Life cycle of Helicodonta obvoluta (O. F. Müll.) was studied in the field and in laboratory. Mating lasts 2-3 hrs and includes: meeting of the partners, recognition, courtship dance, copulation, resting phase and parting. No spermatophores were observed upon dissection of a total of 90 adult individuals which seems to indicate that H. obvoluta does not produce them. The egg-laying snail embeds anterior part of its body 4-6 mm deep in rotting timber. The egg-laying lasts from about a dozen hours to two days. Freshly laid eggs are white, calcified, slightly translucent and get opaque in a few days. They are slightly oval, of 2.10-2.85 mm major and 2.00-2.60 mm minor diameter. In laboratory, eggs are laid in spring (March-June) and autumn (August-November), in the field, the egg-laying periods are somewhat shorter (April-beginning of June, end of August-beginning of October). Most laboratory snails laid eggs only once in their lifetime, the maximum number of egg-laying periods was four. The percentage of hatching eggs in laboratory is ca. 59%. The number of eggs per clutch ranges from 9 to 27. The incubation period ranges from 14 to 31 days, and is shorter for spring (14-18 days) compared to autumn (19-23 days) clutches. Hatching is asynchronous, lasting from 1 to 4 days. With approaching hatching, the white colour of the egg disappears, so that the young snail is surrounded only by a translucent membrane, which gets broken as a result of its movements. Newly-hatched snails have shells of 1 whorl, devoid of periostracal hairs. No egg cannibalism was observed. Out of 174 young hatched in laboratory, 159 reached maturity. During numerous dissections of adult individuals no eggs were found in the reproductive tracts; if there is an egg-retention, it must be very short-lasting. Placing eggs in rotting timber and covering them with mucus protects them from drying-out, ensures a more favourable temperature and limits accessibility to predators. The number, relative and absolute size of eggs, number of clutches per year and per lifetime, and the life span seem to be correlated with size rather than with phylogenetic position of the species. No uniparental reproduction was observed. In laboratory the time elapsing between hatching and maturity (lip completely formed) ranged from 140 to 624 days; it varied between individuals hatched in particular years and seasons, e.g. young of the spring 1997 grew much faster (mean 354 days) than those of the spring 1999 (mean 442 days). The time required to reach full size was not correlated with the ultimate number of whorls. The growth shows three distinct phases: a quick initial phase of 3-4 months, a slow phase, and a short quick phase preceding lip formation. The monthly increment depends on the growth phase: 1.15 whorl in phases 1 and 3, 0.30 whorl in phase 2. The growth rate in the field is similar to that observed in laboratory, though with a wider scatter within growth phases and some differences between years and seasons. Depending on weather conditions, the youngest...
The reproductive system structure in H. obvoluta follows the helicid pattern except for the dart sac which is absent. In juvenile snails the gonad is the first to develop; the later development of male and female reproductive organs is synchronous. At the stage of lip formation the reproductive system is fully developed. At an initial stage of the gonad development (3 and 4 whorls) mitotically dividing cells prevail, and the first pools of oocytes and spermatocytes in meiotic prophase appear. At the stage of 5 whorls the number of mitoses decreases, while the number of cells in meiotic prophase increases considerably, resulting in an increase in the gonad volume. The first growing oocytes appear, while spermatids and mature spermatozoa are absent. The gonad in lip-building snails contains all the cells characteristic of mature hermaphroditic gland. In mature gonad oocytes and spermatozoa are present throughout the year. The number and size of oocytes vary seasonally. Large vitellogenic oocytes are present from April till the beginning of July and from the end of August till October. The pool of growing oocytes appears in August and in November-December. The intensity of divisions leading to formation of the respective gametes changes in a similar way. The development of female lineage cells seems to determine the timing of reproduction, since spermatozoa are present throughout the year.
Balea fallax (Rossm.) collected from the Roztocze Upland (SE. Poland) was kept in the laboratory for four years. Observations were conducted between March and October when the snails were kept at room temperature (18-25°C); in winter they were stored at 3°C. The egg-laying period started in late March and lasted till October, with maxima in spring and early autumn. The snails laid oval, gelatinous eggs with separate calcium carbonate crystals in the external envelope (average egg size 1.96 × 1.73 mm). The eggs were deposited in batches (up to 14 eggs at a time) or singly. The number of batches per snail per year ranged between 1 and 4. Snails isolated before maturation laid defective eggs which failed to develop, which suggest that the species is incapable of uniparental reproduction or at least the ability is very limited. The reproduction rate decreased during consecutive years, probably as a result of the aging or the shortage of allosperm in isolated individuals. Compared to batches of typically oviparous clausiliids, eggs of B. fallax hatched slightly earlier (interval between oviposition and hatching lasted 8-10 days at room temperature). It is likely that the adults retained developing eggs in the uterus for a short time. The juveniles needed at least 6 months to attain the ultimate shell size.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.