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Tuatara: Volume 20, Issue 3, November 1973

A Guide to the Freshwater Mollusca of New Zealand

page 141

A Guide to the Freshwater Mollusca of New Zealand


Recent studies on New Zealand freshwater molluscs have resulted in an improvement in our understanding of their systematics and biology. In particular the families Hydrobiidae, Sphaeriidae, Ancylidae and Lymnaeidae have been revised and as a result several name changes have been made. The main purpose of this paper is to incorporate the findings of these studies with those of earlier work in the form of an up-to-date key to the New Zealand species. The last comprehensive account of the New Zealand freshwater Mollusca was written by Ponder (1964) in the University of Auckland Field Club Journal, Tane, but because of the journal's limited distribution it is not generally available.

The most obvious feature of most molluscs and therefore potentially one of the mose useful features for use in their idendification is the shell. Unfortunately, many species possess highly variable shells and this variation has been one of the main causes of the taxonomic confusion which has existed in New Zealand in the past. This problem has been largely overcome now, however, since the extent and type of shell variation in a high proportion of our freshwater species has been examined and documented. In the key that follows, shell characters are used wherever possible to distinguish species, and information on variation is included. In some cases, shell features are inadequate for making positive species identifications and in these cases anatomical features, sometimes of the living animal, have been employed. In addition, some notes on the biology, ecology and systematics of the species are provided.

A list of the freshwater molluscs occurring in New Zealand along with recent synonymies is given in Table 1.
Table 1 — The Freshwater Mollusca of New Zealand
Recent Synonyms
Class Gastropoda
Subclass Prosobranchia
    Family Hydrobiidae
        Potamopyrgus antipodarum (Gray, 1843)Potamopyrgus antipodum, P. corolla, P. egenus, P. spelaeus, P. subterraneus, P. badiapage 142
        Potamopyrgus estuarinus Winterbourn, 1971***
        Potamopyrgus pupoides Hutton, 1882Potamopyrgus spelaeus pupoides
        Opacuincola caeca Ponder, 1966
        Paxillostium nanum Gardner, 1970
    Family Melaniidae
        Melanopsis (Zemelanopsis) trifasciata Gray, 1843
Subclass Pulmonata
    Family Lymnaeidae
        Lymnaea tomentosa tomentosa (Pfeiffer, 1855)Lymnaea tomentosa waikariensis
        Lymnaea tomentosa hamiltoni (Dell, 1956)*
        Lymnaea columella Say, 1817**
        Lymnaea stagnalis (Linnaeus, 1758)
        Lymnaea truncatula (Mueller, 1774)Lymnaea alfredi alfredi
    Family Physidae
        Physa (Physa) sp. (? acuta Draparnaud, 1805)
    Family Planorbidae
        Gyraulus corinna (Gray, 1850)
        Gyraulus kahuica (Finlay & Laws, 1931)
        Planorbarius corneus Linnaeus, 1758
        Physastra variabillis (Gray, 1843)
        Physastra oconnori (Cumber, 1941)
    Family Ancylidae
        Ferrissia (Pettancylus) neozelanica (Suter, 1905)Gundlachia neozelanica
        Ferrissia (Pettancylus) dohrnianus (Clessin, 1882)Ancylus dohrnianus, Gundlachia lucasi
    Family Latiidae
        Latia neritoides Gray, 1850
Class Bivalvia
    Family Sphaeriidae
        Sphaerium (Sphaerinova) novaezelandiae Deshayes, 1854
        Pisidium (Afropisidium) hodgkini (Suter, 1905)
        Pisidium (Rivulina) casertanum (Poli, 1781) Pisidium novaezelandiae Prime, P. aucklandicumpage 143
    Family Hyriidae
        Hyridella (Hyridella) aucklandica (Gray, 1843)
        Hyridella (Echyridella) menziesi (Gray, 1843)
        Cucumerunio websteri websteri (Simpson, 1902)
        Cucumerunio websteri delli McMichael and Hiscock, 1958

