The foot is broader than the body, and the sides and upper surface, apart for the front third, are covered with cerata (finger-like outgrowths).

The cerata are involved in respiration and pulsate regularly; this helps move the blood around the body, there being no heart in this genus.

The general colour of this sea slug is pale fawn, blotched with brown, green and white.

It also occurs on the Pacific coast of North America from British Columbia to California and in northeastern Asia where it is present in Peter the Great Gulf and the Yellow Sea.

They then each extend their penis, which is armed with a sharp stylet, and push this through the body wall of the partner and transfer sperm by hypodermic injection.