Aplysia cf. parvula from Mayotte

Dear Marina,
Thanks for these photos. It is interesting that both Scott Johnson [see his earlier message] and I consider this to be a colour form of Aplysia parvula. I realise it's not very scientific, but when you have seen a these animals in the field they certainly mirror the ways of A. parvula. You say that 'typical' A. parvula is always found in red algae. But that is the crux of the problem - What is typical A. parvula?. In fact the question of its food may in fact be the answer. Perhaps these black animals are feeding on an alga which darkens their skin? Both your photos shows traces of a black or bluish-black band around the parapodial edge as found in 'typical' A. parvula. Often in Aplysia cf. parvula the parapodial edge seems white or very pale - and that is emphasised by the very black or dark brown of the rest of the animal - but if you look carefully there are often traces of black pigmentation at the edge. I am pretty sure this is a form of A. parvula but am leaving it on a separate page at present so we can be aware of the differences.

The algal garden reminds me of the similar garden on the shell of the animal in the Haminoea cymbalum Fact Sheet. These opportunistic green algae, such as Enteromorpha, settle and grow very quickly on clean surfaces. They don't last long but by growing quickly they can complete a reproductive cycle before being crowded out by some other organism, either plant or animal. It is unlikely that anything else will replace these green algae on the Aplysia shell because the animal is relatively short-lived.
Best wishes
Bill Rudman