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The weird and wonderful life on the seashore

Posted in Biology, Fish, Sea on Monday, 31 October 2011

This edited article about marine life originally appeared in Look and Learn issue number 852 published on 13 May 1978.

Starfish, picture, image, illustration

There are many kinds of starfish

If you take a walk along the seashore, you will find a naturalist’s paradise – a place teeming with all kinds of plant and animal life.

You can watch and study creatures in their own habitat, discover how they survive in the harsh, rugged environment of the sea shore, and observe their behaviour.

The most beautiful animal to be found along the seashore is the sea anemone. A deceptive beauty, it looks like an exotic flower with petals. But these are tentacles armed with innumerable poisonous stinging cells.

You may be lucky enough to observe a sea anemone catching its food, but you will look on in disbelief as it grapples with a crab or a large fish the size of itself; and manages to swallow it.

What happens is that the anemone reaches out to grab its victim with its powerful tentacles, and then pushes the food into its mouth, which is at the top of its body immediately below the crown of tentacles.

The obvious question is: How does it accommodate such a huge victim?

There are strong muscles inside the stomach, and when these contract, the stomach’s digestive surface actually increases.

These muscles also pull the tentacles, together with the victim, inside the mouth.

Once the food is inside the stomach, the mouth closes and the anemone then digests the food.

Then the mouth opens again and the anemone spits out the hard parts of the meal which it cannot digest.

The starfish, found in rock pools low down on the shore, has five arms radiating from the centre. On the underside of these arms are rows of tiny suckers which the starfish employs as both hands and feet.

It will pull itself along the sand or shingle by means of these suckers, and also hold on to a rock firmly enough to avoid being thrown off by movements of the waves.

Although it does not look a very powerful creature and has neither jaws nor teeth, the starfish, like the sea anemone, has a passion for shellfish.

Delicate though it looks, the starfish can force open the hard shells of mussels and even oysters. It grips both sides of the double shell with the suckers on its arms and pulls steadily. It has great stamina, and can keep up this tug-of-war for an hour or more.

Sooner or later, the shellfish surrenders, too exhausted to continue the struggle, and then the starfish makes a meal of its soft body. It does this by pushing its stomach through its mouth and pouring digestive juices over the victim to reduce it to liquid form. In this way, the starfish’s stomach is able to absorb the food.

An asset possessed by the starfish is its ability to grow new arms. Sometimes an arm may be nipped by an angry crab or get caught under a heavy stone. When this happens, the starfish grows another.

One of the starfish’s relatives is the sea urchin.

The sea urchin is covered with fine soft spines which wear off after the creature has died to reveal an off-white shell.

Most sea urchins live among rocks or out at sea, but the Heart Urchin lives in the sand, near the low tide mark.

A narrow shaft connects the burrow it digs with the surface of the sand, and from this shaft it takes in tiny particles of food. The mouth is situated on the underside of its body, and in order to get the food into it the urchin extends its long tube feet from the burrow to the surface of the sand. The food is then passed down the burrow and is pushed into the mouth with the feet.

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