Crellomima derma (Hentschel, 1929) is a thin smooth crust of unknown live colour, which may be only reliably recognized by examination of the spicules. It is an Arctic-Boreal species.
Colour: Yellow-grey to colourless in alcohol.
Shape, size, surface and consistency: Thinly encrusting with smooth surface. Size up to 1 cm in lateral expansion and 0.5 mm in thickness. Surface membrane easily detachable. No obvious oscules. Consistency fragile.
Spicules: Megascleres: Choanosomal tornotes, fusiform, smooth, with endings sharp, grading into blunt, sometimes polytylote: 200-232 x 6 µm; ectosomal acanthostyles, curved, fusiform, not swollen at the base, strongly spined all over: 96-168 x 5-7 µm; choanosomal basal acanthostyles, with strongly spined swollen basal end, lighter spined along the shaft: 126-210 x 6-13 µm.
Microscleres: Anchorate chelae, tridentate, gradually curved shaft: 17-19 µm.
Skeleton: Ectosomal skeleton a parchment-like multiple-layered crust of tangential acanthostyles. Choanosomal skeleton consists of plumose bundles of tornotes, 70 µm in diameter, rising up from a basal plate of spongin in which acanthostyles are embedded with their heads, shafts upwards. Microscleres concentrated in the choanosome, rather rare.
Ecology: On worm tubes and pebbles, 60-120 m
Distribution: Faroes; Arctic.
Etymology: derma (Greek) = skin, referring to the tangential skeleton of Crellidae.
Type specimen information: Hentschel's material is in the Zoological Museum of Hamburg.
This species is ill-known (has in fact been described only once). The combination of thinly encrusting habit, oxea-like tornotes and anchorate chelae distinguish the present species from these others.
Koltun (1959) synonymized C. derma with C. imparidens (Rezvoj, 1925) from the Barents Sea. This is not followed here.
Source: Hentschel, 1929.