Every so often, we find a Hooded Nudibranch, Melibe leonina, on the White Rock beach. Usually, they're dead, ripped out of their eelgrass beds by strong winds and waves. A live one turned up last week, swimming and hunting for food in a pool on the sandy flats.
A nudibranch is a mollusk, a gastropod like snails and slugs. Like snails, the other sea slugs have a toothed radula, which they use to scrape and gnaw at their food. Melibe doesn't. She instead has this great hood, with tentacles taking the place of teeth; the tentacles serve to lock in the prey when the hood closes. (Think Venus fly-trap.)
Young Melibes still search for prey along the floor, like a snail does; they
"hold the hood out horizontally, just above the bottom, and gradually move along feeling, with the tentacles around the edge of the hood, for small prey." (Sea slug forum)Adults fish for their food, waving the open hood around in the water, closing it to trap the goodies. This one was one of the larger ones, and while we watched, cast her* "net" and drew it in, over and over.
Prey include amphipods, copepods, mysids (shrimp-like animals), other small crustaceans, small mollusks, small jellyfish and ctenophores, larvae of other invertebrates and in some cases small fish. (Wikpedia)