My Science School

Arthropod of the Sea

Many kinds of arthropods live in the sea. Lobsters, shrimps, crabs, and barnacles are all arthropods that live in the sea. They are called crustaceans. That means animals with crusts. Every part of a lobster’s body is covered with a crust of hard skin, like armour. Crustaceans have hard shells, 10 leg and 4 feelers, or antennae. Because they live mostly in the water, crustaceans breathe with gills, like fish.

Lobsters use eight of their ten legs for walking along ocean floor. The other two legs are used like arms. Each arm ends in a fierce-looking pincer, or claw. Shrimps look like tiny lobsters. Some kinds of shrimps are so small they can be seen only with a microscope.

Crabs have flat bodies. The tail is tucked forwards under the rest of the body. Instead of walking forwards, crabs scuttle sideways along the seashore or in shallow rock pools. Barnacles are crustaceans that fasten themselves to rocks or the bottoms of ships. They are closed up inside their shells, and only their legs stick out. They wiggle their legs to pull in food that floats past in the water.

The Web Weavers

Many kinds of spiders spin webs to catch flying insects. Each kind of spider makes its own special kind of web, from small, sticky traps to large, tightly woven nets. Orb spiders make webs with threads that stretch from the centre like the spokes of a bicycle wheel. Black widow spiders make tangled webs. Grass spiders make webs like little sheets.

Spider webs are made of silk that comes out of the spider’s body. The silk is a liquid that forms a thin, strong thread when air touches it. After a spider spins its web, it hangs underneath it or hides nearby. An insect caught in the web shakes the web as it struggles, telling the spider that dinner is ready!

Some spiders have other ways to catch their food. Wolf spiders and lynx spiders chase insects. Jumping spiders catch insects by jumping on them. Some spiders even like to fish! They wait beside a stream or pond and catch water insects that swim past.

Crawling on Eight Legs

Many people shudder when they see a spider. But most spiders are harmless, and some are even helpful. How do spiders help people? They eat many harmful insects. They munch grasshoppers and locusts, which destroy crops. They also snap up flies and mosquitoes, which carry disease.

Many people think spiders are insects. But they are not. Insects have wings, feelers, and six legs. Spiders have neither wings nor feelers, and they have eight legs. Eight-legged animals are called arachnids.

Scorpions are close relatives of spiders. Scorpions live in warm, dry places such as deserts. Scorpions have eight legs, like spiders. But mother scorpions don’t lay eggs, as many spiders do. Baby scorpions come out of the mother’s body. They climb up onto her back and hang on as she carries them around.

A scorpion uses its claws to grab its prey. Then it pulls the victim into its mouth and chews it up. Sometimes the scorpion kills its prey with a poisonous sting. The stinger is a sharp, curved spike at the end of the scorpion’s tail. The stings of some scorpions are dangerous to people.

Wood-Ant City

An ant nest is like a little city where hundreds or even thousands of ants live together. Ants make their nests by digging tunnels and storerooms in the ground. Some also build mounds aboveground and cover them with twigs and pine needles.

The picture shows on wood-ant nest. If you look at it carefully, you can see that a lot is going on. Above the nest, a group of workers hunts for food. The ant with wings is a male. Male ants don’t do any work.

Inside the nest, in the top tunnel, two workers are bringing in part of a leaf. They will use it to repair the nest. Other workers are getting ready to carry cocoons to another room. Inside each cocoon is a baby ant. When the young ants grow up, they will break out of the cocoons.

In the lower tunnel is the queen ant. She is much bigger than the workers. She spends her whole life laying eggs. Ants work as if they were quite clever, but an ant does things because its body gets signals, such as smells. Different smells make ants do different things.

The Buzz on Bees

A honey bee lands on a flower. It stretches out its tube-like tongue and sucks up the sweet nectar. As the beep pushes into the flower, a yellow powder called pollen falls onto the bee’s hairy body. The pollen then rubs off on every flower the bee visits after that. A flower needs pollen from another flower of the same kind to make seeds.

Honey bees also take some pollen for themselves. They mix it with a tiny bit of nectar and carry it on their back legs. When the bee is fully loaded with nectar and pollen, it flies back to the hive. There worker bees take the nectar and pollen. In a few days the nectar will thicken to honey.

Inside the hive there are thousands of tiny rooms, or cells. The cells are storerooms. Some are filled with honey or pollen, food for the bees. Others contain eggs or bee larvae. Others hold baby bees in silky cocoons. These young bees are changing into adults.

