Secernentea was a class of nematodes in the Classical Phylogeny System (Chitwood, 1958) and is no longer in use. This morphological-based classification system has been replaced by the Modern Phylogeny system, where taxonomy assignment is based on small subunit ribosomal DNA (SSU rDNA). Characteristics of Secernentea are: Subclasses and orders of Secernentea are: