Opisthobranch of the Week Data
Siphopteron flavum is considered to be rare in Okinawan waters; Atsushi Ono reports (pers. comm.) seeing over five individuals and the species has not as yet been seen in the waters of Okinawa's main island. The above featured animal was found and photographed in an area between mixed coral rubble and sand by Atsushi in January of 1999 from Gahi Island, Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. Atsushi has kindly furnished the above image of this 3mm animal and is used here with his permission.
This attractive little gastropterid was originally described by Tokioka & Baba (1964), as Gastropteron flavum. In Terry Gosliner's revision of the family (1989) the species was placed in the genus Siphopteron. The following comments concerning the species is taken Carlson & Hoff (1974):
Since August, 1969, numerous specimens of G. flavum have been observed on Guam, as well as on other islands of the Mariana chain, Palau, and Truk. Although the general body shape and radula are basically the same there are several variations in color.
The first animals mentioned by Tokioka & Baba (1964) were described as bright yellow, minutely dotted with white. The posterior of the cephalic shield was ivory black, as was the dorso-median crest and the projection on the dorsal hump. Another specimen described by the same authors (Tokioka & Baba, 1965) was yellow, dotted with yellow and had reddish purple on the posterior margins of the funnel, on the dorso-median crest, and on the protuberance. There was an additional reddish purple spot on the posterior of the dorsal hump.
G. flavum is one of the most common opisthobranchs found on Guam, more than 600 specimens having been observed. Most of the animals were found in very shallow water, but some have been seen in depths of up to twelve meters. To the naked eye these animals appear yellow with black markings. Through the microscope they are yellow with large white spots scattered over the dorsum and parapodia. The parapodia are lined with dark brown as is the back edge of the funnel. The dorso-median crest and the protuberance are tipped in black.
REMARKS: G. flavum is normally found under or on the sides of rocks and on rubble. During the season when Caulerpa racemosa is on the reef flats, it may also be found in this algae.
There are to date the following nine described species of Siphopteron known from Okinawan waters, as well as several undescribed species.