Decalcification of vulvar operculum and mating in the ocypodid crab Ilyoplax pusilla

In the mating system of Ilyoplax pusilla, wandering females respond to cour ting, burrow-holding males that wave their chelipeds and enter their burrow s. They pair in plugged burrows where mating occurs. Female I. pusilla spaw ned within 3 days of pairing, after which the male left. The opercula of fe males became decalcified, before, or more often after, pairing. Decalcifica tion normally follows responsiveness to male courtship, but it is not neces sary to produce female receptive behaviour, and pairing with a male in his burrow is not essential to evoke decalcification. After spawning, the numbe rs of calcified females gradually increased, and most ovigerous females wer e recalcified before larval release: The percentage of decalcified, single, non-ovigerous females in the population peaked near the full and new moons . The peak percentage of decalcified, non-ovigerous, paired females occurre d 2 days later than that of decalcified, single, non-ovigerous females. Dec alcified females did not always enter male burrows for mating. Some females remained in their own burrows and laid eggs fertilized with stored sperm. Spawning with stored sperm may be an adaptation to avoid the risk of predat ion and it enables females, not evicted by neighbouring males, to reproduce .