Considerable diversity has been found in the reproductive behaviour of benedeniine (capsalid) monogenean parasites. Mating has been observed in Benedenia sp. 1 from the gills of Lutjanus carponatatus; externally attached spermatophores are not involved and parasites indulge in mutual cross-insemination with intromission. In contrast, there is evidence of spermatophore involvement in Benedenia sp. 2 from the fins of Lethrinus miniatus; mating was not observed but an individual was found carrying an external ovoid spermatophore attached by a stalk lodged in the vagina. In specimens of Benedeniella macrocolpa and B. posterocolpa, in which the male reproductive system was functional and the female system not fully developed, the everted cirrus was seen to be lodged in the parasite's own uterus, with, in some individuals, the tip of the cirrus inside the ootype. This is the first time that the copulatory organ has been observed inside the female reproductive tract of the same individual, not just in benedeniines but in monogeneans in general, and is also the first demonstration that monogeneans are capable of self-insemination via the uterine route.

We examined the relative merits of mitochondrial DNA loci and ribosomal DNA internal transcribed spacers for their use in prospecting for cryptic species of platyhelminth parasites. Sequence divergence at ITS1 and ITS2 was compared with divergence at 2 mtDNA loci (NADH dehydrogenase-1 and cytochrome c oxidase I) between closely related species of trematodes and cestodes. Both spacers accumulated substitutions substantially more slowly than mtDNA, which clearly shows a higher level of divergence among species relative to intra-specific variation. Besides a slow rate of substitution, other caveats that may be encountered when using ITS sequences as a prospecting marker are discussed. In particular, we note recent studies that suggest the existence of substantial levels of intra-individual variation in ITS sequences of flatworms. Because it is likely that closely related species share this phenomenon, it may confound the detection of cryptic species, especially if small sample sizes are studied. Although potential limitations of mtDNA are also recognized, the higher rate of evolution and smaller effective population size of this marker increases the probability of detecting diagnostic characters between cryptic species.