Crella (Pytheas) donsi Burton (1931) is a whitish thin but laterally extensive crust on intertidal rocks. It has been recorded only once from the Trondheim area, Norway.
Colour: Cream-white in alcohol.
Shape, size, surface and consistency: Thin encrustation on rocks, extensive, about 1 mm thick. Surface smooth, even, minutely punctate and showing traces of subdermal canals. Oscules not apparent.
Spicules: Megascleres: Tornotes oxeote, cylindrical, narrowing slightly from the middle outwards and coming to an abrupt point at each end: 240 x 4 µm; long acanthostyles, only sparingly spined: 200 x 6 µm; ectosomal acanthostyles, heavily spined: 100 x 4 µm. No microscleres.
Skeleton: Ectosomal: a tangential crust of acanthostyles. Choanosomal: bundles of tornotes and long acanthostyles.
Ecology: On rocks at low tide.
Distribution: Recorded only once from Norway.
Etymology: Named after Mr Carl Dons of the Trondheim Museum.
Type specimen information: The holotype is in the Trondheim Museum. 3 slides of the holotype are in the Natural History Museum, London: BMNH 1931: 10: 28: 30a.
The characteristic features of this sponge are the absence of microscleres and the oxea-like tornotes.
Source: Burton, 1931.