1. Mollusks and Annelids Section 1: Mollusks Section 2: Annelids
Chapter 29
Mollusks and Annelids
Section 1: Mollusks
Section 2: Annelids 1

2. Section 1
Mollusks
Objectives:
Summarize the evolutionary relationship between mollusks and annelids.
Describe the key characteristics of mollusks.
Describe excretion, circulation, respiration, and reproduction in mollusks.
Compare the body plans and feeding adaptations of gastropods, bivalves, and cephalopods. 2

3. Section 1
Mollusks
A True Coelom
Coelom and Trochophore Mollusks and annelids have a true body cavity and many mollusks and annelids have a larval form called a trochophore. 3

4. Mollusks Key Characteristics of Mollusks
Section 1
Mollusks
Key Characteristics of Mollusks
Key Traits The mollusk body has three distinct parts: a visceral mass, a mantle, and foot. All mollusks except bivalves have a rasping tonguelike radula. Mollusks have a true coelom and well-developed organs.
Organ Systems Most mollusks respire with gills but some respire with a primitive lung. Nephridia enable mollusks to recover the useful substances from their bodily wastes. 4

5. Mollusks Body Plans of Mollusks
Section 1
Mollusks
Body Plans of Mollusks
Gastropods Gastropods (snails and slugs) live in oceans, in fresh water, and on land. Gastropods have an open circulatory system.
Bivalves Bivalves (clams, oysters, and their kin) are aquatic and have hard shells called valves that protect their soft bodies. Bivalves have an open circulatory system.
Cephalopods Cephalopods (octopuses, squids, and their kin) have a well-developed head region, many tentacles, and a closed circulatory system. Most cephalopods have no external shell. 5

6. Section 2
Annelids
Objectives:
Identify the major change in body plan that distinguishes annelids from mollusks.
Describe the basic annelid body plan.
Describe the annelid digestive system.
Compare the three classes of annelids. 6

7. Annelids The First Segmented Animals
Section 2
Annelids
The First Segmented Animals
Characteristics of Annelids Annelids are coelomate worms that have segmented bodies and complex nervous systems. Annelids are classified according to the presence or absence of setae and parapodia. Annelids respire through their skin, and they have a closed circulatory system. 7

8. Annelids Annelid Groups
Section 2
Annelids
Annelid Groups
Marine Worms Marine polychaetes have parapodia and setae. Some are active predators and others are filter feeders.
Earthworms Earthworms burrow through the soil, ingesting it as they crawl.
Hydrostatic Skeleton The fluids within the coelom of each body segment creates a hydrostatic skeleton that supports the segment.
Leeches Leeches lack parapodia and setae, and their segments are not separated internally. They may be aquatic or terrestrial, and some are parasites. 8