Mycale (Aegogropila) retifera Topsent (1924) is a thinly encrusting red sponge with a smooth easily detachable skin. It has a soft consistency. It is a rare species, originally described from the Mediterranean but also recorded from Roscoff.
Shape, size, surface and consistency: Thin, small encrustations. Surface smooth. Consistency soft.
Spicules: Megascleres: Subtylostyles ("mycalostyles"), straight, with elliptical head, with axial canal visible in the head, not particularly fusiform, gradually tapering towards the pointed end: 260-290 x 6-7.5 µm.
Microscleres: Three size categories of anisochelae: largest, with outcurved middle alae, with thick falces, rare, solitary or in rosettes of 5-6: 28-31 µm; middle sized, with almost straight middle alae, numerous: 18-20 µm; smallest: 11-15 µm; two size categories of sigmas: 60-68 x 3-5 µm and 22-26 µm; toxas numerous and variable in length and thickness: 40-130 x 0.8 µm (mostly 40-75 µm), the smallest may show bizarre curves and shapes.
Skeleton: Ectosomal skeleton a reticulation of tangential tracts of about 3 spicules in cross section, easily detachable. Choanosomal skeleton consists of plumose bundles of megascleres.
Ecology: On stones or epibiont on other sponges, from shallow water to at least 60 m.
Distribution: Mediterranean, Roscoff.
Etymology: The name refers to the net-like surface.
Type specimen information: The type is in the Paris Museum.
The peculiar toxas and the colour make this species readily distinguishable from its closest relative, M. (A.) contareni.
Source: Topsent, 1924.