Dear Atsushi,
Thanks very much for the photo. It certainly is much lighter than the earlier photos of Siphopteron sp. 1. Unfortunately I don't think we are going to be able to tell whether this means that Siphopteron sp. 1 and Siphopteron sp. 2 are colour forms of each other until we can compare the internal anatomy of them both. Both seem to have a slender 'tail' off the rear of the visceral hump and another slender projection from the posterior tip of the foot so there are not any other easily visible external characters we can look for.

Best wishes,
Bill Rudmna.

Dear Atsushi,
Thanks for the extra photo. In this photo there doesn't seem to be any sign of a rhinophoral crest. Perhaps this species will turn out to be a Gastropteron. Also in this photo the white speckling doesn't seem to be as pronounced.
Best wishes,
Bill Rudman.

Dear Bob,
I guess the speckled white appearance of Atsushi's Siphopteron sp. 1 is very similar to yours, but my first guess would have been his Siphopteron sp. 2. I guess it depends on whether his Siphopteron sp. 2. is speckled, as in Siphopteron sp. 1, or a much more uniform white?

The close-up of the siphon makes me wonder whether it should be considered a species of Gastropteron as I can't see any indication of the siphonal crest considered characteristic of the genus Siphopteron.

Best wishes,
Bill Rudman.

Dear Atsushi,
I have separated your message into three. The other two species are Siphopteron sp. 2 and Gastropteron sp. 1. I don't recognise any of them. Could you give us a short description of the colour to accompamy the photos. For example this species seems to be translucent with white speckling. The tip of the siphon is deep orange and there appears to be a dark orange smudge on the front edge of the head and another on the siphon. Are there any other colour marks I can't see in the photo? And did the the three animals have the same marks? The reason I ask is that your Siphopteron sp. 2 differs only in not having any colour marks. I wondered if it were possible they were forms of the one species?

The only external character of the genus Siphopteron is that the siphon has a prominent dorsal ridge or crest. I can't see this in your photo. Can you confirm there is one?

Best wishes,
Bill Rudman.

Dear Erwin,
Terry Gosliner proposed the genus in a review of the family Gastropteridae in 1989, to distinguish a group of species which had previously been placed in the genus Gastropteron. Like Gastropteron they have up to 6 outer lateral teeth, but unlike Gastropteron they have a modified penis with a spermatic bulb. The only external character seems to be the presence of a ridge along the siphon which usually extends as a prominent tapering rod at the tip of the siphon. I can't see this feature clearly in either Siphopteron sp. 1. or Siphopteron sp. 2.

Reference: Gosliner. T.M. (1989) Revision of the Gastropteridae (Opisthobranchia: Cephalaspidea) with descriptions of a new genus and six new species. The Veliger, 32(4): 333-381.

Bill Rudman.