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Potamopyrgus pupoides Hutton, 1882 Pl. 1, fig. F Hutton, 1882. New Zealand Journal of Science, 1: 41. Type material. Lectotype (designated by Winterbourn 1970: 286), CMNZ M9930 [ex ZS 250a], and paralectotypes, CMNZ M334 (40), CMNZ M9931 [ex ZS 250a] (5), (dry shells). Label details. CMNZ M334 —‘ Potamopygus pupoides Hutton, R. Heathcote, Christcurch’, pillbox label in Hutton’s handwriting; CMNZ M9930 and M9931—‘ Type, Potamopygus spelaeus pupoides Hutton, loc. Heathcote River, ZS 250a’. Type locality. ‘brackish water of the Heathcote estuary’ (Hutton 1882b: 41); ‘Estuary of the Avon and Heathcote rivers, in brackish water’ (Hutton 1882e: 146). Previous illustrations of type material. Hutton (1882e: pl. 1, fig. D, H). Remarks. Hutton submitted a description of this species to the Transactions and Proceedings of the New Zealand Institute issue for 1881, but publication was delayed until May 1882 (Hutton 1882e: 146), and was preempted by a brief description in an account of ‘Recent Papers on Mollusca (by Prof. F. W. Hutton)’ in the New Zealand Journal of Science issue of February 1882 (Hutton 1882b: 41). Potamopyrgus pupoides Hutton, 1882 is the type species of Halopyrgus Haase, 2008. It inhabits brackish water only (Hutton 1882e: 146, Haase 2008: 108). Current taxonomy. Halopyrgus pupoides (Hutton, 1882) — Haase (2008: 108). Distribution. New Zealand; brackish water in estuaries around New Zealand (Haase 2008: 109)., Published as part of Brook, Fred J., Kennedy, Martyn, King, Tania M., Ridden, Johnathon, Shaw, Matthew D. & Spencer, Hamish G., 2020, Catalogue of New Zealand land, freshwater and estuarine molluscan taxa named by Frederick Wollaston Hutton between 1879 and 1904, pp. 1-73 in Zootaxa 4865 (1) on page 14, DOI: 10.11646/zootaxa.4865.1.1, http://zenodo.org/record/4428428, {"references":["Winterbourn, M. (1970) The New Zealand species of Potamopyrgus (Gastropoda: Hydrobiidae). Malacologia, 10, 283 - 321.","Hutton, F. W. (1882 b) General Notes. Recent papers on Mollusca (By Prof. F. W. Hutton). On the Hydrobiinae of New Zealand. The New Zealand Journal of Science 1 (1), 41. [February]","Hutton, F. W. (1882 e) On the New Zealand Hydrobiinae. Transactions and Proceedings of the New Zealand Institute, 14, 143 - 146. [May]","Haase, M. (2008) The radiation of hydrobiid gastropods in New Zealand: a revision including the description of new species based on morphology and mtDNA sequence information. Systematics and Biodiversity, 6 (1), 99 - 159. https: // doi. org / 10.1017 / s 1477200007002630"]}

Anticholinesterase insecticides constitute a major portion of modern synthetic pesticides and the assessment of cholinesterase (ChE) inhibition is widely used as a specific biomarker for evaluating the exposure of non-target organisms to these pollutants. However, most studies on this biomarker were developed on vertebrates and among invertebrates, gastropod mollusks are rarely used. However, gastropods are important members of aquatic habitats and therefore present a high ecological relevance for freshwater ecosystems. In this context, ChE activities were characterized in two freshwater gastropod mollusks, Potamopyrgus antipodarum and Valvata piscinalis, in order to ascertain their value as sentinel species. Firstly, characterization of ChE activities was performed using different substrates (acetylcholine iodide, butyrylcholine iodide and propionylcholine iodide) and specific inhibitors (eserine, iso-OMPA and BW284c51). Secondly, in vivo effect of a widely used organophosphate insecticide, chlorpyrifos, was tested on ChE activity in both species. Results suggested that P. antipodarum possesses two isoforms of cholinesterases, one isoform which properties are intermediate between an acetyl and a propionyl ChE, and one minor isoform which correspond to a butyryl ChE, while V. piscinalis seems to possess only one isoform which displays typical properties of an acetyl ChE. Chlorpyrifos induced no effect on V. piscinalis ChE. In contrast, P. antipodarum activity was significantly decreased by environmental realistic chlorpyrifos concentrations (2.86 and 14.2 nM) after seven days of contact. The present study suggests that P. antipodarum may be employed as a biological indicator for assessing pesticide contamination.

