CERCARIA DIPTEROCERCA MILLER AND NORTHUP, 1926 AND STEPHANOSTOMUM DENTATUM (LINTON, 1900) MANTER, 1931

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Abstract
The morphology, composition and distribution of the genus Stephanostomum are considered. Taxonomic uncertainties and difficulties are described. It is postulated that the difficulties can be resolved only with knowledge of life cycles, larval forms, and developmental stages. Previous accounts of life-histories in the genus are reviewed. The cercariae described by Miller and Northup (1926) from Nassa obsoleta at Woods Hole, Massachusetts, are listed and their life-cycles are traced. Cercaria dipterocerca penetrated and encysted in laboratory reared specimens of Menidia menidia. They continued development and the mature metacercariae manifested such precise agreement in number and shape of peristomial spines and in general morphology with juvenile and mature specimens of Stephanostomum dentatum, that C. dipterocerca may be the larval stage of S. dentatum. Cercaria dipterocerca is very different from the cercariae described by Martin (1938) and Wolfgang (1954, 1955) as the larvae of Stephanostomum tenue and S. baccatum, respectively. The larvae described by Martin and Wolfgang differ markedly from one another. These differences are far greater than is ordinarily encountered between spp. of a single genus and present as yet unresolved problems. The systematic position of Stephanostomum and the family to which it belongs are equivocal. If the genus is a member of the Acanthocolpidae, and if LaRue''s system is valid, the family must be transferred from the Allo-creadioidea to the Opisthorchioidea.