Invertebrates

Invertebrates, or non-vertebrates, do not have backbones, which are also called vertebrae or spinal bones. Invertebrates make up most of the animal species on Earth, approximate 96%. The other 4% are vertebrates which include mammals, fish, reptiles, birds, and amphibians. Invertebrates include everything else.

The main categories of invertebrates include ocean animals, worms, insects, spiders, centipedes, and scorpions. The largest invertebrate is called a colossal squid, which can be over 1000 pounds and over 40 feet long. The longest can be 180 feet long, called a ribbon worm. The smallest invertebrate can only be seen under a microscope. The tiny vertebrate is the rotifer or wheel animal, which is only about 0.1 to 0.5 mm in length.

The ocean animals include marine invertebrates such as sponges, corals, starfish, jellyfish, and others. Another ocean animal are mollusks. They have a soft body covered by the mantle or an outer layer. Most mollusks live inside a shell. Examples include squid, snails, octopuses, oysters, and several more.

Crustaceans can also be found in water, and are a type of arthropod, meaning they have jointed legs. They also have bones on the outside of their bodies like a shell, called an exoskeleton. When a crustacean outgrows the shell, it will shed it and grow a new one. Examples of crustaceans are crabs, lobster, barnacles, and shrimp. Lobsters, crabs, and shrimp have ten legs, and the two front legs have pincers they use to fight off enemies.

Worms are invertebrates classified as those that do not have legs. They live in soil, in water, or inside other animals as parasites. A parasite feeds off the animal it lives. There are many examples of worms including the leech, earthworm, and tapeworm.

The next invertebrate is the insect. Insects are the largest group of arthropods and there are over one million species of insects. There are more insects in the world than any other type of animal. Most insects are small and range in size from invisible to the eye to as large as over seven inches. A distinguishing feature of an insect is their bodies are made up of three sections, head, thorax, and abdomen. The types of insects include butterflies, bees, moths, flies, grasshoppers, termites, and many others.

Spiders, centipedes, and scorpions are in the final category of invertebrates. Spiders and scorpions are arachnids because they have eight legs. There are some scorpion mothers that protect their young by carrying them on their back. Centipedes and millipedes are called myriapods because they have many, many legs, as many as 750 legs. Centipedes are carnivores and will eat worms and insects, but millipedes are herbivores and eats plants and rotting material. Other species in this category include spiders called tarantulas and black widows.

Other interesting facts about invertebrates include some that do not have heads, and millions living in people's homes called dust mites. Since invertebrates are numerous they can be found all over the world.

In summary, invertebrates make up about 96% of all living animals species on the Earth. There are a wide variety of invertebrates which crawl, fly, and walk. The invertebrate includes the millions of insect species, worms, crustaceans, mollusks and other marine invertebrates, as well as spiders, centipedes, and scorpions. Invertebrates can be found in every corner of the world.




A: 96%
B: 4%
C: 90%
D: 10%

A: Spiders
B: Mollusks
C: Crustaceans
D: Insects

A: Mollusk
B: Myriapod
C: Arachnid
D: Parasite

A: Spiders
B: Worms
C: Mollusks
D: Insects

A: Head
B: Thorax
C: Abdomen
D: Exoskeleton

A: Centipedes
B: Millipedes
C: Crustaceans
D: Leeches








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Starfish Facts
Octopus Facts
Animals with and without Backbones Quiz
Vertebrates Reading Comprehension
Animal Classification Reading Comprehension
Pygmy marmoset Facts
Vampire squid Facts
Coral Facts
Centipedes Facts

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