Potamopyrgus antipodarum (Gray, 1843) Description Collado (2014). Distribution Native to New Zealand and its adjacent islands and invasive in North America and Europe (Winterbourn 1970; Kerans et al. 2005). In Chile this species has been recorded in the city of Santiago in the Parque O’ Higgins (33°28 ′ S, 70°39 ′ W), and Estero La Dehesa (33°22 ′ S, 70°15 ʹ W), and in the city of Salamanca, central Chile, in the Chalinga River (31°46 ′ S, 70°59 ′ W) and in the Estero Consuelo (31°46 ′ S, 70°37 ʹ W) (Collado 2014). Possible mechanism of introduction/Status Unknown/established (Collado 2014). Remarks Generalist species, feeding on aquatic plants, green algae and detritus (Haynes and Taylor 1984). Invasive, ovoviviparous species. EA, I., Published as part of Araya, Juan Francisco, 2015, Current status of the non-indigenous molluscs in Chile, with the first record of Otala punctata (Müller, 1774) (Gastropoda: Helicidae) in the country and new records for Cornu aspersum (Müller, 1774) and Deroceras laeve (Müller, 1774), pp. 1731-1761 in Journal of Natural History 49 (29) on page 1738, DOI: 10.1080/00222933.2015.1006703, http://zenodo.org/record/3997965, {"references":["Gray JE. 1843. Catalogue of the species of Mollusca and their shells, which have hitherto been recorded as found at New Zealand, with the description of some lately discovered species. In: Dieffenbach E, editor. Travels in New Zealand; with contributions to the geography, geology, botany, and natural history of that country. Vol. 2. London: John Murray; pp. 228 - 265; iv + 392 p.","Collado GA. 2014. Out of New Zealand: molecular identification of the highly invasive freshwater mollusk Potamopyrgus antipodarum (Gray, 1843) in South America. Zool Stud. 53: 70.","Winterbourn MJ. 1970. The New Zealand species of Potamopyrgus (Gastropoda: Hydrobiidae). Malacologia. 10: 283 - 321.","Kerans BL, Dybdahl MF, Gangloff MM, Jannot JE. 2005. Potamopyrgus antipodarum: distribution, density, and effects on native macroinvertebrate assemblages in the Greater Yellowstone Ecosystem. J N Am Benthol Soc. 24: 123 - 138.","Haynes A, Taylor BJR. 1984. Food finding and food preference in Potamopyrgus jenkinsi (E. A. Smith) (Gastropoda: Prosobranchia). Arch Hydrobiol. 100: 479 - 491."]}

Studies documenting phenotypic variation among populations show that ecological performance in one activity is sometimes traded off against another. Identifying environment-specific costs and benefits associated with performance trade-offs is fundamental to knowing how conflicting selection pressures shape phenotype-environment matching in populations. We studied phenotypic variation in shell armature (spininess) of the New Zealand mudsnail, Potamopyrgus antipodarum (Gray), and explored how this variability relates to performance trade-offs between flow resistance and predator deterrence. Smooth- and spiny-shell morphotypes exist in populations in New Zealand streams and lakes, but the patterns and correlates of spatial variation of these phenotypes, and the possible hydrodynamical constraints and antipredatory benefits associated with spiny shell armature, are unknown. Samples from 11 rivers and nine lakes on the South Island showed that, on average, nearly 70% of snails in streams were smooth-shelled, whereas80% of snails in lakes were spiny, suggesting dissimilar selective pressures between habitats. A laboratory flume experiment revealed that spines collected seston (i.e., suspended algae) at current speeds40 cm/s, making spiny morphs more prone to flow-induced dislodgment than smooth morphs. However, a fish feeding experiment showed that one benefit of spines on shells was a decrease in predation risk from the common bully (Gobiomorphus cotidianus), a widespread predator of mudsnails in both streams and lakes. All snails egested by bullies were dead, further suggesting that these fishes may exert strong lethal effects on mudsnail populations in nature. Spine expression in lakes also appeared to be temperature related. We conclude that functional trade-offs between risk of flow-induced dislodgment and risk of fish predation affect shell armature frequencies of Potamopyrgus in freshwater habitats.

