What are Starfish?

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What are starfish?

Starfish are marine animals in the category of Echinodermata. That name means "spiny skin" in Greek. The starfish's skeleton is a series of calcium-rich hard plates just beneath the skin that are linked together to allow limited flexibility while maintaining the starfish's shape. The most familiar shape in the starfish is the five-armed body, although there can be fewer or many more arms.

The hard plates just below the skin also support the growth of sharp spines that protrude up from the skin, which act as a defense against being eaten. Be careful when picking one up!

Starfish don't move about by bending their legs and "walking" like land animals do. Their legs are too rigid for that to work well. Instead, on their underside they have a great many small flexible tubes which can be bent and moved, and those act like tiny feet to help the starfish move around. The feet have small suckers on the end, allowing the starfish to have a strong grip on whatever it wants to hold onto.

Another odd thing: The eyes on starfish are at the ends of their arms. The eyes aren't very complex eyes like you'd see in rapidly-moving sea creatures such as fish, but they're able to sense varying degrees of light and darkness, which is sufficient for the slow-moving starfish's needs.

Starfish eat many things, depending on the type of starfish. Some eat mollusks -- either by boring through their shells to reach the animal inside, or in some cases by holding on to both halves of a bivalve and simply slowly pulling the two halves open to reach the animal inside. When they eat the soft parts of a mollusk they leave behind the hard shells, which become the seashells we all admire for their beauty. Other starfish burrow through mud and eat the small edible bits and pieces they find there. And still others eat coral reefs -- one particular species of starfish, the Crown of Thorns, is presently causing great damage to the Great Barrier Reef, eating the living portions of it faster than it can regenerate itself.

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