Reproductive biology of the gregarious Mediterranean vermetid gastropod Dendropoma petraeum

The reproductive biology of the gregarious Mediterranean vermetid gastropod Dendropoma petraeum (Mollusca: Gastropoda) has been studied in the south-eastern coast of Spain. It apparently is a gonochoristic species with the sex ratio biased toward females (71%). A broad peak of more intense reproductive activity occurs in spring months and an inactive reproductive period during winter. The gonad of the males develops about two months before those of females, and storage of sperm by females has been observed. Internal fertilization takes place after the capture of pelagic spermatophores. The egg capsules lie free within the female mantle cavity, and females brood up to 86 capsules simultaneously (the highest number reported for any vermetid gastropod). The size of the capsules is somewhat variable and increases slightly from those containing first stages of development (mean = 678 x 579 mu m) to those containing late stages (mean = 996 x 693 mu m). Each egg capsule usually contains a single large egg or embryo, but sometimes two (8.2% of the capsules) or rarely three (0.24%). Production of egg capsules by females seems to be continuous throughout the reproductive period (from March to October). The unsegmented eggs measure from 440 to 507 mu m in diameter (man = 482) and are the largest reported for any vermetid gastropod. Nurse eggs are not present, and therefore most of the intracapsular nutrition comes from the internal yolk of the embryo. Development is lecithotrophic without a pelagic larval phase. The late intracapsular veliger stage metamorphoses within the capsule and hatching occurs at a crawling juvenile stage. The crawling young snails spend a short time (a few hours) until attachment, and no growth of the shell has been noted during this short period. The protoconch of the hatchlings measures from 680 to 900 mu m in length.