Freshwater Snail Species Research Articles

Apical Shell Sculpture of some African Freshwater Limpets (Mollusca: Basommatophora: Ancylidae)

A Scanning Electron Microscope has been used to describe in detail the apical shell sculpture of sevenAfrican species (three genera) of freshwater limpet snails (Ancylidae). The apical sculpture of Ancylus fluviatilis (? syn. strigatus and ? brondeli) is striate, but quite different in basic pattern from the other three striate species studied, Ferrissia cawstoni, ‘Gundlachia’ burnupi and ‘G.’ I'hotelleriei. The apices of the last three are nearly identical, and most likely all three species are congeneric. The apical sculpturing of radiating punctae of the three species of Burnupia is quite distinct, not only from the striate Ancylus and Ferrissia, but also from the subapically pitted South American Uncaneylus.

A New Species of Snail From Lake Pedder Tasmania, Possibly Belonging to The Family Valvatidae

Abstract A new species of freshwater snail, Valvata (?) pedderi sp. nov. is described from Lake Pedder, Tasmania. It is, tentatively referred to the Family Valvatidae and constitutes the second record of this family for Australia. The structure of the radula and the anatomy are described.

On the Sterols of Mollusks, Snails and Bivalves

The compositions of sterols of snails and bivalves were determined. In this study, six species of marine snails, two species of fresh-water snails, two species of marine bivalves, fresh-water and brackish-water bivalve were examined.The unsaponifiable matter was acetylated and separated in to several fractions by silver nitrateimpregnated silicic acid column chromatography. Sterol composition of each fraction was determined by GLC.It was shown that the sterol composition of snails, fresh-water and brackish-water bivalves is different from that of marine bivalves. Cholesterol was 7090% in snails, 6070% in fresh-water and brackish-water bivalves, and 3040% in marine bivalves.UV absorption spectra showed the presence of Δ5, 7-sterol in these mollusks, and 7-dehydrochole-sterol was isolated. C29-sterols showed the difference with the species of mollusks.

Two new species of Hartmannella amebae infecting freshwater mollusks.

SYNOPSIS. Two new species of small amebae, Hartmannella biparia n. sp. and Hartmannella quadriparia n. sp., were 1st observed in the freshwater mollusks Bulinus globosus and Biomphalaria pallida, respectively. The amebae multiplied in cytoplasmic vacuoles in host cells, particularly in foci in the mantle collar, foot, and intestinal wall. Both amebae had functional contractile vacuoles while within host cells. H. biparia emerged from intracytoplasmic vacuoles in pairs, H. quadriparia in fours, suggesting characteristic reproductive stages.H. biparia had limax‐type motility by smooth lobopodia, was 22 μ long; with vesicular nucleus 3 μ and central endosome 1.5 μ, multiplied by binary fission and formed spherical, smooth‐walled cysts 11 μ in diameter. H. quadriparia had limax‐type motility by lobopodia with fine, acute projections; was 10 μ long, with vesicular nucleus 2 μ and central endosome 0.75 μ, multiplied and formed spherical, smooth‐walled cysts 5 μ in diameter. Neither species multiplied in cysts outside the host.H. biparia was found infecting 12 species and experimentally transferred to 4 more species of freshwater snails; H. quadriparia was found in one species and experimentally transferred to 6 other species.

Cooling ponds and heated industrial waters as potential environments of schistosomiasis in Britain.

An investigation was made to determine whether British species of freshwater snail can reproduce in warm water and become susceptible to infection by Schistosoma mansoni. Twenty-seven species were cultured at 20 and 26°C, and it was found that most of them could reproduce at these temperatures. Sixteen species were exposed at the same temperature to miracidia of S. mansoni of the Egyptian, Liberian and Puerto Rican strains; a cyst was found in A plexa hypnorum exposed to the Egyptian strain, which could be attributed as being a juvenile stage of a sporocyst, but no positive conclusions can be drawn.

