Morphological and ethological aspects of mating in two species of the Family Helicidae (Gastropoda: Pulmonata): Theba pisana (Müller) and Helix aperta Born

The mating behaviour of two Helicidae (Gastropoda Pulmonata) species, Theba pisana (Müller) and Helix (Cantareus) aperta Born, is described. Comparison with prior studies suggests that the position assumed for mating is not determined by the ecology of the species but is an occasionally acquired element. Each partner reacts to the stimuli of the other. The stimuli are necessary for the initiation of the approach and the realization of a correct mating position and appear to induce one snail to accept the other. If one of the subjects is not sufficiently motivated the stimuli are ineffective. The stimuli are not specific and responses indicating a simple cause-effect relationship were not observed. The shooting of the dart marks the beginning of attempts at copulation and occurs when, after repeated stimulation, a threshold of excitement is exceeded. In T. pisana and H. aperta, although the darts are shot simultaneously after the contact organs have been pressed closely together, this happens only after many stereotyped attempts. An exception to this rule is the simultaneous extroflexion of the penes before copulation, performed with the contact organs completely superimposed. Nevertheless this too occurs only after repeated attempts by both partners and is thus linked to a threshold effect. The state of excitation of the partners may lower the threshold and shorten the duration of this phase. The state of excitation does not depend upon the season. The duration of mating does not vary in individuals meeting at different times of the year but may be reduced after a long period of isolation. The tendency towards male and female behaviour is simultaneous in the species examined. Reciprocal copulation thus depends on the sum of these two tendencies. Dart shooting is not a fundamental stimulus for the prosecution of copulation for either the shooter or the receiver, nor has the expulsion of mucus from the digiti-form glands any apparent consequence for the successive development of copulation. It appears that biting in the introductory phase and dart shooting serve to establish the motivation level of the partner. The post-copulatory phase does not seem to depend on having received the spermatophore, but rather on having expelled the spermatophore and retracted the penis. The pauses after dart shooting and copulation observed in certain species do not seem linked to the need for the genital organs to recover or for the transfer of the sperm to the talon but to ecological factors and species specific mechanisms.