Transcript Nonvertebrate Chordates, Fishes, and Amphibians

Nonvertebrate Chordates,
Fishes, and Amphibians
Biology I: Chapter 30
CHORDATES
Chordates
• Phylum Chordata
• Fishes, amphibians, reptiles, birds and mammals
• Four key characteristics:
1. Dorsal, hollow nerve cord
2. A notochord
3. Pharyngeal pouches
4. Tail that extends beyond the anus
Dorsal, Hollow Nerve Cord
• Nerves branch from this cord
at regular intervals
• Nerves connect to internal
organs, muscles and sense
organs
Notochord
• Long support rod
• Runs through the body
just below the nerve
cord
• Most chordates only
have in the embryonic
stage
Pharyngeal Pouches
• Paired structures in the throat
(pharynx) region
• Fishes and amphibians: slits
develop that connect the
pharyngeal pouches to the
outside of the body
• The slits may then develop
into gills that are used for gas
exchange
Tail
• All chordates have a tail
that extends beyond the
anus at some point in
their lives
• The tail can contain
bone and muscles and is
used in swimming by
many aquatic species
Most Chordates are Vertebrates
• More than 99% of all chordates are in the
subphylum Vertebrata
• Vertebrae: individual segments that make up
the backbone; encloses and protects the spinal
cord
• Backbone is part of an endoskeleton, or
internal skeleton
Nonvertebrate Chordates
• The two groups
• Soft-bodied marine organisms
• Have the four key characteristics at some point in their lives
• Tunicates
– Filter feeders
• Lancelets
– Small, fish-like creatures
Fishes
• Aquatic vertebrates that are characterized by:
• Paired fins
– Used for movement
• Scales
– Used for protection
• Gills
– Used for exchanging gases
Evolution of Fishes
• Fishes were the first
vertebrates to evolve
• The evolution of jaws
and the evolution of
paired fins were
important developments
during the rise of fishes
The First Fishes
• Jawless creatures whose
bodies where armored with
bony plates
• Lived in the oceans during
the late Cambrian Period,
about 510 mya
• Fishes kept this armored,
jawless body plan for 100
million years
The Age of Fishes
• Ordovician and Silurian Periods: 505-410 mya, fishes underwent
a major adaptive radiation
• Devonian Period: “Age of Fishes”
• Some were jawless with little armor
• Ancestors of modern hagfishes and lampreys
• Others were armored and ultimately became extinct about 360
mya
The Arrival of Jaws
• Other ancient fishes kept their bony armor and
possessed a feeding adaptation that would
revolutionize vertebrate evolution: JAWS
• Jawless fishes
– Limited to eating small particles of food that they filter out
of the water or suck up like a vacuum cleaner
• Jaws can hold teeth and muscles
– Much wider variety of food
– Defend themselves by biting
The Arrival of Paired Fins
• More control of body movement
• Fin tails and powerful muscles
gave greater thrust when
swimming
• Enabled fishes to move in new
and varied patterns
• This enabled fishes to use their
jaws in complex ways
The Rise of Modern Fishes
• Although the early jawed fishes soon
disappeared, they left behind two major groups
that continued to evolve and still survive today
– Ancestors of modern sharks and rays: skeletons
made of resilient cartilage
– Group that evolved skeletons made of true bone
Form and Function in Fishes
• Adaptations to aquatic life include:
– Various modes of feeding
– Specialized structures for
gas exchange
– Paired fins for locomotion
Feeding
• Herbivores, carnivores, parasites,
filter feeders, detritus feeders
• A single fish may exhibit several modes of feeding
(carp: eat what is available) while others are very
specialized (barracuda: carnivore)
• Pyloric ceca: finger-like pouches found in many
species of fish that secrete digestive enzymes to help
digest food
Respiration
• Most fishes exchange gases using gills located on either side of
the pharynx
• The gills are made up of feathery filaments
• Lampreys and sharks have several gill openings on the side of
the body
• A number of fishes, such as the lungfish, have an adaptation that
allows them to survive in oxygen-poor water or in areas where
bodies of water often dry up
Respiration
Circulation
• Closed circulatory systems with a heart that pumps blood
around the body in a single loop
• Heart consists of 4 parts:
– Sinus venosus: thin-walled sac that collects blood
from the fish’s veins
– Atrium: a large muscular chamber that serves as a
one-way compartment for blood
– Ventricle: thick-walled muscular chamber;
pumping portion of the heart
– Bulbus arteriosus: connects to a large blood vessel called the aorta, which
moves blood to the fish’s gills
Circulation
Excretion
• Most fishes rid themselves of nitrogenous wastes in
the form of ammonia
• Gills, kidneys
– Saltwater fishes
• Lose water by osmosis: kidneys return as much water to
the body as possible
– Freshwater fishes
• Gain water by osmosis: kidneys pump out plenty of
dilute urine
Response
• Well-developed nervous systems organized around a
brain
• Cerebrum: area of the brain responsible for all
voluntary activities of the body
• Cerebellum: region of the brain that coordinates body
movements
• Medulla oblongata: area of the brain that controls the
functioning of many internal organs
Response
• Lateral line system:
sensitive receptor
system that enables
fish to detect gentle
currents and
vibrations in the
water (the 6th sense)
Movement
• Most move by alternately contracting paired sets of
muscles on either side of the backbone
• Because their body tissues
are more dense than the water
they swim in, sinking is an
issue for fishes
• Swim bladder: gas-filled organ found in many bony
fishes that adjusts their buoyancy
Reproduction
• Oviparous: term used to refer to animals whose eggs
hatch outside the mother’s body
• Ovoviviparous: term used to refer to animals whose
young are born alive after developing in eggs inside
the mother’s body
• Viviparous: term used to refer to animals that bear
live young that are nourished directly by the mother’s
body as they develop
Groups of Fishes
• Over 24,000 living species that are extremely
diverse
• Jawless fishes
• Cartilaginous fishes
• Bony fishes
Jawless Fishes
• Have no true teeth or jaws
• Skeletons are made of fibers and cartilage
• Lack vertebrae; keep notochords as adults
• Two main classes:
– Lamprey
– Hagfishes
Sharks and Their Relatives
• Class
Chondrichthyes
• Sharks, rays, skates,
• Also: sawfishes and
chimaeras
• Cartilage, not bone
350 Living Species
• Curved tails
• Torpedo-shaped bodies
• Pointed snouts
• Mouth underneath
• Enormous number of teeth
• Always exceptions!
