Tetilla cranium

(Müller, 1776)

Species Overview

Tetilla cranium (Müller, 1776) is a globular or egg-shaped yellowish sponge with a conulose or warty, hispid surface. It is tough and when cut in half shows a clear radiate structure. It is a northern deep water species similar to T . zetlandica ; the two differ in details of the spicules (microscopic examination necessary).

Taxonomic Description

Colour: Yellowish to whitish.
Shape, size, surface and consistency: Ball-shaped, globular or egg-shaped sponges with conulous, warty, hispid surface. Size may be up to 9 cm in diameter. No apparent oscules. Consistency tough, hard.
Spicules: (Tetilla cranium spics) Megascleres : Oxeas of the cortical region, short, fusiform: 400-1400 x 32-55; oxeas of the radiate skeleton: 2100-9200 x 27-70 µm; protriaenes with shaft 3200-8500 x 8-30 µm, cladi 150-236 µm; anatriaenes with shaft 2100-20, 000 x 11-35 µm and cladi 50-150 µm.
Microscleres : Sigmaspires: 9-20 µm.
Skeleton: Strictly radiate; cortical oxeas are arranged singly, whereas choanosomal oxeas and triaenes are arranged in tracts or bundles.
Ecology: On stones and dead corals, 27-1000 m
Distribution: Norway, Faroes, Shetland, SW Ireland, Sweden; also recorded from many other localities outside European waters, but these need to be confirmed.
Etymology: The name refers to the resemblance to a rounded skull.
Type specimen information: No type material in BMNH.

Remarks

Tetilla zetlandica (Carter, 1872) is similar in appearance and can be told apart only by microscopic examination. It apparently lacks the sigmaspire microscleres and also the sizes of the spicules are considerably smaller than those of the present species.
Source: Arndt, 1935.