MALACOLOGIA, 1970, 10(2) : 283-321 THE NEW ZEALAND SPECIES OF POTAMOPYRGUS Í GASTROPODA: HYDROBIIDAE) Michael Winterbourn' Department of Zoology Massey University, Palmerston North New Zealand ABSTRACT In his revision of the genus, Suter (1905) recognized 6 species and 3 subspecies of Potamopyrgus from the 2 main islands of New Zealand, but the present study has shown that only 3 species exist. They are P. antipodarum (Gray, 1843). P. pupoides Hutton, 1882, and a previously unrecognized species P. estuarinus n. sp. Potamopyrgus estuarinus and P. pupoides are oviparous, possess smooth, unornamented shells and are confined to brackish water, whereas P. antipodarum is ovoviviparous, highly variable in shell size, shape and ornamentation, and inhabits both fresh and brackish water. Populations of P. antipodarum may consist entirely of parthenogenetic females or contain varying numbers of sexually functional males. Rearing of P. anti-podarum in the laboratory has shown that snails do not necessarily breed true with respect to shell ornamentation, and that shell shape and ornamentation are not controlled primarily by environmental factors. The shell oí P. estuarinus is indistinguishable from shells of some P. antipodarum, but P. pupoides is easily recognized by its small, pupiform shell. The radula, operculum, external morphology, body pigmentation and male repro-ductive system are similar in all species and do not provide useful taxonomic characters. In Potamopyrgus antipodarum the lower section of the female reproductive system is modified to form a brood pouch with the open sperm groove running along its floor. In P. estuarinus and P. pupoides the lower reproductive tract is dominated by the strongly developed capsule gland which is physically separated from the spermathecal duct below. The diploid chromosome number of all 3 species is 24. Ion-exchange chromatography of shell periostracal protein has disclosed no significant differences in amino acid composition between species, but considerable intraspecific variation is found. Potamopyrgus antipodarum is abundant in permanent freshwaters of all kinds and has been found in water up to 26 /'o salinity, although experimental work indicates that it is active only in water below l7"5%o salinity. No clear relationship between shell morphology and type of habitat has been found. P. estuarinus is most abundant in tidal estuaries where considerable fluctuations in salinity are found, and where many snails are regularly exposed to the air for part of each tide cycle. P. pupoides occupies a similar habitat, but normally remains fully aquatic at all times. In the laboratory P. estuarinus and P. pupoides remained active at all salinities from fresh to sea water, but they have not been found in fresh water in the field. Laboratory experiments have shown the existence of behavioural differences between species, which are associated with the different habitats occupied by them. Potamopygus-estuarinus shows pronounced amphibious tendencies not found in P. antipodarum and was able to survive in a " dormant " state when exposed to the air for up to 70 days. The Potamopyrgus antipodarum complex is examined in the light of current concepts of the species, and the high degree of variability found in this species is associated with * Current Address: Department of Zoology, University of Canterbury, Christchurch, New Zealand. 283
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