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Amphipods could be described as a kind of shrimp and one of the best known is called a fresh water shrimp. Even though the amphipod is not a shrimp, it has earned no common name but has an important impact on human affairs. Some animals still have no common name simply because they are too small or otherwise unfamiliar even though they are important in their own right. There are over 1,000 known species of amphipods ranging from microscopic size to species which are an inch or more in length. Commonly the amphipod is referred to by its scientific name, which is gammarus.

Most of the gammarus species are found in brine pools, fresh water or brackish water, while others live in the ocean. Amphipods live in burrows made in the mud or inside sponges, amid seaweed or even on the water's surface. There is one species that is considered a pest living in Europe and on the east coast of the United States. This species bores into wooden pilings causing continuous damage to piers. Another species lives under piles of seaweed just above the high tide mark, and when the seaweed is lifted, jump around like fleas. As a consequence of this they have been called sand fleas. All amphipods are scavengers, feeding mostly on dead organic matter whether plant or animal. They are known to prey on animals that are smaller than themselves including those of their own species. Skeleton shrimp are carnivorous amphipods that will lie in wait for their prey. Hanging on with its hind feet, the skeleton shrimp will stretch out, remaining perfectly still until its prey bumps into it. It will then instantly grasp the victim with the first two pairs of legs and devour it. It has been noted that is technique is much like that of the praying mantis.

Freshwater shrimp are often seen in pairs with the slightly larger male carrying the female under his body. Females carry their eggs in a brood pouch which is situated under her thorax. Young fresh water shrimp remain in the pouch for a few days after hatching until the female squeezes the side of the pouch to force them out. Most are reluctant to leave the pouch and hang onto the bristles of their mothers legs. Amphipods in lakes and rivers form the staple diet of many fishes, including trout. Shore birds feast on sand fleas, getting at them by turning over seaweed with their bills, while free swimming amphipods form part of the plankton on which fish, whales and some seabirds feed.

In some cases amphipods are amphibious which allow some species to live on land in tropical areas. Others have become parasitic living on other animals and feeding on their flesh. The whale louse is a good example of this. It will attach itself to a whale it will remain anchored to the spot for the rest of its life, eating the surrounding flesh until it is lying in a cavity. The young settle down close to their parents and eventually thousands cover large patches of skin on the whale. Some marine amphipods will only use their hose as a shelter where they can breed and feed with ease. In this case jellyfish tend to make one of the best homes since they tend to drop edible scraps while feeding. Gammarus are just over 1\2 inch long and greenish brown in color. They have many pairs of legs, using the front legs for walking and the back legs for swimming.