Opisthobranch of the Week Data
Siphopteron fuscum is considered to be very rare on Okinawa's main island as I have collected only a single specimen (illustrated unfortunately with a very poor photograph). However, Atsushi Ono reports the above featured animal is one of over thirty he has seen (pers. comm.). The animal was found and photographed on sand by Atsushi in June of 1999 from the Furuzamami Beach Dive Area, Zamami Island, Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. Atsushi has kindly furnished the above image as well as several addition images of different individuals and these are all used here with his permission.
The species was originally described by Baba & Tokioka (1965), as Gastropteron fuscum. The species was described from a single 4mm animal collected in August of 1964 from the shore of Ayukawa (on the Japan Sea side of Honshu), Japan. It was found in 2 meters of water. The following partial description of the species is taken from the Baba & Tokioka (1965) publication:
The coloration of the type in life is extremely complicated and graceful. The dorsal hump is deep chocolate brown spotted sparsely with white. The lower surface of each parapodium is also deep chocolate brown with a few, bold, irregular markings of white towards the free margin. The horn-like protuberance of the dorsal hump is tinted with vermilion distally. There is a narrow vermilion band along the entire length of the parapodial margin and on the border line between each paradium and foot. The tail is also edged with vermilion. On the cephalic shield, the presence of a transverse vermilion band running parallel to the anterior edge is the first to be noted. Then follow a pair of longitudinal bands of the same colour which extend from the level of the transverse colour band to near the tip of the funnel converging distally and holding a narrow streak of snow white in between. The lateral edges of the shield are stained with deep chocolate brown. The free margin of the funnel is vermilion. The dorso-median crest is vermilion-tinted at the distal and chocolate brown at the proximal. The rest of the body including the sole is translucent and whitish in ground colour. On the underside of the tail there is a snow white streak in the median line which indicates exactly the position of the pedal gland.
The single Okinawa-collected animal as well as Atsushi's Kerama animals don't have the deep vermilion pigmentation described by Baba & Tokioka (1965) as being on the tip of the siphon, the edges of foot and parapodia. Clay Carlson (per. com.) kindly viewed Atsushi's images and commented that although there is some differences relative to the red coloration from the original description they all appear to be S. fuscum. Yasuhiro Shirai has an image posted on the Sea Slug Forum (from Mie, Japan on the Kii Peninsula) which very nicely illustrates the color of this attractive little gastropterid.
There are to date the following nine described species of Siphopteron known from Okinawan waters, as well as several undescribed species.