Dendronotus iris question

Dear Ray,
Thanks for the photo and observations on Dendronotus iris. To answer your questions in sequence, I guess 'herd' is as good a collective noun as I have heard. it would fit many of them, especially Sea Hares, and I quite often use the term myself, though not officially.

On your question about them being stung by the anemones, nudibranchs that feed on stinging food are often stung and you can watch them often trying to avoid being stung. On the problem of nudibranchs with nematocysts in their cerata stinging each other, the answer is that the nematocysts are not released solely through physical contact. The nudibranch has to be alarmed before the cnidosacs release their stolen weapons. Presumably two nudibranchs of the same species in close contact would not be alarmed.

Now to the question about Dendronotus having nematocysts. There has been some confusion in the literature concerning the presence of branches of the gut in the 'gills' or 'cerata' of species of Dendronotus. Firstly there is no evidence to suggest that any species of Dendronotus has cnidosacs at the tip of its dorsal processes in which to store nematocysts. In fact there is no evidence that they store nematocysts from their prey anemones in any part of their body.

The second point concerns branches of the gut. In Dendronotus frondosus some authors reported that it had branches of the digestive gland in its dorsal processes and others said it didn't. What we now know is that there are branches of the gut in the dorsal processes of juveniles but not in adults. In Dendronotus iris there are branches of the gut in the rhinophore stalks and the first pair of dorsal processes but not in any of the other dorsal processes.

Why am I calling them 'dorsal processes'? Well they are clearly not cerata as found in aeolids. Perhaps 'gills' is a better name for them, but I know of no study to show they are important in respiration.

Hope that answers your questions.
Best wishes,
Bill Rudman.