(Vosmaer, 1885)
Species Overview
Hemigellius arcoferus (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 arcoferus spics) 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: Arcoferus (Latin) = carrying a bow, referring to the possession of toxas.
Type specimen information: The lectotype is ZMA POR. 6075, W. Barents Exp., Stat. 20°77'71" N 49°37'5" E, 170 fms (=306 m).
Remarks
Hemigellius arcoferus is characterized by its robust toxa 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 . arcoferus 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 (Table). The similarity in habit, skeletal architecture and form of the spicula of three species is, however, evident.
Burton (1932) considered Gellius esperi Arnesen also a synonym of H . arcoferus . Arnesen's description of the species strongly resembles that of H . arcoferus . 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.