Phylum Chordata Phylum Chordata A

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					Phylum Chordata
        A Tribute to the Diversity We Know
•   Members of the Phylum Chordata include animals
    with which we are probably most likely familiar
    (including fish, birds, reptiles, amphibians and
    beasts like ourselves)

•   As unlikely as it seems, based on embryological
    evidence, the echinoderms appear to be the most-
    likely ancestors to the early chordates

•   Primitive stemmed echinoderms are thought to
    have shifted from arm-feeding to filter-feeding
    acquiring a body plan similar to urochordates

•   Unfortunately, the fossil record is poor and
    intermediates are lacking. The rest of the
    evolutionary picture is better documented.
• Four structural characteristics set
  chordates apart from all other phyla:
   –   a notochord
   –   a pharyngeal gill slits
   –   postanal tail
   –   a hollow dorsal nerve cord

• These attributes are always found in the
  larval forms or early embryo (although
  they may be absent in the adult).
1) The Notochord
• The notochord is mainly
  composed of fibrous          • In animals like ourselves,
  connective tissue              bony structures called
                                 vertebrae develop near
• For those animals in           the notochord and
  which it persists into the     eventually replace it
  adult form, the notochord      during embryogenesis
  provides support (it acts
  like our backbone) and
  increases swimming
2) Pharyngeal Gill Slits
• Pharyngeal gill slits are cuts in   • The morphological equivalent
  the pharynx that connect to a         of gill silts are seen briefly
  cavity surrounding the                during our own development
  pharynx                               (weeks 4-5), but they usually
                                        close or develop into other
• For organisms in which they           structures
  remain in the adult, they are
  often elaborated into               • Occasionally, the slits do not
  respiratory structures (and are       close, resulting in the newborn
  sometimes involved in filtering       having an opening in the neck
  food during feeding).                 area (a cervical fistula).
3) The Postanal Tail
                              • Chordates, on the other
                                hand, follow the anus with
• In all the phyla we have      a tail of variable length
  studied up to this point,     (again, an adaptation for
  the anus was terminal (at     locomotion).
  the tip of the tail)
                              • In us, the tail is short and
                                fused (the coccyx at the
                                base of your spine).
4) Hollow Dorsal Nerve Cord

• Our nerve cord, like that of other chordates
  is hollow (even in the adult).

• Well, what else is there to say?!?!?
Let’s start at the very beginning . . .

• Phylum Chordata is divided into three

  – Subphylum Urochordata
  – Subphylum Cephalochordata
  – Subphylum Vertebrata
Subphylum Urochordata
• At first glance, you might
  mistake this creature for a
• Adult tunicates look like small
  sacs (about 3 cm tall) and are
  stationary, lacking a nerve cord,
  a notochord, and a post-anal
• Lacking three of the four
  distinguishing hallmarks of the
  chordates, it would seem
  impossible for these animals to
  be placed in phylum Chordata.
Subphylum Urochordata
• However, tunicates
  begin life in a larval
  state, which have a
  post-anal tail, a nerve
  cord, and a notochord.

• Therefore, these
  immobile animals with
  tadpole-like larvae are
  considered chordates.
Subphylum Urochordata
             • Urochordates have a
               notochord that extends
               from just behind the tail to
               the head (rather than from
               head to tail; Urochordata
               means "tail-cord")
             • Many urochordates are
               more commonly referred
               to as “sea squirts”
             • Contain cancer-fighting
Subphylum Urochordata
• The body of an adult tunicate is quite simple, being essentially a sack
  with large gill structures that form two siphons through which water
  enters and exits. Water is filtered inside the sack-shaped body.
Subphylum Cephalochordata
• Lancelets are common bottom-
  dwelling forms that possess all
  four chordate characteristics
• They dig into the sand and lie
  with their anterior end
  protruding from the burrow.
• Unlike the urochordates, the
  notochord extends along the
  entire length of their body.
• This structure imparts rigidity to
  their body and permits more
  coordinated swimming
Subphylum Vertebrata
• Members of the Subphylum
  Vertebrata differ from the
  urochordates and
  cephalochordates in having the
  notochord replaced by a vertebral
  column composed of bone and/or
  cartilage. The vertebral column,
  along with the cranium, limb girdles,
  and limbs, make up the
  endoskeleton. This internal
  skeleton is an adaptation for
  efficient locomotion, as was the
Subphylum Vertebrata
• Subphylum Vertebrata has several divisions you need to
  be familiar with:
   – Superclass Agnatha – Jawless Fish; Lampry Eel;
                                Ostracoderm (fossil)
   – Superclass Gnathostomata
      • Class Placodermi – First Jawed Fish (Fossils)
      • Class Chondricthyes – Cartilagenous Fish; Sharks; Rays
      • Class Osteicthyes
         – Subclass Actinopterygii – Ray-finned Fish; Goldfish; Sea Horse
         – Subclass Sarcopterygii – Lobe-finned Fish; Coelocanth
Subphylum Vertebrata
• Subphylum Vertebrata has several divisions you need to
  be familiar with:
   – Superclass Tetrapoda
      • Class Amphibia
               » Order Caudata – Tailed Amphibians; Salamanders; Newts
               » Order Anura – Tailless Amphibians; Frogs; Toads
               » Order Gymnophiona – Caecillians
      • Class Reptilia
          – Subclass Anapsida – Turtles; Tortoises
          – Subclass Diapsida – Crocodiles; Snakes; Lizards
      • Class Aves
          – Subclass Archaeornithes – Archaeopteryx (Extinct)
          – Subclass Neornithes – All Other Birds
      • Class Mammailia
          – Subclass Prototheria – Monotremes – Platypus; Echinda
          – Subclass Metatheria – Marsupials – Kangaroo; Koala
          – Subclass Eutheria – Placentals
Superclass Agnatha
             • Agnatha (Jawless fish) are
               primitive fishes with a fibrous
               skeleton and an eel-like body

