(Lamarck, 1813-14)
Species Overview
Prosuberites epiphytum (Lamarck, 1813-14) is a yellow (or brownish) thin encrustation on the undersides of boulders, on barnacles and mussels or on the thallus and stipes of brown weeds in the lower intertidal and the shallow subtidal. Its consistency is compact and not easily damaged, which may distinguish it from other yellowish usually soft encrustations. It is easily overlooked, but has a wide distribution along the coasts of Western Europe.
Taxonomic Description
Colour: Pale brown or yellow.
Shape, size, surface and consistency: (Prosuberites epiphytum MCS2) (Prosuberites epiphytum France) (Prosuberites epiphytum France 2) Very thin sheets (less than 1mm ?). Surface even, smooth, slightly hispid. Subsurface canal patterns visible in some specimens. Apertures not apparent if canal patterns absent. Contraction slight, accompanied by closure of canals. Consistency compact.
Spicules: (Prosuberites epiphytum drw) (Prosuberites epiphytum spics) The megascleres are tylostyles, usually about: 110-145-180 x 4 µm to 220-300-350 x 7 µm in a given specimen. However, lengths to ca. 600 µm and widths to ca. 11 µm may occur in some specimens. There is no consistent relation between length and width (width is measured just beneath the head). The shafts are usually curved. The curvature occurs about one quarter to one third the length of the shaft from the head and is sometimes pronounced. The shaft tapers gradually to a sharp point in the distal half to one third of its length. The greatest thickness is just above the head. The head is smooth and shaped like an old-fashioned door-handle, weakly mucronate spicules being rare. Thinner spicules often exhibit a smaller additional swelling immediately adjacent to the head. Microscleres are absent.
Skeleton: In very thin specimens, the skeleton consists of tylostyles arranged perpendicularly to the substrate, with the heads nearer to the substrate and sometimes touching it. In thicker specimens the basal spicules are overlain by spicule bundles that anastomize and may run either perpendicular or parallel to the substrate. At the surface the spicule bundles usually support projecting tufts of spicules (causing the hispid appearance), but tangential spicules may also be present in the dermal membrane.
Ecology: On undersides of boulders, shells, other animals and algae. Specimens tend to be small and cryptic. Shore to ca. 12 m.
Distribution: North Sea coast, south and west coasts of British Isles, west coasts of France. Common in Holland.
Etymology: The name refers to the fact that the type specimen was epiphytic on fucoid brown algae.
Type specimen information: The type (Alcyonium epiphytum) is in the Paris Museum; MCS VoucherBELUM: Mc856. Menai Straits, Wales.
Remarks
A microscopic examination is essential. A combination of spicules orientated perpendicularly to the substrate, door-handle like heads and the other spicule characteristics described above can confirm identity. Reliable field identification characteristics are not yet known, but the compact consistency is a good clue.
The closely related Prosuberites longispinus has much longer tylostyles (over 2000 µm).
Source: Ackers et al., 1992; Van Soest, 1977