Cercaria


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cercaria

[sər′kar·ē·ə]
(invertebrate zoology)
The larval generation which terminates development of a digenetic trematode in the intermediate host.

Cercaria

 

the larva of parasitic worms of the class Trematoda. The body, which measures 0.3–1 mm in length, has an oral and a ventral sucker. Cercariae have a furcately branched intestine, a nervous system, sometimes ocelli, cephalic glands, and well-developed protonephridia. Typical of cercariae is the development of a tail, which is sometimes bifurcate (in furcocercariae) or equipped with lateral appendages.

The cercaria develops inside the preceding larval form, the sporocyst or redia, as a result of parthenogenesis. It leaves the body of the first intermediate host, a mollusk, and swims in water by means of its tail. It then penetrates the body of the second intermediate host, an invertebrate or frequently a fish, and becomes a metacercaria. The common liver fluke has no second intermediate host; the cercaria becomes encysted on coastal vegetation and is transformed into the next larval form, adolescarium.

References in periodicals archive ?
Snails coded 3FM35 and 1 M61 demonstrated the presence of both echinostome and fork-tailed cercaria. This represented 0.27% of the total 750 snails collected.
In Caratinga, Mina Gerais, Brazil Ruiz (1953) described the Cercaria caratinguensis from Australorbis glabratus (= B.
Groups of ten experimental cercaria larvae were added to Petri dishes containing 10 mL dechlorinated tap water.
Swimming is accomplished by a tail (~400 [micro]m long) attached subterminally to the body (~150 [micro]m long); the cercaria swims in rapid but intermittent zig-zag pulses as the tail lashes rapidly.
Denton, 1941 chloropus Duct heterolecithoides Brachylecithum Cyanocitta Liver Bile Valid americanum Denton, cristata Duct 1945 Cercaria brachystyla Helisoma Digestive Valid Byrd & Reiber, trivolvis Gland 1940 C brevicauda Byrd H.
(5) found that uninduced free swimming cercaria released relatively small number of non-acetabular gland proteins including enolase, Sm28GST and actin (7), while the major secreted proteins were histolytic serine proteases that likely facilitate degradation of host skin tissue barrier, and factors that may contribute to immune evasion.
Once in subcutaneous tissues, the cercaria loses its tail to become a schistosomule and penetrates peripheral vessels allowing migration to the heart and then the lungs.
Cercaria then is produced and leaves the snail and can now infect humans.
The eggs hatch in water and go through a series of developmental stages in a snail (miracidium, sporocyst, redia I, redia II, cercaria) and enter the gills, muscles or viscera of fresh-water crustaceans.