Phorbas bihamiger (Waller, 1878) is an olive-green, thinly encrusting sponge from shallow-water. It has been reported only from the S coast of England.
Colour: Olive-green (deep olive green alive and pale olive when dried).
Shape, size, surface and consistency: Encrusting. Lateral expansion 5 x 3 cm, thickness 1-3 mm. Surface quoted as smooth, slightly undulating, fleshy. Oscules or pores indistinct. Consistency soft.
Spicules: (Phorbas bihamiger spics) Megascleres: Ectosomal tornotes cylincrical with sharply pointed apices: 190 x 3 µm; acanthostyles in two size categories: 270 x 12 µm, and 120 x 7 µm.
Microscleres: Arcuate isochelae in two size categories: 5-8 µm and 14-20 µm; sigmas 24 µm.
Skeleton: Tornotes strewn singly or in irregular bundles at the surface amidst large numbers of microscleres. Choanosomal skeleton consists of plumose bundles of large acanthostyles, echinated by the smaller acanthostyles. The bundles may penetrate the surface.
Ecology: Shallow water and intertidal, in crevices.
Distribution: Torbay, Plymouth, Wembury (S England).
Type specimen information: No data.
Waller (1878) compared his new species with Phorbas plumosus, with which he was familiar. He remarked that the two differed clearly in colour and in the fact that P. bihamiger possesses sigmas. Since, then two other species with sigmas have been described, viz. P. dives (Topsent, 1891) and P. microchelifer (Cabioch, 1968). All three are closely similar, differing in details of the size of spicules; P. bihamiger may be closest to P. microchelifer of which life colour is not know. Possibly the two are synonymous, in which case P. microchelifer is a junior synonym.
Source: Waller, 1878; Burton's catalogue (unpublished), courtesy of Ms C. Valentine.