(Sollas, 1882)
Species Overview
Sphaerotylus schoenus (Sollas, 1882) is a yellowish papillate flattened or somewhat globular massive sponge. It differs from species of the genus Polymastia , to which it is related, in the strong hispidity of the surface, and in the possession of exotyle-bearing tylotes (microscopic examination). The hispidity causes quantities of mud and other debris to collect at the surface, giving it an additional characteristic. It is common in deep water in the North Atlantic.
Taxonomic Description
Colour: Yellowish, often darker coloured between the papillae because of accumulated mud.
Shape, size, surface and consistency: Massive or occasionally globular, provided with several coarse papillae. Size up to 5 cm in diameter. Surface of main body hispid, of papillae optically smooth. Oscules at the summit of the papillae. Consistency very firm.
Spicules: (Sphaerotylus schoenus spics) Tylostyles in several categories, including exotyles. The latter are tylostyles of the largest category provided with a spined or rugose, globular or irregular swelling at the (originally) pointed end, projecting beyond the surface of the main body: 600-1250 x 8-20 µm; tylostyles of the largest category, subtylostylote, often polytylote: 650-1504 x 14-24 µm; intermediate tylostyles, not very common, often with tyle subterminal: 416-608 x 10 µm; small tylostyles: 96-230 x 2-6 µm.
Skeleton: Like Polymastia , with distinct cortex. The outermost skeleton is a palisade of small tylostyles, carried by scattered intermediate tylostyles. The main skeleton consists of strong bundles of large tylostyles and exotyles, some passing through the cortex to protrude beyond the surface.
Ecology: Deep water, 50-440 m.
Distribution: Norway, North Atlantic; Arctic; also recorded from the Southern Ocean.
Etymology: Schoenus (Greek) = a rush (genus Scirpus ), which forms cushions from which issue thin leaves. Its aptness to describe the form of this species is questionable.
Type specimen information: The type is in the Natural History Museum, London.
Remarks
Through the possession of exotyles this is a clearly demarcated species, which is otherwise close to Polymastia . A second species of Sphaerotylus , S . borealis (Schwartschevsky, 1906) occurs in Arctic waters; it has mushroom-shaped swellings on the the exotyle spicules, and much longer tylostyles.
Source: Arndt, 1935.