Cuthona cf. caerulea from Florida, USA

Dear Linda,
This is an interesting find. It certainly 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 your Florida animal but including most of the lower two-thirds of the cerata in European animals. Also there is a large blue patch on the head in your animal.

Thompson & Brown (1984) mention records from Brazil (Marcus, 1955) and a letter from Clark saying he had found it in 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 your animal is on is definitely not Serturella and instead looks very like a species of Aglaophenia. 

In fact your animal looks quite like Cuthona yamasui  from the Indo-West Pacific, which feeds on Aglaophenia. Have a look Makoto Uesugi's message [#10294]. It would have been nice to show that that C. caerulea occurs on both sides of the Atlantic, but it is just as exciting to discover what appears to be a new species with a close relationship to an Indo-West Pacific species.

• 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

Best wishes,
Bill Rudman