Growth and development of the rare land snail Paryphanta busbyi watti (Eupulmonata : Rhytididae)

Abstract

The rare carnivorous land snail Paryphanta busbyi watti was investigated by following marked snails over a study period of 6.3 years. Large snails were fitted with harmonic radar transponders to aid in locating them. This species is iteroparous and has determinate growth. Shells had maximum diameters of 49.6–61.2 mm. Two to eight large eggs, representing 5%–23% of the live weight of a snail, were laid at a rate of one to two per day over 2–5 days. These eggs were deposited in one to three holes dug in soil by the snails. A newly laid egg was surrounded by an adhesive membrane, which disappeared after a few days, exposing the calcareous shell. The eggs took 5–7.3 months to hatch and the young snails remained underground for a minimum of up to 2.8 months. The shells of these snails increased in size while underground. A non-linear mixed-effects model was used to combine data from 31 snails that were monitored for different lengths of time. Only an approximate estimate could be made of the development rate for young snails. Growth to the adult shell stage was estimated to take 3–4.3 years and fast-developing individuals tended to become larger adults. The maximum time that a snail with an adult shell was monitored was 4.1 years, whereas most snails with an adult shell were monitored for 1–2 years.