From morphology to molecules: a combined source approach to untangle the taxonomy ofClessinia(Gastropoda, Odontostomidae), endemic land snails from the Dry Chaco ecoregion

Abstract

BackgroundLand gastropods of the Dry Chaco merit special attention because they comprise a highly diverse but barely studied group.ClessiniaDoering, 1875 are typical inhabitants of this ecoregion. The inclusion of their distribution areas intoSpixiarange, their shell shape similarities, and a former molecular study raised doubts on the monophyly of this genus. The present study review the species ofClessinia, under a morphological, geometric morphometrics, and molecular combined approach.MethodsAdults were collected, photographed, measured, and dissected for anatomical studies. Shell ultrastructure was studied with scanning electron microscope. Geometric morphometric analyses on shells were performed testing if they gave complementary information to anatomy. Two mitochondrial genes, and a nuclear region were studied. Phylogenetic reconstructions to explore the relationships of DNA sequences here obtained to those ofClessiniaandSpixiaspecies from GenBank were performed.ResultsSpecies description on shell, periostracal ornamentation and anatomy is provided. We raised formerClessinia cordovana striatato species rank, naming it asClessinia tulumbensissp. nov. The periostracum, consisting of hairs and lamellae, has taxonomic importance for species identification. Shell morphometric analyses, inner sculpture of penis and proportion of the epiphallus and penis, were useful tools to species identification. Nuclear markers do not exhibit enough genetic variation to determine species relationships. Based on the mitochondrial markers, genetic distances amongClessiniaspecies were greater than 10%, and whileC. cordovana,C. nattkemperi, andC. pagodawere recognized as distinct evolutionary genetic species, the distinction betweenC. stelzneriandC. tulumbensissp. nov. was not evident.ClessiniaandSpixiawere paraphyletic in the molecular phylogenetic analyses. Species ofClessiniahere treated have narrow distributional areas and are endemic to the Chaco Serrano subecoregion, restricted to small patches within the Dry Chaco.ClessiniaandSpixiaare synonymous, and the valid name of the taxon should beClessiniaDoering, 1875 which has priority overSpixiaPilsbry & Vanatta, 1894.DiscussionOur results support the composition ofC. cordovanacomplex by three species,C. cordovana,C. stelzneri, andC. tulumbensissp. nov. The low genetic divergence betweenC. stelzneriandC. tulumbensissp. nov. suggests that they have evolved relatively recently. The formerSpixiaandClessiniaare externally distinguished becauseClessiniahas a detached aperture from the body whorl forming a cornet, periostracal microsculpture extended over dorsal portion of the peristome, five inner teeth on the shell aperture instead of three–four found inSpixia. Morphological similarities exists between both genera in shell shape, type of periostracum microsculpture, reproductive anatomy, besides the overlap in geographic ranges.