Abstract
Previously unknown gymnophallid parthenogenetic metacercariae (PM), referred to as Cercaria falsicingulae I larva nov., were found in the extrapallial cavities of the snails Falsicingula mundana (Yokoyama) and F. athera (Bartsch) on coasts of Sakhalin and the Kuril Islands. Unlike all other known PM, rather than producing metacercariae infective to the definitive host, their furcocercariae emerge into the environment. The developing cercariae and metacercariae of C. falsicingulae I are described and compared with other gymnophallid larvae from littoral molluscs in the region. Experimental evidence and analysis of metacercarial group composition in naturally infected molluscs indicate that some cercariae leave their molluscan hosts and penetrate other specimens of Falsicingula in which they develop into new cercariae-producing PM. Metacercariae with developing hermaphroditic reproductive organs were never observed in naturally infected molluscs. A probable life-cycle for C. falsicingulae I is presented in which cercarial/metacercarial production is switched seasonally in order to enable the infection of the definitive hosts by PM. Importantly, the ‘cercaria – PM – cercaria’ component of the life-cycle appears to be somewhat autonomous.
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Acknowledgements
I thank Dr S. W. B. Irwin for his comments and the correction of the English and Dr D. I. Gibson for the editing of the manuscript. I am also indebted to two anonymous reviewers for their comments on the manuscript. Special thanks are also due to Dr K. V. Regel and Dr G. I. Atrashkevich for their valuable help during the fieldwork. The project was financed by grants from the RFBR and INTAS.
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Galaktionov, K.V. A description of the parthenogenetic metacercaria and cercaria of Cercaria falsicingulae I larva nov. (Digenea: Gymnophallidae) from the snails Falsicingula spp. (Gastropoda), with speculation on an unusual life-cycle. Syst Parasitol 68, 137–146 (2007). https://doi.org/10.1007/s11230-007-9097-3
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DOI: https://doi.org/10.1007/s11230-007-9097-3