Outdated but established?! Conchologically driven species delineations in microgastropods (Carychiidae, Carychium)
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Valid taxonomic descriptions are paramount in evolutionary biology. Many date back centuries and are based on ambiguous morphological data. Microgastropods, in particular the taxon Carychiidae (Eupulmonata, Ellobioidea), demonstrate a paucity of informative conchological features. However, as exemplified by Carychium mariae Paulucci, 1878, their taxonomic classification is based almost entirely on these few features. Here we investigated the questionable taxonomic status of Carychium mariae combining DNA barcoding, field-emission scanning electron microscopy and conchological data. This taxon occurs in the Southern Alps, where it shows a sympatric distribution with two widely distributed members of Carychium—C. minimum Müller, 1774 and C. tridentatum (Risso, 1826). Our analyses do not support the species status of C. mariae. In contrast, DNA barcoding reveals a monophyletic grouping of C. minimum and C. mariae specimens with averaged intraspecific variability less than 3.2% (barcoding gap for Carychiidae). Hence, C. mariae is treated and should be regarded as a synonym of C. minimum, just representing a different morphotype. The differentiation and monophyletic status of C. tridentatum can be validated by showing an averaged interspecific variability of 5.9% to C. minimum. In general, we are critical of the sole use of conchological characters for microgastropod taxonomy and strongly recommend the implementation of molecular data (e.g., DNA barcoding) to reevaluate established species designations.