New hosts for Temnocephala iheringi (Platyhelminthes, Rhabdocoela) and analysis of inter-population morphological variability

Temnocephala iheringi Haswell, 1893 is a species of temnocephalan endemic to the Neotropical region, distributed from the center of Brazil to Uruguay and the southern Pampean region in Argentina. It is an ectocommensal of gastropods, particularly Ampullariidae snails. Previous studies have noted the morphological variation present in the species. In this study, we present two new host species: Pomacea americanista (Ihering, 1919) (Caenogastropoda, Ampullariidae) and Chilina iguazuensis Gutirrez Gregoric & Rumi, 2008 (Heterobranchia, Chilinidae), representing the first Heterobranchia host for temnocephalids. Using morphological comparisons of the penial stylet (an important diagnostic character) from new material and literature data, we attempt to establish whether the morphological variation could be attributed to geographical range or a difference in host species. Results showed that the stylet from specimens found on P. americanista was the largest recorded among all host species. The introvert in temnocephalans associated with C. iguazuensis and P. americanista was longer than in other populations, and in the case of C. iguazuensis it was also narrower at its base. The record of new hosts for T. iheringi and the characterization of the populations developed on them are a step forward in the understanding of the interactions between host and commensal species and their adaptations.