The phylum : Aschelminthes

The body of the aschelminthes is circular in cross-section, thats why called roundworms. Aschelminthes may be freeliving, aquatic and terrestrial or parasitic in plants and animals. Aschelminthes are bilaterally symmetrical, triploblastic and pseudocoelomate animals. Roundworms have organ-system level of body organisation.

Alimentary canal is complete with a well developed muscular pharynx. An excretory tube removes body wastes from the body cavity through the excretory pore.

Sexes are separate (dioecious). Often females are longer than males. Fertilisation is internal and development may be direct (the young ones resemble the adult) or indirect.

Examples : Ascaris (Roundworm), Wuchereria (Filaria worm), Ancylostoma (Hookworm).