Definitions of terms used in the key and text

Acute sharply pointed
Aperture the opening in a spiral shell
Apex tip
Beaks the opposing points or apices of a bivalve shell
Brackish mixed salt and fresh (water)
Body whorl the last whorl of a spiral shell
Dextral coiled in a right-handed spiral, i.e. the aperture is on the right when the shell is viewed aperture up and with the tip pointing away from the viewer
Digitate with finger like processes
Ecotype an ecological variant of a species adapted to (or produced by) local conditions
Elliptical regularly oval
Endemic confined to a certain region
Euryhaline able to tolerate a wide range of osmotic pressures and salinities. Animals with restricted salinity ranges are termed stenohaline
Globose globe-like, bulbous
Hard water with reference to mollusc distribution this is considered to be water containing more than 20 ppm calcium. Below this level water is soft.
Hermaphrodite an animal which is both male and female
Keeled shouldered, angled
Ligament the elastic material which hinges the valves of bivalves
Mantle a fold of ‘skin’ covering some or all of the body. Its outer surface secretes the shell
Microsculpture fine, raised shell markings
Operculum the lid closing the aperture in the Prosobranchia
Ovate - conic egg shaped to conicalpage 144
Oviparous laying eggs in which the embryos are little developed
Ovoid egg shaped
Ovoviviparous having young developing in a brood pouch within the female
Periostracum the proteinaceous skin on the outside of a shell
Sinistral coiled in a left-handed spiral: the opposite of dextral
Sinuate wavy
Siphon opening to the mantle cavity of a bivalve or prosobranch gastropod
Spire all coils of a gastropod above the aperture
Striae fine lines
Suture junction between whorls of a gastropod
Turreted spire whorls regularly stepped in outline
Umbilicus hollow axis at the base of some gastropod shells
Ventricose swollen

Source of illustrations

Most of the figures provided in this key are based on published illustrations. Their sources are acknowledged below.

Climo and Pullan (1972), Figs. 32, 33, 34, 35; Dell, (1953), Figs. 36, 37, 38, 39; Dell (1956), Figs. 26, 27, 28; Finlay and Laws (1931), Figs. 23, 24, 25; Gardner (1970), Figs. 4, 5, 6; Hubendick (1967), Fig. 17, 18, 19, 20, 21; Kuiper (1966), Figs. 40, 41, 42, 43; Macan (1949), Figs. 22, 31; Ponder (1964), Figs. 1, 15, 16; Ponder (1966), Figs. 2, 3; Winterbourn (1970), Figs. 7, 8, 9, 10, 11, 12, 13, 14.


1. Shell with two valves hinged together Bivalvia 19
Shell in one piece Gastropoda 2
2. With an operculum; shells spired, dextrally coiled Prosobranchia 3
Without an operculum; shells flat or spired, coiled or uncoiled, coiling dextral or sinistral Pulmonata 8
3. Shell up to 30 mm high; spire relatively short compared with body whorl; aperture notched below. Colour dark olive with 1–3 spiral brown bands best seen inside the light bluish aperture. Males lack a penis. Found throughout New Zealand in fresh and brackish water. Melanopsis trifasciata (Fig. 1)
Shell less than 12 mm high; aperture rounded. Males when present with a penis Hydrobiidae 4
page 145
Plate 1: Scale in mm marked on all figures on this and subsequent plates. Figure 1: Melanopsis trifasciata. Figure 2: Opacuincola caeca. Figure 3: O. caeca, head and penis. Figure 4: Paxillostium nanum. Figure 5: P. nanum, head. Figure 6: P. nanum, operculum. Figure 7: Potamopyrgus pupoides.

Plate 1: Scale in mm marked on all figures on this and subsequent plates. Figure 1: Melanopsis trifasciata. Figure 2: Opacuincola caeca. Figure 3: O. caeca, head and penis. Figure 4: Paxillostium nanum. Figure 5: P. nanum, head. Figure 6: P. nanum, operculum. Figure 7: Potamopyrgus pupoides.

