Studies on the heterophyid trematode Apophallus brevis, the "sand-grain grub" of yellow perch (Perca flavescens) I. Redescription and resolution of synonymic conflict with Apophallus imperator Lyster, 1940 and other designations

Apophallus brevis Ransom, 1920, collected from the intestine of a ringbilled gull (Larus delawarensis), has been identified as the definitive stage of metacercariae found encysted in flesh of yellow perch (Perca flavescens). These metacercariae and (or) cysts have been described under various names: Distomum sp. larv. of Cooper, 1915; "sand-grain grub," Tetracotyle sp. of Hunter, 1942; and Apophallus itascensis Warren, 1953. In addition, an aberrant postmetacercarial form was described as Apophallus americanus by Van Cleave and Mueller (1932). Known definitive hosts are ringbilled and herring gulls (L. argentatus), the latter constituting a new host record for this worm species.Apophallus imperator Lyster, 1940, the etiological agent of "black-spot disease" in brook trout (Salvelinus fontinalis), synonymized by Miller (1941) with Apophallus brevis, is here recognized as a distinct species. Except for shape and length of pharynx, adult flukes of these two species are difficult to differentiate unless extremes of characters are present in observed specimens as ranges of measurements of morphological features have considerable overlap. Though these organisms are nearly identical morphologically during the adult stage, they have the following major distinctions: host specificity, sexual development, location and type of cyst and body size as metacercariae, and maturation time and longevity in definitive hosts.