Rissoidae, Gray, 1847

Webster, Nicole B & Vermeij, Geerat J, 2017, The varix: evolution, distribution, and phylogenetic clumping of a repeated gastropod innovation, Zoological Journal of the Linnean Society 180 (4), pp. 732-754 : 739-740

Rissoidae

Warén (1983) mentions that ‘rissoinids’ have internal varices, similar to those of Eulimids, but does not provide details. A single genus Pseudotaphrus has occasional varices on its smooth shell, generally on the last whorl ( Ponder, 1984). These are similar in appearance to the varices in Ellobium in that they appear as a stoppage of growth with associated apertural thickening, followed by a short period of spiral growth to a new aperture. Unlike Ellobium , their placement does not appear consistent enough to warrant the label of a dorsal varix.

These four families, Aclididae , Eulimidae , Epitoniidae , and Rissoidae , cluster relatively closely on the phylogeny of Takano & Kano (2014), but phylogenetic relationships remain uncertain. With the exception of Aclididae and Eulimidae , each family differs quite widely in how varices are expressed. This morphological difference supports four separate evolutionary origins, especially considering the rarity of varices in Rissoidae , Epitoniidae , and Aclididae .