AP Biology
Notes:  VERTEBRATE

Introduction:

·        The vertebrates belong to one of the two major phyla in 
  the Deuterostomia, the chordates.

·        The phylum Chordata includes three subphyla, the vertebrates 
  and two phyla of invertebrates, the urochordates and the 
  cephalochordates.

·     Four anatomical features characterize the phylum Chordata

      1.    The notochord, present in all chordate embryos, is a longitudinal, flexible 
     rod located between the digestive tube and the nerve cord.  

    ·        It is composed of large, fluid-filled cells encased in fairly stiff, fibrous tissue.

    ·        It provides skeletal support throughout most of the length of the animal.

    ·        While the notochord persists in the adult stage of some invertebrate chordates
      and primitive vertebrates, it remains as only a remnant in vertebrates with a more
      complex, jointed skeleton.

      2.    The dorsal, hollow nerve cord develops in the vertebrate embryo from a plate
              of ectoderm that rolls into a tube dorsal to the notochord.

    ·        Other animal phyla have solid nerve cords, usually located ventrally.

    ·        The nerve cord of the chordate embryo develops into the central
       nervous system: the brain and spinal cord.

       3.    Pharyngeal gill slits connect the pharynx, just posterior to the mouth, to the outside of the animal.

    ·        These slits allow water that enters the mouth to exit without continuing 
      through the entire digestive tract.

    ·        In many invertebrate chordates, the pharyngeal gill slits function as 
      suspension-feeding devices.

    ·        The slits and the structures that support them have become modified for gas 
      exchange (in aquatic vertebrates), jaw support, hearing, and other functions 
    during vertebrate evolution.

      4.    Most chordates have a muscular tail extending posterior to the anus.

·        In contrast, nonchordates have a digestive tract that extends nearly the whole 
  length of the body.

·        The chordate tail contains skeletal elements and muscles.

·        It provides much of the propulsive force in many aquatic species.

Invertebrate chordates 

·        Most urochordates, commonly called tunicates, are sessile marine animals that adhere to 
  rocks, docks, and boats.

    ·        Tunicates are suspension-feeders.

·        Seawater passes inside the animal via an incurrent siphon, through the
  pharyngeal gill slits, and into a ciliated chamber, the atrium.

·        Food filtered from the water is trapped by a mucous net that is 
  passed by cilia into the intestine.

        ·        While the pharyngeal slits of the adult are the only link to the chordate

                  characteristics, all four chordate trademarks are present in the larval forms 
         of some tunicate groups.

    ·        Cephalochordates, also known as lancelets, closely resemble the idealized chordate.

·        The notochord, dorsal nerve cord, numerous gill slits, 
  and postanal tail all persist in the adult stage.

·        They live with their posterior end buried in the sand and the
  anterior end exposed for feeding.

·        In lancets, the pharynx and gill slits are feeding structures and play only a minor role in respiration, which primarily occurs across the external body surface.

Vertebrates(Neural crest, pronounced cephalization, a vertebral column, and a closed circulatory system):

Jawless Vertebrates

    ·        The two extant classes of jawless vertebrates, the agnathans, 
      are the hagfishes and the lampreys.

        ·        These are eel-like in shape, but the true eels are bony fish.

        ·        The agnathans are an ancient vertebrate lineage that predates the
          origin of paired fins, teeth, and bones hardened by mineralization 
          (ossification).

    Hagfishes are the most primitive living “vertebrates”

        ·        All of the 30 or so species of hagfishes are marine scavengers, feeding on
          worms and sick or dead fish.

·        Rows of slime glands along a hagfish’s body produce small amounts 
  of slime to perhaps repulse other scavengers or larger amounts to
  deter a potential predator.

        ·        The skeleton of hagfish is made entirely of cartilage, a rubbery
          connective tissue.

·        In addition to a cartilaginous cranium, the hagfish notochord is also 
  cartilaginous, providing support and a skeleton against which muscles
  can exert force during swimming.

     Lampreys provide clues to the evolution of the vertebral column

        ·        There are about 35 species of lampreys inhabiting both marine 
          and freshwater environments.

·        The sea lamprey is an ectoparasite that uses a rasping tongue to 
   penetrate the skin of its fish prey and to ingest the prey’s blood
   and other tissues.

 Fishes

·        Chondrichthyes (the cartilaginous fishes) and Osteichthyes (bony fishes), and the extinct placoderms evolved   during this time.

·        Agnathans either lacked fins or had a single pair.

·        Jaws and paired fins were major evolutionary breakthroughs.

