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(Müller, 1806)

Species Overview

Polymastia mamillaris (Müller, 1806) is a papillate deep-water sponges, so far only known from the Swedish W coast. The name is widely used in the literature for a similar species occurring in shallow waters along the coasts of the British Isles, France and the Iberian Peninsula, now to be called P. penicillus. The two species differ in the structure of the skeleton and the shape and size of the spicules.

Taxonomic Description

Colour: Cream in alcohol.
Shape, size, surface and consistency: The type specimen is a fragment of a cushion-shaped, attached sponge approximately 35 x 18 x 7 mm thick. The upper surface is hispid. The surface of the sponge traps silt and the colour is only discernible on the papillae. The specimen has 26 inhalant papillae and one exhalant. The mean length of the inhalant papillae is 8 x 2 mm in diameter. The exhalant papillae is 11 mm long and approximately 4 mm in diameter.
Spicules: Ectosomal tylostyles are fusiform, straight or slightly bent with a well marked head: 143-196 x 5.3-16 µm (mean 169 x 10.6 µm). Intermediary styles or subtylostyles, straight, 243-561 x 8-15.9 µm (mean 445 x 13.2 µm). Principal spicules are straight, fusiform strongyloxeas, 742-1378 x 8-32 µm (mean 1052 x 24.5 µm).
Skeleton: The ectosomal skeleton is about 400 m thick and composed of three layers: the upper layer is a dense palisade (~300 µm thick) of fusiform tylostyles, the middle layer is collagenous (~20 µm thick) and the lower layer is a tangential layer (~80 µm thick) made of intermediary spicules. Choanosomal tracts of principal spicules are 53-106 µm thick. These tracts are divided into two to three smaller ones below the ectosome. They cross the ectosome and echinate the surface by approximately 875 µm. Groups from two to five ectosomal spicules are scattered between the choanosomal tracts. They are particularly abundant below the tangential layer of intermediary spicules in a layer approximately 500 µm thick. The skeleton of the inhalant papillae consists of ascending multispicular megasclere tracts that run the length of the papillae. These are supported by a network of intermediary tylostyles arranged perpendicularly to the megasclere tracts. Towards the periphery there is a layer of tangentially arranged intermediary tylostyles and external to this a palisade composed of ectosomal tylostyles.
Distribution: Swedish W coast and Skagerrak.
Type specimen information: Holotype: ZMUC '2.1.93' - Bohuslän, North-Atlantic, Swedish west coast, 58°15' N, 11°50' E.

Remarks

Specimens of Polymastia from the Swedish west coast collected between 76 and 225 m deep correspond to the form described by Müller. These show the following characters: ectosomal skeleton composed of three layers, groups from 2-5 ectosomal spicules scattered between the choanosomal tracts and particularly abundant below the tangential layer of the ectosome, shape of the ectosomal tylostyles (101-182 x 5.2-11.7, mean 148 x 8.4 µm) and of the principal choanosomal spicules (strongyloxeas 461-1320 x 10.6-26.5, mean 853 x 20 µm) (Morrow & Boury-Esnault, 2000).
Conversely, the holotype of Polymastia mamillaris does not correspond with what it is commonly called P. mamillaris in the Northeast Atlantic (Channel, North Sea, Irish Sea). The common NE Atlantic Polymastia has a two-layered cortex, free intermediary tylostyles in the choanosome and the shape of spicules is not fusiform (see Boury-Esnault, 1974, 1987). This species is actually P. penicillus (Montagu, 1818) (Morrow & Boury-Esnault, 2000). Spongia mamillaris Müller, 1806, was misidentified as Halichondria mamillaris 'Johnston, 1842' in the original designation by Bowerbank, 1864. The species is known only from the Swedish west coast between 75 and 225 m depth.
In a recent study (Plotkin & Boury-Esnault, 2004), the species Polymastia arctica (Merejkowsky, 1878) was reinstated as a species distinct from P. mamillaris (with which is was synonymized previously). It occurs in the White Sea. Differences are the presence of a thick (90-180 µm) collagenous layer in the cortex, the presence of spicules in the papilla internal laminae and the formation of buds at the top of the papillae. As this recent information is about a species at the very edge of the area treated here we refrain from introducing it in this file.
Source: Morrow & Boury-Esnault, 2000; Boury-Esnault, 2002.

Polymastia mamillaris