Their shells vary in size from small (7 mm in diameter, or about 0.3 inches) to medium (32 mm, about 1.3 inches), usually with a low, flattened spire, a very wide umbilicus, and usually with the upper lip margin (at the aperture) curving downwards or straightened.
Anatomy
They have a number of anatomical peculiarities.
The structure of the radula of these snails (their "teeth") is unusual. Essentially, haplotrematids have fewer cusps than most snails, but they are considerably elongated, suitable for the predatory life they follow. Members of this family have been given the common name "lancetooth" snails, presumably based on this last anatomical characteristic. Their sole food source consists, as far as is known, of other terrestrial mollusks.[5][3]
In this family, the number of haploidchromosomes lies between 26 and 30 (according to the values in this table).[6]
^ abPilsbry, Henry A. 1946. Land Mollusca of North America (North of Mexico). Acad. Nat. Sci. Philadelphia, Monograph 3, vol. 2(1): 201-230.
^Binney, William G. 1878. The Terrestrial Air-Breathing Mollusks of the United States and Adjacent Territories of North America. Vol. 5 (plates). Bull. Mus. Comparative Zool., Harvard. Plate 20.
^Barker G. M.: Gastropods on Land: Phylogeny, Diversity and Adaptive Morphology. in Barker G. M. (ed.): The biology of terrestrial molluscs. CABI Publishing, Oxon, UK, 2001, ISBN0-85199-318-4. 1-146, cited pages: 139 and 142.
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