Hymedesmia crux

(Schmidt, 1875)

Species Overview

Hymedesmia crux (Schmidt, 1875) is a yellow thinly encrusting deep-water sponge. It has very characteristic spined isochelae (microscopic examination). It is a northern species.

Taxonomic Description

Colour: Yellow.
Shape, size, surface and consistency: Thinly encrusting. Up to 35 mm in widest expansion, 1 mm in thickness. Surface smooth but provided with ?oscules on warty papillae. Consistency: soft.
Spicules: (Hymedesmia crux spics) Megascleres : Tornotes oxeote to strongylote, fusiform, abruptly pointed or rounded, polytylote: 270-380 x 6-8 µm; large acanthostyles, slightly curved, entirely spined: 380-400 x 20-30 µm; short acanthostyles, entirely spined: 120-150 µm.
Microscleres : Arcuate isochelae, shaft strongly curved, provided with thorns, alae peculiar in having strongly developed falces and barely any blades: 31-43 µm.
Skeleton: Ectosomal : a crust of chelae; the walls of the papillae have a tight mass of tornotes. Choanosomal : hymedesmioid, with single acnthostyles erect on the substrate and bundles of tornotes fanning out to the surface.
Ecology: Deep water, on corals, down to 1200 m.
Distribution: Norway, Faroes, SW Ireland, Denmark Strait.
Etymology: Crux (Latin) = cross, referring to the shape of the chelae.
Type specimen information: No type material in BMNH.

Remarks

The chelae are unique and make this an easily recognizable species.
Source: Lundbeck, 1910.