Were you aware, dear reader, that the Malibu coast is currently playing host to large numbers of the world’s largest gastropod? While that sounds alarming like the plot of a 1950s B movie, this celebrity among slugs is a peaceful vegetarian, despite a passing resemblance to that movie monster favorite, The Blob.
Although it bears a distinct resemblance to Hollywood's favorite invertebrate horror, A. vaccaria is mostly harmless. Image: Wikipedia
While the California brown sea hare, Aplysia Californica, is a regular tidepool resident in Malibu, this year, its much larger relative, Aplysia vaccaria—the black sea hare—is turning up in large numbers. No one at the Malibu Post can remember seeing more than one or two black sea hares. It's unclear if the vast number showing up this year is related to the unusually warm water or if other factors are in play.
Brown sea hares can grow to be impressively large for a slug, often measuring more than 15 inches from nose to tail. A. vaccaria, however, can grow to be more than three feet long and weigh as much as 30 pounds. That’s one big slug. The largest specimens rarely turn up in the intertidal zone, but this year’s Malibu crop of A. vaccaria is still impressive, resembling a football in size and shape.
There's actually a third giant gastropod on the loose in Malibu: the giant limpet, which is really another type of sea snail and not a true limpet at all. This species, Megathura crenulata, is the only known member of its genus, making it a monotypic genus.
M. crenulata can grow to be nearly a foot in length. It may not be much to look at, but compounds in the blood of this primitive snail apparently hold promise as a cancer treatment. According to a 2011 article in the Journal of Immunology Research, "Keyhole limpet haemocyanin (KLH) appears to be a promising protein carrier for tumor antigens in numerous cancer vaccine candidates."
After a sort of gastropod goldrush in the early 2000s that ran the risk of pushing this rare animal to the edge of extinction, M. crenulata is now being raised via aquaculture techniques.
Here's a side view of M. crenulata, suggesting a very old person shuffling along under a large umbrella, and revealing the creature's true snail nature. Sea hares also have a shell, but it is internal and vestigial.
Sea hares are also important for medical research. According to the Aquarium of the Pacific's sea hare page, the California brown sea hare may not have a lot of brain wattage, but it has "the largest neurons in the animal kingdom, making it possible to identify individual nerve cells that are responsible for specific behaviors. They have been and are being used extensively in studying memory, behavior, and learning."
Humans may not find sea hares or giant limpets lovely to behold, but there's more to Malibu's giant gastropods than meets the eye.