Transcript Chapter 35 Mollusks and Annelids Table of Contents Section 1 Mollusca Section 2 Annelida.

Chapter 35
Mollusks and Annelids
Table of Contents
Section 1 Mollusca
Section 2 Annelida
Chapter 35
Section 1 Mollusca
Objectives
• Describe the key characteristics of mollusks.
• Describe the body plan of mollusks.
• Name the characteristics of three major classes of
mollusks.
• Compare the body plans of gastropods, bivalves,
and cephalopods.
Chapter 35
Section 1 Mollusca
Characteristics of Mollusks
• Phylum Mollusca is a diverse group of invertebrates
such as clams, snails, slugs, squids, and octopuses.
• They are called mollusks, from the Latin molluscus,
which means “soft.” Many mollusks have soft bodies
and some have a hard shell.
• Some mollusks are sedentary filter feeders, while
others are fast-moving predators.
• Mollusks are coelomates.
• Most aquatic mollusks and annelids have a larval
stage called a trochophore.
Chapter 35
Section 1 Mollusca
Body Plan of Mollusks
• The body of a mollusk is generally divided into:
– the visceral mass, which contains the heart and
the organs of digestion, excretion, and
reproduction
– the head-foot, which consists of:
• the head, which contains the mouth and
sensory structures
• the foot, a large, muscular organ for locomotion
• The coelom is limited to a space around the heart.
• A layer of epidermis called the mantle covers the
visceral mass.
Chapter 35
Section 1 Mollusca
Body Plan of Mollusks, continued
• In most mollusks, the mantle secretes one or more
hard shells containing calcium carbonate.
• This disadvantage of a shell is offset by having gills.
• The gills are protected within the mantle cavity.
• Most mollusks are bilaterally symmetrical.
• The nervous system consists of paired clusters of
nerve cells called ganglia.
• The main feeding adaptation of many mollusks is the
radula.
Chapter 35
Section 1 Mollusca
Class Gastropoda
• The largest and most diverse class of mollusks is
Gastropoda, whose members are called
gastropods.
• Most gastropods, including snails, abalones, and
conchs, have a single shell. Others, such as slugs
and nudibranchs, have no shell.
• Gastropods undergo the process of torsion during
larval development.
• Gastropods have an open circulatory system in which
a heart pumps hemolymph from gills or lungs into
the hemocoel.
Chapter 35
Section 1 Mollusca
Class Gastropoda, continued
Snails
• Snails live in moist and aquatic environments.
• Most snails locate food using eyes at the end of
tentacles.
• Snails survive dry periods by retreating into their
shells and sealing the opening with a mucous plug.
Other Gastropods
• Slugs are terrestrial and lack shells.
• Nudibranchs are marine and lack shells.
• Pteropods, or “sea butterflies,” have a foot that is
modified into a winglike flap and used for swimming
rather than crawling.
Chapter 35
Section 1 Mollusca
Class Bivalvia
• The class Bivalvia includes aquatic mollusks such as
clams, oysters, and scallops.
• They are called bivalves because their shell is
divided into two valves connected by a hinge.
• Each valve consists of three layers.
• Most bivalves are sessile filter feeders.
• Bivalves lack a distinct head and have three pairs of
nerve ganglia.
Chapter 35
Section 1 Mollusca
Class Bivalvia, continued
Clams
• Clams are bivalves that live buried in mud or sand.
• The mantle cavity of a clam is sealed except for a
pair of hollow, fleshy tubes called siphons.
– Water enters through the incurrent siphon.
– Water leaves through the excurrent siphon.
Other Bivalves
• Oysters become attached to a hard surface early in
their development.
• Scallops can move through the water by repeatedly
opening their valves and snapping them shut.
Chapter 35
Section 1 Mollusca
Class Cephalopoda
• The class Cephalopoda includes octopuses, squids,
cuttlefishes, and chambered nautiluses.
• They are called cephalopods, which means “headfoot.”
• They are specialized as free-swimming predators.
• They have tentacles and beaklike jaws on the head.
• Their nervous system is very advanced.
• They have a closed circulatory system.
• Many use pigments to hide and disguise themselves.
Chapter 35
Section 1 Mollusca
Class Cephalopoda, continued
Squids
• Squids are cephalopods with ten tentacles.
• They propels themselves by pumping jets of water with the
mantle through an excurrent siphon.
Octopuses
• Octopuses have eight tentacles and are similar to squids.
• They often crawl along the ocean bottom or lie in wait for prey.
Chambered Nautiluses
• The chambered nautilus is the only existing cephalopod that has
retained its external shell.
• The shell is coiled and divided into a series of chambers. The
body is confined to the outermost chamber.
