The hooded nudibranch, also called the lion or lion’s mane nudibranch, is a voracious hunter that swallows its prey whole while secreting a powerful stink to keep predators at bay
This unusual nudibranch has a cowl-like hood at the front end of its body, which it casts over its prey of tiny crustaceans and other planktonic invertebrates.
The ‘oral hood’ is ringed by rows of sensitive, interlocking cirri which trap the prey and draw it in towards its mouth, where it is swallowed whole.
They are found on kelp and sea grasses on the west coast of North America and are often spotted on dive sites around the Northern Channel Islands in California.
The nudibranch’s body is lined with up to six pairs of leaf-shaped structures known as cerata (two are visible in the photo above), which serve a variety of functions.
Cerata extend the surface area of the nudibranch’s body to aid with respiration, but are also used for attack and defence by some species.
The hooded nudibranch’s cerata are capable of autonomy, meaning that – rather like a gecko’s tail – they are capable of self-detaching and wriggling about, serving as a decoy while its owner escapes.
M. leonina grow to about 90mm in length and seasonally swarm in large numbers on the kelp. They are occasionally seen swimming in open water at night, moving to different strands of the seaweed to pick off their prey.
Their main predators are crabs that live among the kelp, against which the hooded nudibranch’s main defence is the secretion of a sweet, but foul smell, from what are known as repugnatorial glands.
The odour is thought to serve both as a deterrent to predators and, possibly, a mechanism through which the swarm maintains contact.
They are simultaneous hermaphrodites with each animal possessing both male and female reproductive organs. Fertilisation occurs internally and individuals can lay up to 30,000 eggs at a time, secreted as strands of mucous in which the egg capsules are deposited on the kelp.
