Trematoda

{{Taxobox | color = pink | name = Trematoda | image = A-ferox_digenean1.jpg | image_width = 250px | image_caption = Botulus microporus, a giant digenean parasite from the intestine of a lancetfish | regnum = Animalia | phylum = Platyhelminthes | classis = Trematoda | classis_authority = Rudolphi, 1808 | subdivision_ranks = Subclasses | subdivision = Aspidogastrea
Digenea
}}

The Trematoda is a classwithin the phylumPlatyhelminthes, which contains two groups of parasitic worms.

Taxonomy

All trematodes are parasiticflatworms. Previous classification systems included the Monogeneaamongst the trematoda, alongside the Digeneaand Aspidogastrea, on the basis that they were all vermiformparasites. The taxonomy of the Platyhelminthes is being subjected to extensive revision thanks to modern phylogeneticstudies, and modern sources place the Monogenea in a separate class within the phylum.

Etymology

Trematodes are commonly referred to as flukes. This term can be traced back to the Saxonname for Flounder, and refers to the flattened, rhomboidal shape of the worms.

There are no known cases of human infection with Aspidogastreans, therefore the use of the term "fluke" in relation to human infection refers solely to digenean infections.

The flukes can be classified into two groups, on the basis of the system which they infect. Tissue flukes, are species which infect the bile ducts, lungs, or other biological tissues. This group includes the lung fluke, Paragonimus westermani, and the liver flukes, Clonorchis sinensis and Fasciola hepatica. The other group are known as blood flukes, and inhabit the bloodin some stages of their life cycle. Blood flukes include various species of the genus Schistosoma.

Life Cycles

Trematodes have a complex life cycle, often involving several hosts. The eggs pass from the host with the feces. When the eggs reach water, they hatch into free-swimming forms called miracidia. The miracidia penetrate a snailor other molluscanhost to become sporocysts. The cells inside the sporocysts typically divide by mitosisto form rediae. Rediae, in turn, give rise to free-swimming cercariae, which escape from the mollusk into water. Using enzymesto burrow through exposed skin, cercariae penetrate another host (often an arthropod) and then encystas metacercariae. When this host is eaten by the definitive host, the metacercariae excyst and develop and the life cyclerepeats. For more information on life cycles, see the respective pages on digeneaand aspidogastrea.

Chemical castration of hosts

Some parasitic trematodes chemically castratetheir host.

Literature

• Gibson,D.I., Bray,R.A. & Jones,A., Keys to the Trematoda, 3 Volumes ISBN 0851995470de:Saugwürmer

fr:Trématode ja:?? pl:Przywry pt:trematoda sl:Sesači

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Trematoda Wikipedia article Trematoda.