In the context of increasing freshwater pollution, the impact on life-traits (survival, growth and fecundity) and locomotion of Potamopyrgus antipodarum of a 5-week field-concentration exposure to the cyanobacterial toxin microcystin-LR and the triazine herbicide, atrazine was studied. Whatever the age of exposed snails (juveniles, subadults, adults), microcystin-LR induced a decrease in survival, growth and fecundity but had no effect on locomotion. Atrazine induced a decrease in locomotory activity but had no significant effect on the life-traits. These results are discussed in terms of consequences to field populations.

Patch selection for cobbles covered by different food types, with and without deposited sediment, by two common New Zealand stream invertebrates, the snail Potamopyrgus antipodarum (Hydrobiidae) and the mayfly Deleatidium sp. (Leptophlebiidae), was quantified. Each taxa was exposed to cobbles covered by (1) filamentous green algae (FGA) or diatoms, and (2) diatoms or heterotrophic biofilms. Two cobbles of each food type were used in each trial, one of which was contaminated by deposited sediment. All cobbles were embedded in plaster in small basins to prevent animals hiding under them, and a known number of animals placed into each basin. The location of each animal was recorded over time, with some observations being made during darkness to see whether this influenced animal movement. More Potamopyrgus were found on cobbles covered by FGA than cobbles covered by diatoms. Sediment-contaminated cobbles covered with FGA also supported more snails than uncontaminated cobbles covered with diatoms. More Potamopyrgus were found on cobbles covered by diatoms than biofilms, and sediment reduced their preference for both these foods. More Deleatidium nymphs were found on diatom-covered cobbles than FGA-covered cobbles. Sediment reduced the preference of Deleatidium for diatoms, but more animals were found on cobbles with sediment-contaminated diatoms than uncontaminated FGA. Patch selection was similar between cobbles covered by either diatoms or biofilms, but sediment reduced the preference of both these foods to Deleatidium. More Deleatidium were recorded on bare plaster during darkness, suggesting they were more mobile at night and searching for new habitats. These results help explain the common occurrence of Potamopyrgus in streams draining developed catchments where FGA blooms and deposited sediment are common, and of Deleatidium in streams draining less developed catchments where FGA and deposited sediment are uncommon.

Although parental care occurs in most phyla encompassing a wide array of forms, little is known about its evolution in invertebrates. Two types of egg capsules have been known among ovoviviparous New Zealand hydrobiid gastropods, elastic capsules and simple membranes. Based on a phylogenetic analysis using two mtDNA sequence fragments, I asked whether the second state was derived from the first or whether brooding had multiple origins. The evolution of ovoviviparity was also investigated in the context of habitat transition between brackish and freshwater. Maximum parsimony and Markov chain models of character state transformations in a maximum likelihood framework suggested that hydrobiids have invaded freshwater three times independently. Two of these invasions were followed by the evolution of ovoviviparity, probably in adaptation to changing water levels during periods of irregular precipitation. The syntopy of two congeneric species, one oviparous and the other one brooding, indicated that the transition between reproductive modes must have occurred rapidly.

1. Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments. 2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers. 3. The selectivity index Q, which provides information on the uptake ratio of 13C to 15N, showed a significant time effect for both grazer species and a significant difference between single- and mixed-grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity. 4. Our results indicate a shift in feeding preferences related to between-species competition and a potential divergence of trophic niches when species coexist.

The structure of gastropod communities was examined from January to June 1999 in four sites of the streams of Mont Saint-Michel Bay along a gradient of salinity, and the occurrence of larval trematodes infecting snails was studied. Abundance and species richness of gastropods increased from polyhaline (95 snails, 1 species) to oligohaline waters (6672 snails, 6 species). Whatever the salinity, the most abundant species was Potamopyrgus antipodarum, an invasive non-indigenous species that represented 80% of the gastropods. Only one male was found in P. antipodarum populations suggesting a predominantly parthenogenetic mode of reproduction. Among 7218 gastropods collected, 1.2% were infected by larval trematodes: 5 species in Lymnaea peregra (4.4%), 4 species in Planorbis planorbis (12.0%), one echinostome in Physa acuta (0.2%), and a new species of Sanguinicola in P. antipodarum (0.5%). This is the first record of infected P. antipodarum in Europe. No parasites were found in polyhaline waters. The prevalence per host population varied from 0 to 100% depending on time of collection, salinity and host species. In the lowest-salinity site, abundance of gastropods and prevalence of trematodes were negatively correlated. The dominance of P. antipodarum in the gastropod communities is discussed in relation with euryhalinity, parthenogenesis and weak rate of parasitism.

