March 4, 2009
From: Brian Mayes
Concerning message #17740:
I thought this nudibranch was a Dermatobranchus species, because the mantle behind the rhinophores is incomplete and fused to the head. It's the second time I've come accross it. Firstly in the Perhentians, Malaysia and now in the Philippines. On both occasions it was found feeding on soft coral.
Locality: Secret Bay, Anilao, 17 metres, Luzon, Philippines, Luzon Sea, 14 February 2009, Sandy. Length: 25 mm. Photographer: Brian Mayes.
firstname.lastname@example.orgMayes, B.R., 2009 (Mar 4) Re: Armina sp. 7 from East Timor. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22300
Its a bit hard using external dorsal features to separate the two genera, because some like Armina juliana clearly 'break the rules' and have the mantle fused to the head. One feature which does seem to hold is that in species of Armina there are gills and secondary leaflets on the underside of the mantle which are absent in species of Dermatobranchus. Another 'rule of thumb' is that species of Dermatobranchus are usually small and live on hard substrates or on soft coral colonies while species of Armina are larger and often buried in soft sediments. Unfortunately there are many quite large species of Dermatobranchus to confuse the issue.
Food used to be quite a good character, with species of Armina feeding on pennatulaceans [sea pens] and species of Dermatobranchus feeding on alcyonaceans [soft corals]. Unfortunately Armina cygnea was reported feeding on the alcyonacean Dendronepthya very early in the history of the Forum [message #4] which broke that rule.
I originally placed this species as an Armina because of its size and soft sediment habitat, but as you, and Brian Francisco in an earlier message show [#17740], Armina sp. 7 also feeds on alcyonaceans.
I suspect it is a species of Dermatobranchus, but it might as well stay as it is until someone looks at its anatomy - or even a peek under its mantle skirt to see if it has gills.