Most members of the genus Ophryotrocha are of uniform size and morphology. During cultivation several new species have been discovered. In addition to complete reproductive isolation they may be distinguished as species by the reproductive patterns and the morphology of the egg masses and of the larvae. In this paper reproduction of 12 Ophryotrocha species is described and discussed. Ten of these have been cultivated in my laboratory, of which 5 are new. Reproductive patterns appear to be related to chromosome numbers. Four groups are distinguished: 1) Gonochoristic (2n == 6), 4 sibling species; 2) Consecutive hermaphrodites (2n = 8), one species; 3) Contemporary hermaphrodite 2n = 10, in one species, 2n = 8), 6 species; 4) Viviparous, one species, chromosome number unknown. Viviparity occasionally occurs in 2 species (one in group 1 and one in 3). Comparisons are made of the reproductive patterns and reproductive rates of the gonochoristic species, between healthy animals and those with sporozoan parasites. Parasites may affect competition between sympatric species. For O. labronica correlations between reproductive rates and salinity, temperature, and food were studied. It has been shown by AKESSON (1972 a) that, in O. labronlca, sex ratio and mating propensity depend on maternal factors the nature of which are not known. A similar factor has been discovered in O. puerilis in crosses between Atlantic and Mediterranean subspecies. In O. puerilis incipient reproductive isolation is due to partial developmental arrest and is different from that of O. labronica. Comparisons are made with reproductive patterns among nereid polychaetes and with the relative intraspecific incompatibility in tisbid copepods.
