BIOLOGY
by Miller & Levine
[complete Table of Contents]

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Chapter 27
Worms and Molluscs

In this chapter, students will read about the general characteristics, life cycles, and major types of worms and mollusks. They will also read about the importance of some types of worms as parasites of humans.

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What are Web Codes?

Web Codes for Chapter 27: • Data Sharing: Investigating Land Snails • Miller & Levine: Zebra Mussels and Other Invasive Exotic Species • SciLinks: Flukes • Self-Test

Section 27-1: Flatworms
Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.
Turbellarians are free-living marine or freshwater flatworms.
Flukes are parasitic flatworms that usually infect the internal organs of their hosts.
Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts.

Section 27-2: Roundworms
Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus.
Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms.Section 27-3: Annelids
Annelids are worms with segmented bodies. They have a true coelom that is completely lined with mesoderm.
Oligochaetes are annelids that typically have only a few setae and live in soil or fresh water.
Leeches are typically external parasites that suck the blood and body fluids of their host.
Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae.

Section 27-3: Annelids
Annelids are worms with segmented bodies. They have a true coelom that is completely lined with mesoderm.
Oligochaetes are annelids that typically have only a few setae and live in soil or fresh water.
Leeches are typically external parasites that suck the blood and body fluids of their host.
Polychaetes are marine annelids that have paired, paddlelike appendages tipped with setae.

Section 27-4: Mollusks
Mollusks are soft-bodied animals that usually have an internal or external shell.
The typical mollusk body plan has four parts: foot, mantle, shell, and visceral mass.
Gastropods are shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side.
Bivalves have two shells that are held together by one or two powerful muscles.
Cephalopods are typically soft-bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms.

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