4. Shells of fully grown snails less than 3 mm high 5
Shells greater than 3 mm and up to 12 mm high 7page 146
5. Shell smooth, globose; spire short; umbilicate. Animal white and lacking eyes. Known only from a cave in Nelson Opacuincola caeca (Figs. 2, 3)
Shells ovoid with a blunt apex 6
6. Shell smooth, whorls slightly flattened at the sides. Inner surface of the operculum with a raised reddish rim and an erect, 3-pronged, calcareous peg. Animal white, semi-transparent. Ovoviviparous. Known from small bush streams and bush swamps in the North Island Paxillostium nanum (Figs. 46)
Shell smooth; sutures often margined below. Head and mantle black. Oviparous. Inhabits brackish streams, lakes and estuaries throughout New Zealand Potamopyrgus pupoides (Fig. 7)
7. Shell highly variable in shape, ranging from slender and elongate to ventricose. Spire long or short, loosely or tightly coiled. Whorls with or without spines or keels. Ovoviviparous. Animal darkly but somewhat variably pigmented. Very common in a great variety of freshwater habitats and also brackish water Potamopyrgus antipodarum (Figs. 811)
Shell up to 7 mm high, always smooth, never with spines. Apical whorls often eroded. Pigmentation of head and mantle always very dark. Oviparous. Inhabits brackish water in the tidal reaches of rivers, and also harbour mudflats near river mouths throughout New Zealand Potamopyrgus estuarinus (Figs. 1214)
8. Shell flattened and limpet-like 9
Shell strongly coiled, either flat or spired 11
9. Shell up to 8 mm long and 3 mm high, its apex slightly coiled at the posterior margin. Tentacles long and slender; eyes at their outer bases. Sides of foot and head with black pigmentation, sole of foot white. Found in North Island streams. Latia neritoides (Figs. 15, 16)
Shell not spirally coiled, its apex well behind the middle of the shell and slightly to the right. The apex with radial microsculpture. Animal transparent white; tentacles short and rather flattened with the eyes at their inner bases 10
10. Shell elongate, elliptical, the sides sometimes with a tendency to be straight. Maximum length 5 mm, width 3 mm, but usually smaller. Height about one fourth length. Animal with a dark patch medioanteriorly on the mantle behind the mantle collar Ferrissia neozelanica (Figs. 1719)
Shell oval, not particularly elongate, and without a tendency to straight sides. Length up to 6.5 mm, width 5.5 mm, height up to one half length. Animal at least partially pigmented dorsally Ferrissia dohrnianus (Fig. 20, 21)
page 147
Plate 2: Figures 8–11: Potamopyrgus antipodarum. Figures 12, 13: Potamopyrgus estuarinus. Figure 14: P. estuarinus, head and penis. Figures 15, 16: Latia neritoides, dorsal and lateral views.

Plate 2: Figures 8–11: Potamopyrgus antipodarum. Figures 12, 13: Potamopyrgus estuarinus. Figure 14: P. estuarinus, head and penis. Figures 15, 16: Latia neritoides, dorsal and lateral views.

11. Shell flat, sinistrally coiled 12
Shell spired 14
12. Shell large, reaching a height of 12 mm and a breadth of 28 mm. Young snails taller than broad. Animal red Planorbarius corneus (Fig. 22)
Shell small, less than 5 mm in diameter. Animal yellowish brown 13page 148
13. Shell with 4 or more whorls when its diameter is greater than 3.5 mm. Widely distributed and common throughout New Zealand. Gyraulus corinna (Figs. 23, 24)
Shell with only 3 whorls when its diameter is 3.5 mm. Known distribution is Hawkes Bay, Gisborne and Kaikoura. Gyraulus kahuica (Fig. 25)
Shell dextrally coiled. Animal with blunt, triangular tentacles Lymnaea 16
Shell sinistrally coiled. Animal with long, narrow tentacles. 15
15. Shell highly variable in size, shape and thickness; height up to 20 mm but more commonly attaining 12–16 mm. Whorls sculptured or smooth, body whorl rounded or keeled, spire short or long. Animal a definite reddish brown. Mantle edge smooth, not digitate. Widely distributed in still waters but apparently not common. Physastra variabilis (Figs. 2628)
Shell smooth, never keeled or sculptured; apex of spire pointed. Height up to 12 mm but mure frequently attaining a height of 7–8 mm fully grown. Often a faint, white thickening runs around the inner lip of the aperture. Animal yellowish grey. Digitate processes arise from the inner mantle edge and spread over the shell on the inner side of the aperture when the animal is active. Widely distributed and common throughout New Zealand in still and running water Physa sp. (? acuta) (Figs. 29, 30)
16. Shell of fully grown individuals with 5–8 whorls and up to 50 mm high. Spire acute and elongate. Shell fragile and pale, usually with fine spiral sculpturing. Established in numerous lakes and ponds throughout New Zealand. Lymnaea stagnalis (Fig. 31)
Shell less than 15 mm high, without a long slender spire and without spiral sculpture — 17
17. Shell with deep sutures and a somewhat turreted outline. Spermathecal duct long and thin. Uncommon; known only from Nelson and Marlborough Lymnaea truncatula (Fig. 33)
Shell not turreted in outline 18
18. Shell highly variable in shape, generally with a rather globose body whorl, a short spire, and no spiral striae. Aperture wide with a wide inner lip. Distributed throughout New Zealand and quite common. Lymnaea tomentosa (Figs. 34, 35)
Shell relatively slender and not highly variable in shape, with wavy spiral striations which may be indistinct, at right angles to the vertical growth lines. Aperture with a narrow inner lip. Mantle beneath shell often black. Widely distributed and quite common. Lymnaea columella (Fig. 32)
page 149
Plate 3: Figures 17–19: Ferrissia neozelanica, lateral, ventral and dorsal views. Figures 20, 21: Ferrissia dohrnianus, lateral and dorsal views. Figure 22: Planorbarius corneus. Figures 23, 24: Gyraulus corinna, lateral and dorsal views. Figure 25: Gyraulus kahuica.

