Question

How do the body structures of parasitic flatworms differ from those of free-living forms?

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Answer 1

Parasite requires a host for their own survival. Major groups of parasites belongs to protozoa, helminths and some arthropods. There are mainly two types of parasites Ectoparasites ( found on the external surface of the body for eg. mite, tick etc) and Endoparasites ( found inside the body such as intestine, blood for eg. Giardia, malaria, flatworm).
Parasites obtain nutrition and shelter from the host and it may or may not be harmful to the host.

Adaptation of Flat worm as parasite :- They are also called as Fasciola hepatica or liver fluke.
The body is dorso-ventrally flattened with 25 to 30mm length and 4 to 5mm breadth.
The posterior end is small and the conical while the anterior end is large and more rounded in front than behind.
It has an oral sucker which is situated apically and highly muscular ventricle suckers are located little posterior to the oral sucker which helps in nutrition.
Mouth is situated at anterior end.
it has simple digestive system, pharynx is muscular, oesophagus is short and branched.

The larva also plays very important role.
The larva also bears a tail and flat and oval body.
It has true suckers which are lost after encystment and flame cells as excretory organ. It attaches to the aquatic plant after swimming for short time and is swallowed by final host sheep.

The other free living forms does not possess the above characteristics. For locomotion flatworm has many tiny cilia on the outer surface of its body. Free living forms have longitudinal muscles which contract to bend their bodies in a thrashing motion.Parasites have simple live cycles and gastrovascular cavity with single opening. Parasites have teguments where as free living form does not possess them.