ABSTRACT: Communal oviposition, the sharing of a single substrate by conspecific individuals for depositing clutches of egg capsules, is common among gastropod molluscs. In soft-bottom habitats, communal oviposition may occur because of a limitation ofsuitable hard substrate. Conspecific cues may be responsible for aggregating females. This study examined the oviposition behavior of the apple murex snail Phyllonotus pomum in seagrass beds in St. Joseph¹s Bay, Florida. Movement patterns obtainedfrom a mark-recapture study conducted during the 5 mo prior to egg-laying season suggest that females are capable of moving, and often move, farther than the distance at which substrate might become limiting. In field surveys, 1 to greater than 14possible suitable substrates were available within a 4 m radius of communal oviposition events, yet females still oviposited communally. In a caged field-substrate manipulation experiment, females contributed to a single communal egg-mass even whenadditional substrates were available within 0.25 m. When given a choice between substrate without and with fresh egg capsules (<8 d old) in a caged field experiment, females deposited an equal number of clutches on each type of substrate. Communaloviposition in P. pomum was not mediated by substrate limitation, and previously laid conspecific egg capsules did not attract females or induce them to oviposit communally. Alternatively, there may be an adaptive advantage to communal ovipositionin P. pomum. It is possible that the process of egg-laying from 1 individual attracts, aggregates and induces oviposition in neighboring females.