Invertebrates are animals without backbones or inner skeletons. There are six main groups of invertebrates: sponges, cnidarians, echinoderms, mollusks, worms, and arthropods. Cnidarians have jelly-like bodies and tentacles. Examples include jellyfish, sea anemones, and corals. Echinoderms have a five-way symmetrical shape and a hard exoskeleton. Mollusks include gastropods with one shell, bivalves with two shells, and cephalopods like octopuses which move by expelling water. Arthropods have an external exoskeleton and include insects, arachnids

1. INVERTEBRATES

2. Characteristics of ALL Invertebrates:
•Invertebrate animals have no inner skeleton or backbone.
•Most invertebrates are very small, but some are enormous.
•Some invertebrate bodies are protected by shells or
exoskeletons, but others have no covering.

3. •Most invertebrates are symmetrical.
•Some invertebrates have a body that has no symmetry.
•Most invertebrates are oviparous.
•A larva hatches from an egg.

4. •Many invertebrates live in the sea, but some live in fresh water,
and others on land.
•Most invertebrates can move.
•Some invertebrates don’t move.
•They attach themselves to rocks or the sea floor.
•Parasites live inside of other animals and harm them.

5. INVERTEBRATE
GROUPS

6. 1. SPONGES
• Sponges have irregular bodies and no symmetry.
• They cannot move from one place to another.
• They attach themselves to rocks or the sea floor.
• They filter seawater and retain the nutritive substances for food.

7. 2. CNIDARIANS
• Cnidarians have jelly-like bodies.
• They have tentacles.
• They are marine animals.
• Some cnidarians, the coral and sea anemone, attach themselves to rocks.
• Other cnidarians, such as jellyfishes, can move about.

8. 3. ECHINODERMS
• Echinoderms have five-way shape.
• They have an exoskeleton made of hard plates, often with spikes.
• They are covered by a thin skin under the spikes or hard exoskeleton.
• All echinoderms are marine animals.

9. 4. MOLLUSKS
• Mollusks have a soft body.
• They don’t have a skeleton or exoskeleton.
• Mollusks don’t have legs, but some have flexible tentacles.
• Most mollusks grow a hard shell for protection.
• Most mollusks are aquatic, but a few live on land.
• There are three main groups of mollusks: gastropods, bivalves, and cephalopods.

10. a. GASTROPODS
• Gastropods have a head with four tentacles.
• These four tentacles have the sense organs of the gastropods.
• Gastropods have one foot to move.
• Marine gastropods eat algae, but most terrestrial gastropods are herbivores.
• Most gastropods have one spiral shell which protects their internal organs.
• Some gastropods have no shell, for example, slugs.

11. b. BIVALVES
• Bivalves have a shell made up of two halves.
• The halves can open and close.
• They can close very tightly for protection.
• Bivalves have a soft body but no head.
• All bivalves are aquatic.

12. • Some bivalves, mussels, attach themselves to rocks on the ocean floor.
• Other bivalves, oysters, move from one place to another.
• To obtain food, bivalves filter saltwater and retain the nutritive substances.
• One process that is unique to bivalves is pearl formation.

13. c. CEPHALOPODS
• Cephalopods have a well –developed brain.
• They have eight or ten tentacles.
• All cephalopods are marine.
• They move their body and expel water to go from one place to another.
• Some of them have a very small internal skeleton, called a cartilage.

14. • All cephalopods are carnivores.
• They capture their prey with the tentacles.
• Some cephalopods can expel black ink from their bodies.
• These cephalopods use the ink to hide.
• Other cephalopods camouflage themselves to hide.

15. 5. WORMS
• Worms have long and soft bodies.
• They are oviparous.
• Some worms have bodies divided into segments.
• Some worms are round, but others are flat.
• Some worms are aquatic, and others are terrestrial.
• Many worms are parasites.

16. 6. ARTHROPODS
• Their bodies are totally covered by an exoskeleton.
• The exoskeleton is like a human skeleton.
• It protects the body, but it is external.
• The exoskeleton is rigid.
• Sometimes the arthropod moults and grows a new
exoskeleton.

17. • The sense organs of arthropods are well developed.
• They have antennae and eyes.
• The eyes can be simple or compound.
• Compound eyes are made up of thousands of smaller, simple
eyes.
• Insects, arachnids, crustacean and myriapods are the four kinds of
arthropods.

18. a. INSECTS
• Insects are the most numerous animal group.
• An insect body is divided into three parts: head, thorax and abdomen.
• The head has a mouth, two eyes, and two antennae.
• The thorax has six legs.
• Many insects have wings on the thorax.

19. • Insects can live everywhere except the open sea.
• They eat many different types of food.
• Some insects, like bees or silkworms, produce substances which are
useful for people.
• Others are harmful, they cause illness, destroy crops or spoil food.

20. b. ARACHNIDS
• These arthropods have eight legs.
• An arthropod body is made up of two parts: the abdomen and the
cephalothorax.
• Scorpions and spiders are arachnids.
• Most are terrestrial and some are carnivorous.
• They hunt and eat other animals.

21. c. CRUSTACEANS
• Most crustaceans are aquatic.
• Many have ten legs, two pairs of antennae and compound eyes.
• The body is made up of two parts: abdomen and the
cephalothorax.
• Crustaceans have joints and can bend their body.
• Many crustaceans are used for food.

22. d. MYRIAPODS
•Myriapods have long bodies made up of many identical
segments.
•Each segment has one or two pairs of legs.
•The head has two short antennae.

23. Answer the questions.
1. What are invertebrates?
2. What are the six groups of invertebrates?
3. What kind of body do cnidarians have?
4. Give three examples of cnidarians.
5. What kind of body do echinoderms have?
6. What kind of body do gastropods have?
7. What are the three kinds of mollusks?
8. What kind of body do arthropods have?
9. What kind of invertebrates are mostly parasites?
10. How do sponges eat?

24. 11. What kind of body do worms have?
12.What happens to arthropod skin?
13.What kind of body do arachnids and crustaceans have?
14.What is the exoskeleton?
15.What are the four kinds of arthropods?
16.Give two differences between insects and arachnids.
17.What is similar between sponges and bivalves?
18.What kind of body do myriapods have?
19.What are the three parts of the body of insects?
20.How do cephalopods move?

25. VOCABULARY REVIEW:
1. Invertebrate 11. crustacean
2. Symmetrical 12. myriapod
3. Cnidarian 13. exoskeleton
4. Echinoderm 14. oviparous
5. Mollusk 15. filter
6. Gastropod 16. nutrient
7. Bivalve 17. attach
8. Cephalopod 18. substance
9. Arthropod 19. tentacle
10. arachnid 20. antennae

26. 21. Marine
22. Aquatic
23. Terrestrial
24. Herbivore
25. Carnivore
26. Cartilage
27. Camouflage
28. Moult
29. Parasite
30. segment