The other day when we got back to the dock, my friend and fellow naturalist Sarah found this nudibranch on one of the dock pilings. Nudibranchs, or sea slugs, are mollusks, so are somewhat surprisingly in the same phylum as chitons, clams, octopi, and squids. There are several different colorful species of nudibranch that can be seen locally. This one is a golden dirona (Dirona aurantia). Members of the Dirona genus are identified by the large, soft "spines" that grow off the back called cerata, and it is through these appendages that oxygen/carbon dioxide exchange occurs.