Mystery aeolid from Florida

Dear Anne,
There is a possibility it is a form of Dondice occidentalis. It has an orange median line on the head and another on each side of the head, and a median white line on the dorsum behind the rhinophores, which are all features of some specimens of D. occidentalis. However from my interpretation of your photos the rhinophores are not lamellate, as occurs in D. occidentalis, but tuberculate.

I thought the tuberculate rhinophores might give me a clue but they lead me to a number of poorly described names. I wish people would realise how important a good description of the external animal is when describing species.

Caribbean species with tuberculate rhinophores;
• Facelina agari Smallwood, 1910 : brown with white spots on cerata and body
• Berghia creutzbergi Marcus & Marcus, 1970 : brown with white spots on cerata and body
• Berghia benteva (Marcus, 1958) : translucent white with white browns spots on cerata
• Moridilla kristenseni Marcus, 1963 : light yellow with silvery white net and black stipples on cerata
• Palisa papillata Edmunds, 1964 : body silvery gray... whole of dorsal surface including cerata.. covered with a network of fine white lines.... digestive gland duct in cerata pale buffish with dark brown spots.

Only Edmunds' original description gives adequate information on the living animal. Facelina agari [F. Glaucidae] and Berghia creutzbergi [F. Aeolidiidae] have white spots like your animal. I suspect your animal is likely to be a glaucid, since it is on hydroids, so I guess that excuses B. creutzbergi. It could be Facelina agari, but there is really no way of knowing just what Smallwood's description refers to.

Distinguishing features of your species seem to be the the red-orange median line on the head, a similar line on each side of the head, the white spots, the blue line on the oral; tentacles and the papillate rhinophores. I don't think this species has been described before, but it really depends on whether the rhinophores are lamellate or tuberculate [papillate].
Best wishes,
Bill Rudman