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Terrestrial molluscs are diverse and are infected by many nematodes. We propose a phylogeny of slug-parasitic nematodes using 18S rRNA gene sequences from nematodes isolated from slugs collected from six countries. Eight species, representing six families of nematodes were identified and trees inferred placed them within four (I, III, IV and V) out of the five clades of Nematoda, indicating multiple origins of slug parasitism. Five species representing three families formed a monophyletic group in clade V. Although these species are closely related, their morphology has changed greatly, suggesting adaptive radiation to fill different niches within the host.

Phylogenetic relationships among gall-forming plant parasitic nematodes of the subfamily Anguininae are reconstructed by maximum parsimony and maximum likelihood analyses. Sequences of the ITS of rDNA from 53 populations and species of gall-forming nematodes and five populations of the Ditylenchus dipsaci species complex were analysed. The phylogenetic trees strongly support monophyly of the genus Anguina and show nonmonophyly for the genera Mesoanguina and Heteroanguina. Morphological and biological characters are generally congruent with the anguinid groups identified in the rDNA phylogeny. Analyses of evolution of different gall types among anguinids reveal that there are apparent evolutionary trends in gall evolution: from abnormal swelling and growth of infested plant organs toward small localised galls, and from infestation of vegetative toward generative organs. Our study demonstrates that the main anguinid groups are generally associated with host plants belonging to the same or related systematic groups. The comparison of the ITS phylogenies of anguinids parasitising Poaceae and their host grasses shows a high level of cospeciation events.

The ITS1, ITS2, and 5.8S gene sequences of nuclear ribosomal DNA from 40 taxa of the family Heteroderidae (including the genera Afenestrata, Cactodera, Heterodera, Globodera, Punctodera, Meloidodera, Cryphodera, and Thecavermiculatus) were sequenced and analyzed. The ITS regions displayed high levels of sequence divergence within Heteroderinae and compared to outgroup taxa. Unlike recent findings in root knot nematodes, ITS sequence polymorphism does not appear to complicate phylogenetic analysis of cyst nematodes. Phylogenetic analyses with maximum-parsimony, minimum-evolution, and maximum-likelihood methods were performed with a range of computer alignments, including elision and culled alignments. All multiple alignments and phylogenetic methods yielded similar basic structure for phylogenetic relationships of Heteroderidae. The cyst-forming nematodes are represented by six main clades corresponding to morphological characters and host specialization, with certain clades assuming different positions depending on alignment procedure and/or method of phylogenetic inference. Hypotheses of monophyly of Punctoderinae and Heteroderinae are, respectively, strongly and moderately supported by the ITS data across most alignments. Close relationships were revealed between the Avenae and the Sacchari groups and between the Humuli group and the species H. salixophila within Heteroderinae. The Goettingiana group occupies a basal position within this subfamily. The validity of the genera Afenestrata and Bidera was tested and is discussed based on molecular data. We conclude that ITS sequence data are appropriate for studies of relationships within the different species groups and less so for recovery of more ancient speciations within Heteroderidae.