Abstract
This paper begins a series aimed at clarifying the structure and function of reproductive organs in Gastrotricha Macrodasyida. Morphological data are presented for Dolichodasys carolinensis sp.n. and D. delicatus sp.n. Both are elongate, have reduced adhesive organs and complex accessory reproductive organs, termed the frontal‐caudal organ system. The system consists of a band of cells behind the gonads in the central body chamber. The anterior portion, the frointal organ, stores foreign spermatozoa; the posterior portion, the caudal organ, may function as a copulatory organ. The caudal organ has two canals forming a loop opening at a single ventral pore. One canal contains a spiralled secretion, the other elongated filaments that appear to be muscle cell derivatives. Systematic groupings are made for other long‐bodied Gastrotricha Macrodasyida.