Phylum Platyhelminthes (Flatworms)

Gallery

Flatworm


Morphology

INTERESTING FACTS

Flatworms are unsegmented, bilaterally symmetrical worms that lack a coelom (acoelomate)
Some forms are free living but many are parasitic.
Flatworms have a cephalized nervous system that consists of head ganglion, usually attached to longitudinal nerve cords that are interconnected across the body by transverse branches. Excretion and osmoregulation by flatworms is controlled by "flame cells" located in protonephridia (these are absent in some forms).
Flatworms lack a respiratory or circulatory system; these functions take place by absorption through the body wall.
Nonparasitic forms have a simple, incomplete gut; even this is lacking in many parasitic species.

CLASSIFICATION

Trematoda
Trematodes are flattened oval or worm-like animals, usually no more than a few centimeters in length.
Their most distinctive external feature is the presence of two suckers, one close to the mouth and the other on the underside of the animal.
The body surface of the trematodes comprises a tough syncitial tegument which helps to protect against digestive enzymes in those species that inhabit the gut of larger animals.
It is also the surface of gas exchange.

Cestoda -tapeworm
The best known species are commonly called tapeworms.
All cestodes are parasitic and their life histories vary
Typically they live in digestive tracts of vertebrates as adults, and often in the bodies of other species of animals.
Over a thousand species have been described, and all vertebrate species may be parasitised by at lease one species of tapeworm .

VIDEO LINKS