FEMALE GENITAL STRUCTURES OF METRIDINIDAE (COPEPODA, CALANOIDA)

The female genital structures of six calanoid copepod species, belongi ng to the genera Gaussia, Metridia and Pleuromamma, were studied using light and scanning electron microscopy (SEM). The copulatory pores an d seminal receptacles are paired in Gaussia and Metridia, but unpaired in Pleuromamma. A thin epicuticle and a spermatophoral plug are the m echanisms by which the pores are closed before and after copulation. T he pores open directly into the receptacles, which are reduced to shal low integumentary depressions in Gaussia. The mode of insemination sug gests two matings in females of Gaussia and Metridia, but only one in Pleuromamma. Paired gonopores and egg-laying ducts are present in the three genera, with a characteristic, closed semicircular configuration ; these are opened during egg-laying by the action of retractor muscle s of the gonoporal plates. The seminal ducts, which open into the gono pores, are long, thin and paired in Gaussia and Metridia, whereas in P leuromamma they are short, broad and unpaired. The opening of the semi nal and egg-laying ducts is synchronized. The shell ducts are paired i n Gaussia and Metridia, unpaired in Pleuromamma; these arise from glan ds situated in the lateral expansions of the last prosomite and lead i nto the distal part of each egg-laying duct in Gaussia and Metridia an d of the egg-laying duct receiving the seminal duct in Pleuromamma. Th e position and anatomy of these structures are compared to those of ot her families and genera, and a functional interpretation of their morp hology is proposed. The main evolutionary trends of the different stru ctural patterns of female calanoid genitalia are presented in tabular form.