Eubranchus spp - how many?

June 7, 2002
From: Bernard Picton

Hi Bill,
I've just read the recent correspondence regarding Eubranchus misakiensis in British Colombia. I'm sure Marli's animals are not Eubranchus misakiensis, partly because they differ from Jun Imamoto's from Japan in ceratal numbers but also they are clearly feeding on a Plumulariid hydroid whilst it has been established that E. misakiensis feeds on Obelia. Here in the UK we have several species of Eubranchus with similar coloration, Eubranchus exiguus, Eubranchus doriae and Eubranchus vittatus (formerly E. cingulatus). There is also E. rupium in the North Sea, (but not yet reported from the British Isles).

E. exiguus feeds on Obelia longissima or Obelia dichotoma whilst E. doriae feeds on Kirchenpaueria similis and E. cingulatus on Kirchenpaueria pinnata (Kirchenpaueria is a Plumulariid). Rob Dekker reports that E. rupium is on Laomedea longissima which I think is the same as Obelia longissima. On the other hand I've found Eubranchus farrani feeding on Obelia geniculata and O. dichotoma, but also on Aglaophenia pluma, which is a Plumulariid, so this is not conclusive evidence that all Eubranchus species are prey-specific. The two Kirchenpaueria species are so similar that some hydroid experts believe them to be a single species, yet the nudibranchs seem to know the difference all right!

The spawn of E. exiguus is a blob - lozenge-shaped is the term used normally, whilst the others have spawn coils similar to the ones in Marli's pictures, but less coiled. I see Rob Dekker provided a picture of E. rupium spawn which looks to me like an elongate blob rather than a coil.

Eubranchus exiguus has one large swelling on each ceras, E. doriae has two swellings and E. cingulatus normally has no swellings, but a hint of three swellings can appear with darker rings between (hence the name cingulatus). Marli's animals have two swellings whilst Jun Imamoto's have one swelling.

In conclusion I think it is likely that there are more species here than we have names for, and that knowledge of the food, spawn and internal characters might help resolve these species. I'm sending some pictures of NE Atlantic Eubranchus [E. exiguus; E. doriae in separate messages.

Picton, B.E., 2002 (Jun 7) Eubranchus spp - how many?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Bernard,
Thanks very much for this summary.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Jun 7). Comment on Eubranchus spp - how many? by Bernard Picton. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from