Siphopteron tigrinum or Siphopteron citrinum?

November 16, 2006
From: C.Carlson & P.J. Hoff

Concerning message #18348:

We think Yuji's animals are probably S. citrinum. It would be nice to find some S. tigrinum in the Marianas but so far we have had no luck. I have attached a sample of S. citrinum from the back yard. The body can be solid yellow, or all pink --generally found as a mixture of the two; the pink being the underlying color.

An example of S. tigrinum from Palau is also included for comparison. Afraid neither of the slides is of recent vintage.

Upper photo: Siphopteron citrinum (Carlson & Hoff, 1974), 3.2 mm; Guam, Bile Bay, 26 March 1970. Photographer: Carlson & Hoff
Lower photo: Siphopteron tigrinum Gosliner, 1989; 4.0 mm; Palau, Ngkesill, reef flat; 6 August 1978. Photographer: Carlson & Hoff

Clay & Patty Jo

Carlson, C. & Hoff, P.J., 2006 (Nov 16) Siphopteron tigrinum or Siphopteron citrinum?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Clay,

Thanks for your comments. I had begun to wonder whether these two species were colour forms of the one species, but on reading your original description I didn't realise the pink you mentioned was this background colour. My feeling is that S. tigrinum must be a colour form of S. citrinum. There is certainly nothing in what we know of the anatomy of the two 'species' to think they were different. I would appreciate your views on the other animals on the Forum which I have identified as S. tigrinum. Would you consider the spotted ones to be S. citrinum? If so I can't see why the yellow-lined ones aren't also that species. The only real colour difference is that in S. tigrinum there is a thin dark bluish line separating the yellow and the pale pink? or bluish? regions.

I am happy to identify them as S. citrinum but I suspect if I do that I may as well remove the S. tigrinum page. What do you think?

  • Carlson, C. H. and Hoff, P. J. (1974) The Gastropteridae of Guam. with descriptions of four new species (Opisthobranchia: Cephalaspidea). Publications of the Seto Marine Biological Laboratory 21: 345-363.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Nov 16). Comment on Siphopteron tigrinum or Siphopteron citrinum? by C.Carlson & P.J. Hoff. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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