Write three characteristics each of the following groups of animals:
$(a)$ Platyhelminthes
$(b)$ Nematoda

(N/A) Platyhelminthes:
$(i)$ They are bilaterally symmetrical.
$(ii)$ They are triploblastic (three germ layers).
$(iii)$ They are dorsiventrally flattened (flatworms).
$(iv)$ They are acoelomate (no body cavity).
$(b)$ Nematoda:
$(i)$ They are bilaterally symmetrical.
$(ii)$ They are triploblastic.
$(iii)$ They possess a pseudocoelom (false body cavity).
$(iv)$ Their body is cylindrical and unsegmented.