Taxonomic Deception via Obvious Traits: Oversplitting in European <i>Vallonia</i> Risso, 1826 (Mollusca: Gastropoda: Valloniidae)

ABSTRACT The status of the six traditionally recognised European Vallonia taxa is considered based on mtDNA and nDNA sequences from five independently sorting loci in combination with morphometric landmark analyses conducted on genetically confirmed shells. These analyses document that only two species are valid ( V. costata and V. pulchella ). Oversplitting was aided because easily observed and apparently dichotomous traits—in this case the presence or absence of shell ribs—are shown via DNA sequence analyses to not convey useful taxonomic information: they say no more about species status than does hair, eye or skin colour in humans. This work is a reminder that taxonomists must empirically document those macro‐scale features which are and those which are not robust indicators of species‐scale taxonomic units prior to the initiation of revision. While impossible to accomplish throughout most of taxonomic history, the great expansion of molecular methods and access to these tools mandates that this empirical step underlie all modern revisionary work.