中口短咽吸虫Brachylaima mesostoma(Rud.,1803)Baer,1933的生活史研究(Trematoda:Brachylaimidae)

STUDIES ON THE LIFE CYCLE OF BRACHYLAIMA MESOSTOMA (RUD., 1803) BAER, 1933 (TREMATODA: BRACHYLAIMIDAE)

寄生于鸟类和哺乳类的短咽科(Brachylaimidae)中的短咽属(Brachylaima)吸虫经记述有60余种,但有关生活史的报道不上10种。本文报道在福州二种陆地蜗牛,Bradybaena similaris和Cathaica ravida sieboldtiana,体内所见的一种短咽类吸虫的幼虫期包括胞蚴,尾蚴和后期尾蚴的观察。因此成熟的后期尾蚴人工感染八哥(Acridotheres c.cristatellus)雏鸟获得中口短咽吸虫(Brachylaima mesostoma)的成虫。本吸虫的天然终宿主在福州有八哥和黑鸫(Turdus merulamandarinus)。

This paper presents the result of studies on the life cycle of Brachylaima mesostoma in Fu-zhou, Fujian Province. The normal hosts of the trematode are Chinese crested myna, Acrido-theres c. critatellus (Linn.) and Chinese black bird, Turdus merula mandarinus Bonaparte. The molluscan intermediate hosts are the terrestrial snails, Bradybaena similaris Ferussac and Ca-thaica ravida sieboldtiana Pfeiffer. Each of them, when infected, serves as the first and second intermediaries, because the developed mature cercariae can migrate to the snail of the same species when they are in contact with each other especially during copulation. The development of the worm can be divided into the following stages:1. Adults living in the intestine of mynas and Chinese black birds, are 1.044-5.436 mm in length and 0.360-1.027 mm in width. They possess the most characteristic feature of this trematode species, Brachylaima mesostoma. 2. Egg and miracidium: The operculated egg is 0.036-0.054×0.018-0.027 mm (0.046×0.022 in average) in size. It contains a miracidium when laid. The miracidium is pear shaped. Its body length and width is 0.030×0.018 mm. On its anterior extremity, there is a rod-shaped stylet. The body of the miracidium possesses four cells arranged in two rows, with two cells in each row. Only one group of cilia in two rows arise from the level of hind row of cells above-mentioned and extend posteriorly over the end of the body.3. Sporocysts: There are two generations of sporocysts, mother sporocyst and daughter sporocyst, developing in the first intermediate host. Branched mother sporocyst is 2.19×0.81 mm in size. Branched daughter sporocysts fill the digestive gland, kidney and connective tissue of land snail host.4. Cercaria: Cercaria with a vestigial small tail is produced from the mature daughter sporocyst. The shape of cercaria is oval, however, it is broader anteriorly and gradually becomes narrower toward the tail. It possesses a short prepharynx, muscular pharynx, short oesophagus and intestinal arch. Two groups of penetration glands, with six or seven cells each are situated on each side of the acetabulum near its hind border; the gland cells lead forward in two bundles of ducts to the anterior edge of oral cavity. From the anterior end of excretory bladder arise two vessels which go anteriorly to about the level of the pharynx and turn backward to the middle of body and divide into anterior and posterior branches. The flame cell formula is 2[2 + ((2 + 2) + 2)] = 165. Metacercaria: The metacercariae when dissected out from the snail appear to be in different sizes. They are 0.586-2.002 mm in length and 0.288-0.925 mm in width. In some cases, the excretory vessels anastomose to form net-work structure. A few precociously developed metacercariae even show ovary and testes.6. Two nestling crested mynas were experimentally fed with eight and twenty metacercariae for each bird. Two mature adults containing some eggs were found from one of the birds 8 days after infections.