The effects of spatial and temporal changes in water velocity on the introduced freshwater snail Potamopyrgus autipodarum (Gray) (Gastropoda: Hydrobiidae) were studied in an artificial stream and in Main Creek, Victoria, Australia. The water velocity at which P. antipodarum became dislodged in the artificial stream was in agreement with their distribution in Main Creek. In Main Creek the density of P. antipodarum on a standard subs trate (half bricks) was negatively correlated with water velocity. However, no evidence was found that increases in water velocity associated with floods affect the densities of P. antipodarum.

In 1991, the hydrobiid snail Potamopyrgus antipodarum (Gray 1843), native to New Zealand, was found 1 km offshore Wilson, New York, in Lake Ontario. This is the first known occurrence of the snail in eastern North America. Densities of P. antipodarum have increased since its discovery, and the snail is expected to spread quickly throughout the Great Lakes area. The biofouling potential of P. antipodarum is probably low; however, its most serious threat may be resource competition with native molluscs. This species was probably introduced in ballast water from transoceanic vessels, thus increasing the list of nonindigenous aquatic organisms introduced into the Great Lakes since the 1800s to 140 different organisms. The risk of other species invasions into the Great Lakes is still possible, despite the now mandatory ballast water regulations.

Key to trematodes infecting Potamopyrgus antipodarum as first intermediate host [Species number in brackets preceding name matches numbering in Fig. 1 and Table 1, and the ordering in the species accounts section.] 1. Lacking daughter parthenitae (sporocysts or rediae), free embryos appear to develop directly to over 100 spherical metacercariae that fill much of visceral mass................................................. [13] Microphallus sp. ���livelyi��� - With parthenitae...................................................................................... 2 2. Cercariae lacking tail, with oral stylet.......................................... [15] Acaudate xiphidiocercaria sp. I - Cercariae with tail (small cup-like, simple, forked, finned or bristled); with or without stylet.......................... 3 3 Tail small and cup-like (not more than 2 x long as wide); stylet with two anterior points���........[11, 12] Coitocaecum spp. - Tail elongate (e.g.,> 3 x long as wide); if stylet present, lacking two anterior points.................................. 4 4 Tail forked........................................................................................... 5 - Tail not-forked........................................................................................ 7 5 Tail stem and furcae each about same length as body............................................ [1] Apatemon sp. I - Tail stem at least 2 x body length; caudal furcae short (much less than 1 / 2 stem length).................. (aporocotylids) 6 6 Cercaria smaller than 6 b (body 130 long, tail stem> 200 long); sporocysts elongate................ [3] Aporocotylid sp. II 7 Cercaria with oral stylet (may be minute & non-descript���see Plagiorchioid sp. I).................................. 8 - Cercaria lacking oral stylet............................................................................. 11 8 With virgula organ (sack-like organ in posterior oral sucker).................................................... 9 - Lacking virgula organ................................................................................. 10 9 Cercaria smaller than 9 b (body 130 long); virgule organ longer than wide, clearly bipartite............ [17] Virgulate sp. II 10 With prominent ventral sucker, Y-shaped bladder, small bullet-shaped stylet (less than 1 / 5 oral sucker length), and obscuring cystogenous glands throughout most of body.............................................. [18] Plagiorchioid sp. I - Lacking ventral sucker, with elongate stylet (> �� oral sucker length); body translucent with prominent penetration glands just posterior to equator............................................................[14] Microphallus sp. ���poulini��� 11 With pigmented eyespots.............................................................................. 12 - Lacking pigmented eyespots............................................................................ 17 12 With ventral sucker................................................................................... 13 - Lacking ventral sucker................................................................................ 15 13 Tail simple, not ornate............................................................. [19] Gymnocephalous sp. I - Tail with lateral bristles................................................................... (lepocreadiids) 14 14 With 4 pairs of penetration glands................................................... [8] Stegodexamine anguillae - With 6 pairs of penetration glands........................................................ [9] Lepocreadiid sp. II 15 Lacking dorso-ventral tail fin; sometimes with medial eye....................................[5, 6] Notocotylus spp. - With dorso-ventral tail fin.............................................................................. 16 16 With penetration glands (gland bodies just pre-equator and gland ducts empty at anterior oral sucker); lacking longitudinal pig- ment bands..................................................................... [10] Telogaster opisthorchis - Lacking penetration glands; with two longitudinal pigment bands........................... [7] Pronocephaloid sp. IV 17 Lacking ventral sucker; tail simple; body filled with opaque cystogenous glands (white with reflected light); prominent lateral arms of excretory system connect anteriorly; smaller than 17 b (body length ~ 500)................[4] Pronocephaloid sp. I - With ventral sucker; tail with dorso-ventral fin; larger than 17 a (body length ~ 1000)���......... [20] Gymnocephalous sp. II, Published as part of Hechinger, Ryan F., 2012, Faunal survey and identification key for the trematodes (Platyhelminthes: Digenea) infecting Potamopyrgus antipodarum (Gastropoda: Hydrobiidae) as first intermediate host, pp. 1-27 in Zootaxa 3418 on pages 5-6, DOI: 10.5281/zenodo.210378

