Text 9 marine coelenterates

Coral Polyps (Anthozoa)

There are many forms related to the Hydra in the seas. The most widespread are the Coral Polyps.

The so-called Red Coral grows on the sea floor and looks like a small shrub with many red branches and white flowers.

The so-called flowers are really the tentacles of the tiny sea animals, called polyps, whose bodies form the shrub.

While the Hydras live as single individuals, the Coral Polyps form colonies.

The red "branches" are built of mineral salts, the same as in the hard skeleton of the animals. They have tubes inside, which link the enterons of the neighbour-polyps.

Food, which is also caught with the tentacles, is digested in a cavity that is identical with that of the Hydra. However, the digested material is distributed along the branch tubes to all the colony and is not used by only one polyp.

The most remarkable feature of the Coral Polyps is their ability to extract from sea water and deposit in their bodies huge quantities of various mineral salts, which they use to make a hard, strong skeleton. Their most important building material is lime.

When the animals die their skeletons are scattered over the bottom of the sea. Gradually they turn into limestone, material highly valued for building.

Medusa (Jellyfish)

Unlike the Hydra and Coral Polyp, the Jellyfish is not anchored and can move about freely in the sea. It has a glassy, semi-transparent, gelatinous body, shaped like a bell or a saucer, turned upside down. When the "saucer" contracts a jet of water is discharged from its undersurface, and the Jellyfish is jerked in the opposite direction. This method of locomotion could be called "jet propulsion".

The "saucer" is fringed with a row of tentacles equipped with groups of stinging cells, which can cause pain even to man. The stinging threads of some species of Jellyfish cause most unpleasant wounds which take a long time to heal.

The food of Jellyfish consists of small animals which are paralysed by the stinging cells and are captured by the tentacles. From the mouth the food goes to the central body cavity (the enteron) where it is digested. The unused food is excreted from the mouth.

Conclusion

The Hydras, the Corals and the Jellyfishes form one group of animals called the Coelenlerata (Coelenterates). Unlike the Protozoa, they are multicellular. The bodies have the form of sacs with two layers of cells in the walls and an enteron within. The enteron has only one open end - the mouth. Most of the Coelenterates remain fixed to one place. Therefore they have a symmetrically-radial structure.

Translate into Russian

Aurelia is one of the commonest of the scyphozoan jelly-fish and occurs all over the world. From ocean liners one often sees large shoals of them drifting along together or swimming slowly by rhythmic contractions of the shallow, almost saucer-shaped bell. They range in size from less than 3 inches to about 12 inches across the bell. Exceptional individuals may reach a diameter of 2 feet.

At the end of a very short manubrium is a square mouth, the corners of which are drawn out into four trailing mouth-lobes. Each lobe has a ciliated groove. Stinging capsules in the lobes paralyse and entangle small animals, which are then swept up the grooves, through the mouth, into a spacious cavity in the centre of the bell, and from there through branched radial canals to the margin of the bell. Flagella lining the entire gastro-vascular cavity maintain a steady current of water, which brings a constant supply of food and oxygen to, and removes wastes from the internal parts of this large animal.

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