Two new genera and four new species of freshwater cochliopid gastropods (Rissooidea) from northeastern Mexico

Abstract

We describe four new species of cochliopid snails from thermal springs in northeastern Mexico (Chihuahua, Coahuila and Durango States). Two of these are placed in Pseudotryonia and represent the first Mexican records for this genus. They are diagnosed by unique or unique combinations of shell and anatomical characters, are well differentiated genetically from both each other and other congeners (mtCOI sequence divergence ≥2.0%) and were resolved as sister species within the Pseudotryonia clade in our molecular phylogenetic analyses. The other two species resemble Ipnobius, Pseudotryonia and Tryonia in having a thin, narrow shell, penis ornamented with a small number of glandular papillae and ovoviviparous reproductive mode, but are well differentiated (from these and each other) by other morphological/anatomical characters and mtCOI sequences (8.6–12.5% and 5.2–12.1% divergence, respectively) and consequently are placed in new monotypic genera (Chorrobius and Minckleyella). Chorrobius and Minckleyella formed a clade with Ipnobius, Mexipyrgus and Tryonia in all of our molecular phylogenetic analyses. Chorrobius was consistently delineated as a divergent lineage within this clade, but its relationships were otherwise unresolved. Minckleyella was nested within Tryonia in most of the trees and was sister to this genus in the others; despite this finding we erected a new genus for this snail because of its highly distinctive anatomical features and large genetic divergence relative to Tryonia (5.2 ± 0.6%). Each of the four new species is endemic to highly disturbed single springs or local spring systems and may require protection.