Two things are occurring right now that justify a posting about my favorite of all sea slugs, the hooded nudibranch (Melibe leonina). The first is that they have been all over Seattle waters in recent months. The second is that they are the inspiration for my Halloween costume, which interns will have to put up with tomorrow in the lab.
Rhoda Green, my diving partner in crime, recently posted this great medley of Melbe leonina video footage:
In Rhoda’s video, you can see their interesting movements when they’re swimming. It is common to see Melibe in doing these side to side movements in the water column, but eventually they settle in seagrass or kelp and get to their real purpose in life: feeding and mating. Melibe doesn’t have a radula like most other sea slugs. Instead, their large oral hood, which is lined with tentacles, closes around food particles like you see in the video. Like many gastropods, Melibe is hermaphroditic. Mating Melibes will reciprocally fertilize one another and then each lay coils of cream-colored eggs on the surface of eelgrass or kelp.
One of my favorite things about Melibe is that when you pull them out of the water and smell them, they have the undeniable scent of watermelon. It’s not even an “essence” of watermelon or a “hint” of watermelon. It’s like chewing Bubbalicious watermelon gum. Oddly, this smell at least in part results from the production of 2,6-dimethyl-5-heptenal and 2,6-dimethyl-5-heptonic acid, two chemicals the organism produces for defense purposes. I’m not sure why smelling like Bubbalicious would deter predators from gobbling you up, but apparently predators of the marine environment have different tastes than I do.