BIOCHEMICAL COMPOSITION OF HELIX SNAILS: INFLUENCE OF GENETIC AND PHYSIOLOGICAL FACTORS

This paper describes the biochemical composition of differentspecies (Helix lucorum, Helix pomatia) and sub-species of snails(Helix aspersa aspersa, Helix aspersa maxima) reared in thesame conditions with a feed (‘Helixal’) speciallydesigned for edible snails. In addition, the composition ofwild H. pomatia and H. lucorum is presented to allow comparisonbetween snails of different origins. Analyses determined thepercentages of proteins, lipids and minerals. They reveal bothsimilarities and differences in composition according to thespecies and the part analysed (whole body, pedal mass, and visceralmass). H. pomatia contains the highest percentage of mineralmatter and the lowest percentage of lipids. Surprisingly, proteincontents are slightly different between artificially rearedH. aspersa maxima of 3 months old and wild H. pomatia. The resultsmake it possible to evaluate nutritional quality of snails withthe composition of the body of four edible snail species. (Received 16 September 1996; accepted 24 May 1997)     

Etude exploratoire de la spermatogenèse induite par la chaleur chez l'escargot Helix aspersa en hibernation: Rôle du cerveau / An exploratory study on temperature-induced spermatogenesis in the hibernating snail Helix aspersa: the role of the brain

Summary

The male cells in the ovotestis of hibernating snails undergo multiplication when the temperature of the environment is raised from 5°C to 25°C. If the temperature is maintained at 25°C for 4 weeks the process of spermatogenesis is completed but the rate of spermatogenesis (DNA synthesis) starts decreasing from the 3rd week (Table 1; Fig. 1).

Brain ablation in hibernating snails maintained at 25°C causes a significant increase in DNA synthesis exclusively in male cells of the ovotestis. This suggests that the brain exerts an inhibitory influence on spermatogenic multiplication. This influence is effective only during the first and the fourth week of exposure of hibernating snails to 25°C (Fig. 1; Table 1) indicating the existence of an endogenous cyclical control. Spermiogenesis is, however, not affected by brain extirpation (Fig. 4 A,B,C).

When reimplanted in the head haemocoel the brain appears normal histologically (Fig. 5 A,B) and it reestablishes the inhibitory influence on DNA synthesis in the ovotestis only during the first day of temperature-induction. During the 1st, 3rd and 4th week the reimplanted brain, deprived of its neural connections, fails to exert its inhibitory influence suggesting that for this influence to function neural connections to the brain are essential. Surprisingly, the implanted brain seems to inhibit DNA synthesis during the 2nd week of temperature-induction (Table 1).

These experiments show that the brain control temperature-induced spermatogenic multiplication in the ovotestis in snails at the onset of hibernation and this control is exerted by one or more inhibitory factors originating from the brain which may function in concert or independently to produce the neuroendocrine effect. It seems therefore justified to consider spermatogenesis in hibernating snails as being neuroendocrinologically controlled.     

INFLUENCE DE LA DENSITE DE POPULATION SUR LA CROISSANCE DIAMETRALE ET PONDERALE DE L'ESCARGOT HELIX ASPERSA MULLER DANS DIFFERENTES CONDITIONS D'ELEVAGE

Increase in density of experimental populations of the snailHelix aspersa has a negative effect on growth. At high densities,growth rates are low, and individuals mature at a smaller size.The formation of a shell-lip (indicating maturity) is delayedand may occur when diameter is less than 28 mm. These effectswill depress reproductive ability. This inhibitory effect appears early in juvenile life, and remainseffective until growth has ceased. The logarithmic ratio ofweight to shell diameter stays constant, throughout, showingthat weight measurements are reliable indicators of growth.There is, however, great variation in size even in snails subjectto the same treatment, and of the same age, indicating thatsize and weight alone are inadequate guides to age. (Received 4 January 1984;     

L'escargot ou les difficultés de l'hermaphrodisme

Summary

The article summarizes the research carried out in Besançon on the stylommatophoran snail Helix aspersa, a pulmonate gastropod mollusc.

The influence that external factors like photoperiod and temperature have on growth and reproduction was studied in this animal. The obtained results made possible a great development of snail breeding.

The potentialities of the hermaphroditism emerge from the observations made on the ovotestis: differentiation and development of the different cell types, presence of fibronectin, richness in neuropeptides, existence of male and female steroids, vitellogenesis processes.

In vivo experiments as well as in vitro cultures demonstrated the involvement of the cerebral complex in the control of reproduction. The dorsal bodies (DB)—(it consists of scattered cells)—stimulate the growth of the oocytes. The DB are under an inhibitory nervous control of the cerebral green cells (CGC); the FMRF-amide might be involved in this process.

A map of the neurons of the cerebral complex has been prepared. It shows the presence and the diversity of neuropeptides. Attention was focused on met-enkephalin and somatostatin. This later peptide seems to be involved in the shell growth. The active molecule, which was isolated from hemolymph and digestive gland is structurally quite similar to vertebrate somatostatin.

The results are compared with those obtained in other molluscs, especially in basommatophora. They reveal that the biological phenomena observed in the snail model are included in the fundamental processes, known in other invertebrates or vertebrates.