Scanning electron microscopy of newly excysted juvenile and adult <i>Cyclocoelum mutabile</i> (Digenea)

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In this study, changes were examined in surface structures and tegumental morphology of newly excysted, migrating, and adult Cyclocoelum mutabile obtained from experimentally infected coots (Fulica americana). Newly excysted juveniles were spinous and had two large depressions situated at the anterior tip of the body and a large acetabulum. Small papillae were scattered around the mouth region and also formed a row that encircled the anterior end of the fluke. Four groups of larger papillae, two ventrolateral and two lateral, originated from points slightly posterior to the mouth region. The two ventrolateral bands of papillae terminated slightly posterior to the acetabulum; the two lateral rows of papillae terminated about three-quarters of the length along the specimen. Six large multilobed papillae were associated with the acetabulum. Juveniles migrating through the liver lost the spines and papillae by day 6, but the anterior depressions persisted into the adult stage. The tegument of 6- and 12-day-old flukes was smooth with a varying number of transverse folds. The tegument of 15-day-old specimens from the body cavity ranged in appearance from folded and pitted to reticulate. The reticulations were more prominent in adults and the entire body was covered with a reticulate pattern of loculus-like structures that are believed to aid in the movement of the flukes within the air sacs of the coot host.