The most significant characteristic of the nematodes is

1)Bilaterally symmetrical, and vermiform. 
2)Body has more than two cell layers, tissues and organs. 
3)Body cavity is a pseudocoel, body fluid under high pressure. 
4)Body possesses a through gut with a subterminal anus. 
5)Body covered in a complex cuticle. 
6)Has a nervous system with pharyngeal nerve ring. 
7)Has no circulatory system (no blood system) 
8)Reproduction normally sexual and gonochoristic. 
9)Feed on just about everything. 
10)Live just about everywhere, many species are endoparasites.

Reduction in overall biodiversity