Green Aeolis Nudibranch, Acadia National Park, Maine

The Green Aeolis (Diaphoreolis viridis, formerly known as Tenellia viridis) is a tiny, trans-Arctic sea slug. It is famous for the bright green food in its back organs. This green color comes from its diet of specific, small, stinging animals called hydroids, particularly the Sertularella specieshydroids. It has a translucent body with white-tipped finger-like projections called cerata. It is very small, growing to a maximum length of about 15 mm (or 0.6 inches). It steals the stinging cells (nematocysts) from its food and moves them to the tips of its back. These cells are stored in white sacs to protect the slug from predators.