 14 A–D

Pachastrella exostotica Schmidt 1868: 16, pl. III fig. 12; Keller 1891: 343, pl. 19 fig. 53, pl. 20 fig. 54.

Calthropella exostitus (sic); Sollas 1888: 111.

Pachastrella (Pachastrella) exostotica ; Lendenfeld 1903: 75.

Halinastra exostotica ; de Laubenfels 1936: 179.

Stoeba exostita (sic); Maldonado 2002: 156. Figs 2 F–G.

Material examined.

Holotype, ZMB 287, Eritrea, Dahlak Archipelago, near Perim Island, Red Sea, 16.75°N; 40.05°E, 52 m, coll. Siemens.

Description.

Black mass (in alcohol) of 3 ×3× 0.5 cm (Fig. 14A). Surface irregular granulated, grooved, no apparent oscules. In cross section, only the surface region is darkly pigmented, but the choanosome is much lighter coloured. According to Keller choanocyte chambers are crowded in the lower parts of the choanosome, size 25 µm.

Skeleton: a confused, dense mass of calthrops with a cover of microscleres at the surface. A few oxeas of widely different sizes were noted by Keller, but these were limited between approx. 100-120 × 2.5 µm of a typical haplosclerid type, in the slide examined by us.

Spicules: calthrops, sanidasters, compressed sanidasters (pseudasters).

Calthrops (Fig. 14B), generally regularly shaped, in a wide size range, usually with one of the cladi slightly longer than the other three (short-shafted triaenes): 45 –128.2– 275 × 5 –18.2– 35 µm.

Sanidasters (Fig. 14C), variable in thickness and spination, but relatively uniform in length, generally ‘stocky’, 15 –23.1– 27.5 × 2.5 –5.3– 7.5 µm.

Compressed sanidasters (pseudasters) (Fig. 14D), globular, irregular in shape (Keller called these 'Sterraster oder Sphaeraster’), 7.5 –10.5– 12.5 µm in diameter.

Habitat.

Deeper water, beyond the reefs

Distribution.

Known only from the Southern Red Sea.

Remarks.

Schmidt (1868) gave hardly any description (some vague remarks on the megascleres of Pachastrella monilifera grading into a statement on the Red Sea specimen), but the drawings of the microscleres show a sanidaster and a globular aster. Keller claims to have had access to Schmidt’s type specimen, but he faithfully reports that there is a discrepancy between Schmidt’s original label and the label of his redescribed specimen, e.g. the original collector was stated to be Ehrenberg by Schmidt, but Keller states it is Siemens, which is probably the correct one.

Maldonado (2002) assigned Pachastrella exostotica to the genus Stoeba and declared Halinastra a junior synonym of that genus. However, he possibly overlooked that Pulitzer-Finali’s (1986) Pachataxa lutea possesses similar spiculation as Pachataxa exostotica (see below). With at least two species sharing the peculiar aster-like compressed acanthorhabds, (and several further species with diversified aster shapes, see below) there is good reason to maintain Halinastra as a distinct taxon, proposed here to be a subgenus.