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Scientists
have named more than a million species of
invertebrates.
That’s a lot of animals that have no backbone! |
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Animals
Without Backbones |
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Most
of the animals on Earth do not have backbones. They are
invertebrates. Some are too small to be seen with the naked eye.
The largest invertebrates,
which are giant squids, can easily stretch
across the width of a
basketball court. Some kinds of invertebrates
include mollusks,
worms, cnidarians, and arthropods. |
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Mollusks |
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A
mollusk has a soft body without bones. This phylum includes
animals
such as snails, slugs, clams, and squids. Some
mollusks, like clams,
have a hard outer shell that protects them
from being eaten. Some
mollusks get oxygen by using gills.
Others are able to absorb oxygen
through their skin. |
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Worms |
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Worms
belong to many different phyla. Flatworms are flat and very
thin.
They live in wet or damp places. Roundworms can live in
water or
on land. Segmented worms include the earthworm. Some
kinds of worms
are microscopic. Some are huge. One of the largest
earthworms caught
was about 7 meters (about 23 feet) long. |
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1. |
List at least 3 different invertebrates.
How are
they alike? |
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Compare and Contrast
How are worms and clams
alike?
How are they different? |
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This
strange-looking
mollusk is called
a lettuce sea slug.
It lives in tropical
waters and eats
algae. |
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This is the head of the lettuce sea slug. |
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