1. Invertebrate Animals 4.1 Most animals are invertebrates. 4.2
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Invertebrate Animals
the BIG idea
Invertebrate animals have a variety of body plans and adaptations.
4.1
Most animals are invertebrates.
4.2
Cnidarians and worms have different body plans.
4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
4.4
Arthropods have exoskeletons and joints.
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2. 4.1 Most animals are invertebrates.
Invertebrates are a diverse group of animals. Species of invertebrates live in almost every environment.
invertebrate
sponge
sessile
larva
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Sponges are simple invertebrates that have several types of specialized cells.
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3. 4.1 invertebrate Most animals are invertebrates.
sponge
An animal that has no backbone.
sessile
larva
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KEY CONCEPT
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4. 4.1 sponge Most animals are invertebrates.
A simple multicellular invertebrate animal that lives attached to one place and filters food from water.
sessile
larva
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5. 4.1 sessile Most animals are invertebrates.
sponge
The quality of being attached to one spot; not free-moving.
sessile
larva
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6. 4.1 larva Most animals are invertebrates.
sponge
A free-living early form of a developing organism that is very different from its adult form.
sessile
larva
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7. Cnidarians and worms have different body plans.
4.2
Cnidarians and worms have different body plans.
cnidarian
Cnidarians have simple bodies with specialized cells and tissues.
Most worms have organs and complex body systems.
tentacle
mobile
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8. 4.2 cnidarian Cnidarians and worms have different body plans.
tentacle
An invertebrate animal such as a jellyfish that has a body with radial symmetry, tentacles with stinging cells, and a central internal cavity.
mobile
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9. 4.2 tentacle Cnidarians and worms have different body plans.
A long, slender, flexible extension of the body of certain animals, such as jellyfish. Tentacles are used to touch, move, or hold.
mobile
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10. 4.2 mobile Cnidarians and worms have different body plans.
tentacle
Able to move from place to place.
mobile
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11. Most mollusks have shells, and echinoderms have spiny skeletons.
4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
Mollusks include bivalves, gastropods, and cephalopods.
Echinoderms have a water vascular system and tube feet.
mollusk
gill
lung
echinoderm
VISUALIZATION
Watch how different cephalopods move.
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12. 4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
mollusk
mollusk
gill
An invertebrate animal with a soft body, a muscular foot, and a mantle. Many mollusks have a hard outer shell.
lung
echinoderm
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KEY CONCEPT
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13. 4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
mollusk
gill
gill
A respiratory organ that filters oxygen dissolved in water.
lung
echinoderm
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KEY CONCEPT
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14. 4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
mollusk
lung
gill
A respiratory organ that absorbs oxygen from the air.
lung
echinoderm
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KEY CONCEPT
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15. 4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
mollusk
echinoderm
gill
An invertebrate sea animal with a spiny skeleton, a water vascular system, and tube feet.
lung
echinoderm
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KEY CONCEPT
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16. Arthropods have exoskeletons and joints.
4.4
Arthropods have exoskeletons and joints.
crustaceans,
and arachnids,
Arthropods, which include insects,
are the most abundant and diverse group of animals.
arthropod
exoskeleton
• Includes shrimp, crabs, lobsters,barnacles, and pill bugs
• Number of body segments and pairs of legs varies, 2 pairs of antennae
• Most live in water; some live on land
Crustaceans
• Includes beetles, bees, wasps, ants, butterflies, moths, and grasshoppers
• 3 pairs of legs, 3 body segments, 1 pair of antennae
• Most live on land
Insects
molting
insect
metamorphosis
• Includes spiders, ticks, mites, and scorpions
• 4 pairs of legs, 2 body segments, no antennae
• Most live on land
Arachnids
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17. 4.4 arthropod Arthropods have exoskeletons and joints.
An invertebrate animal with an exoskeleton, a segmented body, and jointed legs.
molting
insect
metamorphosis
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18. 4.4 exoskeleton Arthropods have exoskeletons and joints.
The strong, flexible outer covering of some invertebrate animals, such as arthropods.
molting
insect
metamorphosis
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19. 4.4 molting Arthropods have exoskeletons and joints.
The process of an arthropod shedding its exoskeleton to allow for growth.
molting
insect
metamorphosis
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KEY CONCEPT
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20. 4.4 insect Arthropods have exoskeletons and joints.
An arthropod with three body segments, six legs, two antennae, and compound eyes.
molting
insect
metamorphosis
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21. 4.4 metamorphosis Arthropods have exoskeletons and joints.
The transformation of an animal from its larval form into its adult form.
molting
insect
metamorphosis
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KEY CONCEPT
SUMMARY

22. 4.1 Most animals are invertebrates. I. Most animals are invertebrates.
A. Invertebrates are a diverse group of organisms.
sponge
B. Sponges are simple animals.
sessile
1. Specialized Cells
larva
2. Reproduction
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KEY CONCEPT
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23. Cnidarians and worms have different body plans.
4.2
Cnidarians and worms have different body plans.
II. Cnidarians and worms have different body plans.
cnidarian
A. Cnidarians have simple body systems.
tentacle
1. Tissues and Body Systems
mobile
2. Reproduction
B. Animals have different body plans.
C. Most worms have complex body systems.
1. Segmented Worms
2. Flatworms and Roundworms
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KEY CONCEPT
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24. Most mollusks have shells, and echinoderms have spiny skeletons.
4.3
Most mollusks have shells, and echinoderms have spiny skeletons.
III. Most mollusks have shells, and echinoderms have spiny skeletons.
mollusk
A. Mollusks are soft-bodied animals.
gill
1. Bivalves
lung
2. Gastropods
echinoderm
3. Cephalopods
B. Mollusks show a range of adaptations.
C. Echinoderms have unusual adaptations.
1. Spines and Skeletons
2. Water Vascular System and Tube Feet
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KEY CONCEPT
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25. Arthropods have exoskeletons and joints.
4.4
Arthropods have exoskeletons and joints.
IV. Arthropods have exoskeletons and joints.
arthropod
A. Most invertebrates are arthropods.
exoskeleton
1. Exoskeletons and Jointed Parts
molting
2. Complex Body Systems
insect
B. Insects are six-legged arthropods.
metamorphosis
C. Crustaceans live in water and on land.
D. Arachnids are eight-legged arthropods.
E. Millipedes and centipedes are arthropods.
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VISUALIZATION
Watch how different cephalopods move.

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