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Chapter 15 Section 2 Mollusks and Annelid Worms Bellringer Unscramble the following words and write a sentence that uses all of the words. • gluss • isalns • sdusqi • klomssul Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Objectives • Explain how mollusks eat, control body functions, and circulate blood. • Describe the four body parts that most mollusks have in common. • Describe the three kinds of annelid worms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Mollusks • Snails, slugs, clams oysters, squids, and octopuses are all mollusks. • Most mollusks fit into three classes: • The gastropods include slugs and snails. • The bivalves include clams and other shellfish with two shells. • The cephalopods include squids and octopuses. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Mollusks • Each kind of mollusk has its own way of eating. • Slugs and snails eat with a toungelike organ covered in teeth called a radula. • Clams and oysters attach to one place and use gills to filter tiny plants, bacteria, and other particles from the water. • Squids and octopuses grab food with tentacles and place it in their powerful jaws. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Mollusks, continued • Ganglia and Brains All mollusks have complex ganglia. They have ganglia to control breathing, movement, and digestion. • Cephalopods, such as octopuses, have large brains that connect all of their ganglia. Cephalopods are thought to be the smartest invertebrates. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Mollusks • Most mollusks have an open circulatory system. In an open circulatory system, a simple heart pumps blood through blood vessels that empty into sinuses, or spaces in the animal’s body. • Squids and octopuses have a closed circulatory system. In a closed circulatory system, a heart pumps blood through a network of blood vessels that form a closed loop. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Annelid Worms • Annelid worms are often called segmented worms because their bodies have segments. A segment is an identical, or almost identical, repeating body part. • Annelid worms have bilateral symmetry, a closed circulatory system and a complex nervous system with a brain. • Annelid worms live in salt water, fresh water, or on land. They eat plant material or animals. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Annelid Worms • Earthworms Earthworms are the most common annelid worms. • Each earthworm has 100 to 175 segments. Most segments are identical, but some have special jobs, such as eating or reproducing. • Earthworms eat soil. Their castings, or waste, improves soil quality. • To move, earthworms use stiff hairs, or bristles, on the sides of their bodies. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 15 Section 2 Mollusks and Annelid Worms Annelid Worms • Marine Worms Marine worms are covered in bristles and come in many colors. • Most marine worms live in the ocean. Marine worms eat mollusks, other small animals, or filter food from the water. • Leeches Some leeches are parasites that suck other animals’ blood. Other leeches eat dead animals or hunt insects, slugs, and snails. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.