Forbes, 1838
Description:
The body-length may reach 45 mm, pale yellow or greyish white in colour. The inflated cerata are not arranged neatly in rows but are packed closely together, especially in the adults where the cerata become so crowded that they are somewhat flattened (E. tricolor-dorsal view). The cerata are translucent white or cream, with a golden yellow subterminal ring, surrounded by opaque white pigment. Deep within each ceras is the red-brown, smooth hepatic lobule, characteristically tinged with violet near the tip. The tentacles are pale yellow-brown with paler tips. Juveniles up to 13 mm in length may be white all over, except for the pale brown core to each ceras.
Habitat:
This species has been recorded from a number of hydroids, but most characteristically it is found by searching the most delicate species such as Obelia geniculata .
Distribution:
It has been recorded all around the British Isles (Distr. E. tricolor); elsewhere, it is reliably reported from Arctic waters, and from the Atlantic coast of France, to 80 m.