Armina abbotti = A. muelleri?

Thanks Néstor,
I look forward to seeing this review when it is published. It would certainly make sense to have one common species from South Carolina to Brazil. However I guess it's best to leave the species A. abbotti until your revision is published. Black or dark reddish bodies and white or yellow edged mantle ridges seem to be almost a generic character in this family, so colour alone needs to be treated cautiously. For example your recently described Armina juliana is almost identical in colour. I know that that species has fewer mantle ridges and a different radular morphology, but I wonder whether these characters also need to be re-evaluated. The problem is that we have no idea whether there are morphological changes within a species as it grows from juvenile to adult. For example, perhaps juveniles begin with a few sparsely arranged longitudinal ridges on the mantle, and as they grow more ridges develop to fill the spaces?

And we know nothing of ontogenetic changes in radular morphology. A good example is found in Tritonia hombergi where the juvenile tooth is so different from that of adults that it was considered a separate species. We see in species of arminids, that some have a central tooth reminsiscent of that of juvenile T. hombergi and others have a tooth similar to that of adult T. hombergi. Perhaps something similar to the ontogenetic changes that occur in some tritoniids also occur in some arminids?

On a more specific level, Ihering described the lateral tooth of A. muelleri as smooth, while Marcus & Marcus (1970) say that there can be a single outer denticle on the innermost lateral tooth, and up to four on the other lateral teeth. In your SEM photo I can see the single denticle, described by Marcus & Marcus, on the innermost lateral tooth. If you compare this with the radula illustrated by Eyster (1981) from South Carolina [as A. tigrina] then the denticulation on the first lateral teeth is quite different. The outer denticles are not a few fine spine-like projections but heavy triangular 'teeth' covering the whole outer edge of the tooth. She describes up to 7 of these denticles. I would think this is a significantly different structure to the teeth in your animals.

However before decisions can be made, I would think we need to have a better understanding on just how variable the tooth morphology, and other characters are in these animals. Unfortunately most studies have been based on a very few specimens from widely separated localities. What needs to be done is comprehensive studies of single populations so the researcher can see colour variability first hand, can see external anatomical features like the shape of the rhinophores and oral veil caruncles before they are preserved and mishapen, and can watch for ontogenetic changes as the animals mature.

• Eyster, L.S. (1981) Observations on the growth, reproduction and feeding of the nudibranch Armina tigrina. J. Moll. Stud., 47: 171-181.
• Marcus, Ev. & Marcus, Er. (1960) Opisthobranchs from American Atlantic warm waters. Bulletin of Marine Science of the Gulf and Caribbean, 10(2): 129-203.

Best wishes
Bill Rudman