Among the groups , which one have no systematic program for their elimination ?
The Ecdysozoa concept divides the taxon into two , the Panarthropoda into which the velvet worms are placed , and the sister group Cycloneuralia , containing the threadworms ( Nematoda ) , horsehair worms ( Nematomorpha ) and three rather obscure groups : the mud dragons ( Kinorhyncha ) ; penis worms ( Priapulida ) ; and brush - heads ( Loricifera ) .