While we were watching the sea gardens, we found a red gilled nudibranch (Phidiana crassicornis) floating upside down on the surface of the water. A nudibranch is a type of sea slug, somewhat like a snail without a shell. It breathes through long, feathery projections (cerata) on its back. Nudibranchs use these projections both for breathing and for defense against predators. When we took a close look, we could see the cerata clearly.
Nudibranchs are commonly found on floats, in eelgrass beds, and in intertidal areas, as well as at the bottom of shallow areas. Floating on the water's surface, this nudibranch could be coated by floating oil. However, in its normal habitat, a nudibranch would only be affected as the oil dispersed farther down into the water. The nudibranch's cerata, which it uses for breathing, could be fouled or impaired by contact with oil or other chemicals.