The Life History of Cryptocotyle concavum (Creplin, 1825) Fischoeder, 1903 (Trematoda: Heterophyidae)

Abstract

This paper results from a parasitological study of a population of three-spined sticklebacks, Gasterosteus aculeatus L., encountered during a hydrobiological survey of the Santa Ynez River directly northwest of Santa Barbara, California. The fish were often so heavily infected with encysted metacercariae (as many as 2,000 cysts in a single fish) that they appeared almost entirely black from the deposition of melanin. Attempts to infect young chicks and ducklings with the metacercaria were successful. The adult trematodes obtained experimentally belong to the family Heterophyidae and the species Cryptocotyle concavum (Creplin, 1825) Fischoeder, 1903. They were assigned to this species since the body is ovoid and the testes are side by side. Thus they differ from C. jejunum Nicoll, 1907, C. echinata (Linstow, 1879) and C. lingua (Creplin, 1825) Fischoeder, 1903, which have linguaform bodies and testes in tandem. Since they possess ovoid eggs they differ from C. cryptocotyloides (Issaitchikow, 1923), and C. quinqueangulare (Skrjabin, 1923) which have reniform eggs. The vitelline follicles extend more anteriorly than in previously described and figured specimens of C. concavum. Considerable variation is found in closely related species as the result of development in different hosts, so this is considered as a variation within the species. As far as is known, members of the Heterophyidae have similar life histories. The cercariae upon emergence from the snail hosts encyst in fishes, or rarely in amphibians, being transferred passively to the definitive host when the infected fish are eaten. One peculiarity of the heterophyids is the lack of specificity in the final host since, at least experimentally, all members which have been fully investigated develop to maturity in both avian and mammalian hosts. To date the local definitive hosts of C. concavum have not been determined although various herons were observed feeding along the stream. According to European workers, the definitive hosts are various aquatic birds. Issaitschikow and Weinberg (1926) identified small heterophyids taken from dogs, cats and rats in the Crimea as C. concavum. This would indicate that this fluke is capable of infecting both birds and mammals. The species is fairly widely distributed in Europe but it has not been previously recorded in North America. SYNONYMY Cryptocotyle concavum was originally described by Creplin (1825) as Distoma concavum. Looss (1899) placed D. concavum and the apparently closely related D. lingua in the genus Tocotrema. Liihe (1899) in the same year erected the genus Cryptocotyle but it remained for Fischoeder (1903) to place both D. concavum and D. lingua in the genus Cryptocotyle. Ransom (1920) in his work on the family Heterophyidae retained both in the genus Cryptocotyle, but Witenberg