Development of the Sporocyst Generations of Glypthelmins quieta (Stafford, 1900) (Trematoda:Plagiorchioidea), a Parasite of Frogs

Abstract

The development of the mother and daughter sporocysts and the paletots of Glypthelmins quieta was studied in laboratory-reared specimens of Physa gyrina. Following the ingestion of embryonated eggs, the miracidia hatch in the snail digestive tract and soon penetrate the intestinal epithelium. Mother sporocysts develop between the epithelium and the underlying basement membrane. At first the mother sporocysts are spherical but later they develop an uneven or lumpy surface as basement membrane cells multiply and invade the mother sporocyst to form cellular membranes around individual daughter sporocysts. These membranes are the paletots. As daughter sporocysts develop they remain in a compact mass, all held together by their paletots. Fully developed paletots are composed of flattened epithelial cells and fine fibers. Cercariae are released between the paletot and the sporocyst body wall. Paletot formation is dependent upon a cellular response to the invading parasite by the host snail. This represents an attempt by the host to isolate or wall off the parasite. The method of development of the sporocyst generations and paletots of G. quieta was found to be similar to that of Haplometrana intestinalis, but quite different from that of Telorchis bonnerensis. On the basis of cercarial anatomy, method of development of the sporocysts, and origin of paletots, G. quieta is thought to be closely related to H. intestinalis. The author suggests that G. quieta be assigned to the family Macroderoididae. Information on the life cycle of Glypthelmins quieta has been published by Rankin (1944) and by Leigh (1937 and 1946). Rankin's observations were made on naturally infected snails. He illustrated only a welldeveloped daughter sporocyst. Leigh (1946) illustrated and described two developmental stages of the mother sporocyst, 18 and 36 days old respectively, and also a young and a welldeveloped daughter sporocyst. Leigh used field-collected snails for his egg-feeding experiments. Cheng (1961) published an account of the life history of G. pennsylvaniensis Cheng which utilizes Helisoma trivolvis (Say) as intermediate host. He illustrated and described four developmental stages of the mother sporocyst and two stages of the daughter sporocyst. He used specimens of H. trivolvis that had been collected from a supposedly helminth-free lake. The present paper is the third in a series published by the author on the comparative development of the paletots and the sporocyst generations of representative genera and species plagiorchioid trematodes. Received for publication 8 January 1962. *This investigation was supported by a research grant (No. E-950) from the National Institutes of Health, U. S. Public Health Service. MATERIALS AND METHODS Mature specimens of Glypthelmins quieta were obtained from the intestine of the bullfrog (Rana catesbeiana), purchased from the Lemberger Co., Oshkosh, Wisconsin. Laboratory-reared specimens of Physa gyrina were used throughout the investigation. The adult snails were collected and brought to the laboratory for oviposition. Egg masses were distributed to large fingerbowls containing aquarium water, stems of Elodea, soaked maple leaves, and powdered calcium carbonate. Young snails having a shell length of 2 to 3 mm were used for egg-feeding experiments. Groups of 25 to 30 snails were placed in 2-inch Stender dishes with embryonated eggs of G. quieta. The snails were permitted to ingest eggs for 15 to 20 minutes, after which they were transferred to clean culture dishes. Examination of snails was begun 1 hour after feeding eggs and continued daily. Most observations were made from living specimens. The snails were dissected in 0.2 per cent solution of sodium chloride and studied as wet preparations under the oil immersion objective. Dilute aqueous neutral red and acetocarmine were used to stain the germinal and somatic cells of the parasite. For more critical observation of histological details some infected snails were removed from their shells, placed in Heidenhain's Susa fixative, sectioned, and then stained with either Ehrlich's haematoxylin or Heidenhain's iron-haematoxylin. The age of the sporocysts is given in days in order to provide a more orderly sequence for the developmental stages. It is realized that the rate of development is affected by changes in the temperature of the environment.