The life cycles of symbiotic Octolasmis species and their hosts are integrated with the important result that cyprid attachment, metamorphosis, and growth to reproductive adults, fit within host intermolt time periods.

Octolasmis cor and Octolasmis angulata cyprid larvae collect on mangrove crabs, Scylla serrata, just prior to host molt. During ecdysis they transfer to the branchial chambers of the newly molted crabs.

The spatial distributions of both barnacle species on the crab gills are nonrandom, uneven, and do not reflect available surface area. The two species are distributed differently on the hypobranchial (inside) and hyperbranchial (outside) gill surfaces. O. cor and O. angulata attain greater average size in some locations over others. Distribution patterns vary with different densities. Areas with higher densities also are areas of higher average fecundity. Thus it is apparent that the selection of the attachment site by the cyprid larvae does impact adult fitness parameters.