New South Wales and Victoria, southeastern Australia.
Port Phillip Bay, Victoria, Australia. March 1986. 4mm long alive. PHOTO: Bill Rudman.
Ilbia ilbi and the closely related runcinids are a group (Rucinoidea) of small herbivorous opisthobranchs with no close links to other cephalaspidean superfamily. Many, but not Ilbia, have a small reduced shell embedded in the skin at the posterior end of the body. The mantle cavity is essentially disappeared and the gill or gills, if present, and the anus, open at the posterior end of the body below the mantle edge.
Their radular teeth are quite distinct and they have four gizzard plates, rather then the usual three. Bulla is the only other cephalaspidean with four gizzard plates.
Runcinoideans are found in both tropical and temperate waters from the intertidal to about 50m. All are small, seldom growing more than about 5mm long. Only three species of the Ilbiidae have been discovered, Ilbia ilbi from southeastern Australia, Pseudoilbia lineata Miller & Rudman, 1968 from New Zealand, and Pseudoilbia mariana Hoff & Carlson, 1990 from the Mariana Islands.
• Rudman,W.B. (1971). Structure and functioning of the gut in the Bullomorpha (Opisthobranchia). Part 1. Herbivores. Journal of Natural History, 5: 647-675.
Rudman, W.B., 1998 (December 18) Ilbia ilbi Burn, 1963. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/ilbiilbi