Adaptations of the Hydra

Cnidocytes

• Hydra catch and kill their prey with the aid of specialized cells on the outside of their bodies called cnidocytes. Cnidocytes contain a coiled, barbed thread laced with neurotoxins. When another object touches a trigger hair on the outside of the cell, the poisonous thread is expelled under high pressure toward the source of the stimulation. Prey often triggers many cnidocytes at once, resulting in a fatal dose of toxins. The hydra grasps the paralyzed food with its tentacles and moves it into its mouth parts for digestion.

Hydramacin

• Hydra are simple creatures with two layers of tissue in their bodies: ectoderm covering the outside and endoderm lining the interior cavity. To prevent infection by bacteria and other microorganisms, hydra produce a specialized protein called hydramacin. Hydramacin acts as an antibiotic agent, killing invading microbes as they attempt to breach the hydra's ectoderm. Hydramacin is effective against both gram-positive and gram-negative bacteria, and may hold promise against antibiotic-resistant bacteria in human medicine.

Somersaulting

• Hydra spend most of their lives attached to other objects like aquatic plants and underwater rocks. Their foot-like basal disc secretes a sticky mucous that holds them in place, where they rely on chance to catch prey that randomly blunders past. In unfavorable conditions, however, hydra can move surprisingly long distances using an inchworm-style of movement called somersaulting, in which they bend sideways to grasp the surface with their mouth parts before releasing the basal disc, flipping over, and reattaching the disc in a new location.

Contraction

• Hydra are relatively inconspicuous on the human scale, but their waving tentacles and relatively sedentary existence make them somewhat vulnerable to aquatic predators. In addition to their stinging cnidocytes, hydra can "hide" by expelling the fluid in their interior gastrovascular cavities. Since the tissue of both their bodies and tentacles is highly contractile, this allows them to quickly shrink themselves into a small, unnoticeable mass only a fraction of their normal size.