Tiny, but Deadly

When you think about dangerous animals, do you think of fierce sharks and hungry lions? You should also think about another dangerous animal—the common housefly. Why? Because flies carry germs, and some germs cause disease!

Flies taste things with their feet. As they walk over all kinds of rotting foods and plants, they collect germs on their feet. Then they land on fresh food, leaving germs everywhere.

Flies also spread germs when they eat. A fly can eat only liquids. It pumps a special juice from its stomach that turns food into liquid. The fly might suck up food that has germs in it. This means some of the germs get into the fly’s stomach. If the fly pumps some stomach juice onto the sugar on your table, the germs get into the sugar. And if you eat the sugar, the germs get into you!

The mosquito can also be a dangerous enemy. Female mosquitoes drink people’s blood! They break the skin and suck the blood with their female mosquito long mouthparts, leaving an itchy bite. Sometimes, when mosquitoes drink blood, they inject tiny germs into the bloodstream. The germs mosquitoes carry can cause serious diseases.

Crawling on Six Legs

They buzz. They prowl. They crawl. Some munch leaves, others sip nectar. Some crunch wood. A few drink blood. They can be as small as the eye of a needle, or as big as a grown-up’s shoe. What are they? Insects!

Insects live just about everywhere, from the steamiest jungles to the coldest mountaintops and the driest deserts. No matter where you live, you’re sure to see insects buzz, prowl, or crawl by.

Flies, ants, bees, grasshoppers, beetles, crickets, and butterflies are all in the group of animals called insects. Like all insects, these creatures have six legs. Most insects also have wings.

Insects do some amazing things. Some insects, like flies, taste with their feet. Most insects smell with two wiggly feelers on their head called antennae. Some insects have no eyes, while others have five or more. Many insects hear with hairs on their bodies, while others have “ears” on their legs or on the sides of their bodies.

Meet the Arthropods

What’s an eight-legged creature that catches other animals in a trap? A spider! What six-legged jumping animal has ears on its sides? A grasshopper! What’s a ten-legged tunnel builder? A crayfish!

The world is full of these many-legged creatures called arthropods. An arthropod’s body is divided into several sections. Each section is covered with an outer shell. Arthropods have no skeleton inside their bodies, but their hard shell protects them. Large arthropods, such as crabs and lobsters, have a thick, heavy shell. Small, flying arthropods like bees and butterflies have a much lighter covering.

Arthropods live everywhere—jungles, deserts, oceans, caves, mountaintops, and in your own garden. You can watch them creep, crawl, and fly all summer long. If it has many legs and its body is divided into several sections, it’s an arthropod.

Dainty but Deadly

Some of the daintiest creatures in the sea are the deadliest to small fish and shrimp. Both the sea anemone and the jellyfish look like pretty flowers, but they sting their prey with poison.

The sea anemone got its name because it looks like the flower called an anemone. The animal lives on the bottom of the sea, often in a warm coral reef or a rock pool. A sea anemone can move slowly, but it prefers to stay in one spot.

To catch small fish and shrimp to eat, the sea anemone spreads out its arms. Those arms are filled with tiny stinging parts. When the anemone touches its prey, it shoots out a poison. The poison stops the creature from moving. Then the sea anemone uses its arms to carry the creature to its mouth.

The jellyfish looks like an upside-down tulip. Its body is like a see-through umbrella with long strings hanging down. The jellyfish is made mostly of water. Washed up on the beach, it looks like a lump of colorless jelly.

The jellyfish swims by opening and closing its whole body. When it stops moving, it sinks to the bottom. As it drifts down, it catches small animals by stinging them with its tentacles.

Starry Creatures

What kind of animal has eyes and feet on its arms and pushes its stomach out of its body when it eats? A starfish!

Starfish have tough-skinned bodies shaped like a star. They usually have five arms, sometimes more. Underneath each arm there are little tubes. These are the feet of the starfish. And the small reddish spots at the end of each arm are its eyes!

When it finds a clam, the starfish climbs on top of it. Its tube feet stick to the clamshell like glue. Then the starfish slowly begins to pull the shell apart. Soon the shell is a little way open-just a tiny crack. The starfish then pushes its stomach through an opening in its body and between the two halves of the shell. Juices from the starfish’s stomach turn the clam to mush. The starfish digests, or breaks down, the clam inside the clam’s own shell.

If a starfish loses an arm, it grows a new one! In fact, if the starfish is torn in two, each half grows into a new starfish.

