卵形半肠吸虫的生活史研究(Trematoda:Mesocoeliidae)

STUDIES ON THE LIFE HISTORY OF MESOCOELIUM OVATUM GOTO AND OZAKI, 1930 (TREMATODA:MESOCOELIIDAE)

本文首次阐明卵形半肠吸虫(Mesocoelium ovatum Goto et Ozaki,1930)的全程生活史。在福州,终宿主为黑眶蟾蜍(Bufo melanostictus),实验中间宿主为蜗牛,Bradybaena similaris和Cathaica ravida sieboldtiana。蜗牛吞食本吸虫卵而受感染。毛蚴在蜗牛肠管内孵化,而后钻到肠壁外发育为母胞蚴、子胞蚴、尾蚴和囊蚴各发育期。囊蚴可在子胞体中形成并可感染黑眶蟾蜍。本文讨论了半肠属(Mesocoelium)的演化系统问题及与外斜睾总科(Plagiorchioidea)中一些吸虫类群的关系。

This brief communication reports on the life history of Mesocoelium ovatum, which is a common parasite of Bufo melanostictus in Fujian Province. The molluscan intermediaries are land snails, Bradybaena similaris and Cathaica ravtda sieboldtiana. The toad becomes infected by eating the infected snails, which contain the mature metacercarial cysts.Experimental infections conducted by feedin land snails with fully embryonated eggs resulted in producing mother sporocysts attaching to the outer surface of the intestinal wall of the snail. The mother sporocyst was found to contain some germinal cells, which subsequently grew to be germ balls, while the early mother sporocyst assumed the appearance of a solid body. At 24 days in summer and 68 days in winter, the largest mother sporocysts have diameters of 0.86-0.95 mm and contained daughter sporocysts of various sizes.The smallest early daughter sporocysts liberated from the mother sporocyst were of the size 0.095-0.206×0.077-0.133mm with a thick wall of a single layer of cells. In experiments performed during the winter season the daughter sporocysts of those land snails infected after 93 days reached 0.162-0.867×0.085-0.170mm in size but their progenies were still in germ ball stage and the cercarial embryos were still not yet differentiated. However, about 100 days after infection some mature daughter sporocysts began to harbour different stages of cercariae and even encysting metacercariae.The cercariae were tailless cercariaeum. The mature cercariae in the daughter sporocysts were of the size 0.238-0.425×0.085-0.153mm. The metacercarial cyst was round or oval in contour, 0.136-0.221×0.119-0.170mm in size. Inside the transparent cyst wall the structure of the metacercaria could be observed.The mature metacercarial cysts, even after dissected out from the daughter sporocysts, when fed to the toad could grow to become juveniles and then fully grown adults.