1. Worms and Mollusks
Biology 112

2. Flatworms Phylum Platyhelminthes
Soft, flattened worms with tissues and internal organ systems
The simplest animals with three germ layers, bilateral symmetry and cephalization
Acoelomates
No coelom between the tissues of flatworms
A coelom is a fluid-filled body cavity that is lined with tissue in the mesoderm

3. Body Functions of Flatworms
All use diffusion for distribution of nutrients and gases
Some have specialized flame cells used to remove excess water from the body
Contain a digestive cavity with one opening – a mouth
A muscular tube, called a pharnyx, pumps food into the digestive cavity

4. Classification of Flatworms
Tubellarians
Free-living flatworms, can live in fresh and salt water
Ganglia control the nervous system
Some contain an eyespot to detect light
Reproduce asexually and sexually
Planarians are the most familiar species

5. Classification of Flatworms
2. Flukes
Parasitic
Infect the internal organs of their host
Reproduce sexually in the primary host and asexually in the intermediate host

6. Classification of Flatworms
3. Tapeworms
long, flat parasitic flatworms
Live in the intestines of their hosts

7. Unsegmented worms that have pseudocoeloms
Roundworms
Phylum Nematoda
Unsegmented worms that have pseudocoeloms
A body cavity that lies between the endoderm and the mesoderm tissues
Also have a digestive system with a mouth and an anus

8. Roundworms and Body Functions
Rely on diffusion for respiration, circulation and excretion
Muscles and fluid in the pseudocoelom act as a hydrostatic skeleton
Reproduce sexually by internal fertilization

9. Characteristics of Roundworms
Most are free-living but some are parasitic
Parasitic include:
Trichinosis-causing worms
Filarial worms
Ascarid worms
Hookworms

10. Annelids Phylum Annelida Earthworms Segmented bodies
Have a true coelom that is lined with tissue from the mesoderm
Internal walls called septa separate the segments that divide the body
Most segments are similar to one another
A few are specialized with eyes or antennae
Many have bristles called setae attached to each segment

11. Internal Structure of Annelids
Complex organ structures
Many contain a pharynx that is used to get their food
Food moves through the crop, where it is stored
Then moves to the gizzard, an organ that grinds it into smaller pieces
Have a closed circulatory system in which blood is contained in vessels

12. Earthworms Class Oligochaeta Hermaphroditic
Has both male and female reproductive organs
When eggs are ready to be fertilized, a clitellum, a band of thickened segments, secretes a mucous ring in which fertilization takes place
Streamlined body with few setae
Can live in fresh water or soil

13. Mollusks Phylum Mollusca
Soft-bodied animals that often have an internal or external shell
Many have a larval stage called a trochophore
Can be herbivores, carnivores, detritophores or parasites

14. Body Parts of a mollusk Foot Mantle Visceral mass Shell
Used for crawling, burrowing and capturing prey
Mantle
A thin layer of tissue that covers most of the body
Visceral mass
Makes up the internal organs
Shell
Glands secrete calcium carbonate

15. Body systems of the mollusk
Either closed or open circulatory systems
When it is closed, blood is pumped through vessels into a large saclike structures called sinuses
When it is open, blood is contained in blood vessels throughout the body
Nervous systems varies from simple to complex

16. Classification of mollusks
Gastropods
Includes pond snails and land slugs
Single-shelled or shell-less
Move by using a muscular foot on their left ventral side
Use a flexible tongue called a radula to eat
Bivalves
Clams, oysters, mussels and scallops
Two-shells held together by muscles
Cephalopods
Includes octopus and squid
Soft-bodied mollusks in which the head is attached to a single foot
Foot is divided into tentacles
Small internal shells or no shell at all
Have complex sense organs