Hydra

What is Hydra? Hydra is a member of the animal phylum Cnidaria. This phylum includes corals, sea anemones and jellyfish. While most cnidarians are marine, Hydra is unusual in that it lives exclusively in fresh water. Hydra was first described by Antoni van Leeuwenhoek (1632– 1723) in a letter he sent to the Royal Society on Christmas day, 1702. The letter included a red chalk drawing of Hydra on parchment (Figure 1A). In 1744, a Dutch tutor named Abraham Trembley published his memoires, which included studies of regeneration, asexual budding and tissue grafting in Hydra. Trembley’s work provided the foundation for nearly 250 years of research on Hydra.