Studies on Larval Monogenea of Fishes from the Chesapeake Bay Area. Part I

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Twenty-one species of Monogenea were collected from 16 species of fish from the Chesapeake Bay area. Eggs of 10 species were collected and yielded larvae for study: Ancyrocephalus parvus, Rhamnocercus bairdiella, Heterocotyloides pricei, Mazocraeoides hargisi, Macrovalvitrematoides micropogoni, Pedocotyle minima, Microcotyle poronoti, Cynoscionicola heteracantha, Heteraxinoides xanthophilis, and Nudaciraxine gracilis. Eggs of the Monopisthocotylea are pyramidal or angular and with a single, typically short, abopercular filament. Those of the Polyopisthocotylea are fusiform and bipolar or, less frequently, globular and unipolar. Both groups have an operculum. Body shapes of both monopisthocotylid and polyopisthocotylid oncomiracidia are pyriform to fusiform. Most have cilia, situated in 3 zones: anterior, equatorial, and on the posterior cone, except Mazocraeoides hargisi, where cilia occur in 8 zones of the body proper in addition to those on the posterior cone. The larval posthaptor is usually well defined and bears the attaching armature. In monopisthocotylid oncomiracidia the armature consists of 14 similar marginal hooks. Polyopisthocotylid oncomiracidia have 10 marginal hooks and one pair of anchors (Mazocraeoides hargisi, Pedocotyle minima, and Macrovalvitrematoides micropogoni); or 10 marginal hooks and 2 pairs of anchors (Microcotyle poronoti, Cynoscionicola heteracantha, Nudaciraxine gracilis, and Heteraxinoides xanthophilis). Comparisons of the larval armature indicate closeness of relationship between Nudaciraxine gracilis, Heteraxinoides xanthophilis, and Microcotyle poronoti, and between Pedocotyle minima and Macrovalvitrematoides micropogoni. The digestive system of monopisthocotylid and polyopisthocotylid oncomiracidia is essentially similar in that both groups possess a pharynx located in the middle third of the body which leads into a rhabdocoel-like intestine. Varying numbers of anterior glands are present: 2 pairs in Cynoscionicola heteracantha, 5 pairs in Pedocotyle minima, 9 pairs in Mazocraeoides hargisi, and 10 pairs in Heterocotyloides pricei. The excretory system consists of paired protonephridia, paired ciliated, or unciliated, excretory tubules, paired bladders located near the level of the pharynx, and paired lateral excretory pores. Monopisthocotylid oncomiracidia possess 4 pairs of flame cells. Polyopisthocotylid oncomiracidia vary. Some have 3 pairs of flame cells (Macrovalvitrematoides micropogoni, Cynoscionicola heteracantha, and Heteraxinoides xanthophilis), some 4 (Nudaciraxine gracilis and Pedocotyle minima), and one has 5 pairs (Mazocraeoides hargisi). Two pairs of pigmented eyespots are present in monopisthocotylid oncomiracidia; known polyopisthocotylid oncomiracidia vary in this character. Nudaciraxine gracilis possesses 2 pairs of eyespots; Microcotyle poronoti, one pair; Mazocraeoides hargisi, Cynoscionicola heteracantha, and Heteraxinoides xanthophilis have one centrally located eyespot; while Pedocotyle minima and Macrovalvitrematoides micropogoni have none. Little research has been done on oncomiracidia of oviparous Monogenea from North American fishes. Fairly complete studies have been made by Jahn and Kuhn (1932) on Neobenedenia melleni (= Benedenia melleni); Fischthal and Allison on Acolpenteron ureteroecetes in 1941, and on A. catostomi in 1942; Remley (1942) on Microcotyle spinicirrus; and Putz and Hoffman (1964) on Received for publication 28 January 1969. Contribution No. 305 from the Virginia Institute of Marine Science, Gloucester Point, Virginia. * Present address: Division of Microbiclogy and Veterinary Medicine, Box 3354, University Station, University of Wyoming, Laramie, Wyoming 82070. t Present address: University of Southern Mississippi, Southern Station, Box 1631, Hattiesburg, Mississippi 39401. Dactylogyrus corporalis. Fragmentary reports on larval development and morphology are found in the works of Bonham and Guberlet (1938) on Acanthocotyle pugetensis and A. pacifica, and Koratha and Martin (1960, 1963) on a number of species. The present study concerns larval Monogenea from 16 host species from the Chesapeake Bay area. Twenty-one species of Monogenea were recovered from these hosts (Table I). Of these, 16 produced eggs and, after incubation, eggs of 10 species hatched. The oncomiracidia were recovered, examined, and