Bowerbank, 1866
Species Overview
Polymastia spinula Bowerbank, 1866 is a small Polymastia with relatively very long, thin and pointed papillae. It is a rare species, recorded a few times from the coasts of the British Isles and France.
Taxonomic Description
Colour: Cream white (dry).
Shape, size, surface and consistency: (Polymastia spinula Bow.) This little sponge is characterized externally by the length of the papillae which exceed 5 cm for a body of about 1 cm2. Their points are sharp. Consistency firm.
Spicules: All the spicules of P . spinula are bent or slightly flexuous. The principal ones are fusiform strongyloxeas, bent or slightly flexuous: 724.5-926.8 x 10.4-15.6 µm; the intermediary ones are also bent, but they are fusiform tylostyles with a slightly marked head: 332.8-478.4 x 5.2-10.4 µm; the ectosomal ones are tylostyles with a well-marked head; they are bent once or twice: 124.8-156 x 5.2 µm.
Skeleton: (Polymastia spinula cross) Ectosomal : the ectosome is 250 µm thick. It is composed of intermediary tangential tylostyles, and a layer of small tylostyles arranged in palisade. Choanosomal : the choanosomal skeleton consists of bundles of tylostyles of 250 µm in diameter. These bundles end arched just below the cortical layer of ectosomal tylostyles. Between the bundles few intermediary spicules are scattered. Papillae : only the inhalant papillae were observed. In contrast with the other species of the genus, the papilla of P . spinula is very simple. The axial skeleton is composed of the bundles of tylostyles slightly protuberant in the single canal of the papilla, a thin layer of tangential tylostyles and the palisade of ectosomal tylostyles. In fact, the wall of the papilla has the same thickness as the palisade, i.e. about 150 µm.
Ecology: Deep water, below 63 m.
Distribution: Described from Shetland by Bowerbank, this species was found again only by Topsent in the Bay of Biscaye. Possibly, Hanitsch 's record of Axinella mamillata concerns this species, and that would extend the distribution to the Liverpool area.
Etymology: The papillae are pointed and thus the specimens may be considered "spined".
Type specimen information: The type is in the Natural History Museum, London, BMNH 1910.1.1.23 (dry + wet subsample), Norman Collection.
Remarks
This species was considered a synonym of P . mamillaris by Topsent (1900), but is regarded to be a good species by Boury-Esnault (1987). The type specimen from Bowerbank has many features different from P . mamillaris , notably the shape, length and skeletal structure of the papillae.
Source: Boury-Esnault, 1987.