Review of the ultrastructure of the nematode body cuticle and its phylogenetic interpretation.

The phylogenetic interpretation of the nematode cuticle ultrastructure is reviewed within the framework of recent DNA-sequence data. In particular, the structure of the median and basal zones is discussed. Several structural elements of the cuticle seem to have arisen independently several times within the Nematoda and thus are highly homoplasious (e.g. the cortical or basal radial striae, spiral fibre layers and a fluid matrix with struts). Moreover, identifying the homology of the nematode cuticle ultrastructures is often very difficult at deep taxonomic levels. Hence, the cuticle appears to be unreliable regarding resolution of deep-level relationships in the Nematoda. However, at less inclusive taxonomic levels (e.g. families, genera, ...) the cuticle seems to be a more reliable phylogenetic marker.