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Activity rhythm of the edible H. lucorum snails is compatible with different skeleton photoperiods and the phase of the peak of the snails activity is correlated to the time interval between the two high pulses in skeleton photoperiods as revealed by the analysis of skeleton photoperiod regimes adaptations in adult Helix lucorum, edible snails. Minimum night length was the only precondition necessary for the maintenance of the daily night rhythm of the snails.

The nitrogen catabolism of two snail species, Xeropicta arenosa and Cermuella virgata, living on coastal dunes, was studied at different seasons and times of the day and at different ages. All the nitrogenous metabolites of the uricolytic enzymatic system were found in body homogenates of the snails, although uric acid was most abundant. The highest levels of these catabolites were observed during the day when the snails were inactive, while the lowest levels occurred during the night when excretion probably took place. The levels of most of the nitrogenous catabolites and the activities of the enzymes were higher in juveniles than in adults. All the enzymes of the uricolytic pathway were shown to be present in both X. arenosa and C. virgata. [ABSTRACT FROM AUTHOR]