Stelletta simplicissima (Schmidt, 1868) is a brownish, massive, knoll-like or pear-shaped sponge, with numerous oscules and a hard consistency. It was originally described from the Mediterranean but was subsequently recorded from the Atlantic coasts of Spain.
Shape, size, surface and consistency: Massive, knoll-shaped or pear-shaped sponge of up to 7 cm in diameter. The surface is rough to the touch. There are numerous oscules. The consistency is hard.
Spicules: Megascleres: Oxeas and triaenes. Oxeas fusiform, frequently fairly strongly bent in the middle, sharply pointed, although some are blunt at one end, up to 2700 x 80 µm; plagiotriaenes, with straight conical rhabdome, up to 1600 x 65 µm, cladi short, conical, not very sharply pointed, 200 µm.
Microscleres: Euasters, apparently of a single continuous range of size and shape. oxyasters to strongylasters: 12-17 µm in diameter.
Skeleton: There is a thin cortex and the choanosome is cavernous. The oxeas and triaenes are arranged radiately; oxeas pentrate the cortxe and the surface where they cause the hispidation. The cladi of the triaenes support the cortex, in which the microscleres are concentrated.
Ecology: In intertidal caves.
Distribution: NW coast of Spain; Mediterranean.
Etymology: The name refers to the relatively simple spicule complement.
Type specimen information: There are several type specimens: the Paris Museum has 2 syntypes and one slide, MNHN DT 758, 759. The Berlin Museum has one, ZMB 6447, and the Natural History Museum, London, has one specimen, BMNH
1910:1:1:859, Norman Collection and one slide, BMNH 1868: 3:2:35 (Schmidt slide). According to Topsent (1938), one of the specimens of Schmidt belonged to a separate species of Stelletta, named S. addita by him.
The species is quite similar to S. hispida (Buccich) in spiculation and the two may prove to be synonyms, in which case the present species has priority.
Source: Sollas, 1888; Lendenfeld, 1894.