is small; in fact, infection may follow consumption of only one raw crayfish.
gouldii, we hypothesize that (1) with size as a proxy for exposure time, the number of metacercariae
per clam will increase with valve length, and (2) because female bivalves are often larger than conspecific males, parasites will be more numerous in female clams.
Thirteen helminth species were found; one species of Cestoda (Distoichometra bufonis); six species of Digenea (Deropegus aspina, Glypthelmins quieta, Gorgoderina multilobata, Haematoloechus kernensis, Megalodiscus microphagus, an unidentified species represented by Echinostome metacercariae
); four species of Nematoda (Cosmocercoides variabilis, Rhabdias ranae, Hedruris sp., a unidentified species belonging to the Physalopteridae [third stage larvae only]; and two unidentified species of Acanthocephala (Centrorhynchid and Oligacanthorhynchid cystacanths).
After several developmental stages (sporozoites, redia, and cercariae) free-swimming cercariae leave the intermediate hosts, swim actively through water, and adhere to plants, where they encyst to form metacercariae
(the infectious stage).
Brittle stars, which transmit Fellodistomum metacercariae
to plaice, become infected by feeding on cercariae which develop in bivalve mollusks (Koie, 1980).
Within the gills, Ascocotyle cercariae enter the blood stream by penetration of the vascular tissue and encyst to form metacercariae
in the fish host.
Since the cercariae penetrate their second intermediate host, it is conceivable that this larval trematode may overwinter as metacercariae
in the frog host.
Subsequently they invade crustaceans, the second intermediate host, and encyst to become the infective metacercariae
. Human and domestic animals become infested by eating raw crustaceans (especially crabs), contaminated foods, or inadequately prepared foods.
Snails from the collection were dissected and the metacercariae
from a total of 25 infected snails were fed to each of four laboratory mice.
Aeby found coral polyps (Porites spp.) become distended following infection with metacercariae
(Plagioporous sp.), causing colonies to suffer reduced growth.
The encysted larvae, known as "metacercariae
," are killed within a few days if exposed to extreme cold or dryness.