Rhopalocercariae in the Trematode Subfamily Gorgoderinae

Publisher Website
Google Scholar
Abstract
Five n. spp. from freshwater clams in Michigan and New York are Cercaria micromyae from Micromya iris and Alasmidonta marginata, C. catatonki from Strophitus undulatus quadriplicatus, C. honeyi from Anodontoides ferussacianus and Alasmidonta calceolus, C. pyriormis from Micromya iris, and C. filicauda from Elliptio dilatatus. All develop in simple, egg-shaped daughter sporocysts lying in the visceral masses of these unionid clam hosts. Within the sporocysts cercariae possess club-shaped tails, each with a much-plaited cuticula lined with large, loosely-arranged cells. Upon emergence into the water the latter is rapidly imbibed by the cuticula which swells into a balloon-like structure into which the cercarial body is quickly retracted. Encystment occurs within these transformed tails, resulting in the metacercarial stage. The cercaria and metacercaria are nearly morphologically alike, differing only in that the latter has one pair of penetration glands less, and also lacks cystogenous glands. Cercariae lack a stylet; have sensory papillae over their bodies; have well-developed penetration glands; have definite circular cystogenous glands; have their reproductive systems differentiated into all their component parts; and have nervous systems of three main pairs of nerve cords. The excretory bladder is thick-walled, its development being similar to that described for stylet-bearing cercariae. Probably the related rhopalocercariae, macro-cercariae and microcercaria have evolved from a common unknown ancestor. A divergence led to the present day rhopalocercariae and another group which further diverged to form the present day microcercaria and the large group of macrocercariae.