Background: Land 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.Methods: Adults 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.Results: Species 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.Discussion: Our 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.

A new approach for biogeography to find patterns of sympatry, based on network analysis, is proposed. Biogeographic analysis focuses basically on sympatry patterns of species. Sympatry is a network (= relational) datum, but it has never been analyzed before using relational tools such as Network Analysis. Our approach to biogeographic analysis consists of two parts: first the sympatry inference and second the network analysis method (NAM). The sympatry inference method was designed to propose sympatry hypothesis, constructing a basal sympatry network based on punctual data, independent of a priori distributional area determination. In this way, two or more species are considered sympatric when there is interpenetration and relative proximity among their records of occurrence. In nature, groups of species presenting within-group sympatry and between-group allopatry constitute natural units (units of co-occurrence). These allopatric units are usually connected by intermediary species. The network analysis method (NAM) that we propose here is based on the identification and removal of intermediary species to segregate units of co-occurrence, using the betweenness measure and the clustering coefficient. The species ranges of the units of co-occurrence obtained are transferred to a map, being considered as candidates to areas of endemism. The new approach was implemented on three different real complex data sets (one of them a classic example previously used in biogeography) resulting in (1) independence of predefined spatial units; (2) definition of co-occurrence patterns from the sympatry network structure, not from species range similarities; (3) higher stability in results despite scale changes; (4) identification of candidates to areas of endemism supported by strictly endemic species; (5) identification of intermediary species with particular biological attributes.

This paper reports for the first time the occurrence of four exotic terrestrial slug species in Argentina: Lehmannia valentiana (Férussac, 1823) (Limacidae), Deroceras invadens Reise et al. 2011 (Agriolimacidae), Arion intermedius Normand, 1852 (Arionidae) and Meghimatium pictum (Stolyczka, 1873) (Philomycidae). The study is based on specimens deposited in museums in Argentina. Both the morphologic characteristics and the mitochondrial cytochrome oxidase I gene sequences were used to identify the exotic species. Phylogenetic analyses were also carried out in order to explore the location of their origins. Lehmannia valentiana had the oldest records and has been widely distributed in Argentina. Deroceras invadens and A. intermedius were found to be restricted to the southern portion of the country. Meghimatium pictum was recorded in the northwest and northeast Argentina, and the DNA sequences analyzed from this species were more closely related to specimens from the west of the Strait of Taiwan. A determination of the origin of the other species was impossible because either the sequences analyzed grouped with samples from different geographical origins or only few sequences were available for comparison. In view of the invasive potential of these slug species, the present work provides new and potentially useful DNA sequence data obtained from morphologically-confirmed specimens. Information provided from these analyses should assist in making a rapid identification of these exotic slugs by nonspecialists and governmental authorities who are responsible for managing and controlling the presence of exotic species.