Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer Unscramble the following words and write a sentence that uses all of the words. gluss isalns sdusqi klomssul Chapter 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 2 Mollusks and Annelid Worms

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Annelid Worms Chapter 15 Section 2 Mollusks and 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Annelid Worms Chapter 15 Section 2 Mollusks and 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.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Annelid Worms Chapter 15 Section 2 Mollusks and 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.