The nematodeCaenorhabditis eleganshas been central to the understanding of metazoan biology. However,C. elegansis but one species among millions and the significance of this important model organism will only be fully revealed if it is placed in a rich evolutionary context. Global sampling efforts have led to the discovery of over 50 putative species from the genusCaenorhabditis, many of which await formal species description. Here, we present species descriptions for ten newCaenorhabditisspecies. We also present draft genome sequences for nine of these new species, along with a transcriptome assembly for one. We exploit these whole-genome data to reconstruct theCaenorhabditisphylogeny and use this phylogenetic tree to dissect the evolution of morphology in the genus. We show unexpected complexity in the evolutionary history of key developmental pathway genes. The genomic data also permit large scale analysis of gene structure, which we find to be highly variable within the genus. These new species and the associated genomic resources will be essential in our attempts to understand the evolutionary origins of theC. elegansmodel.