M. Sars, 1846
Description
Planktonic larva. The young larval body is disc-like to hemispherical, later becoming cylindrical with a rounded to sharply pointed aboral end. The aboral pore appears in a late stage of development.
The marginal tentacles are conical in the early stage, later becoming very long and thread-like; the labial tentacles are of median length.
The body is colourless, translucent; the tips of the tentacles, the actiniopharynx and the filaments are brownish; the labial tentacles are darker brown.
In the North Sea, A. albida occurs in the surface plankton from April-May till autumn, when the maximum larval size is attained. A. albida is absent from the North Sea in wintertime.
Size
Body length up to 15 mm; body diameter 7 mm; marginal tentacles up to 40 mm.
Depth range
Surface layer, but also recorded from 1000 m in Atlantic Ocean.
Remarks
The adult of A. albida is unknown. A. albida may be conspecific with Arachnanthus sarsi Carlgren, 1912, of which adults are reported from the NW coasts Ireland and Scotland.
Distribution in the North Sea
Northern North Sea, rare in the southern North Sea (record SE off England).
World distribution
Subarctic and NE Atlantic Ocean, rare in the Mediterranean Sea.