Desmanthus topsenti Hentschel, 1912

(Fig. 2G, H)

HOLOTYPE. — Aru Islands . Stn 77, Merton coll. (SMF 1560).

DISTRIBUTION. — Aru Islands (eastern Indonesia), on rocks at 20 m.

DESCRIPTION

Thinly encrusting, about 0.5 mm thick and 1.7 cm long. Surface hispid. Colour grey or brownish grey in alcohol. Structure compact.

Skeleton

The main skeleton consists of an irregular layer of desmas on which monactinal spicules are erected. Spicules

Desmas which can be separated in basally arranged smaller desmas (Fig. 2H), presumably desmas I, with more tuberculate cladi, dimensions: 240-270 × 20 µm, and peripherally arranged more robust desmas (Fig. 2G), presumably desmas II, dimensions cladome: 200- 310 × 30-45 µm. They are not clearly separated morphologically and the larger desmas lack a distinct rhabdome. Monactinal spicules are styles and rhabdostyles, variable in form, size and curvature, the smaller sizes tend to be rhabdostyles, dimensions: 224-1000 × 14-31 µm.

REMARKS

Hentschel (1912) states that this species differs from D. incrustans mainly in the absence of clear rhabdomes in the desmas. A syntype specimen from the Senckenberg Museum was re-examined (SMF 1560, from stn 77 of the Merton collection described by Hentschel). The rhabdomes are certainly inconspicuous, but nevertheless there is a clear division in thinner and more robust desmas. So far no other specimens of this species have been recorded, but it is possible that some of the Indian Ocean records of D. incrustans are referable to this species.