Starfish Facts for Kids - What is a Starfish?

Starfish belong to the same group of invertebrates that live in the sea. 
These animals are echinoderms, which means "spiny skinned".
Starfish are flatter and have disk-shaped bodies, with a number of arms around the outside of the central body.

Most starfish have five arms, but some species have as many as fifty! 

If we turn a starfish, we'll see hundreds of tiny, sucker-like tubes waving about on the undersides of its arms. These are tube feet, and they are very useful to the starfish.
The suckers on the tube feet can stick to rocks or shells. The starfish moves along by pushing out, or extending, the tube feet on one of its arms so that they will stick to a nearby rock or to the seabed.
When the tube feet shrink, or contract, the starfish is pulled forwards.

Each tube foot has little strength, but hundreds of tube feet together are much stronger.
Starfish use their tube feet to pull apart the shells of clams and oysters so that they can eat the soft flesh inside.
To eat, the starfish pushes its stomach out of its mouth and folds it around the food!

Starfish are not fish and do not have gills to take in oxygen from the seawater.

Instead, they use their tube feet to absorb oxygen from the water.

Jellyfish Facts for Kids - What is a Jellyfish?

Have you ever seen a jellyfish?

It looks like an umbrella with projections, called tentacles, hanging down from the edges.
The body of a jellyfish is like a hollow bag with thick sides. These sides have an "outer skin" and an "inner skin."
Between these two "skins" is a jelly-like substance. This substance gives the jellyfish its shape.

Jellyfish live in the sea, but they are not fish. 

Fish have backbones and move forward by swimming. Jellyfish do not have backbones, and they move up and down in a unique way.
They expand like an opening umbrella, then pull together again rapidly. This squeezes water out from beneath, and the jellyfish moves upward.

Jellyfish eat small sea animals after stinging them with their tentacles. 

The tentacles are covered with thorny threads. When another animal bumps into the jellyfish, these threads lash out like tiny, poisonous whips.
The threads paralyze the victim, and the jellyfish then uses its tentacles to pull the trapped animal into its mouth.

The tentacles of a jellyfish are covered with tiny capsules.
Inside each capsule is a thorny stinging thread.
The jellyfish whips out these threads to paralyze small animals.

DANGER!

If you see a jellyfish, even one that has been washed up on the beach, don't touch it.
The poison from some jellyfish stings can be deadly to human beings. 

Anyone stung by a sea wasp, a kind of Australian jellyfish, will almost certainly die within a few minutes.

But common jellyfish sting do not kill.

Jellyfish and corals belong to a group of invertebrates called coelenterates.

The term coelenterate means "hollowbody."

Some species of jellyfish produce their young from eggs.
The eggs grow into hollow cylinders, called polyps, which attach themselves to the seabed.
New jellyfish start to grow on these polyps.
Each bud of a mature polyp looks like a tiny saucer.
When a bud is big enough, the polyp releases it into the sea and it grows into an adult jellyfish.

Why is the Sea Salty?

Put two or three pinches of table salt into half a glass of water and stir the water with a spoon.
What happens?
The salt seems to disappear.
In fact, it is still there, but it has dissolved in the water.
The salt and water have formed a solution. Each grain of salt is a crystal. This is a group of particles arranged in a regular pattern. Water molecules break the crystals up into individual salt particles, which are too small to be seen. This is why the salt seems to disappear.

Most of the earth's surface is covered with a solution.
We call this solution sea water.
There are many things dissolved in it, but the most common substance is a chemical called sodium chloride.
We know it better as table salt.
It makes the sea taste salty.

You may think the salt has disappeared. But taste the water and you will find the salt is still there. You cannot see it because it has dissolved.
Some of our salt comes from the sea. First, sea water is allowed to flow into large shallow pools.
The heat of the sun evaporates the water, leaving the salt behind.
Substances which dissolve in water are described as soluble substances.
We can make soluble substances dissolve faster by stirring, shaking or warming them.

What would happen if you continued to put more salt into the water? 

After a time, no more would dissolve, however much you stirred it, shook it or warmed it. The solution would be saturated. A saturated solution cannot hold any more of a soluble substance.

Ocean Food Chain

There are plants in the seas and oceans as well as on land. Tiny plants and animals are part of a layer of millions of living things near the surface of the oceans. All these things are called plankton. The plankton that are plants use light from the sun to help make their own food. The plankton that are animals eat the plants or each other.
Fish, shellfish, and seabirds feed on the plankton. Then these creatures are eaten by larger animals, such as seals and some types of whales. This makes a food chain in the sea. So the food chains of the sea begin with plankton.