Opisthobranch of the Week Data
Thuridilla undula is a remarkably attractive elysiid and is unknown from Okinawa Island as of late-February, 2002. The close proximity of the main island of Okinawa to the Kerama Islands, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on Okinawa proper. The above featured animal is one which was photographed in the waters of Gahi Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. The featured animal was photographed by Atsushi Ono on the 21st of June, 2001, on a rock in 20m of water. Atsushi's photograph is used here with his kind permission and he considers the species to be very rare; Atsushi reports (per. comm.) seeing only two individuals in the Keramas, and only a single individual has been collected.
The following, in part, is taken from Gosliner (1995):
The living animals are turquoise bluish green. The parapodial margin is a broad undulating band of burnt orange. Below that is a narrow undulating line of black. This is followed by an undulating region of vivid blue reflective pigment. There is black and reflective blue pigment on the head. The base of the rhinophores are the same color as the rest of the body. At about the middle of the rhinophores are narrow bands of blue and black. The apex has a broad orange band. Orange, black and blue bands are also present on the anterior margins of the foot.
Gosliner chose the specific name, undula, in reference to the undulating bands along and below the parapodial margins.
There are no other elysiids currently known from Okinawan waters which are apt to be confused with T. undula. However T. lineolata and T. neona (both currently unknown from Okinawan waters) are similarly colored. There are several photographs of the similar appearing T. lineolata posted by Jim Anderson (2001) from NE Sulawesi, Indonesia, on the Sea Slug Forum.
Thuridilla undula is one of eleven described species of Thuridilla found in Okinawan waters. The eleven species are:
T. albopustulosa T. bayeri T. carlsoni T. flavomaculata T. gracilis To be featured at an later date T. hoffae T. kathae T. livida T. splendens T. undula (the above featured animal) T. vatae