Pseudosuberites Topsent 1896

Genus Pseudosuberites Topsent, 1896

Pseudosuberites Topsent, 1896: 127.

Type species. Pseudosuberites hyalinus (Ridley & Dendy, 1887) (by subsequent designation).

Diagnosis. Massive, globular, thinly to thickly encrusting, lobular, digitate sponges, with a smooth surface, due to the presence of a tangential ectosomal skeleton of tylostyles. Choanosomal skeleton ranges from a confused arrangement, to loose tracts of megascleres that diverge from the base of encrusting sponges, or has some degree of axial compression in lobular or digitate sponges, where discrete tracts diverge towards the surface where they form thick bouquets. Ectosomal skeleton is a thin or thick, detachable, flaky, tangential layer of tylostyles. Spicules are tylostyles that occur in a variety of sizes, without clearly distinct or localised size categories (modified from Van Soest 2002).

Remarks. Van Soest (2002) noted that in Topsent’s treatment of Pseudosuberites (Topsent 1896, 1900), he (Topsent) intended the well-established, thinly encrusting European species, P. sulphureus (Bowerbank, 1866: 208, as Hymeniacidon), as type of the genus, although he omitted to clearly state this. A second, thickly encrusting to digitate species, Hymeniacidon ? hyalinus Ridley & Dendy, 1887, from the channels and fjords of Southern Chile, was mentioned by Topsent, and subsequently named the ‘genotype’ of Pseudosuberites by Burton (1930), rendering the status of Pseudosuberites unclear.

The general form of the type species, P. hyalinus, is massive amorphous to digitate, with a skeleton of loose tracts of relatively large megascleres (tylostyles about 1200 µm long), that diverge towards the surface forming subectosomal brushes, the spicules of which are disposed obliquely and then tangentially at the surface (tylostyles about 200 µm long). In general terms, the architecture of the type species and the size of the megascleres, is similar to that of species of the Southern Ocean genus Plicatellopsis, with the axial compression, extra-axial skeleton emerging as subectosomal bouquets, between which are large subdermal spaces. The primary difference between the two genera is the presence of a compact (detachable) crust of oblique to tangentially disposed megascleres, carried by surface brushes, in Southern Ocean Pseudosuberites species, absent in all Plicatellopsis species except P. antarctica (Carter), albeit rudimentary in this species.