An overview of glossiphoniid leech development

Dramatic advances in understanding the development of selected "model" orga nisms, coupled with the realization that genes which regulate development a re often conserved between diverse taxa, have renewed interest in comparati ve development and evolution. Recent molecular phylogenies seem to be conve rging on a new consensus "tree," according to which higher bilaterians fall into three major groups, Deuterostoma, Ecdysozoa, and Lophotrochozoa. Comm only studied model systems for development fall almost exclusively within t he first two of these groups. Glossiphoniid leeches (phylum Annelida) offer certain advantages for descriptive and experimental embryology per se, and can also serve to represent the lophotrochozoan clade. We present an overv iew of the development of glossiphoniid leeches, highlighting some current research questions and the potential for comparative cellular and molecular studies.