Effect of Freezing and Boiling on the Infectivity of Third-Stage Larvae of Angiostrongylus cantonensis Present in Land Snails and Freshwater Prawns

Third-stage larvae of Angiostrongylus cantonensis recovered from land snails (Achatina fulica) and freshwater prawns (Macrobrachium rosenbergi) which had been exposed at 0 C for 24 hr were found infective when fed to rats. The larvae, however, were not infective when recovered from snails or prawns which had been exposed in a freezer for 12 or 24 hr at -15 C. Some of the larvae recovered from snails that had been boiled in water for 1 min were infective to rats, but larvae recovered from snails boiled for 2 or 3 min or from prawns boiled for 1 min were not infective. The thermal death point of the third-stage larvae in water has been found to be somewhere between 50 and 55 C. Reports indicate that in some areas of the Pacific Islands and Southeast Asia, certain species of freshwater prawns (Macrobrachium sp.) and snails (Pila ampullacea) used as food are frequently infected with third-stage larvae of Angiostrongylus cantonensis and are believed to serve as major sources of human infection with this parasite (Alicata and Brown, 1962; Punyagupta, 1965). Since freezing or boiling would appear to constitute a simple and practical method of destroying the vitality of the infective larvae present in snails or prawns, experiments were conducted to determine the efficacy of these methods in rendering these infected invertebrates safe as food, as far as it concerns cerebral angiostrongylosis. Even though the species of snails and freshwater prawns used in the present study are not necessarily the same as those used for food in Angiostrongylus endemic areas, it is believed that the results obtained would be generally applicable to other species of snails or prawns, or other animals of approximately the same

Studies on Angiostrongylus cantonensis in Molluscan Intermediate Hosts

First-stage larvae of Angiostrongylus cantonensis from rat feces developed to infective third-stage larvae in 20 of 26 species of freshwater mollusks experimentally exposed. Numbers of larvae up to 2,000 per snail and survival of larvae for a year were observed in Biomphalaria glabrata. First-stage larvae were susceptible to drying but survived at least 3 weeks in freshwater and were infective to snails after at least 2 weeks in either freshwater or seawater. B. glabrata was routinely infected by ingestion of infected rat feces, and first-stage larvae were observed penetrating the wall of the intestine. A cellular reaction enclosed the developing larvae in tissue nodules. Isolated third-stage larvae were susceptible to drying but survived up to 11 days in B. glabrata removed from water, larvae remaining alive 4 days after death of the snails. Rats became infected by drinking water containing third-stage larvae, and larvae were observed active in freshwater for up to a week. Infected B. glabrata died a few minutes after immersion in seawater, but yielded by digestion numerous infective larvae after 4 days in seawater, and a few infective larvae after 5 days. Results suggest the potential importance of freshwater mollusks as intermediate hosts and the possibility of infection of marine hosts. The life cycle of Angiostrongylus cantonensis (Chen) Dougherty, the rat lungworm, was described by Mackerras and Sandars (1955). A. cantonensis has been suspected as the etiologic agent of eosinophilic meningoencephalitis in several Pacific Islands (Rosen et al., 1961, 1962; Horio and Alicata, 1961; Alicata, 1962a, 1962b; and Alicata and Brown, 1962). Human infections were reviewed by Rosen et al. (1962); by Weinstein et al. (1963); and by Kuntz and Myers (1964). Terrestrial mollusks, both slugs and snails, have been infected (Mackerras and Sandars, 1955; Weinstein et al., 1962; and Alicata, 1962a). Experimental infection of the freshwater snail Fossaria ollula was reported by Alicata and Brown (1962). Liat et al. (1965) found three species of freshwater snails infected in nature with A.

Distributional Trends of Four Species of Freshwater Snails in South Africa With Special Reference to the Intermediate Hosts of Bilharzia

Distributional Trends of Four Species of Freshwater Snails in South Africa With Special Reference to the Intermediate Hosts of Bilharzia

LIFE CYCLES OF FOUR FRESHWATER SNAILS IN LIMITED POPULATIONS IN LOCH LOMOND, WITH A DISCUSSION OF INFRASPECIFIC VARIATION

