Pisidium chilense (d'Orbigny, 1846) and new species of Pisidium C. Pfeiffer, 1821 from southern Chile (Bivalvia, Sphaeriidae)

Pisidium chilense (d'Orbigny, 1846), a species only known from a rather poor original description, is here fully redescribed and figured. Pisidium huillichum n. sp. and Pisidium llanquihuense n. sp. respectively from Llanquihue lake, Chiloé Island and Yelcho lake, southern Chile, are described. Both new species share as common features the presence of only one demibranch, one siphonal aperture and brood pouches developing from the upper and posterior part of inner demibranchs. As it was described for other Patagonian species, the ligament in both new species is internal, however, in Pisidium llanquihuense n. sp. the ligament is slightly visible from the exterior.