Armina wattla? from the Caribbean

Dear Dave,
This is an arminid nudibranch, almost certainly of the genus Armina. Species of Armina are usually sand-dwellers and feed on sand-dwelling cnidarians such Sea Pens, and in some cases Soft Corals.

As to identifying your species, that could be a bigger problem as little detailed work has been done on the group in the Caribbean. Eveline Marcus (1977) in her checklist of warm water western Atlantic opisthobranchs, lists 3 species of Armina, including the Mediterranean species, Armina tigrina Rafinesque, 1814. The two species which were described from the western Atlantic are Armina mulleri (von Ihering, 1886) and Armina wattla Marcus, 1967.

The colour of the living animal of Armina mulleri was redescribed by Marcus & Marcus (1967) as "has a black notum, with light ridges, a yellowish hyponotum and bright pink sole" Unfortunately there are many species with very similar colour patterns. However, although Armina wattla has only been reported once, [from Georgia, USA] features of its colour pattern do match your photo rather well. Unfortunately the Marcus' description s based on preserved animals but they do describe the preserved animals as 'whitish with black pigment in the furrows between the notal ridges ... in the middle of the [oral] veil .....". In the drawings accompanying the description there is a black band running down the middle of the oral veil just as in your photo. However there is no mention that the black continues along the edge of the oral veil as well.

Basically, I can't give a definite identification, as we know too little about the arminids from the Caribbean. However there is a possibility your animal could be Armina wattla.

• Marcus, Ev. & Marcus, Er. (1967) Some opisthobranchs from Sapelo Island, Georgia, U.S.A. Malacologia, 6(1-2): 199-222.
• Marcus, Er. & Marcus, Ev. (1967) American opisthobranch mollusks. Part 1, Tropical American opisthobranchs. Studies Tropical Oceanography, Miami, 6(1-2): 1-137. (Figs 1-150, Pl.1, figs 1-9)
• Marcus, Ev. (1977) An annotated checklist of the western Atlantic warm water opisthobranchs. J. Moll. Stud. (Suppl. 4): 1-23.

Best wishes,
Bill Rudman