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(Carter, 1872)

Species Overview

Craniella zetlandica (Carter, 1872) is a whitish ball-shaped sponge with "spiny" surface and firm consistency. Typically there is a single oscule at the apex. It is similar in appearance to Craniella cranium and can be discriminated from it only by microscopic examination. It is a northern deep water species, known from NW Ireland, W Scotland, Shetlands and the Arctis.

Taxonomic Description

Colour: White, brown, yellow (? looks whitish in one photograph).
Shape, size, surface and consistency: Massive-globose, being spherical to hemispherical, slightly flattened at the base. Up to 6 cm in diameter. Surface even, conulate, spinose (the spicules projecting through the conules), with a rough texture exhibiting high friction. Typically a single oscule at the apex. Described as having an "offensive, ammoniacal odour" when fresh. No slime. Consistency firm, incompressible.
Spicules: (craniella_zetlandica_spics.jpg) There are four types of megascleres. Cortical oxeas are 800-1400 x 50 µm. Choanosomal oxeas are ca. 2560-4600 x 60 µm, and are longitudinally asymmetrical. The triaenes are long shafted, with relatively small rayed ends: protriaenes are 3490-7100 x 18 µm; anatriaenes are ca. 5300-8570 x 25 µm, diminishing to 13 µm wide. There are no microscleres.
Skeleton: Choristid, i.e. strongly radiate, with a well developed cortex. The thick radially arranged tracts of megascleres, which can be seen with the unaided eye in some specimens, run perpendicular to the surface. The cortical skeleton is a dense palisade of the smaller oxeas supporting bundles of protriaenes, which project from the surface with their clad (i.e. rayed) ends.
Ecology: Seated in cup shaped sponges (Axinella infundibuliformis /Phakellia ventilabrum), or attached to stones at depths of 15-680 m (recent observations by divers are from ca. 40 m).
Distribution: Shetland, Faroes. Reported recently from the Aran Islands, Galway Bay, Western Scotland, Norway. Also generally reported from the Arctic, Atlantic and—probably incorrectly—from Indian and Pacific Oceans.
Etymology: Zetland is the old name of Shetland.
Type specimen information: The type is in the Natural History Museum, London. MCS Voucher BELUM: Mc695, Aran Islands, W Ireland.

Remarks

Craniella cranium (Müller), a similar species, is described as yellowish white in spirit. It is reported to be identical to C. zetlandica in external appearance, but it possesses sigmaspire microscleres. The similarity between these two sponges has resulted in some authors synonymising C. zetlandica under C. cranium, or making it a "variety" thereof.
Tethya citrina is similar in shape and size, but is usually orange, not as firm and coarse as C. zetlandica, and typically found in shallower water. The spiculation of these two sponges is quite different. C. zetlandica is a northern, deeper water sponge, only likely to be encountered occasionally by scuba divers.
Source: Ackers et al., 1992.

Craniella zetlandica