Nonvertebrate Chordates,
Fishes, and Amphibians
Chapter 30
30-1 The Chordates
 A chordate is an animal that has, for at least
some stage of its life, all of the following…
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Dorsal hollow nerve cord: runs along the back
part of the body with nerves that branch and
connect to organs
Notochord: long supporting rod that runs
through the body just below the nerve cord
Pharyngeal pouches: found in the pharynx
region – may develop into gills
Post anal tail: contains bone and muscle and is
used in swimming by aquatic species
What is a Chordate?
Most Chordates Are Vertebrates
 About 96% of all chordates
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are in the subphylum
Vertebrata.
Most vertebrates have a
backbone.
The anterior end of the
vertebrate backbone
develops into a brain.
The backbone is made of
vertebrae.
The backbone is part of an
endoskeleton.
Most Chordates are Vertebrates
Nonvertebrate Chordates
 The two groups of nonvertebrate chordates
are tunicates and lancelets

Both are soft-bodied marine organisms
Tunicates
 Tunicates are filter feeders that exhibit all of the chordate
characteristics as larva but not as adults
Lancelets
 Lancelets are small, fishlike creatures that
thrive on the sandy ocean floor

An adult lancelet has a head region that
contains a mouth
30-2 Fishes
 Fishes are aquatic vertebrates that are
characterized by paired fins, scales, and gills
Evolution of Fishes
Doryaspis
 The earliest fish were
jawless, armored
with bony plates
(about 400 million yrs
ago).
 Jaws allowed fish
better feeding ability
as well as defense.
 Paired fins aided
movement and
provided more
control of movement.
Pacific Hagfish
The Rise of Modern Fishes
 While most early jawed fishes disappeared, they
left behind two major groups that continued to
evolve and still survive today:
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Cartilaginous fishes (sharks & rays)
Boney fishes (modern fishes)
Form & Function in Fishes
 Adaptations to aquatic life include various
modes of feeding, specialized structures for gas
exchange, and paired fins for locomotion
Fish Anatomy
Fish Feeding
 Fish can be herbivores, carnivores, parasites, filter feeders,
and detritus feeders.
 The diagram below highlights some internal organs
important during the fish’s digestion
Fish Respiration
 Most fishes exchange gases using gills located
on either side of the pharynx
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Oxygen-rich water is pulled in through the mouth
and over the gill filaments
Oxygen-poor water is pushed out through the
openings in the sides of the pharynx
 Some fishes, including the lungfish, have a lung-
like adaptation that allows them to survive in
oxygen poor water
Fish Respiration
Fish Circulation
 Fishes have closed circulatory systems with well
developed heart that pumps blood around the
body in a single loop:
From
the heart to the gills
From
the gills to the rest of body
Back
to the heart
Fish Circulation (Heart)
Fish Circulation
Fish Excretion
 Fishes rid themselves of nitrogenous wastes in the form of ammonia

Kidneys help fishes control the amount of water in their bodies
Fish Response
 Fishes have well-developed nervous systems
organized around a brain which has several parts:
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Olfactory bulb – sense of smell
Cerebrum – voluntary activities of body
Optic lobe – eye function
Cerebellum – coordinates body movement
Medulla oblongata – controls internal organ functions
Spinal cord
 Most fishes can detect gentle currents and vibrations in
the water with a sensitive receptor called the lateral
line system
Fish Response
 Fish have well-developed nervous systems and highly
developed sense organs.
 The lateral line system can detect gentle currents and
vibrations in water with sensitive receptors.
Fish Response
 Lateral line system:
sensitive receptor
system that enables
fish to detect gentle
currents and
vibrations in the
water (the 6th sense)
Fish Movement
 The streamlined body shapes of most fishes
help to reduce the amount of drag (friction) as
they move through the water

Fins assist in movement
 Many bony fishes have an internal, gas-filled
organ called a swim bladder that adjusts their
buoyancy

Because their body tissues are more dense
than water, sinking would be an issue without
the swim bladder
Fish Movement
 The swim bladder is
found in bony fish.
 The swim bladder is
an internal, gas-filled
organ that can adjust
the buoyancy. It lies
just beneath the back
bone.
Fish Reproduction
 Fishes whose eggs hatch outside the mother’s
body are oviparous

As the embryos develop, they obtain food from
the yolk in the egg
 Fishes whose eggs stay inside the mother’s
body are ovoviviparous

