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(Schmidt, 1870)

Species Overview

Polymastia uberrima (Schmidt, 1870) is a spherical sponge provided with numerous osculiferous papillae on the upper side. It differs from most Polymastia species in being as high as wide or even higher. In this respect it is similar to Weberella bursa, from which it differs clearly in spicule size and categories. It is a N Atlantic deep water species.

Taxonomic Description

Colour: Yellowish.
Shape, size, surface and consistency: It is a spherical sponge of up to 12 cm diameter, with about 15 papillae at the top. It is fixed on pebbles and fragments of bryozoans. All the papillae end by an osculum.
Spicules: Principal straight, slightly fusiform strongyloxea: 1315-1770 x 17-25 µm; intermediary straight tylostyles, with a poorly marked head: 556-754 x 8-10µm; ectosomal slightly bent tylostyles: 307-350 x 5 µm.
Skeleton: (Polymastia uberrima skel) Ectosomal: there is a very thick cortex of about 2.2 mm. It is composed of two layers: a layer of tangential tylostyles 1.5 mm thick, and a layer of tufts of small tylostyles which constitute an irregular palissade of about 0.75 mm thick. Choanosomal: the bundles of principal spicules are 200-250 µm in diameter. They reach the basis of the palissade of tylostyles without passing through. Between these bundles small fascicles of intermediary spicules are dispersed. Papillae: the papillae are very wide. There is a central exhalant canal and the inhalant canals are at the periphery. The structure from inside to outside is respectively: the central canal, the surface of which is echinated by intermediary tylostyles; the bundles of spicules which are the axial framework of the papilla and which are linked by intermediary tylostyles; the inhalant canals which open between these bundles; at the surface, the tufts of small tylostyles similar to those of the cortex.
Ecology: Fixed to pebbles and bryozoans in deep water, 26-1000 m
Distribution: Described from Iceland by Schmidt, the species has always been collected in cold water. It was found along the coasts of Norway (Topsent, 1913), and in Greenland (Lundbeck, 1909).
Etymology: uber (Latin) = udder or teat, referring to the papillae.
Type specimen information: The type is in the Copenhagen Museum, with a slide in the Natural History Museum, London, BMNH 1870:5:3:99.

Remarks

Polymastia uberrima was badly described by Schmidt, and thus it was misinterpreted by Thiele (1903) and Hentschel (1929), who confused it with Weberella bursa. Subsequently, Burton (1959) synonymised the two species.
The confusion was heightened when Koltun (1966) separated the specimens described by the different authors under the name "uberrima ", into two groups. One group with only Schmidt's citation is P. uberrima sensu stricto and the other one with all the other citations is erected as a new species: P. thielei. But Koltun did not give any argument for this separation or why he decided that Lundbeck's and Topsent's specimens have to belong to this new species. In fact, in his description of P. uberrima, Thiele (1903) mentioned groups of small tylostyles arranged like trichodragmata between the choanosomal bundles. The creation of a new species for the sponge of Thiele seems consistent. But these trichodragmata are not present in P. uberrima.
Many of the citations of P. uberrima are very brief without giving any details on the skeleton, thus it is impossible to decide without a careful reexamination of the specimens which are related to P. uberrima and which to P. thielei.
Source: Boury-Esnault, 1987.

Polymastia uberrima