Let’s discover are hydras more advanced than sponges? You might easily overlook a hydra in a pond, lake or stream, because when disturbed, it contracts its body from the normal length of about half-an-inch to a tiny blob of jelly that you can only see if you look very carefully.
Most people are more familiar with its marine relatives the sea anemones, jellyfishes and corals which are, of course, much larger and more colorful.
This group of animals belongs to the phylum Coelenterate which means simply ‘hollow gut’. The hydra is basically a bag with a fringe of tentacles around the mouth at one end, and a disc at the other with which it sticks to a surface.
Instead of a loose arrangement of the cells into groups with different functions (as in the sponges), the body wall of consists of two definite layers.
The cells act to-sponge. The hydra is also more responsive and active than the sponge and has a network of nerve cells which make up a primitive nervous system. It also has single muscle cells which enable it to bend and contract its body.
How do hydras catch their prey?
The tentacles of the hydra, like those of the anemones and jellyfishes, are armed with special stinging cells which fire poisonous barbed threads into the nay unfortunate creature that happens to brush against them.
Other cells of this type release long thread which coils around the prey and helps hold it until it can be maneuvered to the mouth and engulfed.
Once inside the bag of the hydra, the small water flea or worm is quickly digested and any remains are spat out from the mouth. It is an interesting fact that the hydra can catch and eat much larger animals than the sponge.
What is the Portuguese man-o´- war?
Although it looks very much like a jellyfish, the Portuguese man-o´-war is really a floating colony of hydra-like animals called polyps, clustered together under a gas-filled bladder.
The bladder acts as a sail and the Portuguese man-o’-war is driven about the warm seas of the world completely at the mercy of the wind. (A jellyfish, of course, can actively swim.)
The animal itself is about 6 inches long, but the trailing tentacles of the polyps can extend up to 60 feet. The tentacles of some of the polyps bear stinging and holding cells similar to those of the hydra.
They can catch and hold fishes as large as mackerel. Once overcome the prey is quickly drawn up within reach of other polyps which eat and digest it.
Sometimes storms drive masses of these animals on to the beaches of seaside towns where they become a serious menace.
They are usually left stranded high up the beach and the bladders soon dry and shrivel. The tentacles can still give a nasty sting if touched, however, and bathing is often prevented until the Portuguese men-o’-war is removed.
The Portuguese man-o’-war is common in the warm seas of the world and particularly in the North Atlantic, and areas of the Indian and Pacific Oceans.