ABSTRACT: The cheilostome bryozoan Celleporella hyalina (L.) was used as a model to test the hypothesis that sessile animals fertilising retained eggs by water-borne sperm should produce sperm with relatively prolonged fertility during thedispersal phase. Ramets of each of several recipient clones were exposed to suspensions of allosperm obtained by induced release from ramets of donor clones. Allosperm was presented to each series of ramets at a concentration of 10 to 10²ml^-1, in aliquots of increasing age after release. Control ramets of the recipient clones isolated from allosperm failed to produce embryos, indicating the absence of autogamy. Experimental ramets exposed to fresh allosperm copiously producedembryos, but the frequency of embryos declined sharply in ramets exposed to allosperm suspension of increasing age. The estimated fertile half life of water-borne sperm was 1.2 h, which is at the upper limit of the range of values reported for othermarine animals at comparable concentration. C. hyalina maximises fertilisation success by efficient dissemination, capture and storage of relatively long-lived sperm.