Species with internal shell, hidden beneath a papillate mantle with lateral flaps. These flaps are in some genera fused to enclose the shell. The thin shell is smooth and contains two to three
whorls of which the
body whorl is rapidly expanding into a large
aperture. Some species have a thick, hairy
periostracum. They resemble dorid
nudibranches, but differ by their smooth tentacles and the absence of a dorsal gill circlet.[2]
^P.J. Hayward and J.S. Ryland - Handbook of the Marine Fauna of North-West Europe; Oxford University Press 1995; ISBN 0 19 854054 X
Troschel, F. H. (1848). Mollusca, Gastropoda. Pp. 536–568, in: A. F. A. Wiegmann & J. F. Ruthe, Handbuch der Zoologie, ed. 3. Lüderitz, Berlin. iv + 651 pp.
Thiele, J. (1929-1935). Handbuch der systematischen Weichtierkunde. Jena, Gustav Fischer, 1154 pp. Vol. 1 part 1: 1-376
Bouchet P., Rocroi J.P., Hausdorf B., Kaim A., Kano Y., Nützel A., Parkhaev P., Schrödl M. & Strong E.E. (2017). Revised classification, nomenclator and typification of gastropod and monoplacophoran families. Malacologia. 61(1-2): 1–526.