·        Jaws, with the help of teeth, enable the animal to grip food items firmly and slice them up.

·        A jawed fish can exploit food supplies that were unavailable to earlier agnathans.

·        Paired fins, along with the tail, enable fishes to maneuver accurately while swimming.

 Class Chondrichthyes: Sharks and rays

·        The streamlined bodies of most sharks enable them to be swift, but not maneuverable, 
  swimmers.

·        Powerful axial muscles power undulations of the body and caudal fin to drive the fish forward.

·        The dorsal fins provide stabilization.

·        While some buoyancy is provided by low density oils in large livers, the flow of water
  over the pectoral and pelvic fins also provides lift to keep the animal suspended in the
   water column.

·        Most sharks are carnivores that swallow their prey whole or use their powerful jaws and sharp 
  teeth to tear flesh from animals too large to swallow.

·        In contrast, the largest sharks and rays are suspension feeders that consume plankton.

·        Shark teeth probably evolved from the jagged scales.

·        The intestine of shark is a spiral valve, a corkscrew-shaped ridge that increases 
  surface area and prolongs the passage of food along the short digestive tract.

·        Acute senses are adaptations that go along with the active, carnivorous lifestyle of sharks.

·        Sharks have sharp vision but cannot distinguish colors.

·        Their acute olfactory sense (smelling) occurs in a pair of nostrils.

·        Sharks can detect electrical fields, including those generated by the muscle contractions 
  of nearby prey, through patches of specialized skin pores.

·        The lateral line system, a row of microscopic organs sensitive to pressure changes, 
  can detect low frequency vibrations.

·        In sharks, the whole body transmits sound to the hearing organs of the inner ear.

·        Shark eggs are fertilized internally.

·        Males transfer sperm via claspers on their pelvic fins to the reproductive
  tract of the female. Oviparous sharks encase their eggs in protective cases 
  and lay them outside the mother’s body.

·        Ovoviviparous sharks retain fertilized eggs in the oviduct. The embryo completes
  development in the uterus, nourished by the egg yolk.

·        A few sharks are viviparous, providing nutrients through a placenta to the developing 
  offspring.

·        Rays are closely related to sharks, but they have adopted a very different lifestyle.

·        Most rays are flattened bottom dwellers that crush mollusks and crustaceans in their jaws.

·        The enlarged pectoral fins of rays are used like wings to propel the animal through the water.

·        The tail of many rays is whiplike and may bear venomous barbs for defense against threats.

 Osteichthyes:  ray-finned fishes, the lobe-finned fishes, and the lungfishes

    ·        Nearly all bony fishes have an ossified endoskeleton with a hard matrix of 
       calcium phosphate. The skin is often covered with thin, flattened bony scales. Like sharks, 
       fishes can detect water disturbances through the lateral line system,  part of which is visible 
       as a row of tiny pits along either side of the body.

    ·        Bony fishes breathe by drawing water over four or five pairs of gills located in 
      chambers covered by a protective flap, the operculum.

    ·        The reproductive modes of fishes vary extensively.

·        Most species are oviparous, in which external fertilization occurs after the
   female sheds large numbers of small eggs and males synchronously release
  clouds of sperm (milt).   However, internal fertilization occurs in many fish 
  groups and some are even viviparous.

·        Most fishes have an internal, air-filled sac, the swim bladder.

·        The positive buoyancy provided by air counters the negative buoyancy of
   the tissues, enabling many fishes be neutrally buoyant and remain suspended
   in the water.

·        The swim bladder evolved from balloonlike lungs that may have been used to 
   breathe air when dissolved oxygen levels were low in stagnant shallow waters.

·        Bony fishes are generally maneuverable swimmers.

·        Their flexible fins are better for steering and propulsion than the stiffer fins of sharks.

·        The fastest bony fishes can swim up to 80 km/hr in short bursts.

·        Lobe-finned fishes  have muscular pectoral and pelvic fins supported by extensions 
 of the bony skeleton.    Many lobe-fins were large, bottom dwellers that may have used their paired, 
  muscular fins to “walk” along the bottom.  

·        Three genera of lungfishes  live today in the Southern Hemisphere.

·        They generally inhabit stagnant ponds and swamps. They can gulp air into lungs connected 
  to the pharynx of the digestive tract to provide oxygen for metabolism. Lungfishes also have gills,
  which are the main organs for gas exchange in Australian lungfishes.  When ponds shrink during
   the dry season, some lungfishes can burrow into the mud and aestivate.