Is Enterobius gregorii Hugot, 1983 (Nematoda: Oxyuridae) a distinct species?

A series of 849 male pinworms collected from a 64-yr-old Japanese male was examined. They were classified by the spicule morphology into 87 Enterobius vermicularis (Linnaeus, 1758), 754 Enterobius gregorii Hugot, 1983, and 6 immature adults, whereas 2 worms lacked spicules. The worm length of E. vermicularis was significantly larger than E. gregorii. The shape and length of the distal tubular portion of the spicule were identical in these forms, whereas the basal portion was different. The immature adults just after the final molt or still within the cuticle of the fourth stage had only a distal tubular portion, indicating that the basal portion is added during subsequent development. Moreover, various transitional forms were observed in the spicule morphology in the worms with intermediate body size between E. vermicularis and E. gregorii, showing that the basal portion of the spicule of E. vermicularis develops after the completion of E. gregorii-type basal portion. It is suggested that E. gregorii is a young stage of E. vermicularis.