Spanish dancer in the water

I saw a really cool animal yesterday in the water near the lab. At first I thought it was a piece of trash, but then I looked again and it turned out to be a nudibranch. A nudi-what? They are sea slugs, like snails without shells. Nudibranchs come in all different cool colors, but this one is bright red. Usually nudibranchs crawl across the bottom, but this one floats up in the water column and undulates its sides, so it looks like a flamenco dancer twirling its skirts. It is called a Spanish dancer (species name is Hexabranchus morsomus).