Tilesius, 1802
Description
— Aggregate form a very large animal, with a thick and firm test that has a broad dorsal depression. The five muscle bands are interrupted dorsally and ventrally. M1-M3 converge dorsally but do not join. The gut is rather compact and is located in a ventral swelling of the test.
—ÊSolitary form a very large animal, with a thick and firm test that is somewhat triangular in section; it has two distinct posterior projections. There are numerous, weakly developed muscle bands, about 20 or more. The muscle bands are often broken and interrupted dorsally and ventrally. The rather compact gut is located at about one third of the body length from the posterior end. The stolon extends forwards before it turns posteriorly to the left of the gut.
Size
Length of aggregate form: up to 250 mm; length of solitary form: up to 240 mm.
Depth range
Distribution in the North Sea
Possible occurring in the northern North Sea; very rare.
World distribution
Cosmopolitan, eurythermic species occurring in all oceans, except the Red Sea, the Arctic, Antarctic and Subantarctic waters.