Nth America west coast - Vancouver Is. region, Canada, to Baja California, Mexico.
NOTE added 14 July 2003: see Jeff Goddard's message suggesting that E. olivaceus is a synonym of Eubranchus rupium
The following description is from O'Donoghue (1922):
The body is aeolidiform and elongated, with a noticeable tail. The cerata are relatively large and fewer in number than other species of the Aeolididae, reaching up to 15 only. The head is relatively large and sub-globular and bears two long cylindrical oral tentacles. The rhinophores are long and non-retractile. There is a fairly broad, wavy band of deep olive green dorso-medially on the dorsum; cerata with distinct, subterminal band of reddish-brown to olivaceous green, cores deep olivaceous green; rhinophores frosted with small, opaque white dots distally and with a subterminal band of brownish to olivaceous green; body color pale, translucent yellowish-green, with numerous light brown spots. The largest specimen from the original description measured 11 mm long.
Also reported from east coast of Nth America. See Eubranchus cf. olivaceus.
• Lambert, W.J. (1991) Coexitence of hydroid-eating nudibranchs: recruitment and non-equalibrial patterns of occurrence. Journal of Molluscan Studies, 57(4), Supplement, T.E.Thompson Memorial Issue: 35-47.
• Meyer, K.B. (1971) Distribution and zoogeography of fourteen species of nudibranchs of northern New England and Nova Scotia. Veliger, 14(2): 137-152.
• O'Donoghue, C.H. (1922) Notes on the Nudibranchiate Mollusca from the Vancouver Island Region. III. Records of species and distribution. Transactions of the Royal Canadian Institute, Toronto, 14(1): 145-167.
Rudman, W.B., 2003 (May 15) Eubranchus olivaceus (O'Donoghue, 1922). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/eubroliv