Dercitus Stoeba extensus (Dendy, 1905)

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 : 23-24

Dercitus Stoeba extensus (Dendy, 1905) Figs 11 A–D

Stoeba extensa Dendy 1905: 70, pl. V fig. 1;? Vacelet and Vasseur 1971: 70, fig. 13.

Halina plicata ; Thomas 1970: 207, fig. 9.

Material examined.

BMNH 1907.2.1.5a, two slides from type, R.N. 167, Gulf of Mannaar, Sri Lanka.

Description

(partially from Dendy, 1905). Encrusting extensively over calcareous algae and filling crevices, 4.5 × 3.3 cm in lateral expansion. Surface smooth, no apertures. Colour pale grey (alcohol). Consistency tough, fleshy. Dendy mentions the presence of large cells with inclusions (cystencytes) of 60 µm.

The two slides contain thin cross sections of the peripheral regions.

Skeleton (Fig. 11A): irregular mass of short-shafted triaenes covered by a thin ectosomal crust of microscleres.

Spicules: megascleres predominantly dichocalthrops, but also normal calthrops or calthrops with one or two bifid cladi, sanidasters.

Calthrops (Fig. 11C), cladi 57- 87.0-123 × 8 –14.9– 23 µm, cladomes 108 –158.9– 210 µm.

Dichocalthrops (Fig. 11B), protocladi 39 –46.9– 54 × 5 –15.5– 21 µm, deuterocladi 8 –37.9– 61 × 4 –11.1– 18 µm, rhabds 24 –65.6– 124 × 5 –15.1– 27, cladomes 84 –155.2– 192 µm.

Sanidasters (Fig. 11D), oxea-like (Dendy: ‘microxeas’), 14 –19.6– 26 × 1 –1.55– 2 µm.

Habitat.

Encrusting calcareous algae at depths of 18-63 m.

Distribution.

Sri Lanka,?Madagascar.

Remarks.

The spicule complement reminds of Dercitus (Stoeba) pauper Sollas (1902), but the cladi and rhabds of the triaenes in this species are distinctly thinner (5-27 µm in extensus, 3-10 µm in pauper), precluding synonymy of the two species for the time being, until variation of these features is better established.

It is likely that the record of Halina plicata of Thomas (1970) belonged to the present species as most descriptive remarks fit except for the upper size of the cladome ( ‘chord’) of the dichocalthrops which was quoted as 330 µm.

Vacelet and Vasseur (1971) reported this species from Madagascar. Live colour was noted as black, which was maintained in alcohol. Dichocalthrops measurements provided were: protocladi 20-40 µm, deuterocladi 60-80 µm, rhabds 150-180 µm. Sanidasters were 25-30 µm. No mention of calthrops. No further spicule data. The colour difference, lack of calthrops, and slight differences in spicule sizes and shapes render it doubtful whether this material belongs to Dercitus (Stoeba) extensus .