With dredged samples from an isolated bank in Loch Lomond providing standards, data are presented on the interpopulation variations in growth and reproduction which occur in five species of freshwater snails. Infraspecific differences between populations in Planorbis albus and Valvata piscinalis involve only growth rates and the time and intensity of the breeding season. In Physa fontinalis, Lymnaea peregra and Ancylus fluviatilis, interpopulation differences involve the seasonal course of the reproductive cycle (and the number of generations per year), as well as growth rates. A series of the known life cycles of freshwater pulmonates is then considered: two patterns of simple annual cycle, and two patterns each involving a second generation annually, are described, besides certain more exceptional life cycles. All four patterns have been found in different populations of P. fontinalis and L. peregra.Variations in breeding are dependent both on environmental factors, water temperature being most important, and on endogenous causes involving the growth of the snails; variation in mortality may involve environmental limitation. Most interpopulation variations can be environmentally evoked, but some differences seem genetically determined. It is suggested that adaptive plasticity, as found in several aspects of the physiology of these snails, is of fundamental selective value, given the temporal and spatial peculiarities of the freshwater environment.

RELATIONS BETWEEN PRE- AND POST-ANAEROBIC OXYGEN CONSUMPTION AND OXYGEN TENSION IN SOME FRESH WATER SNAILS

1. The respiration of four species of fresh water snails was somewhat dependent on the oxygen tension below 21 per cent oxygen with only minor differences among the various species.2. The degree of dependency was influenced little, if any, by alteration of the metabolic rate of Australorbis glabratus, but some changes were obtained in the cases of Helisoma duryi and Lymnaea stagnalis.3. All species showed a long lasting respiratory rebound after 16 hours anaerobiosis. The post-anaerobic respiration was more dependent on the oxygen tension than the pre-anaerobic respiration if referred to the normal rate shown at 21 per cent oxygen. But if the post-anaerobic rates were compared with the rates sustained pre-anaerobically at an identical oxygen tension, an approximately equal percentage increase was observed over a wide range of tensions.4. The implications of these observations and auxiliary observations dealing with the rate of the heart-beat under various conditions are discussed insofar as they shed light on the mechanism of the pre- and post-anaerobic respiration. It is concluded that diffusion alone cannot be the sole limiting factor that reduces the over-all oxygen consumption when the tension is lowered below a critical point, and the idea is discussed that the oxygen tension as such may be more important for certain cellular processes than usually assumed.

Schistosomiasis at Lake Bunyonyi, Kigesi district, Uganda

In two widely separated places of Lake Bunyonyi at Chabahinga, near Kabale, and in Muko, we found the same three species of fresh water snails: 1. (1) Pl. pfeifferi Krauss. 2. (2) B. coulboisi Bourg. and B. mutandaensis Preston. 3. (3) L. natalensis (undussumae) von Martens. Bulinus were the most abundant, Planorbis also numerous, and Lymnaea comparatively rare. Amongst the Planorbis (and Bulinus) of Chabahinga we found none infected with Schistosoma cercariae, but amongst the Planorbis at Muko we found two specimens shedding Schistosoma cercariae. Both Planorbis died before we had time to try an animal experiment. We did not examine the natives of Muko, but amongst those of Chabahinga, near Kabale, we found a few boys infected with S. mansoni. Infection, however, was very light, and none of the affected complained of any symptoms. S. mansoni thus exists at an altitude of 6,300 feet.

Calcification in the Guinea Worm

Infestation by Dracunculus medinensis is common in certain parts of Africa and India. The embryos mature to larvæ in a species of freshwater snail, and further development in man occurs after drinking infested water. The larvæ make their way from the stomach to the subcutaneous tissues, nearly always of the feet and lower parts of the legs, where the adult female matures to a length of between one and four feet. A small blister is then raised on the skin, often associated with local urticaria and a moderate systemic disturbance; and the blister rupturing, large quantities of minute embryos are discharged from the sinus. The worm can usually be seen, and palpated subcutaneously.

Bilharziasis in Natal

In the following pages I shall endeavour to describe the present state of our knowledge of Bilharziasis in Natal and the result of some personal observations extending over the last seven years. The investigations of the Bilharzia Mission to Egypt have drawn attention to the various forms of cercariae which infest several species of fresh-water snail in African rivers. The cercariae which give rise to Bilharzia disease in Egypt are furcocercous cercariae, i.e. they possess a. tail which is divided for a greater or shorter portion of its length. They are characterised, further, by the absence of a pharynx at the commencement of the oesophagus. Similar cercariae are present in one of the species of fresh-water snail which abounds in the infected areas of Natal.