Van Soest, 1980
Definition: Typically massive, vase-shaped or volcano-shaped sponges, sometimes encrusting, bulbous, and less commonly branching growth forms. Texture is characteristically stony, brittle, reflecting that in most species siliceous spicules are clearly dominant over spongin. Ectosomal skeleton is an isotropic reticulation of single spicules or spicule tracts forming a crust, giving the surface a smooth appearance. Choanosomal skeleton is more-or-less a regular isotropic reticulation of multispicular tracts, without distinction between primary or secondary tracts, bound together with minimal spongin, forming oval meshes. Microscleres may include microxeas and microstrongyles. Reproduction is oviparous. (Petrosia crassa drawings)
Remarks: Five nominal genera are included in the family, only three of which are now recognised (Petrosia , Xestospongia , Cribrochalina ). Review: Van Soest (1980).
Source: Hooper's Internet Sponge Guide.
Genus represented in the area:
Petrosia Vosmaer, 1885 (type species Alcyonium ficiforme Poiret, 1789) (syn. Schmidtia Balsamo-Crivelli, 1863): ectosomal skeleton present as an isotropic spicule crust; choanosomal skeleton is basically lamellate-isotropic reticulate composed of dense spicule tracts bound with very little spongin giving the sponge a stony texture; oxeote or strongylote spicules in at least 2 size categories.
Species included:
Petrosia crassa
Species not treated here:
Petrosia clavata (Balsamo-Grivelli, 1863), Azores, deep water
Petrosia ficiformis (Olivi, 1791), NW Spain, deep water
Petrosia vansoesti Boury-Esnault et al. (1994), Straits of Gibraltar, deep water