Chapter

38 Echinoderms and Invertebrate Chordates Table of Contents Section 1

Echinoderms

Section 2

Invertebrate Chordates

Section 1 Echinoderms

Chapter

38 Objectives

•

Discuss

four distinguishing characteristics of echinoderms.

•

Describe

representative species from each of the five classes of echinoderms.

•

Describe

the water-vascular system and other major body systems of echinoderms.

•

Compare

stars.

sexual and asexual reproduction in sea

Section 1 Echinoderms

Chapter

38 Characteristics

•

Echinoderms

are radially symmetrical

deuterostomes.

• Most living species of echinoderms are motile, but some are sessile.

• Most echinoderms have: –

pentaradial symmetry

– an endoskeleton made up of

ossicles

– a

water-vascular system

–

tube feet

Section 1 Echinoderms

Chapter

38 Classification

• There are about 7,000 species of echinoderms.

• There are five major classes of echinoderms: –

Crinoidea

–

Ophiuroidea

– – –

Echinoidea Holothuroidea Asteroidea

Section 1 Echinoderms

Chapter

38

Classification, continued

Class Crinoidea

• Members of the class Crinoidea, called

crinoids

, include the sea lilies and feather stars.

• In both types of crinoids, five arms extend from the body and branch to form many more arms —up to 200 in some feather star species.

Section 1 Echinoderms

Chapter

38

Classification, continued

Class Ophiuroidea

• The 2,000 species of basket stars and brittle stars make up the largest echinoderm class, Ophiuroidea, which means “snake-tail.” • Members of this class are distinguished by their long, narrow arms, which allow them to move more quickly than other echinoderms.

Section 1 Echinoderms

Chapter

38

Classification, continued

Class Echinoidea

• The class Echinoidea consists of about 900 species of sea urchins and sand dollars.

• Echinoidea means “spinelike.” • The internal organs are enclosed within a fused, rigid endoskeleton called a

test.

Section 1 Echinoderms

Chapter

38

Classification, continued

Class Holothuroidea

• Sea cucumbers belong to the class Holothuroidea.

• Holothuroidea means “water polyp.” • Most of these armless echinoderms live on the sea bottom, where they crawl or burrow into soft sediment by using their tube feet.

Section 1 Echinoderms

Chapter

38

Classification, continued

Class Asteroidea

• The sea stars, or starfish, belong to the class Asteroidea, which means “starlike.” • Sea stars are economically important because they prey on oysters, clams, and other organisms that humans use as food.

Section 1 Echinoderms

Chapter

38 Structure and Function of Echinoderms External Structure

• The body of a sea star is composed of several arms that extend from a central region. Two rows of tube feet run along the underside of each arm.

• The side of the body where the mouth is located is referred to as the

oral surface

. The opposite side is called the

aboral surface

.

• The body of a sea star is usually covered with short spines. Surrounding each spine in many sea stars are numerous tiny pincers called

pedicellariae.

Section 1 Echinoderms

Chapter

38 Structure and Function of Echinoderms,

continued

Water-Vascular System

• The water-vascular system is a network of water filled canals that are connected to the tube feet. • This coordinated system enables sea stars to climb slippery rocks and capture prey. • Water enters through the

madreporite,

the

stone canal

to the

ring canal,

passes down then through the

radial canal

feet.

to the end of each arm and to the tube • The upper end of each tube foot is a bulblike sac called an

ampulla.

Section 1 Echinoderms

Chapter

38 Structure and Function of Echinoderms,

continued

Feeding and Digestion

• The sea star can turn its

cardiac stomach

through its mouth when it feeds.

inside out • The cardiac stomach transfers food to the

pyloric stomach

, which connects to a pair of digestive glands in each arm. • Most sea stars are carnivorous.

Section 1 Echinoderms

Chapter

38 Structure and Function of Echinoderms,

continued

Other Body Systems

• Like other echinoderms, the sea star has no circulatory, excretory, or respiratory organ systems.

• The nervous system consists mainly of a nerve ring and a radial nerve that runs along each arm.

Section 1 Echinoderms

Chapter

38 Structure and Function of Echinoderms,

continued

Reproduction and Development

• Most echinoderms have separate sexes.

• Each arm of the sea star contains a pair of ovaries or testes. • Fertilization occurs externally in water.

• Each fertilized egg develops into a bilaterally symmetrical, free-swimming larva called a

bipinnaria.

• Echinoderms have remarkable powers of regeneration.

Chapter

38 Anatomy of a Sea Star Section 1 Echinoderms

Section 1 Echinoderms

Chapter

38 Characteristics of Echinoderms Click below to watch the Visual Concept.

Visual Concept

Section 1 Echinoderms

Chapter

38 Water Vascular System Click below to watch the Visual Concept.

Visual Concept

Section 1 Echinoderms

Chapter

38 Anatomy of a Sea Star Click below to watch the Visual Concept.

Visual Concept

Section 1 Echinoderms

Chapter

38 Types of Echinoderms Click below to watch the Visual Concept.

Visual Concept

Section 2 Invertebrate Chordates

Chapter

38 Objectives

•

List

the major characteristics of chordates.

•

Describe

the evolution and classification of invertebrate chordates.

•

Describe

the structure of lancelets.

•

Describe

the structure of tunicates.

Section 2 Invertebrate Chordates

Chapter

38 Characteristics

•

Chordates,

phylum Chordata, are characterized by having a

notochord.

• In most vertebrates, the notochord is present in embryos but reduced in adults.

• In addition, all chordates have the following characteristics during some stage of their life: – a dorsal nerve cord – pharyngeal pouches – a postanal tail

Section 2 Invertebrate Chordates

Chapter

38 Evolution and Classification

• Echinoderms and chordates likely evolved from a common ancestor. • The phylum Chordata is divided into three subphyla: –

Vertebrata

– –

Cephalochordat Urochordata

Section 2 Invertebrate Chordates

Chapter

38

Evolution and Classification, continued

Subphylum Cephalochordata

• The subphylum Cephalochordata contains about two dozen species of

lancelets

.

• Lancelets retain their notochord, dorsal nerve cord, pharyngeal pouches, and postanal tail throughout their life.

• Lancelets feed by filtering water through the slits in the pharynx. The water leaves the body through the

atriopore.

Section 2 Invertebrate Chordates

Chapter

38

Evolution and Classification, continued

Subphylum Urochordata

• The subphylum Urochordata contains about 2,000 species commonly called

tunicates

or

sea squirts

.

• As adults, most tunicates are sessile, barrel-shaped filter feeders that live on the sea bottom. They may be solitary or colonial. • Tunicates are hermaphrodites.

Chapter

38 Lancelet Interior Section 2 Invertebrate Chordates

Section 2 Invertebrate Chordates

Chapter

38 Exploration of a Lancelet

Chapter

38 Adult Tunicate Section 2 Invertebrate Chordates

Section 2 Invertebrate Chordates

Chapter

38 Characteristics of Invertebrate Chordates Click below to watch the Visual Concept.

Visual Concept

Section 2 Invertebrate Chordates

Chapter

38 Parts of a Chordate Click below to watch the Visual Concept.

Visual Concept

Section 2 Invertebrate Chordates

Chapter

38 Anatomy of a Lancelet Click below to watch the Visual Concept.

Visual Concept

Section 2 Invertebrate Chordates

Chapter

38 Anatomy of a Tunicate Click below to watch the Visual Concept.

Visual Concept