Evidence for the influence of food type and heavy metals on shell growth and fertility is presented for a freshwater population of the snail P. jenkinsi. When fed an excess of lettuce or lamb heart (protein source), growth rates were higher for lettuce. Highest growth rates occurred at a diet of lettuce plus lamb heart. Fertility was favoured by a diet of lamb heart. When fed an excess of lettuce, the EC50 growth values were 16 µg Cd l−1, 13 µg Cu l−1, and 103 µg Zn l−1 in lake water; snail fertility was inhibited at 25 µg Cd l−1 and 30 µg Cu l−1. A diet of lake detritus spiked with Cd or Cu resulted in a decrease of approximately 50% in growth rates, when compared with growth on non-spiked detritus. Spiked detritus lost metals into lake water. Food type positively interacted with metal stress, both for growth rate and fertility. The assessment of inhibitory effects of detritus contaminated either in the field or, notably, by spiking, and serving as food source for deposit feeders is hampered by sampling problems in the field and by redistribution processes of pollutants between particles and water in laboratory-scale experiments.

The upper thermal tolerances of 12 New Zealand freshwater invertebrate taxa were compared using a laboratory lethality testing protocol. Temperatures that were lethal to 50% of the test organisms (LT50S), following acclimation to 15°C, generally declined over the 4 day period of the tests. LT50 values after 48 and 96 h exposure ranged from 24.5 to > 34°C and 22.6 to 32.6°C, respectively, indicating that temperatures that occur in summer in many NZ streams and rivers may limit the distribution and abundance of some of these invertebrate species. Larval insects included both the most sensitive species (a plecopteran and two Ephemeroptera) and the most tolerant (the larvae of the elmid beetle Hydora sp.) in this study. The two molluscs studied (Potamopyrgus anti- podarum (Prosobranchia: Hydrobiidae) and Sphaerium novaezelandiae (Bivalvia: Sphaeriidae)) showed high thermal tolerance, whilst two crustaceans {Paratya curvirostris (Atyidae) and Paracalliope fluviatilis (Eusiridae)) were moder- ately tolerant. The effect of a higher acclimation temperature (20°C) on thermal tolerance was also investigated for the three most sensitive species. This appeared to increase the thermal tolerance of the two Ephemeroptera {Deleatidium spp. and

The composition of the hydrobiid fauna in a coastal water of the southern Baltic was studied in 1990/91 at three stations with different sediment characteristics (grain size, organic content). Four species were found (Hydrobia ventrosa, H. ulvae, H. neglecta and Potamopyrgus jenkinsi). H. ventrosa was dominant at all stations. The mean hydrobiid abundances were 4,000 (stn. C), 18,000 (stn. B) and 40,000 (stn. A) ind./m2 respectively. Abundance was found to correlate with the organic content of the sediment. The reproduction and growth of H. ventrosa was studied. Two reproduction phases were observed, one in summer and the other in late autumn. The autumn reproduction peaks were staggered owing to the different growth rates at the various stations. Possible correlations between the differences in shell size of H. ventrosa at the various stations and both sediment characteristics and abundance are discussed.

