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(Schmidt, 1870)

Species Overview

Halichondria (Eumastia) sitiens (Schmidt, 1870) is a cushion-shaped sponge with numerous, characteristic upstanding papillae, which may be branched, and may bear an oscule. Live colour has not been recorded, possibly pale yellow. Superficially it may be confused with species of Polymastia, but microscopic details are distinctive. It is a northern deep water species.

Taxonomic Description

Colour: Live colour not recorded; in alcohol it is white with slight yellowish red tinge.
Shape, size, surface and consistency: Cushion-shaped with numerous upstanding papillae (Halichondria sitiens Arn), wich may be branched, and may have an oscule. Size up to 15 cm across. Surface smooth, Papillae hollow, conical, stubby at the summit, or more tapering if they bear a terminal oscule. Consistency rather firm.
Spicules: (Halichondria sitiens spics) Exclusively oxeas, gradually tapering and sharply pointed, in a single but variable size category: 360-1020 x 7-20 µm.
Skeleton: Ectosomal skeleton a tangential "skin" of intercrossing bundles of oxeas; subdermal lacunae make the ectosome easily detachable. Choanosomal skeleton ill-defined spicule tracts and many loose single spicules; spicule tracts which may reach a diameter of 90 µm. In the papillae longitudinal supporting fibres may be as thick as 1500 µm.
Ecology: On Pecten or other hard objects, 15-160 m
Distribution: Norway, Northern Ireland, Iceland, Greenland, NE Canada.
Etymology: sitiens (Latin) = thirsty, referring to the numerous papillae.
Type specimen information: Two type specimens are in the Copenhagen Museum, Egdesminde,W Greenland, 56–100 m, coll. Olrik. Microscope slide: BMNH 1870.5.3.112 – labelled “Grönland 50”.

Remarks

This species was originally assigned to a separate genus Eumastia, but this was synonymized with Halichondria by Van Soest et al. (1990). The status of the genus was retained at the subgenus level in the Systema Porifera (chapter by Erpenbeck & van Soest, 2002). The species is distinctive and cannot be easily confused with others in the area.
Source: Lundbeck, 1902.

Halichondria sitiens