Hymedesmia versicolor

(Topsent, 1893)

Species Overview

Hymedesmia versicolor (Topsent, 1893) is a thinly encrusting Mediterranean species reported also from the Atlantic coasts of France. It is possible that the latter records concern Hymedesmia paupertas , because they are reported as bluish or greenish. Further research is necessary.

Taxonomic Description

Colour: Greenish or blue (Western Europe); also reported as yellow (Mediterranean).
Shape, size, surface and consistency: Thinly encrusting. Areolate porefields slightly raised, rounded, visible as lighter areas.
Spicules: Megascleres : Tornotes anisotylote, may be polytylote: 235-325 x 2-5 µm; large acanthostyles, spined mainly near the head: 260-460 x 5-11 µm; small acanthostyles, entirely spined: 115-180 x 2-5 µm. Microscleres : Arcuate isochelae with short alae: 24-32 µm.
Skeleton: Hymedesmoid: acanthostyles erect on the substrate; bundles of ectosomal tornotes.
Ecology: On stones, in caves, in deeper water below 20 m.
Distribution: Mediterranean, Roscoff, Le Portel (Straits of Dover).
Etymology: The name refers to the variable live colour.
Type specimen information: The type is in the Paris Museum.

Remarks

The blue specimens are indistinguishable from Hymedesmia paupertas (Bowerbank) and thus part of the material ascribed to H . versicolor (including the Western European specimens) may belong to that species.
Source: Topsent (1936).