Starfish

Starfish can be recognized at first glance: their disc-shaped body and five arms make them unmistakable.

Characteristics

What do starfish look like?

Common starfish belong to the echinoderm phylum and are there to the starfish class. They are related to sea urchins, sea cucumbers, and sea cucumbers. The special feature of the echinoderms and also the starfish is their calcareous skeleton, which protects the body. Typical for starfish is that they have no head and their body also has no front and rear end:

Rather, they have a disc-shaped body with several arms. The common starfish has five arms and a diameter of up to 30 centimeters. Some specimens even grow up to 50 centimeters. The common starfish comes in different colors: it can be reddish, yellowish, grey, brown, violet, or greenish.

The top has small spikes. Four rows of small feet with suction cups sit on the underside of the arms. The mouth opening is on the underside of the body. It is connected to the stomach by a short gullet. A pair of blind-ended intestinal tubes lead from the stomach to the arms. The blood vessels run in the upper wall of these intestinal tubes. The anus sits on top of the disc of the body.

Starfish has neither a brain nor a heart. They do, however, have a nervous system and a water-vessel system that runs throughout the starfish’s body. The calcareous skeleton consists of calcareous plates that are mobile and connected to each other by muscles.

Starfish have simple sensory cells with which they can perceive mechanical, chemical, and optical stimuli. For example, on the tips of their arms, they have several light-sensing cells that form a kind of primitive eye.

Where do starfish live?

Starfish are only found in the sea. The common starfish lives in the Atlantic from the White Sea in the north to the coast of Senegal as well as in the North Sea and in the western part of the Baltic Sea. It stays at depths of up to 200 meters. The common starfish inhabits mainly rocky, stony coasts. There he lives below the so-called low tide line – that is, in the areas of the coast that are not dry even at low tide.

How old do starfish get?

Starfish can live six to seven years.

Behavior

How do starfish live?

With their little feet and suction cups, starfish can move very skillfully: Due to the pressure of the water vessel system, these feet become firm and lift the body off the ground. This allows the starfish to walk properly on its feet by alternately stretching them forward and pulling them together again.

This is how starfish move across the ocean floor in search of food. With the help of the suction cups, the common starfish can also hold on to the ground. Like all starfish, the common starfish has no lungs or gills but absorbs oxygen directly from the water via tiny protuberances in the water vascular system.

Starfish have incredible powers of regeneration: if they lose an arm or are cut in half, the lost part of the body can be replaced. And a severed arm can even grow back into a whole starfish.

Friends and foes of starfish

Adult starfish have few enemies. Only very rarely are common starfish caught by their conspecifics, the sun stars. Young sea stars, on the other hand, live dangerously: crabs and diving ducks hunt them down.

How do starfish reproduce?

Reproduction is very simple for the common starfish: in summer – usually in July – the males put their seeds into the water, which are mixed with certain signal substances. These encourage the females to release their eggs into the water as well. The so-called swimming larvae, from which the young starfish develop, develop from the fertilized eggs. In summer you can then observe numerous young starfish on seaweed leaves.

Care

What do starfish eat?

Common starfish are predatory. They feed mainly on mussels, snails, sea urchins, hermit crabs, and crabs. They have developed a sophisticated technique to open the shells of the mussels: they lay their underside on the mussels. They cling to her with the upper part of their arms. They push themselves off the ground with the lower part of their arms and thus pull the shell halves of the mussel apart.

As soon as the shell opens slightly, the starfish puts its stomach inside it and begins to digest and eat it. Smaller mussels also swallow the starfish whole. The appetite of the common starfish is enormous: they can eat several times their body weight.

In bad times, however, they also starve for weeks. Common starfish can cause major damage to mussels and oyster farms. Young starfish mainly eat barnacles.

Keeping Starfish

Common starfish can be seen in many zoos with marine aquariums.