A. brunnea has a brown mantle with white and black spots. Most of the mantle is covered with semi-transparent gray papilla. They grow to about 20mm long.
It is described that when handled, Acanthodoris brunnea emit the smell of cedar.[5]
^Turgeon, D.; Quinn, J.F.; Bogan, A.E.; Coan, E.V.; Hochberg, F.G.; Lyons, W.G.; Mikkelsen, P.M.; Neves, R.J.; Roper, C.F.E.; Rosenberg, G.; Roth, B.; Scheltema, A.; Thompson, F.G.; Vecchione, M.; Williams, J.D. (1998). Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks. 2nd ed. American Fisheries Society Special Publication, 26. American Fisheries Society: Bethesda, MD (USA). ISBN1-888569-01-8. IX, 526 + cd-rom pp.
^Behrens, D. W., & Hermosillo, A. (2005) Eastern Pacific nudibranchs, a guide to the opisthobranchs from Alaska to Central America. vi + 137 pp., 314 photos. Sea Challengers, Monterey, California, page 55.
^Hallas, JM and Gosliner, TM. (2015) Family Matters: the first molecular phylogeny of the Onchidorididae (Mollusca, Gastropoda, Nudibranchia). Molecular Phylogenetics and Evolution, 88: 16-27.
^Hallas, J.M., Simison, W.B. & Gosliner, T.M. (2016) Dating and biogeographical patterns in the sea slug genus Acanthodoris Gray, 1850 (Mollusca, Gastropoda, Nudibranchia). Molecular Phylogenetics and Evolution, 97: 19-31.