While investigating tide pools near San Francisco, I found several cool creatures, this was one of them. It is a medium-sized, shell-less colorful Sea Slug – a marine gastropod mollusk. Its common name comes from this animal’s visual similarity to a lemon, featuring roughened skin, an oval shape (when seen from above), and its yellow coloration.
Its bright colors are an advertisement to its distastefulness; its fruity, penetrating odor and acidic taste repels most predators, though Sea Slugs eat other Sea Slugs, this type feeds mainly on sponges. Like a land slug, it uses its filelike tongue to scrape sponges, its favorite being the Breadcrumb Sponge.
The Sea Lemon has a ring of upright feathery gills, which are quickly retracted when a disturbance is sensed, similar to how a land slug retracts its eyes. It is hermaphroditic, possessing both male and female organs. This fascinating invertebrate is relatively short-lived, having a lifespan of about a year.