Plate 3: Figures 17–19: Ferrissia neozelanica, lateral, ventral and dorsal views. Figures 20, 21: Ferrissia dohrnianus, lateral and dorsal views. Figure 22: Planorbarius corneus. Figures 23, 24: Gyraulus corinna, lateral and dorsal views. Figure 25: Gyraulus kahuica.

19. Large, elongate shells up to 100 mm long with dark brown pericostracum on the outside and a smooth, pearly inner surface. Freshwater mussels. Found in lakes and streams 20
Small pale, rounded shells less than 6 mm long, their inner surfaces not pearly. Pea mussels. Found in lakes, ponds and streams. 23
20. Shells up to 90 mm long with sculpturing continuing onto page 150 the posterior part of the shell as nodules or ridges. Cucumernuio 21
Plate 4: Figures 26–28: Physastra variabilis. Figure 29: Physa sp., latero-ventral view of animal showing digitate mantle margin. Figure 30: Physa sp. Figure 31: Lymnaea stagnalis. Figure 32: Lymnaea columella. Figure 33: Lymnaea truncatula. Figures 34, 35: Lymnaea tomentosa.

Plate 4: Figures 26–28: Physastra variabilis. Figure 29: Physa sp., latero-ventral view of animal showing digitate mantle margin. Figure 30: Physa sp. Figure 31: Lymnaea stagnalis. Figure 32: Lymnaea columella. Figure 33: Lymnaea truncatula. Figures 34, 35: Lymnaea tomentosa.

Shells smooth, up to about 100 mm long Hyridella 22
21. As described above for the genus; up to 70 mm long. Known from North Island localities from south of Auckland to Foxton Cucumerunio websteri websteri (Fig. 36) page 151
As described for the genus but the shell sculpture confined mainly to the beaks. The rest of the shell showing only traces of nodulation. Up to 90 mm long. Known only from localities north of Auckland. Cucumerunio websteri delli (Fig. 37)
22. Shell elongate, narrow, the ventral margin typically sinuate (concave medially), the dorsal margin fairly flat rather than arched. Known from scattered localities throughout New Zealand. Hyridella aucklandica (Fig. 39)
Shell highly variable in shape; ventral margin straight or convex; dorsal margin typically elevated posterior to the beaks. Widely distributed throughout New Zealand. Hyridella menziesi (Fig. 38)
23. Shell very variable in shape, up to 8.2 mm long but generally less than 6 mm. Beaks median; ligament visible externally. Animal with 2 separate siphons and 2 pairs of gills. The commonest sphaeriid clam in New Zealand. Sphaerium novaezelandiae (Figs. 40, 41)
Shell less than 4.5 mm long. Beaks post-median in position. Ligament may be externally visible or invisible. Animal with one (upper) siphon and only one pair of gills. Pisidium 24
24. Shell oval and triangular, the dorsal margin more curved than the ventral margin but not highly so. Ligament not visible externally. Periostracum quite glossy. Sculpture of irregular concentric striae. Pisidium casertanum (Fig. 42)
Shell approaching triangular, and quite high, the dorsal margin slightly angled rather than arched. Sculpture almost absent. Ligament visible externally, Periostracum dull, light brownish. Pisidium hodgkini (Fig. 43)

Notes on Biology, Ecology and Systematics


Five species of Hydrobiidae are known from New Zealand. These include three species of Potamopyrgus, but only one, the ubiquitous P. antipodarum occurs in fresh water. It is widely distributed through the country in almost all kinds of freshwaters except temporary ponds and also inhabits brackish waters. It is highly variable in shell size, shape and ornamentation, occurring in both smooth and spiny forms. Rearing studies (Winterbourn, 1970a) have shown that snails do not necessarily produce young of like shell ornamentation. P. antipodarum also exhibits a considerable degree of variation in radular structure and body pigmentation. It is ovoviviparous and many populations may contain equal numbers of males and females or only occasional males. In populations studied near Palmerston North (Winterbourn, 1970b) young were released throughout the year with peak breeding in spring and summer. page 152
Plate 5: Figure 36: Cucumerunio websteri websteri. Figure 37: Cucumerunio websteri delli. Figure 38: Hyridella menziesi. Figure 39: Hyridella aucklandica. Figures 40, 41: Sphaerium novaezelandiae. Figure 42: Pisidium casertanum. Figure 43: Pisidium hodgkini (l = ligament).

Plate 5: Figure 36: Cucumerunio websteri websteri. Figure 37: Cucumerunio websteri delli. Figure 38: Hyridella menziesi. Figure 39: Hyridella aucklandica. Figures 40, 41: Sphaerium novaezelandiae. Figure 42: Pisidium casertanum. Figure 43: Pisidium hodgkini (l = ligament).

