Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Biology






Lissorchis heterorchis



Physical Description

1 online resource (v, 49 leaves, ill. 28 cm.)


Many Flumenicola virens (Lea) collected from Crystal Springs Creek and Tualatin River, Portland, Oregon, were found to shed large numbers of a species of microcercous cercariae containing refractile granules. They resembled the cercariae of Triganodistomum mutabile (=Lissorchis mutabile Cort, 1918 as described by Wallace (1939), and subsequent experiments proved that they were the larval stages of what was described by Macy and Krygier (1969), as Lissorchis heterorchis. Encystment of these cercariae was induced experimentally in uninfected adult brown planarians collected partly from Crystal Springs Creek and partly from Carolina Biological Research Station in Gladstone, Portland, Oregon. Adult flukes were obtained by feeding infected planarians to rough-scaled suckers which occur in some creeks and rivers in Oregon. In another experiment, eggs recovered from adult Lissorchis heterorchis Macy and Krygier, were experimentally fed to snails, Flumenicola virens (Lea). The snails after five weeks of incubation in an aquarium developed cercariae which matched both in morphology and measurements with the cercariae from the naturally infected snails, Flumenicola virens. The experimental cercariae were also induced to encyst in the uninfected planarians from the Crystal Springs. These cysts matched with cysts from the first experiment with respect to the measurements.

Thus, this life cycle follows the same pattern described by Wallace (1939) in which the eggs of the adult Lissorchis mutrmediate host develops into rediae that gave rise to lissorchid cercariae. The cercariae produced encyst in planaria or an annelid, tentatively identified as Chaetogaster limnaei v Baer the metacercariae of which when eaten by a sucker develops into adult Lissorchis mutabile.

For this life cycle under investigation, two intermediate hosts are necessary, one, a snail, and two, a planarian or an annelid. Direct infection of the definitive host with the eggs or the unencysted cercariae shows that no adults are formed. Attempted infection of the definitive host with infected planarians in which the cysts were less than five weeks old in the planaria also shows that no adults were formed.

Experiments carried out on the shedding rate of cercariae shows that the cercariae are shed in small numbers so that the productivity of cercariae is low. Examination of 7200 Flumenicola shows that there is only 3% incidence in these snails and there is no marked seasonal variation in the incidence. Continous light inhibits the rate of cercaria discharge whereas continuous darkness promotes the rate of cercaria discharge.


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Portland State University. Department of Biology

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