"Sphaerotylus borealis (Swarczewsky, 1906)
Thickly encrusting cushion-shaped sponges. The surface is extremely hispid. The papillae are small and their number does not exceed 30 per specimen. The choanosomal skeleton is constituted by the radial tracts of principal styles and free-scattered small tylostyles. The cortex is constituted by a tylostyle palisade and a parapalysade irregular layer of intermediary subtylostyles. Both are echinated by the tracts ascending from the choanosome and by very long exotyles. The heads of the latter display a great variety in shape, being spherical, hemispherical, cone-like or even smooth (Fig. 4b). No exotyles were observed in the choanosome. The papilla skeleton consists of the spicule axial framework of tracts and the cortex-like wall without exotyles. Each papilla possesses a central exhalant canal and several inhalant ones at the periphery."
(Plotkin, 2004: 543-544)
