Redescription of two endemic species of Chilinidae (Gastropoda: Hygrophila) from Del Plata Basin (South America)

The Chilinidae comprises 17 species currently cited for Argentina, mostly distributed in Patagonia. All original descriptions of these species have been based on shell characters, and their internal anatomy is poorly known. Characters of the shell, radula and nervous system are described here for two endemic species of Chilinidae from Del Plata basin (South America), Chilina rushii Pilsbry and C. gallardoi Castellanos & Gaillard. Materials were collected during the years 2000 and 2005 in the rivers Uruguay and Rio de La Plata from Del Plata basin, Argentina. Shell: Chilina gallardoi shows, sometimes, the keel in the last whorl, and the most significant difference between these species are the length of the aperture and the size of the last whorl. Radula: it has 58 rows in C. gallardoi, whereas in C. rushli it has 48 rows; first lateral is tricuspid in C. gallardoi, whereas in C. rushii is tetracuspid; last teeth have up to five cusps in C. gallardoi, whereas in C. rushii they have up to seven. Nervous system: differences between the species are based in the distances between the ganglions, and the one that shows the most significant difference is the distance between the left pleural and the parietal. As a conclusion, some measures of shells (mainly the ones that are relationed with the aperture) as well as the length between the nervous ganglia and characteristics of radula, can be used to differentiate species of Chilindae in the Del Plata basin.