You may recall an earlier blog post where we provided an overview on the mollusca phylum, but this post focuses on two molluscs in particular: snails and sea slugs (or nudibranchs), which are very similar looking to the snails and slugs we know on land. In the case of sea slugs, however, the term “nudibranch” means naked gills because the breathing organs on a nudibranch are up high and on the outside. Other than that, a sea slug looks like a snail without its shell, the same as on land.
Snails are often identified by their shells, as with the very round, smooth shell of the large Lewis’s moonsnail (Euspira lewisii), a shell which sometimes is seen with the foot wrapping up onto it, as in the left photo below. The leafy hornmouth (Ceratostoma foliatum) is another large snail with an obvious shell that has wavy, flared wings coming up off the shell – see right photo.
Sea slugs, or nudibranchs, also have different colours. The yellow-rimmed nudibranch (Cadlina luteomarginata) is frequently seen in Howe Sound, with a yellow rim around the body and yellow tips of the bumps on the body. The tuft of gills is a white plume at one end. The giant nudibranch (Dendronotus iris), pictured as the featured photo, can have different colours on its many large flaps of skin (called “cerata”). This nudibranch attacks and eats tube-dwelling anemones, and it can rapidly bend its body back and forth to swim off the bottom of the sea floor.
With the support of Sitka Foundation, the Vancouver Aquarium is embarking on a two-year project to train divers to identify marine life in Howe Sound, as part of our commitment to the research and conservation of this area. The information they glean on Howe Sound’s sea life will be presented in this series of blogs, and will be used to educate students taking part in the Aquarium’s school programs and AquaVan visits to inspire the next generation to keep learning more about marine biodiversity in British Columbia.