Abstract

Embryonated eggs of Haematoloechus breviplexus Stafford, 1902 were fed to laboratoryreared specimens of Gyraulus similaris (F. C. Baker, 1919). Miracidia hatch in the snail intestine, then invade the intestinal epithelium, many penetrating only as far as the basement membrane, but some passing through to the hemocoel of the snail. In either location they metamorphose to the mother sporocyst which enlarges gradually as the germinal cells multiply. Those mother sporocysts that are enclosed by basement membrane soon become pedunculate and detach from the intestine when the basement membrane ruptures. By the 12th day, the limiting membrane of many mother sporocysts ruptures, freeing the germinal cells which continue multiplying in the hemocoel of the snail. Between the 12th and 22nd days, the germinal cells give rise to many daughter sporocyst embryos which also undergo their development in the hemocoel. There is no host cellular response to the parasite, and consequently, paletots do not develop around the sporocysts. Xiphidiocercariae of the Omatae group are produced within 31 days and encyst in the branchial basket of naiads of the dragonfly, Aeschna multicolor Hagen, 1861. Metacercariae were fed to newly metamorphosed specimens of Rana pretiosa (Baird and Girard, 1853), and young adults of H. breviplexus were recovered 22 and 23 days later. The development of sporocysts of H. breviplexus is compared to that of several other species of plagiorchioid trematodes formerly studied by the author. Sporocyst development of H. longiplexus Stafford, 1902 and H. parviplexus (Irwin, 1929) was also observed and found to be identical to that of H. breviplexus. New host and distribution records are given for H. longiplexus and H. breviplexus. The present report represents part of the results of a long-range investigation of sporocyst and paletot development of plagiorchioid trematodes. The work was done during the summers of 1963 and 1964. Knowledge of the life cycle of Haematoloechus variegatus (Rud., 1819) was contributed by van Thiel (1930), who fed metacercariae, from anopheline larvae, to frogs and recovered adults of H. variegatus. Krull (1930 and 1931) reported on the life histories of H. medioplexus Stafford, 1902 and H. parviplexus (Irwin, 1929). The host snail for the latter species is Gyraulus parvus (Say, 1817), whereas, Planorbula armigera (Say, 1818) serves as host for H. medioplexus. He observed all stages except the mother sporocyst, and found that dragonfly naiads of the genus Sympetrum Newman, 1833 serve as second intermediate hosts for both species. The definitive host for H. parviplexus is Rana clamitans Latreille, 1802, while R. pipiens Schreber, 1782 serves as host for H. medioplexus. Krull (1932) found metacercariae of H. longiplexus Stafford, 1902 in the damselfly, Lestes vigilax Hagen, 1862, fed some to bullfrogs, and recovered adults of this species. The host snail was unknown. Krull Received for publication 24 November 1964. (1933 and 1934) observed the daughter sporocysts and cercariae of H. complexus (Seely, 1906) in Pseudosuccinea columella (Say, 1817). Naiads of three species of dragonflies serve as second intermediate hosts, and Rana clamitans serves as definitive host. Ingles (1933) investigated the life cycle of H. oxyorchis Ingles, 1932 from Rana aurora (Baird and Girard, 1852) and found that Gyraulus parvus and G. vermicularis (Gould, 1847) serve as first intermediate hosts. Ingles observed a 50-dayold daughter sporocyst and found that the cercariae encyst in dragonfly naiads of the genus Sympetrum. None of the above authors observed the mother sporocyst of any species. MATERIALS AND METHODS Second and third generation laboratory-reared specimens of Gyraulus similaris (F. C. Baker, 1919) were used throughout the investigation. Snails were maintained in enameled pans of aquarium water to which was added powdered calcium carbonate and an abundance of aquatic plants. The thick basal parts of lettuce leaves were added as food. As the lettuce decayed, the snails fed on it readily. Only young snails, having a shell diameter of 1.5 to 2 mm, were used. Mature specimens of H. breviplexus were obtained from the lungs of Rana pretiosa (Baird and Girard, 1853). The trematodes were placed in dishes of aquarium water for release of eggs.

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