Egg yolk is used for nourishment
 Fishes whose embryos stay in the mother’s
body and get nourishment from the mother are
viviparous

These fishes are born alive
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(Fish are not viviparous.)
Groups of Fishes
 All living fishes can be classified into three groups:
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Jawless fishes – have no true teeth or jaws
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Cartilaginous fishes (class Chondrichthyes) –
skeletons are built entirely of cartilage, not bone
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Lampreys and hagfishes
Sharks, rays, skates
Bony fishes (class Osteichthyes) – skeletons are
made of hard, calcified bone
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Most other fishes
Groups of Fishes
 All living fish can be
classified into 3 groups:
1. Jawless fish (Agnatha)
2. Cartilaginous Fish
(Chondrichthyes)
3. Bony fish (Osteichthyes)
Jawless Fishes
 Jawless fish (Class Agnatha)
have no true teeth or jaws.
 Their skeleton is made of fibers
and cartilage.
 They lack vertebrae and retain
their notochord as adults.
 They have fish-like bodies, no
scales, and unpaired fins.
Hagfish
 Two types:
Hagfish & Lampreys.
Lamprey
Cartilage Fishes
 Belong to Class
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Chondrichthyes.
Includes sharks, skates,
rays.
The skeleton is entirely
cartilage (no bone).
Possess tooth-like
scales.
Gills are not protected
with bony covering.
Bony Fishes
 Belong to Class Osteichthyes.
 Skeletons are made of bone.
 Divided into two groups
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Ray-finned fish (have bony
spines or rays in the fins)
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Perch
Trout
Lobe-finned fish (fleshy fins
have bones)
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Trout
Lungfish
Coelocanth
Coelocanth
30-3 Amphibians
 An amphibian is a vertebrate that, with some
exceptions, lives in water as a larva and on
land as an adult, breathes with lungs as an
adult, has moist skin that contains mucus
glands, and lacks scales and claws
 Amphibian adaptations for life on land include:
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Limb bones become stronger
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Lungs and breathing tubes
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Sternum to protect internal organs
Amphibian Feeding
 Tadpoles are filter feeders whereas adult
amphibians are carnivorous
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Many have long, sticky tongues used to
capture insects
 Digestion involves food traveling from the
mouth down the esophagus into the stomach
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From the stomach into the small intestine
From the small intestine to the large intestine
From the large intestine into the cloaca (the
pathway for waste to leave the body
Frog Digestive System
Amphibian Respiration
 In larval amphibians, gas exchange occurs
through the skin and gills
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Lungs replace gills in adult amphibians – but some
gases continue to diffuse through the skin
Amphibian Circulation
 In adult amphibians, the circulatory system forms
a double loop
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1st loop carries oxygen-poor blood from the heart to
the lungs and skin and takes oxygen-rich blood
from the lungs and skin back to the heart
The 2nd loop transports oxygen-rich blood from the
heart to the rest of the body and oxygen-poor blood
from the body back to the heart
Amphibian Circulation
Frog Circulatory & Heart
 The amphibian heart has 3 chambers:
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Left atrium, right atrium, and ventricle
Amphibian Excretion
 Amphibians have kidneys that filter wastes
from the blood
Amphibian Reproduction
 Amphibian eggs must be kept moist to avoid
drying out
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External fertilization
Eggs are abandoned after the frogs lay them
Offspring metamorphosize from tadpoles into
frogs
Amphibian Movement
 Amphibian larvae move
like fishes
 Adult salamanders have
legs that stick out
sideways – walking
involves moving the body
into an S-shaped curve
 Frogs and toads have
well-developed hind
limbs that enable them to
jump
 Tree frogs have disks on
their toes that serve as
suction cups for climbing
Amphibian Response
 The brain of an amphibian is very similar to
that of a fish
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They have well developed nervous systems
They hear through tympanic membranes
(eardrums) located on each side of the head
Groups of Amphibians
 Salamanders have long
bodies and tails. Most have
four legs. Adults and larvae
are carnivores.
 Frogs and toads share their
ability to jump. Frogs tend to
have long legs and jump
longer. Frogs are more closely
tied to water. Adult frogs and
toads lack tails.
 Caecilians are legless
amphibians that live in water
or burrow in moist soil.
Amphibian Concept Map