Rhabditida

Rhabditida is an order of usually free-living microbivorous nematodes (roundworms) living in soil.

Genera include:

Bursilla (Mesorhabditis)
Caenorhabditis – of which C. elegans and C. briggsae have had their genomes deciphered
Cruznema
Enterobius (pinworms/threadworms) which are significant parasites
Heterorhabditis
Panagrellus which includes the microworm
Pelodera
Rhabditis
Steinernema
Strongyloides