Anatomical evidence for the occurrence of Lymnaea (Galba) palustris (O.F. Müller, 1774) and L. (Galba) corvus (Gmelin, 1778) (Gastropoda: Lymnaeidae) in the Netherlands

A study was made on the Lymnaea (Galba) palustris complex in The Netherlands. Investigations on the genitalia proved that in The Netherlands two species are present, viz. L. palustris (O. F. Müller, 1774) and L. corvus (Gmelin, 1778), which can not in all cases be distinguished by shell characters. Genitalia were prepared, drawn and several measurements were carried out to investigate the variation within the two species. It appeared that most characters show a partial or total overlap. Some characters appeared to separate the two species absolutely. One of these is very useful for a quick distinction of both species, viz. the situation of the truncus receptaculi with respect to the oviductus, which character is already visible after a general dissection of the mantle. Other reliable characters are the length of the vas deferens and the length ratio phallotheca proximalis/ phallotheca distalis.