Hymedesmia zetlandica

Bowerbank, 1864

Species Overview

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.

Remarks

This species is the type of the large genus Hymedesmia , but its specific characters remain insufficiently known. It is an unusual Hymedesmia in possessing both tylotes as ectosomal tornotes and sigmas in dragmata.
Source: Stephens, 1920.