Cuthona cf. caerulea
Known only from Florida
Lake Worth Lagoon, 15 feet, Florida, USA, Atlantic Ocean, 13 May 2006, Intertidal, sandy, rubble. Photographer: Linda Ianniello.
This species has similarities to Cuthona caerulea but there seem to be some consistent differences including the blue band on the cerata, which is quite narrow in this animal but includes most of the lower two-thirds of the cerata in European C. caerulea. Also there is a large blue patch on the head in this animal.
Thompson & Brown (1984) mention records of C. caerulea from Brazil (Marcus, 1955) and a letter from Clark reporting it from Florida. I have looked at Marcus's report and his animal had a yellow cap to the cerata and a blue line down the outer edge of the cerata which is quite different from your animal. Unfortunately there is no way of checking on Kerry Clark's animals. Miller (1961) reports that C. caerulea has a strong preference for the hydroid Sertularella. The hydroid Cuthona cf. caerulea is on is definitely not Serturella and instead looks very like a species of Aglaophenia.
In fact this species looks quite like Cuthona yamasui from the Indo-West Pacific, which feeds on Aglaophenia [see Makoto Uesugi's message #10294].
Marcus, E. (1955) Opisthobranchia from Brazil . Boletim da Faculdade de Filosofia, Ciencias e Letras. Universidade de Sao Paulo, Zoologia 20: 89-261.
Miller, M. C. (1961) Distribution and food of the nudibranchiate Mollusca of the south of the Isle of Man. Journal of Animal Ecology, 30(1): 95-116.
Thompson, T.E. & Brown, G.H. (1984) Biology of Opisthobranch Molluscs, Vol 2. 1-229. 41 Pls., Ray Society: London
Rudman, W.B., 2006 (May 17) Cuthona cf. caerulea [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/cuthcfcaer