Opisthobranch of the Week Data
Members of the genus Chelidonura are usually recognizable as such because of the immediately apparent split and disproportionately sized tail which most possess. The mantle shield is long and tapering and the left lobe of the tail is considerably larger and longer, giving the genus the common name of "Tailed Slugs".
The above featured animals were photographed and collected by Atsushi Ono from Zamami Island in the Kerama Islands, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa Capitol, Naha. These featured animals were found by Atsushi during June of 1998 in 6m of water from a sandy bottom. I've not personally seen C. sandrana in the waters of Okinawa's main island but Atsushi reports (per. comm.) seeing in excess of three hundred individuals, but exclusively from two separate sites off Zamami Island (Furuzamami and Nishihama Beaches).
There is a fair amount of confusion between C. sandrana and C. tsurugensis (Baba & Abe, 1959). Some color pattern variations of C. sandrana are very similar to that of C. tsurugensis. There is a discussion of this on the Sea Slug Forum and it may well be that this is a complex of closely related species or possibly a single variable species (if so, C. tsurugensis would have priority). At least for the time being I'm going to continue to call the Okinawan specimens with a dark notum and having bright yellow or orange spots to be C. tsurugensis.
In addition to the above image, kindly furnished by Atsushi, he has also allowed me to use two additional images of the species, showing some of the variation seen within the species.
C. sandrana is one of seven described members of the genus known from Okinawan waters. The seven species found here are: