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invertebrates. In this case, we are starting lesson number two. Groups of

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invertebrates one and two. First of all, how many groups of invertebrates are

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there? There are six groups of invertebrates. One, arthropods. Two, mollusks.

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In this lesson, we are focusing on two groups. Group number one, arthropods.

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Group number two, mollusks. Group number one, arthropods. Arthropods have a

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segmented body and limbs. Remember that limbs include arms and legs. Arthropods

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have an exoskeleton. An exoskeleton is an external protection or armor. There are

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four groups of arthropods. Arthropods, one, are insects. For example, this bee.

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Insects, like bees, are arthropods. They have a head, a thorax, an abdomen, six legs,

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two antennae, and some of them also have wings. Arthropods number two, arachnids.

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Arachnids, like spiders, are also arthropods. They have a head and thorax,

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an abdomen, and eight legs. Arthropods three, crustaceans. Crustaceans, like crabs,

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are arthropods. They have two eyes, four antennae, two claws, eight legs, and a carapace or shell

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to protect themselves. Arthropods number four, myriapods. Myriapods, like centipedes,

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are also arthropods. They have two antennae, many, many segments, and a lot of legs.

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Group number two, mollusks. Mollusks have a soft body. Some mollusks, like slugs or snails,

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have a shell for protection. Other mollusks, like octopuses, have tentacles.

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Okay, let's now continue with the three different groups of mollusks. Remember that mollusks have

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a soft body. There are three groups of mollusks, gastropods, cephalopods, and bivalves. Let's

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explain group number one, gastropods. They have two antennae with eyes. Some have a shell for

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protection, and they can live on land or in water. Group number two are cephalopods. They have a

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large head with tentacles. Some also have a shell for protection, and they live in water. Some use

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camouflage to protect themselves. Group number three are bivalves. Some have two shells for

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protection, and they live in water.