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Bowerbank, 1864

Species Overview

Hymedesmia (Hymedesmia) zetlandica Bowerbank (1864) is a yellow very thinly encrusting sponge from deep-water. It has a characteristic spiculation (microscopic examination).

Taxonomic Description

Colour: Yellow (brownish yellow).
Shape, size, surface and consistency: Thinly encrusting. Lateral expansion about 20 mm. Surface smooth. No visible oscules.
Spicules: Megascleres: Ectosomal tylotes, straight, uniform in size: 225-255 x 5-8 µm; acanthostyles 80-145 x 10-20 µm, divisible in two size categories. Microscleres: Arcuate isochelae, in two categories: larger with slightly curved shaft, rather short alae: 20-30 µm, and smaller, reduced, with a spined shaft: 10-15 µm; sigmas, in bundles (sigmodragmas), extremely slender: 40-50 µm.
Skeleton: Acanthostyles vertically on the substratum, points outward. The tylotes are arranged in bundles.
Ecology: On pebbles, deeper water below 65 m.
Distribution: Shetlands, SW Ireland.
Etymology: Zetland is the ancient name for Shetland.
Type specimen information: The type is in the Natural History Museum, London, BMNH unregistered, Bk. 467.


This species is the type of the large genus Hymedesmia, but it is an unusual Hymedesmia in possessing both tylotes as ectosomal tornotes and sigmas in dragmata.
Source: Stephens, 1920.

Hymedesmia zetlandica