Distinguish between

Question

Distinguish between Platyhelminthes and Nemathelminthes.

Vidyadip · Accepted Answer

The members of this phylum are called as flatworms.
Unique features of phylum Platyhelminthes:

Body shape: Body of these animals is dorsoventrally flattened.
Coelom: They are acoelomates.
Germ layers: Platyhelminthes are triploblastic.
Body organization: They show organ-system grade of organization.
Forms: Most of them are endoparasites and few are free-living. Parasitic forms have hooks and suckers for attachment to the hosts’ body. In parasitic forms, body is covered by cuticle and in free-living forms it is covered by cilia.
Digestive system: Parasitic forms generally lack digestive system. In free-living forms, the digestive system is incomplete.
Body plan: They show blind-sac body plan.
Excretion and osmoregulation: It occurs by flame cells or protonephridia.
Reproduction: They are mostly hermaphrodite (bisexual). Self fertilization is seen. Few animals show high power of regeneration and show polyembryony.
e.g. Planaria, Taenia (Tapeworm), Fasciola (Liver fluke) are included in this phylum.
Phylum Aschelminthes (ascus – sac, helminth – worm) is also called as Nemathelminthes (Nema = thread, helmins = worms).

Characteristics of Aschelminthes:

Forms: These are mostly parasitic. However, few forms are free-living.
Body shape: The body is long, cylindrical, thread-like, circular in cross-section, hence they are known as roundworms.
Body symmetry: These are bilaterally symmetrical.
Coelom: They are pseudocoelomate animals.
Germ layers: These animals are triploblastic.
Body plan: They show tube within a tube type body plan.
Body covering: The body is covered by tough, resistant cuticle.
Muscles: Body wall has longitudinal muscles, but circular muscles are absent.
Digestive system: Alimentary canal is complete with mouth and anus, at opposite ends.
Excretion: Excretion takes place either by canals or gland cells.
Nervous system: Nervous system consists of a nerve ring and nerves.
Reproduction: Animals are unisexual i.e. sexes are separate. Fertilization is internal. Development may or may not include larval stages. It shows sexual dimorphism.
e.g. Ascaris (Roundworm), Wuchereria (filarial worm) and Ancylostoma (hookworm).

Answer