Nonvertebrate Chordates,
Fishes, and Amphibians
What Is a Chordate?
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Members of the phylum Chordata are
called chordates.
A chordate is an animal that has, for at
least some stage of its life, a dorsal,
hollow nerve cord; a notochord;
pharyngeal pouches; and a tail that
extends beyond the anus.
Characteristics of Chordates
Muscle segments
Tail
Anus
Notochord
Hollow nerve cord
Mouth
Pharyngeal pouches
Characteristics of Chordates
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The notochord is a long supporting rod
that runs through the body just below the
nerve cord.
Pharyngeal pouches are paired
structures in the throat (pharynx) region.
The tail can contain bone and muscle and
is used for swimming by many aquatic
species.
What Is a Chordate?
Most Chordates Are Vertebrates

About 96 percent of all chordate
species are vertebrates.
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Most vertebrates have a vertebral
column, or backbone.
In vertebrates, the dorsal, hollow nerve
cord is called the spinal cord.
What Is a Chordate?

As a vertebrate embryo develops, the
front end of the spinal cord grows into a
brain.
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The backbone is made of individual
segments called vertebrae.
In addition to support, vertebrae enclose
and protect the spinal cord.
Phylogeny of Chordates
Sharks
& their
Jawless
relatives
fishes
Nonvertebrate
chordates
Bony
fishes
Invertebrate ancestor
Reptiles Birds
Amphibians
Mammals
Nonvertebrate Chordates

The two groups of nonvertebrate
chordates are tunicates and lancelets.
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Similarities in anatomy and embryological
development indicate that vertebrates and
nonvertebrate chordates evolved from a
common ancestor.
Both tunicates and lancelets are soft-bodied
marine organisms.
Tunicates (Larva)

The larval form of filterfeeding tunicates have
all of the chordate
characteristics.
Tail
Hollow
nerve cord
Wasteeliminating
organ
Notochord
Mouth
Intestine
Pharynx
with gill
slits
Stomach
Heart
Larva
Tunicates (Adult)
Siphon to mouth
Pharynx with gill slits
Siphon from anus
Anus
Tunic
Intestine
Reproductive organs
Heart
Stomach
Adult
Lancelets
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Lancelets are small, fishlike creatures that
live on the ocean bottom.
Notochord
Hollow nerve cord
Segmented muscles
Mouth
Tail
Anus
Pharynx with gill slits
Intestine
Reproductive organs
Lancelets
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An adult lancelet has a definite head
region that contains a mouth.
As water passes through the pharynx, a
sticky mucus catches food particles.

The lancelet swallows the mucus into the
digestive tract.
Lancelets

Lancelets use the pharynx for gas
exchange.
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Lancelets are thin enough to exchange
gases through their body surface.
Lancelets have a closed circulatory
system and do not have a true heart.