Morphometric variation of the Chiorchis trematodes, parasitic in the American manatee (Trichechus manatus)

Morphological variation was studied in the adult cladorchiid trematodes <i>Chiorchis</i> spp. (Trematoda: Digenea), that parasitize the intestinal tract and caecum of the American manatee (<i>Trichechus manatus</i>). Specimens were collected from 22 manatees between 1980 and 1998 in Puerto Rico, Cuba, Dominican Republic, Mexico, and Florida. We found statistically significant differences in analyses of variance in 31 morphological measurements from 284 specimens across different geographical regions, consistent with the existence of two species. Some specimens from Florida corresponded to the description for <i>Chiorchis fabaceus</i> Diesing1838, while specimens from the Dominican Republic, Mexico, Puerto Rico, and some from Florida, previously misidentified as <i>C. fabaceus</i>, corresponded to the description of <i>C. groschafti</i> Coy-Otero1989. The latter supports the distinction of two <i>Chiorchis</i> species parasitic on the American manatee. These species differ mainly by the presence or absence of an esophageal bulb, testes shape, position of the genital pore, and shape and distribution of the vitelline follicles.