Known only from central Japan.
Hachijo Island, Japan. July 2001. Photo: Jun Imamoto.
Small black runcinid with a submarginal translucent yellowish band down each side of the mantle to join posteriorly. A similar submarginal band occurs on the foot. In some specimens, the submarginal band appears reddish. The small reduced shell is totally enclosed in the posterior part of the mantle. Particularly common in Autumn (September - November) in shallow upper tidal pools, crawling on rocky bottom or on juvenile plants of the filamentous green alga Enteromorpha. Grows to approximately 7mm in length. It has direct developing larvae which hatch from the egg as crawling young about 40 days after laying. During development in the egg, the embryo passes through a recognisable, but modified, veliger stage.
• Baba, K. (1954) Runcina setoensis, a new and rare species from the coast of Kii, Middle Japan (Opisthobranchia). Publications of the Seto Marine Biological Laboratory, 3: 373-374.
• Baba, K. (1967) Supplementary notes on the anatomy of Metaruncina setoensis (Baba, 1954), (N.G.) (Opisthobranchia - Cephalaspidea). Publications of the Seto Marine Biological Laboratory, 15: 185-197, Pls 2-5.
• Baba, K. & Hamatani, I. (1959) The direct development in Runcina setoensis Baba (Opisthobranchia- Cephalaspidea). Publications of the Seto Marine Biological Laboratory, 7: 281-290.
Rudman, W.B., 2001 (July 9) Metaruncina setoensis (Baba, 1954). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/metaseto