We studied herbivory and grazer performance (i.e., fitness correlates) for the hydrobiid snail Potamopyrgus antipodarum, the leptophlebiid mayfly Deleatidium spp., and the conoesucid caddisfly Pycnocentrodes aeris, common, co-occurring algivores in many New Zealand streams. Grazing effects and costs of coexisting differed among these taxa reared at ambient densities in different combinations in microcosms with algal food conditions (on clay tiles) characteristic of heavily grazed streams. The prostrate diatoms Staurosirella leptostauron, Cymbella novazealandia, and Achnanthidium minutissimum were the dominant algal species on pre- and post-grazed tiles. The relative abundance of erect physiognomic forms, dominated by Synedra ulna and Fragilaria vaucheriae, were 2–3× higher in ungrazed controls and in snail alone treatments than in other grazer treatments. The green filamentous algae Mougeotia sp. and Stigeoclonium lubricum, and the cyanophyte Merismopedia glauca were present only in ungrazed controls. Grazers significantly reduced algal community biomass in treatments by 26–52% relative to controls, except snails alone. Snails (15–30%) burrowed into surrounding sand substrates, dampening their grazing impact on tiles. Caddisflies were more effective than mayflies or snails at removing algae because of higher foraging rates, a larger body size, and an abrasive sand-grained case. Algal biomass reductions did not affect grazer growth. However, pre-pupation rates of caddisflies and emergence rates of subimago mayflies were significantly higher in caddisfly-alone and mayfly-alone treatments, respectively, than in combined-species treatments. These results imply that a limited periphytic food supply ( < 0.3 mg AFDM cm−2) even over a relatively brief period ( ≤ 16 d) may have population-scale consequences for co-existing P. aeris and Deleatidium spp.

Parasitism often influences the phenotype of individuals. Many of the resulting changes are due to changes in resource allocation that come with infection. Here we examine the effect of a trematode parasite on the shape and defence morphology of a New Zealand freshwater snail, Potamopyrgus antipodarum. The trematode Microphallus sp. asexually produces hundreds of metacercarial cysts in the snail. The length, width and 2-dimensional area of each snail were measured. Snails were also assessed for their degree of spininess. Snails were dissected to determine gender, brooding condition and parasitism. Snails infected with Microphallus sp. were found to be significantly less spiny than uninfected snails. Microphallus-infected snails were also found to have a significantly greater width to length ratio at larger sizes than their uninfected counterparts. These trends could be explained in at least 3 ways. (1) Infection causes the snails to not produce spines and to become wider. (2) Spiny and narrower snails are more likely to die when they become infected. (3) Spiny and narrower snails are more resistant to infection. The changes in phenotype observed are unlikely to be adaptive for either the host or parasite and probably represent physiological by-products of the host-parasite relationship.

Populations of coexisting and of allopatrically occurring species of hydrobiid snails (Hydrobia ulvae, H. neglecta, H. ventrosa and Potamopyrgus jenkinsi) have been studied in 90 localities within three different areas. When H. ventrosa coexists with H. ulvae they show character displacement, i.e., the average body size of the former is smaller and that of the latter is larger. When these species live alone they are of approximately the same size. It is shown here that the size ratio between the coexisting species usually found (1.3-1.5) allows stable coexistence based on food praticles size selectivity alone. Variation in the degree of character displacement from locality to locality is explained by different degrees of genetical isolation of the populations. Coexisting H. ventrosa and H. ulvae have shorter, more well-defined periods of reproduction than they do when they occur alone. H. neglecta is larger than coexisting H. ventrosa and smaller than coexisting H. ulvae. Due to the patchy distribution and the fluctuating populations of this species, and due to the fact that pure H. neglecta populations are rare, data on this species are difficult to interpret. Potamopyrgus jenkinsi shows a different food particle size selection than the Hydrobia spp. of identical sizes. Competitive interactions between P. jenkinsi and coexisting Hydrobia spp. are therefore probably weak. In accordance with this, P. jenkinsi does not show character displacement when coexisting with, e.g., H. ventrosa.The fact that the major study area, the Limfjord, is only 150 years old as a marine habitat as well as various more recent man-made changes of the coast line allow estimates of the time scale of the microevolutionary changes which lead to character displacement.

The four species of Hydrobiid mudsnails found in Danish brackish water habitats are ranked with respect to reproductive effort. The biology of the species indicate that Hydrobia neglecta and Potamopyrgus jenkinsi, showing the highest reproductive effort are also more r-selected than the other species, H. ventrosa and H. ulvae.

