Drifting silently in the ocean, often near the surface, are jellyfishes. Moved by the currents, these pale, delicate creatures look defenseless. But jellyfishes and their relatives have a hidden weapon.

A typical jellyfish has a large, squashy, umbrella-like body. Dangling from the body are thread-like tentacles. Each tentacle has structures called nematocysts. At the tip of each nematocyst is an arrow-shaped barb which contains poison.

When a jellyfish brushes against an animal floating by, the barbed nematocysts shoot out and stun the victim. Even though these poison arrows are so small that we need a microscope to thee them, the are deadly effective when fired off by the hundreds and thousands. The jellyfish then pulls it tentacles, with the dead or stunned prey, up to its mouth on the underside of its umbrella-shaped body and digests its meal.

Usually, if a jellyfish stings you, it can only give you a mild sting. Even so, the burning feeling may last several hours. But several kinds of jellyfishes have poison so strong that they can kill humans. The large Portuguese man-of-war jellyfish that lives in the Atlantic Ocean usually feeds on small, surface-swimming fishes. But a swimmer who brushes against its tentacles will get a very painful burning rash that lasts for days. If someone is stung by too many tentacles, the shock to the body can be so strong that the swimmer may drown. In the Indo-Pacific, the sea-wasp jellyfish is even more venomous, and its sting can kill a person in less than half an hour.

Sea anemones are relatives of the jellyfishes that attach themselves to corals, rocks, mangrove roots, and other firm surfaces. They have fleshy bodies and tentacles with nematocysts to stun little animals that touch them.

The orange or yellow-tan fire coral also is related to the jellyfishes. When touched it fires off poisonous darts. The pain of its sting can last many days.

The fire worm is another stinging creatures that deserves its name. A fire worm has rows or bunches of hair-like bristles along the sides of its body. These become erect when it bends. The erect bristles are hollow and full of a poison that the fire worm injects into anything that touches it, whether a hungry fish or a curious human. Its painful, fiery sting repels most things that bother it.

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