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| This large Lions Mane Jelly is an invertebrate. |
If all the sea animals with back-bones could be put at the right and all those without back-bones at the left,—where would you put the fishes? Almost all of the fishes would be placed at the right, of course. And where would you put the sponges? Some of them have a skeleton, but not one of them has a back-bone. Zoologists,—that is, people who study and write about animal life,—place all the back-boned animals in one class and call them vertebrates. They place all the spineless creatures in another class and call them invertebrates.
Millions of invertebrates live in the sea. Some of them have shells, such as the oyster, the crab and the lobster. Some become hard and stony after a time, such as the coral and the starfish. Others remain rather soft during their entire life time, such as the jelly fish, the sponge and the sea anemone.
The beautiful sea anemone is an animal which borrowed its name from a plant. It resembles the lovely anemone flower of the woods in its delicate shades of color and in its general shape, with the fringe at the top. The body of the sea anemone is shaped somewhat like a spool of thread standing upright, with the hole in the center forming a large stomach. The creature seems to be almost all stomach. Perhaps that is why it is so often hungry. It usually hides in the mud of the sea bottom until some sea creature, which is good to eat, swims by. Then up comes the body of the sea anemone like a jumping jack. Suddenly a fringe of arm-like processes called “tentacles.” which surround the entrance to the stomach, reach out and grab the “food.” Sometimes the small fish and other sea creatures which serve as food to the sea anemone are stung to death by its tentacles before they reach the stomach of that hungry invertebrate.
The sea anemone has no legs. Although the creature usually remains fixed to the bottom, it can move from place to place by means of a suction pad which forms the base of the body. When it changes location, the sea anemone settles where strong currents of water pass over it, bringing new supplies of food. Sometimes the sea anemone gets a free ride by attaching itself to the back of a crab. The crab travels along without seeming to notice' its burden and the sea anemone reaches for food as it rides comfortably along.
Like the sea anemone, the starfish has a borrowed name. Its body has the shape of a pictured star and it lives in the water as fishes do. Of course it isn’t a star; and it isn’t even a fish; for it has no back-bone. Perhaps you always thought that a living starfish was as hard or as brittle as the dead ones you pick up along the sea shore. A living starfish is almost as soft as some sponges. It has a kind of skeleton, to be sure; but its whole body bends easily in almost any direction as it moves rapidly through the water. A starfish is so flexible that it can squeeze through a crack between rocks.
Most starfishes have five “arms” or more; and some have as many as forty. A groove or depression extends along the center on the under side of each arm. When the starfish “walks” the soft tube-like feet bulge out from inside the grooves. The feet are suckers which cling firmly to the road on which the creature travels.
Starfishes have big appetites. When one of them finds a bed of oysters, a feast is almost sure to follow. Perhaps you wonder how the starfish can manage to pry open the oyster’s shell. A hungry starfish fastens itself firmly by its sucker feet to both shells and then proceeds slowly to straighten out its arms. The constant pull of the arms on the shell, in opposite directions, tires out the muscle which holds the oyster shells together, and the oyster gapes open. Then the mouth of the starfish, which is in the very center of its body, reaches for the soft oyster and eats it all up.
Men who raise oysters for the market discover that it does not pay to cut up the starfish which attempt to rob them of their oysters. The hungry creatures must be killed by depriving them of water rather than by chopping off their arms. Starfishes have the strange power of developing new arms in place of the missing ones. The creature grows new parts so easily that if only one arm and a portion of the body remains, an almost perfect starfish may develop. When a few starfishes are punished for eating oysters by being cut up and thrown overboard, a whole school of starfishes may result. Thus the oyster men may multiply the enemy and subtract from their supply of oysters.
The starfish, the sea anemone and the oyster are only a few of the many sea animals which do not possess a back-bone. All of them are invertebrates. See how many others you can name. Pyatt.
Ocean Invertebrates vs Vertebrates
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