Desmanthus, Topsent, 1893

Van Soest, Rob W. M. & Hajdu, Eduardo, 2000, New species of Desmanthus (Porifera, Demospongiae) with a discussion of its ordinal relationships, Zoosystema 22 (2), pp. 299-312 : 308

Desmanthus (?) macphersoni Uriz, 1988

MATERIAL EXAMINED. — None.

DISTRIBUTION. — Namibia, on rocks in deeper water, 160 m.

DESCRIPTION

Thinly or thickly encrusting sponge covering extensions of up to 25 cm 2 on rock, and attaining a thickness of 8 mm. Consistency stony. Surface extremely hispid, traversed by grooves acting as surface current channels. Oscules 1-1.5 mm in diameter, usually located at the confluence of two subectosomal canals. Colour translucent grayish blue in life, cream in alcohol.

Skeleton

Ectosome conspicuous, easily detachable where it lines the subectosomal aquiferous canals. Densely packed with tangential, triactinal desmas. Choanosomal skeleton composed of several overlapping layers of fused, tetracrepid desmas (II) with the cladi pointing towards the substratum and the rhabdome pointing upwards. Curved styles with the head resting on the upper layer of desmas, piercing the ectosome perpendicularly.

Spicules

Basal, tetracrepid desmas II with irregularly branching, tuberculate cladi and a short rhabdome, dimensions cladome: 330-490 µm; rhabdome, dimensions: 120-170 × 35-45 µm. Ectosomal desmas (?), highly tuberculate, with lightly spined tubercles, dimensions: 80-190 µm. Styles, very large, variably curved, sharp apex, dimensions: 440-2750 × 28-60 µm.

REMARKS

The description of Uriz (1988) mentions rhabds in both desma types, which are differentiated apparently mostly in size, the peripheral ones being smallest. The latter are also packed in the ectosomal region which is distinctly different from the arrangement in e.g. D. meandroides n. sp. Moreover, these ectosomal “desmas” do not appear to be proper desmas. Judging from the excellent illustrations provided by Uriz, they resemble large microscleres dubbed acanthamphiasters (Wiedenmayer 1994), such as found in e.g. Alectona (Hadromerida, Clionidae ). Further examination is necessary to determine whether these spicules are really proper to the sponge; if so then it probably belongs to an undescribed genus. This suggestion is strengthened by the large size of the styles which is unusual for the genus Desmanthus . The presence of acanthamphiaster-like spicules in an otherwise obviously desmanthid sponge would provide a distinct clue to the affinities of the family (cf. below).