Trapania sp., or the white-lined nudibranch.
Trapania sp., or the white-lined nudibranch.
Ancula sp., or the giraffe-spot nudibranch.
Ancula sp., or the giraffe-spot nudibranch.
Photos Guido Zsilavecz
Two rare nudibranchs were recently spotted at Oudekraal, both on the same smallish red branching sponge. While Ancula sp. has been seen at Oudekraal before, as well as on the wreck of the Katzu Maru, and numerous individuals near Rooi Els, it is a rather uncommon species.
The second species, Trapania sp. is even rarer, and was previously only known from Knysna. We have seen it before near Rooi Els, but only a single specimen.
The two species are related, and both have a few extra appendages near the head - note how on Trapania sp. two fold behind the rhinophores, a bit like the horns of a buffalo. Both also have tall extra-branchial processes - slim extensions around the gills, which exist probably to protect the vulnerable gills from predators. Both species are reported to feed on arborescent bryozoa, so it is interesting to only see them on red sponges - encrusting, branching or wall sponges.
Nudibranchs of Southern Africa - a guide to the opisthobranch molluscs of southern Africa, T Gosliner, 1987.