Gigantic Discovery: Man Finds Enormous Black Slug, the Size of a Small Dog, in California Beach Tide Pools (Video).

Measuring up to 99-centimeters-long, and weighing up to 14 kilograms, Aplysia vaccaria, also known as the black sea hare or California black sea hare, is the world’s largest sea slug.

I knew slugs could get pretty large, but i never imagined one as big and heavy as a medium-sized dog. Then again, Aplysia vaccaria, is a very rare sight, even if you live near its very limited habitat – off the coast of California and in the Gulf of California – as it only ventures into shallow water to lay eggs. Like most other sea slugs, these giant mollusks are herbivores, with brown algae and kelp making up most of their diet. The color of the plants the slug east determines its own color, which is why it is black or dark brown, while other member of the Aplysia family are reddish or green.

Apart from its impressive size, the California black hare – so called because of the two ear-like protrusions that grow out of its head – is also known for its defense mechanisms. While its other relatives are known to release an ink that confuses predators and makes them lose their appetite, Aplysia vaccaria is incapable of producing this substance. However, research has shown that this inability is an evolutionary consequence of a more advanced form of defense.

Aplysia vaccaria is capable of producing toxins from compounds they receive from their food, and their diet determines the kind of toxins they produce. Brown algae produces the toxin acetoxycrenulide, which the slug extracts and allows to accumulate in its tissue. Because acetoxycrenulide is highly toxic to fish, it can effectively discourage predation.

Luckily the high levels of acetoxycrenulide are not a danger to humans, a fact demonstrated by YouTuber and TV host Coyote Peterson a few years back, when he picked up a mid-size specimen and held it in his hand for a few minutes, during an episode of Brave Wilderness.

But just because humans can safely touch the Aplysia vaccaria sea slug, doesn’t mean most actually want to do it. The sight of Coyote Peterson holding the black, slimy mollusk put off a lot of people, many of whom commented that they wouldn’t go near it for all the money in the world. And his find wasn’t even a large specimen; it weighed around four kilograms.

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