Cheryl Urbanek, age 9, of Fortage, Ind.
What is a hydra?
The hydra lives in ponds and freshwater streams, He shares his watery world with the amoeba and a host of other one‑celled animals. To these tiny midgets, the hydra is a towering giant, terrible as a tiger. But we rate him as one of the simplest of animals, just one step higher than the amoeba. He is grouped with the busy little coral, the pretty sea anemone and the jellyfish. These simple creatures belong in the phylum Coelentera, a fancy word which means the hollow‑stomach ones.
At first sight, we might mistake the hydra for a tiny underwater tree. His small trunk seems to be firmly rooted to a stone, a waterweed or even on the solid back of a turtle. The top of his trunk spreads out into a handful of spindly branches and the tallest hydra is less than two inches high. As we watch him, it soon becomes plain that he is not a tree. For no tree catches food and stuffs it into its mouth or turns somersaults,
The waving branches of the hydra a‑re actually tentacles set in a circle around a little round mouth. Each tentacle is armed with tiny stickers, with coiling threads or poisoned darts. These are deadly weapons for catching our friend the amoeba and his relatives. They even can pierce the crusty coat of a water flea,
The hydra’s trunk is the main part of his body. The top two‑thirds of the trunk is occupied by a hollow stomach. When the waving tentacles trap a victim, they stuff it into the little round mouth like greedy fingers. Down it goes into the stomach where it is broken down into soupy liquid. Small fragments of food then pass into special cells in the stomach lining. These are food vacuole cells, very much like the food vacuoles of the amoeba, The nourishment from the food then seeps through the hydras body from cell to cell.
From time to time, the hydra decides to move to better hunting grounds. The tentacles tip down to the ground and the bottom of the trunk swings up and over and sets down on the other side. To the hydra, each step is a somersault. Sometimes he changes shape. He draws in his tentacles and the top of his trunk becomes a fist of knobby knuckles. These antics prove that the hydra is not a plant. For no tree draws in its branches, goes for a walk or turns somersaults.
In one respect, however, the hydra can act like a plant, He can multiply by growing a bumpy bud on the side of his trunk. The bud grows and develops tentacles and in a few days breaks off to become a new hydra.
The strange little creature also can be born from cells coming from two parents or from male and female cells from the same parent.