· Abraham Trembly , a Swiss biologist discovered Hydra in 1744 AD. · Linnaeus gave the name Hydra, after the great serpentine nine-headed dragon from the ancient · Greek mythology is based on its ability to regenerate the lost parts in 1758 AD. · The name Hydra is an old Greek word for "water-serpent". · Hydra is a solitary polyp found in freshwater (stagnant). · Hydra is diploblastic and radially symmetrical. · Separate coelom is absent in Hydra, so can be called acoelomate . Among coelenterates, Hydra is one of the smallest polyps. · Hydra has tissue grade of organization. · Body of Hydra has no segmentation. · Hydra has a cylindrical body with 6‑10 hollow tentacles. · The tentacles of Hydra help in locomotion and food. · The basal part of Hydra has a pedal or basal disc. · Mouth is situated on a manubrium or hypostome. It is the most...