P. pupoides and P. estuarinus are restricted to brackish waters, the latter frequently being abundant in estuaries or on harbour mudflats near river mouths. The shells of both species are very constant in shape, in contrast to P. antipodarum, and never have spines. Both are oviparous and the sexes are normally present in approxi- page 153 mately equal numbers. P. estuarinus cannot always be distinguished from P. antipodarum on the basis of shell characters alone, but it is easily separated on the gross morphology of the female reproductive system.

Paxillostium nanum is a minute gastropod which was recently discovered by Gardner (1970) among dead leaves and debris in hillside seepage in Northland bush areas. The distinctive operculum with its calcareous peg distinguishes it from Potamopyrgus. Like P. antipodarum it is ovoviviparous and all adult specimens examined in May by Gardner contained two embryos, one large and one less developed. Embryos just prior to their release from the brood pouch have more whorls than those of P. antipodarum, i.e. they appear to be released at a later stage of development.

Opacuincola caeca is another minute species which was originally collected from a mile inside George Creek Cave at East Takaka, Nelson, and described by Ponder in 1966. It is blind and non-pigmented with a colourless shell. All these features can be correlated with its subterranean habitat.


Melanopsis trifasciata is the largest freshwater prosobranch in New Zealand. It is a euryhaline species and is found in brackish estuaries and streams as well as freshwater streams throughout the country, although its occurrence is spasmodic. Recently, Bedford, (1971a, b; 1972; in press), has studied osmoregulation in this species. Her results show that it remains active in all salinities from fresh to sea-water and is capable of intracellular isosmotic regulation. The structure and function of the stomach have been described by Morton 1952).


Until very recently the flat, coiled species of Planorbidae found in New Zealand were placed in the genus Planorbis. However, a recent examination of some New Zealand material by D. S. Brown of the British Museum (Natural History) has shown that our snails are typical Gyraulus, another almost cosmopolitan genus (Ponder, pers. comm.). The commonest local species is G. corinna and Ponder (1964) believes that G. kahuica is probably only a subspecies of corinna. Little work has been done on the New Zealand Planorbidae and as no recent systematic studies have been made at the species level this question remains unanswered.

Some information on the biology of G. kahuica is provided by Jonathan (1950) in a report on the life histories of rumen flukes of cattle in New Zealand. She found that this snail acts as the intermediate host of the domestic cattle fluke and also harbours an echinostome cercaria. In the Wellington area, eggs of G. kahuica were laid throughout the year but mainly in spring, so that in December some 90% of the snails present were immature.

page 154

The large red planorbid, Planorbarius corneus known in the United Kingdom as the Great Ramshorn has been introduced to New Zealand mainly in aquaria. In 1968 a large population was flourishing in the warm Waipahihi Stream (temperature about 35°C) near Taupo. It is fairly common in hard waters in the United Kingdom, especially in southern, central and eastern England (Macan, 1949).

Physastra variabilis is an endemic species referred to in much of the early literature under the generic name Isidora, it is notable for its extreme morphological plasticity both between and within populations. Its occurrence is sporadic and large populations seem to be uncommon. In much of the New Zealand literature, references to P. variabilis almost certainly should refer to Physa sp. These misidentifications have occurred because the two species have very similar shells which cannot always be used to distinguish the species. It has not been realised that Physa is very widely distributed and frequently abundant. In fact Physa is far more common than P. variabilis. In some localities Physa seems to have replaced P. variabilis, for example in the Hutt and Heathcote Rivers where specimens of the latter species examined by Dell (1956) were collected, but where now only Physa is found, and in great abundance. P. variabilis is particularly uncommon in the vicinity of towns and in bodies of water influenced by man's activities. By contrast it is regularly found in lakes and ponds in more remote areas, such as south Westland. The only place in which I have seen it coexisting with Physa is in the littoral region of Lake Wanaka, and even there Physa was far more abundant.

A second species, Physastra oconnori is known as a subfossil from the Waikari Moa Swamp, Wanaka (Cumber, 1941). It is larger and has a longer spire and narrower shell than P. variabilis.


