INVERTEBRATES2

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INVERTEBRATES

Animals without a backbone or spinal column.

Arthropods

Arthropods is a huge phylum of animals -- it includes eleven animal

classes: Merostomata, Pycnogonida, Arachnida, Remipedia, Cephalocarida,

Branchiopoda, Maxillopoda, Malacostraca, Chilopoda, Diplopoda, and Insecta.

Any animals that have more than four, jointed legs are arthropods.

Insects, spiders and crustaceans all belong to this class of animals.

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Echinoderms: Starfish, Sea Urchin and Family

Echinoderms are marine animals that live in the ocean.

Common echinoderms include the sea star, sea urchin, sand dollar and sea

cucumber. Most echinoderms have arms or spines that radiate from the center of

their body. The central body contains their organs, and their mouth for

feeding.

Annelids:

Worms and Leeches

Here are about 9,000 species of Annelids known today, including worms

and leeches. They can be found almost anywhere in the world. Annelids have

existed on Earth for over 120 million years.

Annelids have bodies that are divided into segments. They have very

well-developed internal organs. One common characteristic of annelids is that

they don't have any limbs.

Some annelids may have long bristles. Others have shorter bristles and

seem smooth, like the earthworm shown here.

There are many types of worms. Commonly

known worms include earthworms, roundworms and flatworms. Most worms are

small, measuring fractions of an inch to several inches long. Other worms,

such as the ribbon worm, can grow up to 100 feet in length. Some worms are

considered parasites, in that they live inside the human body.

Mollusks

Mollusks were among the

first inhabitants of the Earth. Fossils of mollusks have been found in rocks and date back over 500

million years. Mollusk fossils are usually well preserved because of their hard

shell.

Most mollusks have a soft,

skin-like organ covered with a hard outside shell. Some mollusks live on land,

such as the snail and slug. Other mollusks live in water, such as the oyster,

mussel, clam, squid and octopus.

Crustaceans

Crustaceans are a type of Arthropod. The name may

not sound familiar, but you probably know them. You may even have eaten one.

Crustaceans live mostly in the ocean or other

waters. Most commonly known

crustaceans

are the crab, lobster and barnacle.

Crustaceans have a hard, external shell, which protects

their body. Crustaceans have a head and abdomen. The head has antennae, which

are part of their sensory system. The abdomen includes the heart, digestive

system and reproductive system.

The abdomen also has appendages, such as legs, for crawling and

swimming. Many crustaceans also have claws that help with crawling and eating.

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