Placospongia decorticans (Hanitsch, 1895) forms a thin hard crust with characteristic, raised grooves. It is a rare southern species.
Colour: Yellowish white to greyish in alcohol.
Shape, size, surface and consistency: A thin flat crust of stony consistency, measuring 4 x 3 cm and 0.5-1 mm in thickness. The surface is raised into conules and ridges enclosing polygonal meshes. The ridges are double-walled and include deep grooves, which are expanded in live specimens.
Spicules: Megascleres: Tylostyles: 510 x 8 µm.
Microscleres: Selenasters: 80 x 28 µm in fullgrown condition, growth stages are spined rods and spiraster-like forms; spirasters: 14 µm; spherasters with a very large centre and short rays: 12 µm; spherasters with a small centre and long rays: 16 µm.
Skeleton: Ectosomal: a thick cortex consisting of a layer of selenasters covered on the outside by a layer of thick-centred spherasters. Choanosomal: pairs of bundles of tylostyles traverse the choanosome and protrude through the cortex at regular distances forming the conules. In between these bundles there is a sunken space (forming meandering grooves) containing the inhalant and exhalant openings.
Ecology: No data.
Distribution: West coast of Portugal; Mediterranean.
Etymology: The name presumably refers to the cortex-less grooves which may extend considerably in live specimens.
Type specimen information: No type material in BMNH.
There are no sponges with which this very characteristic sponge can be confused. The selenasters superficially resemble the sterrasters of Geodia, but the possession of tylostyles easily distinguishes the present species.
Source: Hanitsch, 1895