There is probably only one species of Physidae in New Zealand. The identity of this snail has yet to be finally confirmed but evidence accumulated by the writer points to it being Physa acuta, a species endemic to the Mediterranean region of Europe. The discrimination of species of Physa has proved to be particularly difficult throughout the world largely because of the high degree of morphological variability found within the genus. Dell (1956) suggested that the species found in New Zealand may be Physa fontinalis, another European species which he suspected could have been introduced originally as aquarium stock. Careful examination of the shells, and anatomical studies I have made on our snails indicate that they are definitely not P. fontinalis, however. Non-morphological evidence also suggesting an affinity with P. acuta is provided by the presence of the New Zealand snails in warm-water streams at temperatures of up to 34°C (Winterbourn, 1968). In the United Kingdom where P. acuta is not common, it is mainly found in warm water in green- page 155 houses and engine ponds (Macan, 1949) and Langford (1971) has recorded it in large numbers in the warm discharge water, cooling ponds and towers of power stations at temperatures greater than 30°C.

Physa is widely distributed in New Zealand and is frequently present in large numbers in ditches, ponds, streams, rivers and in the littoral region of lakes, especially in agricultural and urban areas. As Physa seems to be primarily an air breather (a bubble of air is normally present in the mantle cavity) it is usually found close to the water surface and probably does not inhabit the deeper waters of lakes.


Four species of Lymnaea are now known to be living in New Zealand, the presence of two of them, L. columella and L. truncatula having been recognised only recently (Pullan, 1969; Climo and Pullan, 1972). In the past the generic names Myxas, Succinea and Simlimnaea have been used to describe lymnaeids from New Zealand but now all four species are considered to belong to the cosmopolitan genus Lymnaea

L. tomentosa is the only endemic species and it also occurs in Australia. It is morphologically highly variable and much of this variation has been shown to be environmentally induced (Boray and McMichael, (1961). L. tomentosa, L. columella and L. truncatula all act as intermediate hosts of the liver fluke Fasciola hepatica and because of this the former snail species has been the subject of several ecological studies in Australia (Boray, 1964a, b; Boray and McMichael, 1961; Lynch, 1965, 1966). A subspecies, L. tomentosa hamiltoni is known from the Waikari Moa Swamp (Dell, 1956).

L. columella occurs widely in North, Central and South America and may have been introduced to New Zealand with tropical fish, perhaps in the 1930′s (Pullan, 1969). Before 1969 it was not realised that L. columella was present in New Zealand and undoubtedly in most cases it was thought to be L. tomentosa. Both these species are widely distributed in this country although L. columella does not seem to be common on the east coast of the North Island and has not been recorded south of Canterbury (Climo, Pullan and Mansfield, 1972). One of the important habitats of both species is freshwater seepage and L. columella is frequently found very close to, or on, the surface of the water. It has also been found in warm-water streams and thermal seepage (misidentified as L. tomentosa) in the Rotorua-Taupo area at temperatures up to 35°C (Winterbourn, 1968).

The presence of L. truncatula in New Zealand was first recognised by Climo and Pullan (1972), but specimens have been known for over 80 years under the name of L. alfredi. The earliest specimens collected came from the Hooker and Tasman Valleys in Canterbury but the species is apparently absent from the area now and is only page 156 known to be living in a few parts of Nelson and Marlborough. In Europe, L. truncatula is the main intermediate host of liver fluke and according to Macan (1949) is commonly found at the edge of ditches, rivers and small streams as well as in damp places in fields.

L. stagnalis has also been introduced from Europe where it is often common in both lakes and rivers. It has an irregular distribution in New Zealand and is very common in some of the Rotorua Lakes (e.g. Tarawera). It is probably the commonest snail sold locally for home aquaria.


Latia neritoides is generally considered to be one of the most primitive basommatophorans and somewhat related to the South American Chilina (Burch and Patterson, 1963). It possesses a haploid (n) chromosome number of 18 unlike all Ancylidae (the major family of freshwater limpets) where n = 15 or 17.

L. neritoidex appears to be restricted to the North Island where it occurs on and under stable stones in streams. Its distribution is very patchy, but occasionally large, localised populations occur as in the Waitakere Stream near Auckland and the Makahika Stream near Levin. Perhaps the most interesting feature of L. neritoides is that apart from glow-worms, it is the only luminous, freshwater animal known. The luminous secretion of L. neritoides is green and is secreted from the mantle groove when the animal is disturbed (Bowden, 1950). Light is produced by the luciferin-luciferase reaction which is brought about when a luminescent substrate luciferin is catalysed by an enzyme luciferase. The structure of the radula and reproductive tract have been discussed by Hubendick (1962).


Two small freshwater limpets formerly placed in the genus Gundlachia are now considered to belong to Ferrissia, a genus characterised by having the shell apex ribbed (Hubendick, 1967). In his revision of the Australian, Pacific and Neotropical Ancylidae, Hubendick has given names to what he calls form-groups rather than biological species as his study was based primarily on shell material. These form-groups are distinguished from each other by morphological dissimilarities and effectively represent (morpho-) species.

