Opisthobranch of the Week Data
I've never personally seen Thordisa albomacula in the waters of Okinawa's main island and Atsushi considers the species to be uncommon in the Keramas. * He reports (pers. comm.) that he's seen approximately ten individuals. Atsushi mentions finding this small Discodorid on the side of dead coral. The above image of T. albomacula is used with Atsushi's kind permission. I've added a second page with an additional image of a second animal also photographed by Atsushi. Also, Scott and Jeanette Johnson have a series of photographs of T. albomacula on their Underwater Kwajalein site.
The following morphologic description of Thordisa albomacula is taken from Chan J.M. & Gosliner T.M. (2007):
The body is round in shape and ranges in length from 6 to 25 mm. The rhinophores are lamellate and have 12 lamellae each. The notum bears short filamentous papillae dispersed throughout the dorsum. The gill is completely retractile and is surrounded by an even sheath. The six gill leaves are tripinnate and do not extend beyond the edge of the notum. The anterior margin of the foot is bilabiate and notched. The oral tentacles are digitiform and do not extend beyond the margin of the foot. Labial pits are absent. The ground color of the notum can range from reddish brown, dark brown to a mottled gray. Some specimens have small white spots on the notum. The foot color of the live animal is not known, but the preserved specimens have an even color through out the body. The papillae, gill, and rhinophores are a contrasting tan to white color. There is a large white spot in the center of notum that extends from the anterior of the gill pouch toward the midsection.
In the above reference the authors note the presence of a large white spot in the center of the notum that extends from the anterior of the gill pouch toward the midsection. With the two images furnished by Atsushi the white spot is barely noticeable, if at all. Perhaps the Keramas animals have only a slight white spot or is entirely absent(?). In Gosliner, et al (2008, p. 171) there is an image of T. albomacula showing the prominent white spot.
In addition to the above featured animal, I've previously presented on these pages two additional Thordisa species from Okinawan waters, these two are:
* Keramas = the Kerama Islands Group, located 30 ~ 40 kilometers west of the Okinawa capitol, Naha.