THE LIFE CYCLE AND BIONOMICS OF LEVINSENIELLA CHARADRIFORMIS YOUNG, 1949 (TREMATODA: MICROPHALLIDAE)

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Abstract
Successive stages in the life cycle of Levinseniella charadriformis are described: sporocysts are found in the snail, Littorina scutulata; metacercariae parasitize the crabs Hemigrapsus oregonensis and Hemigrapsus nudus; adults were recovered from naturally infected gulls, Larus glaucescens, and experimentally infected L. glaucescens, mice, ducklings, chicks, goldfish, and frogs.In experimental infections of crabs, cercariae enter the gills, pass to the ventral blood sinuses and connective tissues, encyst, and develop rapidly. Three weeks after infection, the metacercariae have gonads, traces of the terminal genitalia, and stylets. Metacercariae removed from crabs at 5 weeks and placed in seawater cultures at 40 °C excyst and produce eggs. At 7 weeks, a thick cyst layer of host origin prevents excystment but the metacercariae still produce eggs in in vitro cultures. At this time, the metacercarial cysts resemble those found in natural infections of crabs.Temperatures of 30° and 40°, but not 23 °C, stimulated egg production in worms kept in seawater and seawater diluted 1:4; ovigerous worms lived up to 4 days. Experimental hosts such as goldfish and frogs that were kept at elevated temperatures were successfully infected with L. charadriformis.The complicated terminal genitalia of Levinseniella are discussed and adaptations to self-fertilization are suggested for L. charadriformis.