(Fristedt, 1885)
Species Overview
Hemigellius pumiceus (Fristedt, 1885) is a thickly lamellate light brown sponge, with a roughly hispid surface and brittle consistency. It is a very coarse Haplosclerid, easily distinguishable from the more supple lamellae of species of the Axinellidae. It is a rare species known only from deep fjord habitats in Norway and Sweden.
Taxonomic Description
Colour: Light brown; off-white in alcohol.
Shape, size, surface and consistency: (Hemigellius pumiceus BandW) Thickly fan-shaped, lamellate, elongate, not stalked, so apparently broadly attached to the substrate. Size up to 6.5 x 3 x 1.2 cm. Surface rough, strongly hispid, very irregular, with numerous pores (punctate), varying in size between 0.1 and 2 mm. Consistency brittle, but not fragile.
Spicules: (Desmacella pumicea) Megascleres are oxeas, long and slender, slightly curved, ending in a long sharp point: 910-985 x 21-28.5 µm.
Microscleres are toxas, very slender, sharply (angularly) bent, with straight legs or with slightly recurved apices, in three size categories: 48-100 x 2 µm, 26-41 x 0.2-2 µm and 6-20 x 0.2-0.7 µm.
Skeleton: (Hemigellius pumiceus BandW) The ectosomal skeleton consists of short spicule tracts which construct an irregular reticulum. The choanosomal skeleton is a strong, somewhat confused reticularion of multispicular primary lines, which are irregularly connected by unispicular secondary lines.
Ecology: Deep water (80-120 m), in sheltered environment.
Distribution: Norway, Sweden.
Etymology: Pumiceus (Latin) = like pumice-stone, referring to the consistency.
Type specimen information: No data.
Remarks
This is a clearly recognizable species through its thick-lamellated habit in combination with a coarsely hispid surface, lacking any indication of suppleness which characterizes lamellate Axinellids. In the Arctic there is a second species of Hemigellius , viz. H . arcoferus , which is similar in habit but has sigmas as well as toxas for microscleres; the megascleres of that species are only about half the size of those of H . pumiceus .
A suspected third Hemigellius is Gellius styliferus Von Lendenfeld, 1897, described from 100 m near Rockall, but this has to be confirmed.
Source: De Weerdt and Van Soest (1987).