Differences in the 5.8S rDNA sequences among ascarid nematodes.

Sequences of the 5.8S rDNA were obtained for 14 species of nematode from different superfamilies and families within the order Ascaridida. All sequences were 157 bp in length. Sequence differences among species ranged from 0 to 18 bp (0-11.5%). A phenetic analysis of the sequence data groups the 14 taxa into their respective superfamilies and families, but does not discriminate fully at the subfamily level. A phylogenetic analysis of the sequence data failed to resolve the evolutionary relationships at the superfamily level. The 5.8S gene may be useful for phylogenetic studies of the phylum Nematoda at the ordinal level.