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(Vosmaer, 1885)

Species Overview

Hemigellius arcofer (Vosmaer, 1885) is a thickly fan-shaped sponge, with a coarse fibrous structure. It occurs only in deep water in the Northern Atlantic N of 60°N

Taxonomic Description

Colour: Greyish-yellow (in alcohol).
Shape, size, surface and consistency: Fan-shaped, firmly attached to stones; size up to 15 x 8.5 x 3 cm.Towards the top the thickness gradually tapers to 1 cm. Strongly fibrous; at the surface of the fan, the spicule fibers are more or less tangentially orientated, but with numerous fibres projecting through the surface; numerous circular and oval canal openings of 1-4 mm are situated at both sides of the fan, giving the surface a very open and loose appearance; part of these openings is covered by a thin, transparent dermal membrane. Consistency: soft, fragile.
Spicules: (hemigellius_arcofer_spics.jpg) Megascleres: Oxeas, robust, slightly curved, with long, sharp points: 450-650 x 15-22 µm. Microscleres: Sigmas, slightly and unevenly curved, but with strongly curved points, abundant: 12-28 x 1.0-1.9 µm; toxas, rather thick, robust, evenly bent, with recurved apices, numerous: 95-180 x 3.0-6.8 µm.
Skeleton: Ectosome: part of the choanosomal spicule fibres becomes tangentially oriented at the surface. They form an irregular reticulation around the canal openings. Choanosome: the choanosomal skeleton is a rather close-meshed reticulation of strong multispicular primary lines, 125-400 µm thick. These are irregularly connected by unispicular secondary lines. Spongin very scarce, confined to the nodes of the spicules.
Ecology: Deeper than 70 m, on stones.
Distribution: Trondheim (Norway), Spitsbergen, between Iceland and Faroe; Barents Sea, Kara Sea, Greenland, Gulf of St. Lawrence, Baffinland.
Etymology: arcofer (Latin) = carrying a bow, referring to the possession of toxas.
Type specimen information: The lectotype is ZMA POR. 6075, W. Barents Exp. 20°77'71" N 49°37'5" E, 170 fms (=306 m).

Remarks

Hemigellius arcofer is characterized by its robust toxas of variable size. In habit it is quite similar to Hemigellius pumiceus, but this species has much thinner toxas, which lack the recurved apices. Apart from this H. pumiceus has no sigmata, and much larger oxeas.
The conspecificity of Gelliodes plexa and Gelliodes consimilis with H. arcofer has already been suggested by Burton (1948), and is confirmed by De Weerdt and Van Soest (1987). The spicules, both megascleres and microscleres, of the type specimen of G. consimilis are somewhat larger than those of G. plexa. The similarity in habit, skeletal architecture and form of the spicula of three species is, however, evident.
Burton (1932) considered Gellius esperi Arnesen (1903) also a synonym of H. arcofer. Arnesen's description of the species strongly resembles that of H. arcofer. The species was described as fan-shaped, 20 x 15 cm, with a choanosomal skeleton consisting of coarse, multispicular primary lines. Megascleres evenly bent oxeas, 450-560 x 16 µm and smaller oxeas of 300 µm. Microscleres sigmas of 8 µm and toxas of 160 µm. Arnesen described the species from a specimen in the collection of the Trondheim Museum but of which no further data were available.
Source: De Weerdt and Van Soest, 1987.

Hemigellius arcofer