Platyhelminthes: Flatworms


Flatworms are comprised of rather simple, bilaterally symmetrical, unsegmented, flattened soft-body that unlike other worms lack a body cavity and respiratory organs. All flat worms are limited to sized and shapes that can be supplied with oxygen by diffusion. Many flatworms are hence microscopic and leaf-like, although elongated species as large as 60 cm also occur.

One subgroup, the planarians, are known for their capacity to regenerated from fragments. Most ‘Turbellaria’ are predators or scavengers that can be brightly colored.

Traditionally, four major groups were included in the flatworms including three parasitic groups and the turbellarians. A new system, however, has been proposed in which the Acoelomorpha, formerly within the Turbellaria, were separated out and it was suggested the term ‘Turbellaria’ be no longer used.

There are a total of about 130 species free-living species known from the Arctic, the number of parasitic species is completey unknown.

Page Author: Bodil Bluhm
Created: Sept 20, 2010

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