Artemisina arcigera (Schmidt, 1870) is a cushion-shaped or irregular globular sponge of northern deeper waters. The surface is optically smooth, velvety, and the consistency is firm but compressible. The oscules are irregular, partly elevated, and surrounded by a raised rim. Colour is beige. The sponge resembles the genus Suberites, and spicule examination is necessary to make a certain identification. Probably an Arctic species extending southwards to the Faroes and southern Norway.
Colour: Yellowish grey to beige, in life and in spirit.
Shape, size, surface and consistency: A more or less high cushion, often with an oblong contour, irregular. Occasionally specimens may be higher than wide and become cylindrical. Size up to 5.5 cm long, 2.5 cm wide and 1.7 cm high. Surface optically smooth, velvety, may feel slightly rough. Oscules on the upper surface, 3-7 in the average specimen, with thick raised rims, thus resembling papillae, greatest diameter 3 mm (Artemisina arcigera Ldb). Consistency firm but compressible, like Suberites spp.
Spicules: (Artemisina arciger Ldb spics) Subtylostyles, palmate isochelae and toxas. Megascleres: Ectosomal subtylostyles, rather fusiform, thickest in the middle, with narrow neck: 290-428 x 9-18 µm; choanosomal subtylostyles, longer, slimmer and less fusiform: 450-650 x 6-9 µm. Microscleres: Palmate isochelae, small, of the usual microcionid shape: 7-15 µm; toxas, strongly and deeply curved, with swollen, heavily spined ends, quite variable in length: 70-320 x 1-4 µm.
Skeleton: Ectosomal skeleton consists of closely adhering bouquets of ectosomal subtylostyles forming a palisade. They are carried by strong subectosomal bundles of choanosomal subtylostyles; between these there are extensive subdermal lacunae. The choanosomal skeleton is a largely confused, halichondroid mass of single spicules, here and there arranged in vague bundles.
Ecology: Encrusting hard substrates, pebbles, shells, etc. Depth: 72-549 m.
Distribution: Arctic: Greenland, between Norway and Spitzbergen. Boreal: Nova Scotia, Iceland, Norway, Faroes.
Etymology: arciger (Latin) = carrying a bow, referring to the possession of toxas.
Type specimen information: The type is in the Copenhagen Museum; a slide is in the BMNH: 1870:5:3:90 (Desqueyroux and Stone, 1992)
The synonymy with Vosmaer's A. suberitoides was established by Lundbeck (1905) after comparisons of the type specimens. The distinctness from Artemisina transiens Topsent, 1892 from NW Spain rests on the spined toxas (smooth in transiens) and the smoothness of the heads of the subtylostyles (microspined in transiens).
The species cannot be easily mistaken for another sponge if microscopically examined. Its habit reminds of several Suberites species (S. ficus, S. carnosa and S. domuncula), but the small raised oscules are not found in any of the European species of that genus.
Source: Lundbeck, 1905.