Functional morphology and taxonomic relevance of the female genital structures in Acartiidae (Copepoda: Calanoida)

Observations of female genital structures using light and scanning electron microscopy in 25 species of Acartiidae (Copepoda: Calanoida) show the presence of paired gonopores and egg-laying ducts with a typical semicircular configuration in all specimens. In the genus Acartiella, there is no seminal receptacle and the external genital area serves as storage site of the spermatophoral products forming an external mass. Unlike in the other acartiids, the genital structures present a complex organization with paired adjacent gonopores and copulatory pores. In almost all the species, the seminal receptacles exhibit characteristic loop-shaped seminal ducts which connect them to the egg-laying ducts. The functional morphology and taxonomic relevance of genital structures are discussed. The present results do not justify the Steuer's subgenus division of the genus Acartia, the very predominant one of the family.