(Alder & Hancock, 1842)
Description:
The translucent white body may reach 28 mm in length (slightly larger in Arctic specimens). The body colour is white or pale yellow while the cerata contain brown, orange or rose-red digestive lobules. Animals taken from female colonies of the prey, the athecate hydroid Hydractinia echinata , are usually darker than those from male colonies in which the male gonozoids are colourless. On either side of the body there are over twenty oblique, irregular rows of cerata, arranged in up to 16 clusters. A total of 279 cerata were counted in an 18 mm preserved specimen. Epidermal glands are usually visible as minute white specks, becoming more concentrated towards the ceratal apices (C. nana).
Habitat:
As indicated above, the diet consists of the hydroid Hydractinia , epizoitic on hermit (or spider) crab shells, usually found in the British Isles in sheltered shallow waters having full salinity.
Distribution:
C. nana has a boreo-arctic range, from Brittany to Norway, W. Greenland and the north east seaboard of America as far south as New Hampshire (Distr. C. nana).