Alderia modesta

(Lovén, 1844)

The flattened body may reach 10 mm in extended length and is pale fawn in colour with blotches of green, brown and white, the whole effect being rather dark and drab. The cerata are arranged dorso-laterally and may total up to 32 per individual, arranged in up to seven rows, each containing up to six cerata per half-row. Regular pulsations of these cerata (visible with a lens) bring about blood-circulation; no heart is present. Through the skin of the cerata and of the foot, the ramifying diverticula of the digestive can be seen. The anal opening is posterodorsal.

This tough little sacoglossan is always associated withVaucheria in saltmarshes. It is resistant to salinity changes within the range 5-36 parts per thousand.

It has a wide geographical distribution, from Norway to the Atlantic coast of France, and along the Pacific coast of north America (Distr. A. modesta).