Nonvertebrate Chordates, Fishes, and Amphibians

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Nonvertebrate Chordates, Fishes, and Amphibians

• Biology I Chapter 30

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CHORDATES
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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

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Dorsal, Hollow Nerve Cord

• Nerves branch from this cord at regular intervals
  
• Nerves connect to internal organs, muscles and
  sense organs

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Notochord

• Long support rod
• Runs through the body just below the nerve cord
• Most chordates only have in the embryonic stage

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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

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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

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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

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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

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Fishes

• Aquatic vertebrates that are characterized by
• Paired fins
• Used for movement
• Scales
• Used for protection
• Gills
• Used for exchanging gases

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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

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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

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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

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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

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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

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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

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Form and Function in Fishes

• Adaptations to aquatic life include
• Various modes of feeding
• Specialized structures for
  gas exchange
• Paired fins for locomotion

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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

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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

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Respiration
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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 fishs 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
  fishs gills

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Circulation
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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

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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

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Response

• Lateral line system sensitive receptor system
  that enables fish to detect gentle currents and
  vibrations in the water (the 6th sense)

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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

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Reproduction

• Oviparous term used to refer to animals whose
  eggs hatch outside the mothers body
• Ovoviviparous term used to refer to animals
  whose young are born alive after developing in
  eggs inside the mothers body
• Viviparous term used to refer to animals that
  bear live young that are nourished directly by
  the mothers body as they develop

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Groups of Fishes

• Over 24,000 living species that are extremely
  diverse
• Jawless fishes
• Cartilaginous fishes
• Bony fishes

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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

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Sharks and Their Relatives

• Class Chondrichthyes
• Sharks, rays, skates,
• Also sawfishes and chimaeras
• Cartilage, not bone

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350 Living Species

• Curved tails
• Torpedo-shaped bodies
• Pointed snouts
• Mouth underneath
• Enormous number of teeth
• Always exceptions!

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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

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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

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AMPHIBIANS
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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 lifelive in both water
  and on land

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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

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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

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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

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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

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Evolution of Amphibians

• Only three orders of small amphibians survive
  today
• Frogs and toads
• Salamanders
• Caecilians

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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

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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

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Respiration

• Larval amphibians
• Gas is exchanged through the skin and gills
• Adult amphibians
• Lungs and skin

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Circulation

• Double loop
• 3 chambered heart
• First Loop
• Carries oxygen-poor blood heart ? lungs and skin
• Takes oxygen-rich blood lungs and skin ? heart

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Circulation

• Second Loop
• Transports oxygen-rich blood heart ? rest of the
  body
• Transports oxygen-poor blood body ? heart

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Circulation
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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

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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

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Reproduction

• The male climbs onto the females 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

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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!

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Movement

• Amphibian larvae
• Often move very much like fishes, wiggling their
  bodies and using a flattened tail for propulsion

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Movement

• Adult amphibians
• Most use their front and back
  legs to move in a variety
  of ways
• Jump, climb, run, etc.

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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

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Response

• Tympanic Membrane
• Eardrum of amphibians
• Inside the skull
• Vibrates in response to sound, allowing hearing

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Groups of Amphibians

• Salamanders Order Urodela
• Long bodies and tails
• Four legs
• Carnivores
• Frogs and Toads Order Anura
• Frogs Long legs and lengthy jumpers
• Toads short legs and short hops
• Adults lack tails

• Caecilians Order Apoda
• Legless animals that live in water or burrow in
  moist soil or sediment

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Ecology of Amphibians

• Have no feathers, fur or scales
• Many are ideal for predators such as birds and
  mammals

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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