Kingdom Animalia Phylum Platyhelminthes The third phylum is Platyhelminthes which includes flatworms which are unsegmented by laterally symmetrical worms. Flatworms show a definite level of organization. They are the first and the simplest organisms having an organ system.
Flatworms do not have a definite skeleton, but have a cuticle which protects their bodies. Flatworms have a highly branched cut, with a mouth, but the anus is absent. A muscular septorial pharynx is present, for taking in the food.
Flatworms mark the beginning of cephalization. Cephalization is the development in the head region of life-sensitive organs called ocelli. For example, planaria have eye spots at the anterior end. Non-parasitic flatworms respire through their body's surface. while parasitic worms are mostly anaerobes.
Parasitic flatworms bear organs of adhesion such as hooks, suckers and spines. In flatworms, the central nervous system consists of a head ganglion connected to nerve cords which are interconnected across the body by transverse nerve connections excretion and osmoregulation in flatworms is controlled by the flame cells flame cells beat incessantly resembling a flickering flame and are hence called flame cells most flatworms can reproduce sexually or asexually. They are hermaphrodites, that is, both sexes are present in the same individual, except in the case of planarians, which are monoecious.
The development may be direct, where eggs hatch into small tiny worms that resemble the adult, or it may be an indirect development, where the eggs hatch into small tiny worms that resemble the adult. into saluted novel forms phylum platyhelminthes is further divided into three classes double area trematode a and says toda classed a malaria includes non-parasitic and aquatic flatworms which possess a great power of regeneration an example of the same is planaria trematode which is the second class includes parasitic flatworms that live inside the host these worms are commonly known as flukes examples of this class are fasciola hepatica and sheep liver fluke flatworms which belong to the third class that is Cestoda are known as tapeworms. All tapeworms are internal parasites.
At the anterior end of their body, the scollex, they have suckers and hooks for effective anchoring to host tissues. A good example of this category is tinea. The most primitive flatworms resemble the planula larva of cilenterates. in this structural organization majority of flatworms are endoparasites and cause diseases in humans, sheep, goats, dogs and other domesticated animals