Bony Fishes
• Class Osteichthyes
• Skeletons made of hard, calcified
tissue: bone
• Ray-finned fishes
– Rays or spines that support the fins
– Only 7 living species of bony fish are not
ray-finned
• Lobe-finned fishes
Ecology of Fishes
• Anadromous: fishes that spend most of their lives in
the ocean but migrate to fresh water to breed
– Examples: lampreys, sturgeons, and salmon
• Catadromous: fishes that spend most of their lives in
fresh water but migrate to the ocean to breed
– Example: European eel, American eel
AMPHIBIANS
Amphibian
• Have survived for hundreds of millions of years
• The only modern
descendants of an
ancient group that
gave rise to all other
land vertebrates
• Amphibian means “double life”…live in both water
and on land
Amphibian
• Vertebrate
• Lives in the water as a larva
and on land as an adult
(with some exceptions)
• Breathes with lungs as an adult
• Has moist skin that contains mucus glands
• Lacks scales and claws
Evolution of Amphibians
• The first amphibians to climb onto land
probably resembled lobe-finned fishes similar
to the modern coelacanth
• The amphibian had legs,
appearing about 360 mya
Evolution of Amphibians
• Early amphibians evolved several adaptations that
helped them live at least part of their lives out of
water:
– Bones in the limbs and limb girdles became stronger for
more efficient movement
– Lungs and breathing tubes enabled them to breathe air
– The sternum formed a bony shield to support and protect
internal organs, esp. the lungs
Evolution of Amphibians
• Soon after they appeared, amphibians underwent a major
adaptive radiation
• Some were huge: Eogyrinus
was about 5 meters long!
• Amphibians became the
dominant form of animal life
in the warm, swampy fern forests about 360-286 mya
• Climate changes caused many of the swamps to disappear
• Most amphibians became extinct
Evolution of Amphibians
• Only three orders of small amphibians survive
today:
• Frogs and toads
• Salamanders
• Caecilians
Form and Function in Amphibians
• Although the class Amphibia is relatively
small, it is diverse enough to make it difficult
to identify a typical species
• We will focus on the structures found in
frogs…
Feeding
• Tadpoles
– Filter feeders or herbivores that graze on algae
– Eat almost constantly
• Adult amphibians
– Almost entirely carnivorous
• Mouth esophagus  stomach  small intestines
 large intestines  cloaca
Respiration
• Larval amphibians
– Gas is exchanged
through the skin
and gills
• Adult amphibians
– Lungs and skin
Circulation
• Double loop
• 3 chambered heart
First Loop
• Carries oxygen-poor blood: heart  lungs and skin
• Takes oxygen-rich blood: lungs and skin  heart
Circulation
Second Loop
• Transports oxygen-rich
blood: heart  rest of
the body
• Transports oxygenpoor blood: body 
heart
Circulation
Excretion
• Amphibians have kidneys that filter wastes from the
blood
• Urine: The excretory product of the kidneys
• Urine travels through tubes called ureters into the
cloaca
• Urine is passes outside or temporarily stored in a
bladder above the cloaca
Reproduction
• Eggs do not have shells and tend to dry out if they are
not kept moist
• Most species lay eggs in the water
• The male fertilizes them externally
• In a few species (most salamander), eggs are
fertilized internally
Reproduction
• The male climbs onto the
female’s back
• The female releases the eggs that
are then fertilized
• The eggs are in a transparent
jelly, useful for attaching the
eggs to underwater plants and
that provides nourishment to the
growing cells
Reproduction
• Some amphibians
abandon their eggs
after they are laid
• Others incubate the
young in their mouth,
on their back, or even
in their stomach!
Movement
• Amphibian larvae
– Often move very
much like fishes,
wiggling their
bodies and using a
flattened tail for
propulsion
Movement
• Adult amphibians
– Most use their front and
back
legs to move in a variety
of ways
– Jump, climb, run, etc.
Response
Nictitating Membrane:
• Moveable transparent
membrane in amphibians
located inside the regular
eyelid
• Protects the surface of the
eye from damage under
water and keeps it moist on
land
Response
Tympanic Membrane
• Eardrum of amphibians
• Inside the skull
• Vibrates in response to
sound, allowing hearing
Groups of Amphibians
• Salamanders: Order Urodela
– Long bodies and tails
– Four legs
– Carnivores
• Caecilians: Order Apoda
• Frogs and Toads: Order Anura
– Frogs: Long legs and lengthy jumpers
– Toads: short legs and short hops
– Adults lack tails
– Legless animals that live in
water or burrow in moist soil
or sediment
Ecology of Amphibians
• Have no feathers, fur
or scales
• Many are ideal for
predators such as
birds and mammals
Ecology of Amphibians
• Amphibians have adaptations
to protect themselves
• Many have skin colors and
markers that allow them to
blend in with the environment
• Some release toxins
• Some are brightly colored as a
warning to predators