Both species occur in the North and South Islands, although Hubendick (1967) records F. neozelanica only from the South Island and F. dohrnianus only from the North. The latter species is found under stones in streams and the former on weeds in ponds and streams.

page 157


The New Zealand Sphaeriidae are a poorly known group whose three species are difficult to distinguish using shell characters alone. Formerly they were known under the generic name Corneocyclas but now two genera Sphaerium and Pisidium are recognised. Two of the three species are endemic and the third P. casertanum has a cosmopolitan distribution. According to Kuiper (1966), all three species are common in a variety of habitats in many parts of New Zealand and are often found living together. They may inhabit weed (e.g. Elodea canadensis in farm ponds) and are frequently found burrowing in the sand of stream beds. S. novaezelandiae is probably the commonest species. Sphaeriids are remarkably active bivalves, they are hermaphroditic and incubate their young in their gills.


At various times the Australasian freshwater mussels have been included in the families Unionidae, Mutelidae and Hyriidae. The use of Hyriidae here follows Williams (1968), this family comprising the Australasian and South American species.

Hyridella menziesi is the commonest species in New Zealand. Its shell shape is highly variable and numerous ecological ‘forms’ occur. H. aucklandica is known from scattered localities in both islands. Its specific status is still in doubt, however, and Ponder (1964) has sugested that it may be merely another ecotype of H. menziesi. The interesting life history of Hyridella has been described by Percival (1931) who found that the tiny glochidia larvae were produced from the end of November to the end of January in western Canterbury lakes. After being released from the females they attached themselves to the pectoral fins, head and mouth of small Galaxias brevipinnis and Gobiomorphus gobioides and later dropped off to begin an independent life.

Cucumerunio has been collected from the North Island only and is believed to be a recent arrival from Australia (McMichael, 1958).


I would like to thank Dr. George Gibbs who encouraged me to write this key and Dr. Winston Ponder for criticising the manuscript and making a number of useful suggestions for its improvement.

Bibliography of recent papers relating to the New Zealand freshwater Mollusca

(Names in brackets after a reference indicate species referred to if this is not clear from the title).

Bedford, J. J. 1971a: Osmoregulation in Melanopsis trifasciata Gray 1843. page 158 III — The intracellular nitrogenous compounds. Comp. Biochem. Physiol, 40A: 899–910.

——, 1971b: IV — The possible control of intracellular isosmotic regulation. Comp. Biochem. Physiol. 40A: 1015–27.

——, (in press): I —The environmental range. N.Z. Jl. mar. Freshwat, Res.

——, 1972: II — The osmotic pressure and the principal ions of the hemocoelic fluid. Physiol. Zool. 45: 261–69.

Boray, J. C. 1964a: Studies on the ecology of Lymnaea tomentosa, the intermediate host of Fasciola hepatica. I History, geographical distribution, and environment. Aust. J. Zool. 12: 217–30.

——, 1964b: II. The sexual behaviour of Lymnaea tomentosa. Aust J. Zool. 12: 231–7.

Boray, J. C. and McMichael, D. F. 1961: The identity of the Australian, Lymnaeid snail host of Fasciola hepatica and its response to environment. Aust. J. mar. Freshw. Res. 12: 150–63. (Lymnaea tomentosa)

Bowden, B. J. 1950: Some observations on a luminescent freshwater limpet from New Zealand. Biol. Bull. 99: 373–80 (Latia neritoides)

Burch, J. B. and Patterson, C. M. 1963: Cytotaxonomic studies of freshwater limpets (Gastropoda: Basommatophora). II The New Zealand river limpet, Latia neritoides. Malacologia I: 313–19.

Climo, F. and Pullan, N. B. 1972: A taxonomic review of the family Lymnaeidae (Mollusca: Gastropoda) in New Zealand. J. roy Soc. N.Z. 2: 5–13.

Cumber, R. A. 1941: Two new species of freshwater molluscs from the Waikari Moa Swamp. Rec. Cant. Mus. 4: 359–60. (Physastra oconnori, Lymnaea tomentosa hamiltoni)

Dell, R. K. 1953: The freshwater Mollusca of New Zealand. Part I — the genus Hyridella. Trans. roy. Soc. N.Z. 81: 221–37.

——, 1956: Part II — The species previously assigned to the genera Limnaea and Myxas. Part III — The genus Physastra. Trans. roy. Soc. N.Z. 84: 71–90.

——, 1969; Notes on the freshwater Mollusca. In: The Natural History of Canterbury, Knox, G. A., ed. A. H. & A. W. Reed, Wellington, p.487–89.

Finlay, H. J. and Laws, C. R. 1931: A second species of Planorbis from New Zealand. Trans. N.Z. Inst. 62: 23–25. (Gyraulus kahuica).

