Without getting too bogged down in detail, this striking little pin stripped sea slug, Polycera capensis, belongs to the phylum Mollusca which includes snails, mussels, octopus, squid and their relatives! Sea slugs are also called nudibranchs (pronounced nudibranks) which means naked gills because in their evolution they have lost their true gills, and instead have a protruding frill of gill like structures on their backs. They have also lost their shells, perhaps because their ancestors burrowed into the sand and shells would have been inconvenient. You’d think that without a shell they’d be easy prey but most nudibranchs possess toxic chemicals and their bright colours serve as a warning to predators. Many of them acquire these toxins by feeding on animals that have stinging cells and then storing the stinging cells in their own bodies for use as defense. One type of nudibranch is so toxic that it can even kill fish kept in the same aquarium. Toxic or not, they are amongst the most beautiful creatures in the sea.