Armina from the Gulf of Mexico

Dear Gary,
This is a species of Armina, many species of which feed on sea pens [Pennatulacea]. I suspect your animal is a species I have identified on the Forum as Armina abbotti but I must warn you there is not total agreement on its identity [See Néstor Ardila's message #12433 suggesting it is a synonym of Armina muelleri]. I am afraid this is one of those occasions when the original descriptions of species are so poor that it is probably impossible to be sure just what a name means. Armina muelleri was described from southern Brazil by Ihering (1886) but as I say on the Fact Sheet, the description was not adequate and the type specimen is lost. Marcus & Marcus (1970) examined specimens from Sao Paulo which they tentatively identified as A. muelleri mainly on the grounds that their animals were also from Brazil. So essentially we don't really know what A. muelleri is.

In the meantime an Armina was being found in the southeastern USA and identified as the Mediterranean A. tigrina. Thompson et al (1990) argued it wasn't that species and named it A. abbotti. A third species, Armina wattla, with a distinctive black mark on the head, has also been reported from the region. However Ardila & Valdes (2004) considered   A. abbotti and A. wattla to both be synonyms of A. muelleri despite the uncertainty surrounding that name.  Even more puzzling is that in the recent Caribbean book (Valdes, Hamann, Behrens & DuPont 2006) Armina muelleri and A. wattla are accepted as distinct species and A. abbotti is considered a synonym of A. wattla. In this book, your animal is identified as A. muelleri. [I've only included one reference below, the rest will be found on the relevant pages on the Forum.]

I can't really advise you on what name to use. Firstly, there seem to be many species of Armina with very similar external colour patterns and no one has ever had enough material of any one species to determine how variable they can be in colour. Secondly, I don't see how we are going to resolve the identity of A. muelleri. Personally I would stick with the name Armina abbotti because it can be identified with this relatively common animal from southeastern USA because it may be many years before the taxonomists know enough about this family to sort out these names.  

• Ardila, N. E. and Valdés, A. (2004) The genus Armina (Gastropoda: Nudibranchia: Arminidae) in the southern Caribbean, with the description of a new species. The Nautilus 118: 131-138.

Best wishes,
Bill Rudman