Page 20 - Science Course 2 (Book 1)

Mo1-L2a: What is an Invertebrate?

Echinoderms
SUMMARY
• An echinoderm, from the phylum Echinodermata, What is an Invertebrate?
feels spiny due to the hard endoskeleton
just beneath its thin outer skin. Invertebrates do not have a backbone; they

support their bodies with an exoskeleton, an
• All echinoderms live in salt water and endoskeleton, or a hydrostatic skeleton.
move slowly with tiny suction-cup like
feet called tube feet.

• Echinoderms have bilateral symmetry when they
are young and radial symmetry as adults.

Sponges and cnidarians are the oldest
branches on the animal family tree.

Key Concept

What is an invertebrate?
How do the groups of invertebrates differ?

Arthropods have three body parts—the head,
the thorax, and the abdomen.

Head
Thorax

Abdomen

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