Phestilla melanobrachia in East Pacific

Dear Ali,
Firstly, its a common error to call this species melanobranchia [= black gills] when the correct spelling is melanobrachia [= black arms]. Larry Harris did a lot of work on Phestilla melanobrachia many years ago [see Fact Sheet for references] and as I discuss in an earlier message he found that it preferred, or at least was found most commonly, in broken off bits of Tubastraea lying on the substrate beneath large intact colonies. In general though, these large coral-eating species seem to be quite a catch for fish and you seldom find large animals in the field, and if you do they usually hide in crevices or under the base of the coral colony during the day. Although I sympathise with your feelings towards some aquariists, keeping some species in aquarium conditions is very useful. As I discovered many years ago, and aquariists have found out recently, a good way to find nudibranchs with specialist feeding habits is to keep the food in an aquarium for some time. If there is a nudibranch feeding on that particular colony - coral or soft coral - are two obvious choices, then they are able to grow without the danger of being picked off by fish. I was able to produce multiple generations of Phestilla lugubris, Phestilla minor and Cuthona poritophages by keeping small Porites colonies alive, in somewhat primitive aquarium conditions.

I suspect if you could find broken off pieces of Tubastraea it might be worth trying to keep them alive in an enclosed aquarium system. In this way if there are invisible juvenile nudibranchs present, thye ould have a chnace to grow to visible size.

Concerning Phestilla lugubris in Panama. I described some specimens of Phestilla from Panama as a new species Phestilla panamaensis. My argument was that its radular morphology was, in my opinion, rather different from the radula of Phestilla lugubris which was a constant shape from east Africa to eastern Australia. Terry Gosliner is of the opinion that it is just Phestilla lugubris. I suspect we will need to learn a lot more about their repective biologies, and perhaps their DNA before we can be sure one way or the other.
Best wishes,
Bill Rudman