What is the difference between a DPY-10, DPY-11, and DPY-13?
Dpy is a class of genes. Usually they're written in lowercase when referring to a mutant allele. The name Dpy itself stands for dumpy and comes from the morphological change that occurs when one or more of the genes are mutated: the worms appear short and fat, or dumpy. 

Another big class is Unc. Mutations in those genes cause uncoordinated movement. 

For a description of the genes, see http://www.wormbase.org