Opisthobranch of the Week Data
Aldisa albatrossae is considered to be uncommon in Okinawan waters. I've collected twelve specimens from the main island of Okinawa and have seen, but neither photographed nor collected, another half dozen or so animals. Ono (1999) has a photograph of a 30mm specimen (p. 110) from Gahi Island in the Kerama Islands (30 ~ 40km west of the Okinawa capitol, Naha). In addition, Masuda (1999) illustrates a photograph of a 25mm specimen (p. 105), also from the Kerama Islands. The above featured animal is from a photograph of the holotype* specimen (CASIZ** 89034) deposited at California Academy of Sciences. This animal was found crawling on the upper surface of strewn coral rubble. It was collected during a mid-day SCUBA excursion in an area of mixed silty-sand and coral rubble amid spur & groove formations of a living stony coral (Porites sp.) reef.
Aldisa albatrossae is currently the only described member of the genus reported from Okinawan waters. I've photographed several unknown red-mantled Aldisa from local waters but they have miscellaneous sponge-like mantle pits which are characteristic of many of the species and are of course quite dissimilar in appearance from A. albatrossae.
The following description of external characters is taken from Elwood, et al. (2000):
EXTERNAL MORPHOLOGY - The living animals are 11-21mm [sic : 11-22mm] in length. The dorsum of the living animal is a bluish color. This color is darker at the edges and lighter towards the middle of the dorsum. It is interrupted by the presence of numerous white tubercles. The dorsum also contains a distinctive black pattern, which is virtually identical in all specimens examined. The black pattern begins as a T-shape crossing in front of and between the rhinophores. Behind the rhinophores, the T-shape connects with a black rectangular mark that spans the dorsum to the branchial pocket. Two black lines extend from the rectangular mark around the sides of the branchial pocket. In one specimen the black marks form a continuous band around the posterior margin of the branchial sheath. These characteristic markings on the dorsum can also be seen in the preserved specimens. Yellow-orange splotches are present on the dorsum of the living animal. These marks of yellow-orange lie at the front edges of the T of the black mark and along the anterior edge of the rectangular portion of the black mark. Yellow-orange lines also extend from the sides of the branchial pocket to the posterior edges of the dorsum.
The rhinophores are dark, uniformly off-white and lamellate, containing 18 lamellae in a 21 mm long specimen. The branchial leaves are a darker gray than the rhinophores and range from 6-9 in number. They are bipinnate and relatively sparsely branched.
There are numerous rounded tubercles over the surface of the body. Four to five rows of tubercles are found outside of the broad black ring on all sides of the body. An additional four to five rows are found within the black band. The tubercles of the body are smaller towards the edges of the dorsum with a row of small tubercles around the entire margin. Around the branchial pocket, there are two rows of tubercles. The tubercles nearest the gill are equally spaced and of alternating large then small size. The other row also consists of tubercles of alternating sizes. Each rhinophore is surrounded by four tubercles. These tubercles also alternate large and small with the larger tubercles on the left and right sides of each rhinophore. All tubercles are opaque white and conical.
The anterior portion of the foot is grooved but not notched. The head has short oral protrusions with a short groove along their outer edge.
Elwood, et al. (2000) named the animal based on the Albatross Expedition of 1907-1910 to the Philippines, from which a specimen was collected and illustrated. I've added an additional page illustrating the Albatross Expedition animal, which is a painting of the original collected animal (this image is scanned from the Elwood, et al. ,2000 publication). I've also added a third page with several additional photographs of A. albatrossae, which illustrates the relatively consistent color and pattern of the species. This third page includes several different paratype* specimens.
* Holotype & Paratype: See "Type" Dictionary for explanation.
** CASIZ: California Academy of Sciences, Invertebrate Zoology