$(a)$ State two characteristic features of nematodes.
$(b)$ Identify the phylum with the help of the following features:
$(i)$ Spiny-skinned,radially symmetrical,and have tube feet.
$(ii)$ Triploblastic,worm-like,having a segmented body.

(N/A) Characteristic features of nematodes:
$(i)$ Nematodes have a cylindrical,bilaterally symmetrical,and triploblastic body.
$(ii)$ They are often parasitic and can cause diseases in plants and animals.
$(b)$ $(i)$ The phylum is $Echinodermata$. These organisms possess a spiny skin (calcareous ossicles),radial symmetry in adults,and a water vascular system with tube feet for locomotion.
$(ii)$ The phylum is $Annelida$. These organisms are triploblastic,coelomate,and exhibit true segmentation (metamerism) in their worm-like bodies.