Phylum-Aschelminthes or Nemathelminthes :
(i)They are called roundworm as they appear circular in cross section.
(ii)Free living, aquatic, terrestrial or parasitic.
(iii)Organisation of body is organ level.
(iv)Bilaterally symmetrical animals.
(v)They are triploblastic and pseudocoelomate.
(vi)Alimentation complete with muscular or pharynx.
(vii)Sexes are separate.
(viii)Body is covered by cuticle.
(ix)Fertilization is internal.
(x)Examples are filaria worm (Wuchereria), Ascaris, Hookworm (Ancylostoma) and Pinworm (Enterobius)