Ultrastructure and morphology of the cycliophoran female

Knowledge on the morphology of the cycliophoran female has mostly been based on observations of immature females in brood chambers of feeding stages. With the use of light- and transmission electron microscopy, the morphology and ultrastructure of the free and fully mature female of Cycliophora is described now for the first time. The external morphology is characterized by a ciliation consisting of an anteroventral ciliated field, a posterior ciliated tuft, and four sensory structures extending anteriorly from the anteroventral ciliated field. In addition, a small ciliated structure in the midventral region is interpreted as a round-shaped gonopore. Internally, a bilateral cerebral ganglion is situated in the anterior region and a large oocyte is located medially in the body. Several glands are present anteriorly, while posteriorly a pair of glands is associated with the ciliated tuft. Dorsal and ventral longitudinal muscles, as well as, dorsoventral muscles are identified by electron microscopy. Muscle fibers attach to the endocuticle via the epidermis, by means of attachment fibers. An unknown endosymbiont is present throughout the body of the female. We discuss the functional implications of the morphological and ultrastructural aspects of the cycliophoran female. Finally, we compare this life cycle stage with that fromother phyla, suggested as phylogenetically close.