Sollas, 1880
Species Overview
Isops phlegraei Sollas, 1880 is a globular, yellowish grey, hispid sponge, often encrusted or sedimented. Oscules small and scattered, through which it may be distinguished from similar Geodia-like sponges which have them organized in groups, often in depressions or cavities. It has a hard consistency. It is a northern deep-water sponge.
Taxonomic Description
Colour: Pale yellowish grey.
Shape, size, surface and consistency: More or less spherical, size up to 20 cm in diameter. Surface hispid due to projecting spicules, often overgrown or sedimented. Oscules small, 1-2 mm, and scattered, mostly conspicuous. Consistency hard.
Spicules: (Isops phlegraei spics) Megascleres : Oxeas up to 6000 x 65 µm; plagiotriaenes up to 4000 x 425, with clads 600 µm, occasionally dichotriaene modifications occur; protriaenes likewise long, but size not recorded, thickness 20 µm; anatriaenes, ditto.
Microscleres : Sterrasters, ellipsoid, maximal size 90 µm; spherasters in two size classes: cortical ones with conical rays, 12 µm, choanosomal with longer thinner rays, up to 20 µm.
Skeleton: Radiate; cortex about 650 µm in thickness, consisting chiefly of the sterrastral layer, below that there is a thin fibrous layer. Inner skeleton confused.
Ecology: 85-900 m
Distribution: Sweden, Norway.
Etymology: Phlegraeus (Greek) = from the ancient city of Phlegra in Macedonia; its connection with the present species in unknown.
Type specimen information: The type is in the Natural History Museum, London. Type locality: Kors Fjord, Norway, 364 m.
Remarks
Several other Isops species have been recorded from the area (I . globus Schmidt, from Portugal, I . pallida Vosmaer from the Arctic, and I . sphaeroides Vosmaer, likewise from the Arctic) but the status of these is unclear; it is likely that at least the latter two are synonyms of I . phlegraei .
The Mediterranean Isops intuta differs from the present species in overall smaller size of the megascleres (e.g. oxeas are only up to 2500 x 28 µm), and the absence of anatriaenes and protriaenes.
The genus Isops is distinguished from Geodia by the scattered oscules, which are grouped in Geodia . With Geodia and Pachymatisma it shares the sterrasters. Pachymatisma johnstonia are dark greyish masses; the spiculation includes microstrongyles, which are absent in both Geodia and Isops . The validity of a separate genus Isops remains debatable.
Source: Sollas, 1880, 1888.