Hymedesmia (Hymedesmia) mamillaris (Fristedt, 1885) is a thinly encrusting sponge with short raised crater-like porefields, resembling papillae. Colour brown-red. It is known only from the Scandinavian fjords where it occurs from 30 m downwards.
Colour: Brown-red (Alander, 1942, says: blood-red).
Shape, size, surface and consistency: Encrusting, with crater-like, cylindrical and conical raised porefields resembling papillae. Thickness 1 mm, lateral expansion up to 12 cm. Surface smooth. Oscules on the papillae.
Spicules: (Hymedesmia mamillaris spics) Megascleres: Ectosomal tornotes fusiform or strongylote, with abruptly pointed ends which may be subapically constricted: 266-440 µm long; main acanthostyles, lightly but entirely spined all over, more densely spined at the heads: 350-600 µm long; echinating acanthostyles, entirelyheavily spined: 110-200 µm long. Microscleres: Arcuate chelae 19-32 µm; occasionally reduced C-shaped forms occur.
Skeleton: Acanthostyles erect on the substrate, but towards the periphery some bundles of acanthostyles and tornotes are observed; the surface is strewn with chelae.
Ecology: In the fjords from 30-400 m.
Distribution: Sweden, Arctic.
Etymology: The name refers to the condition of the surface.
Type specimen information: No data.
This species stands out among Hymedesmia species by its high/long papillae. The size and spination of the acanthostyles are also discriminating.
Source: Fristedt, 1885