from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The parasitic larva of a trematode worm, having a tail that disappears in the adult stage.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The parasitic larva of trematodes; its tail disappears when adult.
from the GNU version of the Collaborative International Dictionary of English
- n. The larval form of a trematode worm having the shape of a tadpole, with its body terminated by a tail-like appendage.
from The Century Dictionary and Cyclopedia
- n. In zoöl, the second larval stage of a trematoid worm or fluke, named by O. F. Müller in 1786 as a genus of infusorians.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. tadpole-shaped parasitic larva of a trematode worm; tail disappears in adult stage
Inside the snail, the parasite passes through several generations before producing a missile-shaped stage called a cercaria.
The infective form of schistosoma, called a cercaria, secretes proteases upon detection of human skin lipids (McKerrow & Salter, 2002).
A fluke, for example, hatches into a delicate form covered with hairlike cilia that swim in search of a snail; a couple of generations later, a cercaria emerges from the snail to find its mammal host.
The cercaria then penetrates human skin and becomes an adult that finally ends up in the veins of its human host.
In this stage it grows into a cercaria which possesses a single opening digestive tract, suckers and a tail, enabling it to leave the snail and seek out the secondary intermediate host, usually an arthropod or a fish, where it encysts, becoming a metacercaria.
During the cercaria stage they develop both a tail which enables them to find a host and a digestive tract and suckers.
In an internal organ of the snail (equivalent to the liver and pancreas combined) the miracidium transforms into a cercaria (the infective larval stage) in about a month.
Systemic treatment and cooking of all food had cleaned up the infective cercaria and individual infections, and after six months of intensive search, quarantine, and investigation, Kennon was morally certain that the disease had been eradicated.
The _daughter redia_ or _cercaria_, as they are now termed, leave the body of the snail and finally become encysted on the stems of grass, cresses and weeds.
The period of development varies from ten to twenty weeks; each sporocyst may give rise to from five to eight _redia_ and each redia to from twelve to twenty _cercaria_.