Fuzzy Biscuits and More

The ocean is full of amazing animals. A sand dollar looks like a fuzzy biscuit, but it’s an animal that lives in the sand. It moves about on many feet that look like tiny tubes. People often find the white coin-shaped skeletons of sand dollars on the beach.

A sea cucumber isn’t found in a garden. It’s an animal with a long round body that looks a little like a garden cucumber. At one end are its “fingers” and mouth. The animal uses its fingers to catch food floating in the water. Then it puts each finger, one at a time, into its mouth and enjoys a tasty meal.

Another unusual animal looks like a creeping pincushion. This creature, called a sea urchin, is related to the starfish, but it is round and plump.

Sea peaches belong to the family of animals called sea squirts. Most kinds of sea squirts are just round bodies with two openings like little mouths. One mouth sucks water in. The other squirts water out. The sea squirt eats the tiny animals and bits of plants in the water it sucks in.

Life under a Microscope

If you picked up a cupful of seawater, you might see a few creatures. But, if you looked at the same cup of water under a microscope, you would see hundreds or thousands of little creatures!

Some of the creatures are tiny animals. Some are the young of bigger animals. You’d also see living things like plants. Huge masses of these animals and plants drift in the ocean. Together they are called plankton. Plankton is food for a great many sea creatures, from shrimp to whales.

In a cupful of pond water you would see different creatures. One looks like the bottom of a shoe. It’s called a paramecium and has no head and no legs. It doesn’t have eyes or a mouth either. Its body is covered with rows of little hairs called cilia that it uses like oars to move through the water.

Another creature looks like a funnel with a long tube. It creates a little whirlpool around the top of the funnel to draw food into its body. This creature is called a vorticella.

Another creature found in ponds is an amoeba. It looks like a blob of grey jelly, and it changes shape every time it moves.

Even though these creatures are microscopic, they are an important part of the world of animals. Without them, many other animals would go hungry.

An Underwater Garden

When is a garden made of animals? When it is made by tiny animals called corals! Beautiful “gardens” cover the seafloor in warm, shallow parts of the ocean.

Thousands of corals live together in colonies. Coral colonies are made from limestone. The limestone forms a home where the corals live. Coral colonies can be shaped like fans, beach balls, candlesticks, and other shapes. They can be red, pink, orange, blue, green, or purple.

Each individual coral is called a polyp. Corals are actually relatives of jellyfish. Like jellyfish, coral polyps send out special feelers that sting tiny ocean creatures. The polyps eat these creatures.

Together, many corals form a coral reef. Coral reefs are the richest parts of the ocean. They provide a home for countless fish and other ocean animals. Many colourful creatures live and hide in the crevices and tunnels created by coral.

A Real Live sea Monster

It has eight long, rubbery legs and two huge, staring eyes. The octopus is so scary-looking to some people that it is sometimes called the devilfish. But octopuses rarely attack people. They use their strong arms, called tentacles, to catch shellfish and swim away from danger. Some kinds also have a poisonous bite.

There are about 50 kinds of octopuses. Most of them are about the size of a kitten. But some measure 8.5 metres from arm tip to arm tip.

The octopus is a mollusc. It has no bones, but a tough covering called a mantle protects its body and gives it shape. Rows of round muscles under each arm act as suction cups. These suckers can hold onto an object even if the octopus’s arm is cut off!

When an octopus is frightened it produces a cloud of inky liquid. The inky liquid makes it hard for an enemy to see or smell the octopus. That’s how the octopus gets away.

Magnificent Molluscs

Imagine having a soft body, with no backbone to hold you up and only one foot to help you move. That’s what clams are like. Clams belong to a group of animals called molluscs. Molluscs have soft bodies with no skeleton. Some molluscs, such as snails, clams, oysters, and scallops, have outer shells for protection. Slugs, octopuses, and squids are molluscs that have no outer shells.

Molluscs live in most parts of the world. Land snails and slugs live on land. Octopuses, squids, and oysters, live in the seas and oceans. Some clams and snails live in rivers, lakes, ponds, and streams.

Wherever molluscs live, they must keep their bodies moist to stay alive. That’s why slugs and some land snails can be found under damp leaves or in the soil.

Some molluscs live between two shells that can open and close like a book. These animals are called bivalves. Clams, cockles, mussels, oysters, and scallops are bivalves. Bivalves usually keep their shells open just a little so that food can drift in. They eat tiny plants that float by in the water.