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

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

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

Mollusks Key Characteristics of Mollusks Section 1 Mollusks Key Characteristics of Mollusks The mollusk body has three distinct parts: visceral mass, mantle, and foot. 4

Section 1 Mollusks Key Characteristics (Con.) 4

Mollusks Key Characteristics (con.) Section 1 Mollusks Key Characteristics (con.) All mollusks except bivalves have a rasping tonguelike radula. Mollusks have well-developed organs. 4

Mollusks Key Characteristics (con.) Section 1 Mollusks Key Characteristics (con.) 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

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. 5

Mollusks Body Plans of Mollusks Section 1 Mollusks Body Plans of Mollusks Bivalves Bivalves (mussels, clams, oysters, and their kin) are aquatic and have hard shells called valves that protect their soft bodies. Bivalves have an open circulatory system. 5

Mollusks Body Plans of Mollusks Section 1 Mollusks Body Plans of Mollusks 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

Section 1 Mollusks Zebra Mussels: Exotic Species 3

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

Annelids The First Segmented Animals Section 2 Annelids The First Segmented Animals Annelids are coelomate worms that have segmented bodies and complex nervous systems. 7

Annelids Characteristics of Annelids Section 2 Annelids Characteristics of Annelids Annelids respire through their skin, and they have a closed circulatory system. 7

Annelids Hydrostatic Skeleton Section 2 Annelids Hydrostatic Skeleton The fluids within the coelom of each body segment creates a hydrostatic skeleton that supports the segment. 8

Annelids Classification of Annelids Section 2 Annelids Classification of Annelids Annelids are classified according to the presence or absence of setae and parapodia. 7

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. 8

Annelids Annelid Groups Section 2 Annelids Annelid Groups Earthworms Earthworms burrow through the soil, ingesting it as they crawl. 8

Annelids Annelid Groups Section 2 Annelids Annelid Groups Leeches Leeches lack parapodia and setae, and their segments are not separated internally. They may be aquatic or terrestrial, and some are parasites. 8