Investigations were conducted into aspects of the reproductive biology of the Cyclostomata, a relatively understudied ancient order of bryozoans. Evidence for polyembryony (cloning of sexually produced embryos) in all three major cyclostome clades was obtained using a molecular genetic approach (Chapter 2) confirming historical inferences based on microscopy and supporting the widely held view that this apparently paradoxical reproductive mode characterises the order. The paradoxical nature of polyembryony in the case of cyclostomes was investigated. Genotyping provided evidence for the prolonged production of genetically identical larvae from a single brood in Filicrisia geniculata and the presence of genetic diversity between broods within the same colony (Chapter 5). By cloning multiple progeny genotypes at a given time and testing each against varying environmental conditions over a substantial period, polyembryony may be less paradoxical in this group than first assumed. Variation in gender roles among colonies of Filicrisia geniculata was investigated using cultured material (Chapter 4). Two distinct categories of colony were discovered. Sperm were produced exclusively by ʻmaleʼ colonies, composed solely of autozooids. ʻFemaleʼ colonies comprised regular autozooids and gonozooids. These observations are consistent with at least very pronounced gender specialisation, apparently amounting to outright gonochorism, at the colony level. This is the first properly documented example of separate sexes in bryozoans. Mating trials investigating the effect of exposure to conspecific allosperm on brood chamber development revealed variation in reproductive traits between the two cyclostome species studied (Chapter 3). Tubulipora plumosa demonstrated greater production of gonozooids and larvae in the presence of conspecific allosperm, but with evidence of some selfing when in reproductive isolation. Similar investigations with Filicrisia geniculata revealed that, in female colonies, completion of gonozooid development and brooding occurred exclusively in the presence of allosperm.