Gardner, N. W. 1970: A new genus and species of freshwater snail (Hydrobiidae) from northern New Zealand. Trans. R. Soc. N.Z. Biol. Sciences 12: 181–84. (Paxillostium nanum)

Hubendick, B. 1948: Studies on Bulinus. Arkiv. f. Zool. 49: 1–63. (Physastra variabilis)

——, 1951: Recent Lymnaeidae. Their variation, morphology, taxonomy, nomenclature and distribution. K. svenska Vetenskakad Handl. 3: 1–223.

——, 1962: Studies on Acroloxus (Moll. Basomm.). Göteborgs Kungl. Vetensl. Vitterh. — Samh. Handl. Sjattee Följden Ser. B. 9: 1–68 (Latia neritoides)

——, 1967: Studies on Ancylidae. The Australian, Pacific and Neotropical formgroups. Acia Reg. Soc. Scient. Litt. Gothoburgensis. Zoologica 1: 1–52. (Ferrissia neozelanica, F. dohrnianus)

Jonathan, S. R. 1950: The life history of the rumen flukes of cattle in New Zealand. Aust. Vet. J. 26: 149–51. (Gyraulus kahuica)

Kuiper, J. G. J. 1966: Critical revision of the New Zealand sphaeriid clams in the Dominion Museum, Wellington. Rec. Dominion Mus. 5: 147–62.

Langford, T. E. 1971: The biological assessment of thermal effects in some British rivers. Paper presented to the C.E.R.L. Symposium: Freshwater Biology and Electrical Power Generation. (Physa acuta)

Lynch, J. J. 1965: The ecology of Lymnaea tomentosa (Pfeiffer, 1855) in South Australia. Aust. J. Zool. 13: 461–73.

——, 1966: The physical environment and aestivation in Lymnaea tomentosa (Pfeiffer). Aust. J. Zool. 14: 65–71.

Macan, T. T. 1949: A key to the British fresh- and brackish-water gastropods with notes on their ecology. Freshwater Biological Association Sci. Pub. 13. 45pp. (Physa acuta, Planorbarius corneus)

McMichael, D. F. 1958: The nature and origin of the New Zealand freshwater mussel fauna. Trans. R. Soc. N.Z. 85: 427–32.

McMichael, D. F. and Hiscock, I. D. 1958: A monograph of the freshwater mussels (Mollusca: Pelecypoda) of the Australian region. Aust. J. mar. Freshw. Res. 9: 372–508.

Morton, J. E. 1952: The role of the crystalline style. Proc. malac. Soc. Lond. 29: 85–92. (Melanopsis trifasciata).

Pereival, E. 1931: A note on the life history of Diplodon lutulentus Gould. Trans. N.Z. Inst. 62: 86–91 (Hyridella menziesi)

Ponder, W. F. 1964: The freshwater Mollusca of New Zealand. Tane 10: 12–35.

——, 1966: On a subterranean snail and a tornid from New Zealand. J. malacol. Soc. Australia 10: 35–40 (Opacuincola caeca)

Pullan, N. B. 1969: The first record in New Zealand of Lymnaea columella Say (Mollusca: Gastropoda) an intermediate host of the liver-fluke Fasciola hepatica L. N. Z. Vet. J. 17: 255–6.

Pullan, N. B., Climo, F. M. and Mansfield, C. B. 1972: Studies on the distribution and ecology of the family Lymnaeidae (Mollusc: Gastropoda) in New Zealand, J. Roy. Sac. N.Z. 2: 393–405.

Williams, W. D. 1968: Australian freshwater life. The invertebrates of Australian inland waters. Sun Books, Melbourne, 262pp. (Hyriidae)

Winterbourn, M. J. 1968: The faunas of thermal waters in New Zealand. Tuatara 16: 111–22. (Physa sp., Lymnaea columella)

——. 1969: Water temperature as a factor limiting the distribution of Potamopyrgus antipodum (Gastropoda-Prosobranchia) in the New Zealand thermal region. N.Z. Jl. mar. Freshwal. Res. 3: 453–58.

——, 1970b: The New Zealand species of Potamopyrgus (Gastropoda: Hydrobiidae). Malacologia 10: 283–321.

——. 1970b: Population studies on the New Zealand freshwater gastropod. Potamopyrgus antipodarum (Gray). Proc. malac. Soc. Lond. 39: 139–49.

——, 1972: Morphological variation of Potamopyrgus jenkinsi (Smith) from England and a comparison with the New Zealand species, Potamopyrgus antipodarum (Gray). Proc. malac. Sac. Lond. 40: 133–45.

*** Inhabitants of brackish water only

* Subfossil species

** Introduced species