Aldisa andersoni - another phyllidiid mimic

July 10, 2004
From: Dave Behrens

Here is another Blue Aldisa, A. andersoni to add to the list. You were so right when you stated, "I used to think of Aldisa as a genus of red dorids which mimicked sponges, but now it seems they include a group of nodulose species which mimic phyllidiids." [m6412]. This species has recently been named from Pigeon Island, Trincomal, Sri Lanka, after Dr. Charles Anderson, the collector.

The living animals are 20-30 mm in length. The body is oval and the notal surface covered with a series of low conical tubercles. The tubercles form distinct ridges running longitudinally along the center of the notum, and perpendicular laterally along the margin of the notum. Rows of these tubercles are situated in regions of opaque blue pigment. These regions are separated by areas of black. There is an opaque, bright yellow saddle across the notum behind the rhinophores. This saddle extends right to the edge of the mantle. A few bright yellow patches may partially encircle the gill pocket. Some specimens have yellow patches posterior to the rhinophores.

It is similar in coloration to Aldisa albatrossae, Aldisa williamsi and Aldisa erwinkoehleri, but differs in a number of characteristics. In Aldisa andersoni, the low conical tubercles are clearly arranged in rows or ridges. Tubercles on the notum of Aldisa albatrossae, A. williamsi and A.erwinkoehleri are randomly distributed. The black coloration on A. williamsi and A. erwinkoehleri forms concentric rings, and in A. albatrossae forms a rectangle on the dorsum with a T-shape mark anterior to the rhinophores. In A. andersoni, the black pigmentation is found uniformly over the mantle separating the rows of tubercles. The opaque yellow pigmentation on Aldisa andersoni is quite similar to that found on A. albatrossae and A. erwinkoehleri. There are however consistent differences which clearly separate them. A. williamsi has no yellow pigmentation. The yellow pigmentation covers the tubercles in A. erwinkoehleri and in A. andersoni, but not in A. albatrossae, where it occurs between the tubercles. The yellow color markings on A. andersoni are far more extensive than in the other species, with a yellow saddle extending to the very edge of the mantle that is not isolated into smaller broken patches, as in A. erwinkoehleri. The rhinophores differ in color between all four species. In A. albatrossae they are white-grey; in A. williamsi pale brown; in A. erwinkoehleri black, while in A. andersoni they are the same blue as the body. The arrangement of tubercles around the rhinophoral pockets differs among the four species.

Aldisa albatrossae has four similarly sized equally separated tubercles; A. erwinkoehleri has two large and two small tubercles while A. andersoni and A. williamsi have two equally sized tubercles, separated on either side of the pocket. Differences exist also in the tubercles around the gill sheath. A. albatrossae has a double row of tubercles; A. williamsi has a single row of eight tubercles; A. erwinkoehleri a single series tubercles while A. andersoni has a single series of twelve tubercles around the sheath.

• Gosliner, T. M. & Behrens, D. W. (2004) Two of New Species of Dorid Nudibranchs (Gastropoda, Opisthobranchia) from the Indian Ocean. Proceedings of the Californian Academy of Sciences, 55(1): 1-10.

Dave Behrens

Behrens, D.W., 2004 (Jul 10) Aldisa andersoni - another phyllidiid mimic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Dave,
Bill Rudman

Rudman, W.B., 2004 (Jul 10). Comment on Aldisa andersoni - another phyllidiid mimic by Dave Behrens. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Aldisa andersoni