Chapter 35
Section 1 Mollusca
Mollusk Body Plan
Chapter 35
Section 1 Mollusca
Characteristics of Mollusks
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Visual Concept
Chapter 35
Section 1 Mollusca
Anatomy of a Trochophore
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Visual Concept
Chapter 35
Section 1 Mollusca
Anatomy of a Mollusk
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Visual Concept
Chapter 35
Section 1 Mollusca
Radula
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Chapter 35
Section 1 Mollusca
Types of Mollusks
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Visual Concept
Chapter 35
Section 1 Mollusca
Characteristics of Gastropods
Chapter 35
Section 1 Mollusca
Anatomy of a Snail
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Visual Concept
Chapter 35
Section 1 Mollusca
Characteristics of Bivalves
Chapter 35
Section 1 Mollusca
Anatomy of a Clam
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Visual Concept
Chapter 35
Section 1 Mollusca
Characteristics of Cephalopods
Chapter 35
Section 2 Annelida
Objectives
• Identify the structures that provide the basis for
dividing annelids into three classes.
• List the advantages of body segmentation.
• Describe the structural adaptations of earthworms.
• Compare the three classes of annelids.
Chapter 35
Section 2 Annelida
Characteristics of Annelids
• The phylum Annelida is made up of bilaterally symmetrical,
segmented worms.
• This phylum includes common earthworms, feather-duster
worms, and bloodsucking leeches.
• They are called annelids, which means “little rings” and refers to
the many body segments.
• Annelids have a true coelom that is divided into separate
compartments by partitions.
• Most annelids have external bristles called setae (singular,
seta), and some have fleshy protrusions called parapodia
(singular, parapodium).
Chapter 35
Section 2 Annelida
Class Oligochaeta
• Annelids of the class Oligochaeta generally live in the soil or in
fresh water and have no parapodia.
• Oligochaeta means “few bristles”; these annelids have a few
setae on each segment.
• The most familiar member is the earthworm.
Structure and Movement
• An earthworm’s body has over 100 nearly-identical segments.
• Circular and longitudinal muscles line the interior body wall.
• Locomotion is made possible by segmentation.
Chapter 35
Section 2 Annelida
Class Oligochaeta, continued
Feeding and Digestion
• Earthworms ingest soil as they burrow through it.
• Soil is moved through these structures:
– mouth
– pharynx
– esophagus
– crop
– gizzard
– intestine
• includes the typhlosole
– anus
• Earthworms play an important role in the condition of soil.
Chapter 35
Section 2 Annelida
Class Oligochaeta, continued
Circulation
• Contractions of the aortic arches and the dorsal blood vessel
force blood through the closed circulatory system.
Respiration and Excretion
• Oxygen and carbon dioxide diffuse through the skin, which
contains many small blood vessels and must be kept moist.
• Cellular wastes and excess water are excreted through
nephridia.
Neural Control
• The nervous system of an earthworm consists of a chain of
ganglia connected by a ventral nerve cord.
• Sensory structures are found in all segments but are
concentrated at the anterior end.
Chapter 35
Section 2 Annelida
Class Oligochaeta, continued
Reproduction
• Earthworms are hermaphrodites, but an individual worm
cannot fertilize its own eggs.
• During mating, earthworms press their ventral surfaces
together.
• They are held together by their setae and by a film of mucus
secreted by each worm’s clitellum.
• The sperm from each worm move through the mucus to the
seminal receptacle of the other.
• The clitellum secretes a tube of mucus and chitin.
• Fertilization occurs inside the tube, which forms a protective
case for the young worms.
Chapter 35
Section 2 Annelida
Class Polychaeta and Hirudinea
• Most annelids are members of the class Polychaeta, which
means “many bristles.”
• Polychaetes differ from other annelids in that they have
antennae and specialized mouthparts.
• They are the only annelids that have a trochophore stage.
• Hirudinea is the smallest class of annelids, consisting of about
500 species of leeches.
• Leeches have no setae or parapodia.
• Many leeches are carnivores but some are parasites that suck
blood from other animals.
Chapter 35
Section 2 Annelida
Anatomy of the Earthworm
Chapter 35
Section 2 Annelida
Characteristics of Annelids
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Visual Concept
Chapter 35
Section 2 Annelida
Segmentation
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Chapter 35
Section 2 Annelida
Types of Annelids
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Visual Concept
Chapter 35
Section 2 Annelida
Anatomy of an Earthworm
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Visual Concept
Chapter 35
Section 2 Annelida
Movement of an Earthworm
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Visual Concept
Chapter 35
Section 2 Annelida
Feeding Habits of an Earthworm
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Visual Concept