| Summary: | This investigation has shown that only three species of Potamopyrgus Stimpson can be recognized from New Zealand, compared with the six species and three subspecies recognized by Suter (1913). The species are, P. antipodum Gray 1843, P. pupoides Hutton 1882, and P. estuarinus n. sp. P. dawbini Powell 1955 from the Auckland Islands is probably referable to P. antipodum, but the position of (?) P. melvilli (Hedley 1916) from the Kermadec Islands has not been determined. The European species P. jenkinsi (Smith 1889) cannot be separated from P. antipodum on morphological or anatomical grounds and may also be referable to that species. All species now placed in Fluviopupa Pilsbry 1911 should probably be referred to Potamopyrgus. P. estuarinus and P. pupoides are both smooth-shelled, bisexual, non-ovoviviparous and confined to brackish water. P. antipodum is highly variable in shell size, shape and ornamentation, inhabits fresh and brackish water, is ovoviviparous, and populations may consist entirely of parthenogenetic females, or contain variable numbers of sexually functional males. Rearing of snails in the laboratory has shown that snails do not necessarily breed true with respect to shell ornamentation, and that shell shape and ornamentation is not determined primarily by environmental factors. The shell of P. estuarinus cannot be distinguished from that of some P. antipodum but P. pupoides may be readily identified using shell characters alone. No significant interspecific differences in operculum, external morphology, body pigmentation or structure of the male reproductive system are found but P. pupoides possesses minor radular differences, and P. antipodum differs in the condition of the female reproductive system. The diploid (2n) chromosome number of all three species is 24. Qualitative paper chromatography of crude foot muscle and mantle edge extracts, and quantitative ion-exchange chromatography of shell periostracal protein have disclosed no important biochemical differences between species. P. antipodum ...
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