Summary Figures are presented for the proportions of the sexes and shell types in collections of the fresh water prosobranch Potamopyrgus from area of Australia. Findings are compared with those from populations in New Zealand. N.B. Representative material from these collections has been deposited in the Australian Museum, Sydney, and from the Victorian localities, also in the National Museum of Victoria, Melbourne.

The distribution of the mud snails Hydrobia ventrosa (Montagu), H. neglecta Muus, and Potamopyrgus jenkinsi (Smith) was studied in the Kysing Fjord estuary, Denmark, from November 1977 to February 1979. The hydrobiids show habitat selection with regard to salinity but coexist in large areas of the estuary: P. jenkinsi at the innermost parts of the estuary together with H. ventrosa, with the latter species extending its distribution further to the mouth of the estuary, where H. neglecta dominates. H. ventrosa and H. neglecta are the only species that have permanent populations in the estuary. P. jenkinsi dies out in the estuary in the winter, but recolonizes there from a small river in the spring and builds up a population in the innermost parts of the estuary during the summer. H. ventrosa and H. neglecta coexist in the middle part of the estuary due to continued dispersal into this area.

The author's earlier ideas on the distribution and systematics of New Zealand Hydrobiidae are reviewed and revised. There are two main components to the fauna — an ancient subterranean group whose ancestors were widespread before rifting of Gondwanaland and have a distribution taking in New Zealand, Europe and Japan, and a more recently evolved group. The more recent group was probably a Gondwanian development and is typified by Australasian Hemistomia group and Fluviopupa group genera such as Potamopyrgus Stimpson and Opacuincola Ponder. Kuschelita Climo, 1974 and Phreatica Velkovrh, 1970 are synonymised with Saganoa Kuroda and Habe, 1958, the latter elevated from sub generic ranking in Akiyoshia Kuroda and Habe, 1954. Iglica Wagner, 1927 may be an earlier name for this complex. The genus Horatia Bourguignat, 1887 is tentatively introduced to the New Zealand fauna with description of a new species, H. nelsonensis. Opacuincola troglodytes Climo, 1974 is transferred to Potamopyrgus. Potamopyrgus c...

The edibility of two endemic Australian macrophytes (Ottelia ovalifolia and Triglochin procera) to three species of herbivorous stream invertebrates (Triplectides ciuskus and Notalina fulva: (Trichoptera: Leptoceridae) and Potamopyrgus niger (Gastropods: Hydrobiidae)) was investigated. Each macrophyte species was offered to the test animals in 5 different conditions: fresh, boiled, and three conditions of decomposition. In 5 out of 6 feeding trials, consumption rates of animals were greatest on decomposed tissues. Boiling increased edibility of both plant species to Triplectides larvae and of Triglochin to Notalina larvae. Boiled tissue was consumed least by Potamopyrgus. Analysis of nitrogen, phosphorus, and calorific content of macrophyte tissue and some terrestrial plant materials known to be eaten by the animals suggested that nutritional enrichment of decomposed and boiled tissues was unlikely to explain their greater edibility. Instead, the loss of anti-gustatory compounds is implicated.

Osmotic balance was studied in Hydrobia ulvae and Potamopyrgus jenkinsi over the range 100% sea water to fresh water, by determining the freezing-point depression of the urine in the different solutions. Hydrobia ulvae was slightly hyperosmotic from 100 to 50 % sea water, and sometimes initially markedly hyperosmotic in 25 % sea water at 5° C. The urine was always markedly hyperosmotic relative to fresh water, and the animals were withdrawn. Experiments with phenol red indicated that the tissues were not shut off from the medium. Potamopyrgus jenkinsi was hyperosmotic from fresh water to 100% sea water. Osmotic balance in fresh water is maintained in part by the excretion of a urine hypo-osmotic relative to the blood. There was some variation in the reaction of different ecological groups of Hydro-bia ulvae and Potamopyrgus jenkinsi to the experimental conditions. In the Hydrobiidae, whether transformed from a lower to a higher salinity or vice versa, survival outside the viable range was longer at 5° C. than at 15° C., although, within the range, activity occurred more rapidly at 15° C. In fresh water, winter animals of both species had a higher osmotic concentration of the urine than summer animals, but no differences in osmotic concentration correlated with temperature were demonstrated.