Chelonaplysilla noevus (Carter, 1876) is a dark purple encrusting species with a very characteristic surface reticulation of sand grains visible to the naked eye or with a low magnification. There are coarse sharp conules, similar to those of Aplysilla. It is a southern species reaching its northern limits off the west coasts of France, occurring at depths of 15-115 m.
Colour: Dark purple-violet, in life as well as in alcohol.
Shape, size, surface and consistency: Encrusting, conulose, several mm in thickness and of indefinite lateral expansion. Conules coarse, sharp, several mm apart. Surface bears a characteristic reticulation of sand grains visible to the naked eye (C. noevus surface). Oscules conspicuous, wide, slightly raised. Consistency soft.
Skeleton: Dendritic fibres rise from a basal spongin plate adhering the substrate, similar to the condition found in Aplysilla species. They are 75-80 µm diameter at the base, 20-30 µm near the surface. Spongin purple coloured, layered, with a wide darker area in the centre (pith). Fibres may divide a few times but seldom anastomose. Surface reticulation of sand grains with meshes of 160-170 µm diameter.
Reproduction: In the Mediterranean, violet-black larvae, with a posterior crown of long flagellae, were reported from a specimen collected on October 7.
Ecology: On rocks in the shallow sublittoral, 15-115 m.
Distribution: Roscoff, Naples, Monaco, Azores, Cape Verde Islands; a rare species in Western Europe.
Etymology: noevus (Latin) = birthmark, referring to the shape of the type specimen according to its author.
Type specimen information: No data.
Along the coasts of Western Europe in shallow water this is the only representative of the genus Chelonaplysilla, and through its surface reticulation of sand grains is easily recognizable. The Mediterranean species Aplysilla arenosa Topsent (1925) is considered a junior synonym. In deeper waters off the Azores and alos in more northern Atlantic waters, C. psammophila (Topsent, 1928 as Aplysilla), occurs which may be distinguished by having a much paler colour. In the Eastern Mediterranean, a third species, C. erecta, occurs which is very similar to the present species, but it forms creeping or erect branches.
Source: Topsent, 1925a (as Aplysilla arenosa); Vacelet, 1959.