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Lest you think that slugs only exist on land to slime up and eat your lettuce crop, pity the world’s oceans, which have to contend with 3,000 species of these shell-less, bone-less beauties. While ‘land slugs’ are unpopular with gardeners, divers hold the nudibranch in very high regard for their brilliant colours and outrageous patterns, and consider the more common name, ‘sea slug’, a bit of an insult.
All nudibranchs are carnivores, and many are remarkably adapted to absorb the defence mechanisms of their prey for use against predators. The Glaucus atlanticus, for example, can eat a jellyfish’s sting cells, which then make their way to the sea slug’s skin. Once there, they can use the jellyfish stingers to defend themselves.
Other nudibranchs can absorb the poisons of sponges without being harmed, and become more deadly than the sponge itself. In addition to jellyfish and sponges, nudibranchs also eat hydroids, anemones, barnacles, and, in some parts of the world, corals. Little is known about who likes to eat nudibranchs, but if you would like to conduct your own research, you will find them from the low tide zone to the outer margins of the continental shelf, on corals and sponges and various seafloor substrates.
The sex life of the nudibranch is also remarkable because they are hermaphrodites—able to mate with and mutually fertilize any adult of their species that happens along. After meeting head-on, they touch tentacles for a minute, then begin the half hour process of sidling up to each other (that’s the scientific term: ‘sidling’). After some lunging and biting, the rest boils down to about two seconds of mating activity that, with any luck, results in fertilized eggs.
The eggs are laid out in a suitable nursery area, and the work is done. Nudibranch take no part in rearing their young. Because of their ability to absorb the most interesting chemicals from such creatures as sponges, scientists in some parts of the world are conducting research on the nudibranch for anti-tumour, anti-viral, anti-bacterial, and anti-fungal applications, which could decrease the populations of some already-rare species, if not carefully managed. Other threats to the nudibranch include pollution (such as agricultural runoff), warming oceans, habitat loss, and coastal gardeners with a serious grudge, patrolling the beach at low tide.