1. KEY CONCEPT Flatworms, mollusks, and annelids belong to closely related phyla.

2. Flatworms are simple bilateral animals.
Flatworms have a solid body and incomplete or absent gut.
There are three classes of flatworms.
planarians
head
pharynx
mouth
sucker
eyespot
reproductive
system
gut cavity

3. Flatworms are simple bilateral animals.
Flatworms have a solid body and incomplete or absent gut.
There are three classes of flatworms.
planarians
flukes

4. Flatworms are simple bilateral animals.
Flatworms have a solid body and incomplete or absent gut.
There are three classes of flatworms.
planarians
flukes
tapeworms

5. The intermediate host in the tapeworm life cycle is the flea.

6. Mollusks are diverse animals.
Mollusks and other bilateral animals have a complete digestive tract.
A complete digestive tract has two openings: a mouth and an anus.
Flatworms are the only bilateral animals without a complete digestive tract.

7. Mollusks share at least one of three features.
radula (scraping “teeth”)
mantle (skin-like tissue, may form a shell)
Ctenidia (flat gills, also called book lungs)
intestine
stomach
digestive gland
foot
anus
salivary gland
crop
mouth
radula
mantle
mantle cavity
heart

8. Most mollusks are classified into three (of seven) classes.
gastropods
pelecypods (also called bivalves)
cephalopods

9. Mollusks have a variety of reproductive strategies.
Most strategies involve sexual reproduction.
Some species are hermaphrodites.
Have both male and female sex organs
(But don’t reproduce with themselves)
Examples: tapeworms, snails, earthworms

10. Annelids have segmented bodies.
Segmentation refers to the repeated sections of an annelid’s body.
The coelom is a fluid-filled space completely surrounded by muscle.
blood vessels
muscle
hearts
brain
mouth
digestive tract
nerve cord
segment

11. There are three groups of annelids.
earthworms
marine worms
leeches