Life cycle and population dynamics of Discus perspectivus (Megerle von Muhlfeld, 1818) (Gastropoda: pulmonata: Endodontidae)

Life cycle and population dynamics of Discus perspectivus (Mühlf.) were studied in the field and in the laboratory. No courtship, copulation or uniparental reproduction could be observed. The eggs, laid in June, July and August on rotting timber are calcified, ellipsoidal, ca. 1 mm in major diameter; the number of eggs per batch is 1–9 (mostly 3–4), with a total of 17–33 eggs per individual per season. The incubation period is 24–35 days, hatching is nearly synchronous; the proportion of hatching eggs laid by individuals brought from the field is 51% (for eggs brought from the field 38.7%). The hatchlings have shells of 1.8–2.3 whorls; they consume their egg envelopes immediately after hatching. The egg cannibalism is prolonged into adult stage; only conspecific eggs are consumed; juveniles eat eggs of their own and alien batches. The growth rate in the laboratory is 1 whorl per 49–188 days (slower in the field); the growth is faster in juvenile and slower in mature snails. The snails reach maturity at slightly over 5 whorls (mature gametes present in the gonad), the life span is 173–849 days, the reproductive life constituting ca. 7% total life span. In the field juveniles hatch from June till October, with the maximum in August; till their first hibernation they reach 2.6–3.5 whorls and become mature in their second season to reproduce in the same or next year. The population density exceeds 50 m-2 in summer, and ranges from 25 to 30 m-2 during the remaining seasons. D. perspectivus shows aggregated distribution in August and October, in the remaining months the distribution is even. Some laboratory-born individuals have very much elevated spires and their shells become scalariform at the level of 5.3–5.75 whorls.