Favorinus tsuruganus

Photo courtesy of the Webmaster
Photograph taken at Tulamben, Bali, Indonesia, Oct. 2000

Favorinus tsuruganus Baba & Abe, 1964

Originally described from Tsuruga Bay, Japan, (the basis for its name) this small species is one of the specialized feeders of the sea slug community, feeding on the egg masses of other opisthobranchs. Favorinus tsuruganus is a member of the aeolid family Glaucidae. It has been recorded from Japan, eastern Australia and New Caledonia.

Favorinus tsuruganus' bright orange-red cerata with black tips and the huge black perfoliate rhinophores make it easy to identify. The area between the cerata and the cephalic tentacles is opaque white.

Opisthobranchs of Izu Peninsula by Suzuki, presents this species on page 158. As Suzuki indicates this species reaches about 20 mm in length and is found to a depth of 15 m feeding on the eggs of other opisthobranchs. Mike's photo here establishes this species in Indonesia. We have also collected this species in the Batangas region, of the Philippine Islands.

There are a half dozen or more Favorinids known from the tropical Indo-Pacific, but only a couple have been described. These are Favorinus japonicus Baba, 1949 and F. mirabilis Baba, 1955. Favorinus japonicus has variably colored ceratal cores (related to the color of the egg mass it most recently fed upon) varying from green to red. There is an irregular opaque white bull-eye shaped patch on the head, with opaque white down the centerline and white specks covering the ceratal surfaces. Bill Rudman's Sea Slug Forum shows a variant from Heron Island with cherry red nodules on the cerata. This species has annulate rhinophores.

Favorinus mirabilis, is known from Japan and the Marshall Islands. This species has red ceratal cores also, but it has a distinctive concentration of white specks at the tip of each cerata. The black rhinophores are perfoliate, like F. tsuruganus.

Ono's Opisthobranchs of Kerama Islands, on page 164 reports another Favorinus from Japanese waters, the ceratal color of this species being the reverse of F. tsuruganus. See also the ornate color variant of Favorinus reported by Bob Bolland on Rudman's Sea Slug Forum.


Baba, K.; Abe, T. 1964. Record of Favorinus tsuruganus n. sp., from Tsuruga Bay, Japan (Nudibranchia - Eolidoidea).
Publications of the Seto Marine Biological Laboratory 12(2):163- 164.

Dave Behrens
Danville, Calif
Jan. 2001

Taxonomic information courtesy of Dave Behrens

David W. Behrens

Author: Pacific Coast Nudibranchs
Co-Author Coral Reef Animals of the Indo Pacific
Propriator of Sea Challengers Natural History Books !

Send Dave mail at seachalleng@earthlink.net

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