The superfamily Criconematoidea has been studied since 1886. It is composed of two families: Criconematidae (subfam. Criconematinae, Hemicycliophorinae) and Tylenchulidae (subfam. Tylenchulinae, Paratylenchinae and Tylenchocriconematinae). Multiple species in genera have been identified and differences and similarities have been found. Species belonging to genera Mesocriconema and Criconemoides show very few differences making their identification difficult. Seventy two populations were studied. They were collected in Arkansas and/or received from the following states: California, Florida, Kansas, Missouri, North Carolina and Tennessee. Populations of the following species were identified: Mesocriconema curvatum, M. kirjanovae, M. onoense, M. ornatum, M. sphaerocephala, M. surinamense, M. vadense, M. xenoplax, Criconemoides informis, Bakernema inaequale, C. petasum, C. sphagni, C. mutabile, Ogma octangulare, Xenocriconemella macrodora, Hemicriconemoides chitwoodi, Hemicycliophora epicharoides, H. gigas, H. labiata, H. typica, H. pruni, H. shepherdi, H. vidua, H. zuckermani, Gracilacus straeleni and Paratylenchus labiosus. The new species reported are Mesocriconema ozarkiense n. sp., Criconema arkaense n. sp., Criconema warrenense n. sp., Hemicaloosia uarki n. sp and Hemicycliophora wyei n. sp. In addition, species were characterized morphologically and molecularly using the conserved region 18S for some species and the Internal transcriber spacer 1, ITS1, from ribosomal DNA for all. Phylogenetic studies were performed using both rDNA amplicons to study the relationship among genera and species rejecting the hypothesis of a common ancestor
