During a visit to the KwaZulu Natal coast, I found some amazing creatures in the tidal pools. One of them was this sea slug which is about 10" (20cm) in body length. It was laying eggs at the time and they are marked in the last picture.
Dwarf Sea Hare (Aplysia parvula) family Aplysiidae
Although called a Dwarf or pygmy, various sites list it as growing to about 5cm which is incorrect. This specimen found in a tidal pool on the beach in South Africa, is about 18cm (7” inches) in length.
This species is found in warm waters worldwide and will sometimes wander out of the water to feed on plankton and algae.
It opens it wing-like flaps in order to attract females.
They are impressive animals growing to 40 cm and weighing up to 2 kg. Most found in Britain have been smaller, but the specimen from Poole was a large one of 30 to 35 cm and 1.5 kg.
While called sea slugs they are very different from garden slugs, being some of the most spectacular and beautiful of molluscs.
The sea hares have a small thin internal shell, largely covered by the large wing-like body flaps which also protect their gills. These give it a bat-like appearance when swimming. They vary from bright red to brown in colour, have a clear head, tiny eyes and have two pairs of tentacles, the larger of which look like rabbits ears. It is these tentacles along with its large size and rounded body shape that give it a rabbit-like look and consequently its common name. When stressed they release a purple ink into the water which is contains the toxin opaline. The animals are said to be mildly toxic but are eaten in some areas of the world.
Most sea slugs feed on other animals including sea anemones, but the sea hares are vegetarians preferring seaweed.
They come inshore to breed, usually in the Spring. Each sea hare is both male and female being a simultaneous hermaphrodite. They are known to form long mating chains, with each animal being a male to the one in front of it and female to the one behind. The penis is on the side of the head just below the right anterior tentacle. They then lay a pink to orange chain of eggs forming large spaghetti-like masses at the bottom of the shore or in shallow water. The young hatch from these, spend some time as a veliger larva in the plankton and them settle on algae as a tiny 1-2 mm sea hare. They grow rapidly reaching full size in a year, before breeding and dying.
They are a rare southern species but a combination of climatic conditions appear to have brought quite a few to our southern shores this year. This is probably a one-off occurrence, and there is no reason at present to link it to climate change, though it could be related to changes in oceanic currents.