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Vallonia excentrica Sterki, 1893
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Species name:
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Vallonia excentrica Sterki, 1893
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Taxon name:
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Vallonia excentrica Sterki, 1893
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Originally described in:
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Sterki, V. 1893. Genus Vallonia Risso. (Vol. III, p. 169.). - pp. 247-261, pl. 32, 33, 43, 56, in: Pilsbry, H. A.: Manual of conchology; structural and systematic. With illustrations of the species. Second series: Pulmonata. Vol. VIII [= 8]. Helicidæ, Vol. VI [= 6]. -- pp. 1-314, Pl. 1-58. Philadelphia.
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Distribution:
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E North America (Mississippi to Newfoundland), Europe: Ireland, Scotland and Pyrenees to S Sweden, Albania, Bulgaria, Ukraine and Caspian Sea
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Diagnosis:
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Shell weakly coloured and transparent, much like Val. pulchella, usually smaller (3 whorls only), last quarter of last whorl remarkably increased giving the shell an elliptical shape, lip not so distinctly visible from above as in Val. pulchella.
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Size:
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0.9-1.4 x 2.0-2.2 mm
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Biology:
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Open and usually dry habitats, short meadows, rock rubble, sandy dunes, not in forests and swamps. Tolerates less calcareous soils than Vallonia costata. In Switzerland in up to 1500 m, in Bulgaria 1200 m, rare in Scottish highlands.
Copulations are rare and take place only between euphallic animals. Eggs are laid one by one, not in clutches, one egg every few days, at the soil between soil particles or in small crevices, juveniles hatch after 1-2 weeks, depends on the temperature, full shell size is reached after 7 weeks (25°C). 2 generations per year in New Zealand, hibernating snails reach maturity in spring, snails hatched in spring reach maturity in autumn.
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Threatened:
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In Britain more frequent than Vallonia pulchella and more tolerant against human disturbance than Val. costata.
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Family:
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Valloniidae
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Higher group:
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Gastropoda
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Comments:
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References: Damjanov & Likharev 1975: 134, Kerney et al. 1983: 130, Dhora & Welter-Schultes 1996: 123, Gerber 1996: 68, Turner et al. 1998: 172, Kerney 1999: 109, Hubenov 2007, www.naturamediterraneo.com (2007), Welter-Schultes 2012: 207 (range map Europe).
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