Last year a large molecular study was published by Saadi & Wade, which aimed at studying the deep divisions at the base of the Stylommatophoran phylogenetic tree. Their abstract was “The deep divisions at the base of the stylommatophoran land snails and slugs have proved to be controversial, with the phylogenetic position of the Scolodontidae remaining unresolved. Here we present a phylogenetic analysis of 34 stylommatophoran genera based on a combined dataset (5782 sites) of four loci with the aim of resolving the position of the Scolodontidae and their relationship to the ‘achatinoid’ and ‘non-achatinoid’ clades. We also evaluate the phylogenetic utility of different genes and gene partitions. The deep phylogenetic relationships within the Stylommatophora are now clearly resolved. The Scolodontidae are shown categorically to be the sister group to all other stylommatophoran groups with robust support and with all phylogeny re-construction methods. The ‘achatinoid’ and ‘non-achatinoid’ clades are also strongly supported in the tree. The original LSU 1-5 fragment used extensively in studies of the Stylommatophora was found to be the most informative gene fragment and works well at resolving relationships at most levels in the Stylommatophora but does not reliably resolve the deep level relationships at the very base of the clade. The concatenated dataset of four genes employed in this study is not only informative at lower levels but also resolves the deep level relationships at the base of the Stylommatophora with robust support“.
As this tree shows, the ‘Scolodontidae’ genera used herein are Guesteria and Systrophia. As Salvador & Cavalleri has recently shown, there is a clear distinction between the Scolodontidae and Systrophiidae to which the two mentioned genera belong. The authors may have been misled by the classification used by MolluscaBase which still classifies them with the Scolodontidae. As such not a disaster, but it shows that if the taxonomy is not up-to-date, even the conclusions of a thorough study are prone to failure.
Saadi, A.J. & Wade, C.M., 2019. Resolving the basal divisions in the stylommatophoran land snails and slugs with special emphasis on the position of the Scolodontidae. Molecular Phylogenetics and Evolution 139: e106529 (9 pp.).