Abraham Trembley was the tutor-in-residence for the children of Count Bentinck of The Hague in Holland when, circa 1740, he discovered his “freshwater polyps with arms shaped like horns” and began to conduct experiments with them. Trembley described three kinds of polyps: a small green one (Hydra viridissima), a “common brown, unstalked one” (H. vulgaris), and a long-armed one with a narrow tail (H. oligactis). Since Trembley’s times hydra has become an experimental model for the study of animal development and, more recently, an essential reference for the study of the evolution of animal development. Yet, more than 250 years after the publication of Trembley’s “Mémoires, pour servir à l’histoire d’un genre de polypes d’eau douce, à bras en forme de cornes” in 1744, the we do no really know how many species of hydra inhabit our planet.Several years ago, I began a collaboration with Dr. Richard Campbell (UCI) to sample the hydras of the world and establish their evolutionary relationships using sequence data. We have collected hydra from many regions of the world but large areas remained unexplored. My role in the CnidToL project is to generate a molecular phylogeny of hydra. The laboratory work for this project will be completely carried out with the help of undergraduate students at Pomona College.