Form: Massive-globose, being spherical to hemispherical, slightly flattened at the base. Up to 6cms in diameter.
Colour: White, "brown, yellow". Recent observations of living specimens indicate that they are white when alive, but Tetilla cranium is brown or yellow. (Tetilla cranium is described as "yellowish white in spirit").
Smell: ? (T. cranium is described as having an "offensive, ammoniacal odour" when fresh). Slime : None
Consistency: Firm, incompressible.
Surface: Even, conulate, spinose (the hairs projecting through the conules), with a rough texture exhibiting high friction.
Apertures: Typically, a single oscule at the apex (??).
Skeleton: Choristid, with a well developed cortex. The thick radially arranged tracts of megascleres, which can be seen with the unaided eye in torn specimens, run perpendicular to the surface. The cortical skeleton is a dense palisade of the smaller oxea (see below) supporting bundles of protriaenes, which project from the surface at their clad (i.e. rayed) ends.
Spicules: There are four types of megascleres. Cortical oxea are 800-1400Ám long, by 50Ám wide. Choanosomal oxea are ca. 2560-4600Ám long, by 60Ám wide, and are longitudinally asymmetrical. The trianes are long shafted, with relatively small rayed ends. The protriaenes are 3490-7100Ám long, by 18Ám wide. The anatriaenes are ca. 5300-8570Ám long, by 25Ám, diminishing to 13Ám wide. There are no microscleres.
Habitat: Seated in cup shaped sponges (Axinella infundibuliformis/Phakellia ventilabrum), or attached to stones at depths of 15-680metres (recent observations by divers are from ca. 40m).
Distribution: Shetland. Also generally reported from the Arctic, Atlantic, Indian and Pacific Oceans. Known recently from the Aran Islands, Galway Bay and Western Scotland.
Distribution Map from NBN: Grid map (fast) : Interactive map (slower, requires login to view records) : National Biodiversity Network mapping facility, data for UK.
Identity: Tethya citrina (q.v.) is similar in shape and size, but is usually orange, not as firm and "coarse" as T. zetlandica, and typically found in shallower water. The spiculation of these two sponges is quite different. T. zetlandica is a northern, deeper water sponge, only likely to be encountered occasionally by scuba divers. T. cranium (Muller, 1776: 255) is reported to be identical to T. zetlandica in external appearance, but possesses distorted 'S' shaped microscleres called sigmaspires. The similarity between these two sponges has resulted in some authors synonymising T. zetlandica under T. cranium, or making it a variety thereof.
Voucher: BELUM : Mc695. Aran Islands, Galway.
Editors: D. Moss.
|Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland |
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