             • They lack a jaw as well as the
               scales and paired fins we
               usually associate with fish

             • Agnathans are mostly
               represented as heavily armored
               fossil forms, but today’s living
               species are smooth-skinned,
               completely unprotected by
Superclass Agnatha
• Many species are parasitic
  (they attach to the outer surface
  of a fish with their sucker-like
• Rasping teeth (arranged in a
  whorl) cut into the host. The
  lamprey then sucks blood from
  the wound (a fish hickey?).
• When it is finished its
  bloodmeal, the fish is released.
  The injured fish usually dies
  from blood loss or infection.
    Superclass Agnatha
•   The agnaths are considered
    to be an evolutionary dead
    end, a side branch in the
    phyletic tree that did not
    lead to the more advanced

•   The first agnaths were

•   Though extinct, they give us
    clues into how vertebrates
    evolved from the
Superclass Agnatha
             • Notice the similarities of
               the agnath larve to the

             • There are two main
               classes under Agnatha:
                – Class Petromyzontes
                – Class Myxini (hagfish)
Superclass Gnathostomata
             •   Gnathastomata (Jawed fish)
                 contain a verticle biting appendage

             •   Jaws are what makes it possible
                 for some gnathostomes to crack
                 nuts, rip of sections of meat, and
                 even crop grass.

             •   Teeth have modified into a wide
                 range of forms, from teeth
                 designed to bite off and chew, to
                 teeth designed to strip bark, to
                 teeth designed to inject poison, to
                 teeth grown out into defensive
Superclass Gnathostomata
 Superclass Gnathostomata can be broken up
  into the following classes:
   • Class Placodermi – First Jawed Fish (Fossils)
   • Class Chondricthyes – Cartilagenous Fish; Sharks;
   • Class Osteicthyes
      – Subclass Actinopterygii – Ray-finned Fish; Goldfish; Sea
      – Subclass Sarcopterygii – Lobe-finned Fish; Coelocanth
Class Placodermi
•   The Placodermi are characterized by a
    dermal armor consisting of a head
    armor and a thoracic armor.

•   In the thoracic armor, the foremost
    dermal plates form a complete "ring"
    around the body and always include at
    least one median dorsal plate

•   Jaws probably developed from the
    anterior visceral arch that first served to
    support the gills. The presence of jaws
    and development of paired appendages
    resulted in efficient eating and
Class Chondricthyes
              • Sharks, skates, rays, and
                chimaeras are all members of
                the Class Chondrichthyes.

              • Their endoskeleton is entirely
                cartilaginous (Chondros =
                "cartilage"; "icthys" = "fish") and
                all are carnivorous (as
                exemplified by the great white

              • The notocord persists into the
                adult, and they have both
                median and paired fins
Class Chondricthyes
              •   They have two-chambered hearts
                  (one auricle, one ventricle). Only
                  deoxygenated venous blood flows
                  through the heart (which is then
                  pumped through gills before going
                  to the rest of the body).
              •   Red blood cells are present, but
                  they're nucleated and oval.
              •   Respiration is by five to seven
                  pairs of gills, each located in a cleft
                  and supported by cartilaginous
                  visceral arches.
              •   Sexes are separate (dioecious),
                  and the gonads are usually paired.
Class Chondricthyes
•   The caudal fin of sharks differs from that of bony
    fishes because it is asymmetrical. This heterocercal
    fin provides both lift and forward thrust for the animal
    when swimming (an important consideration since
    sharks are heavier than water and have no swim
    bladder to keep them buoyant).

•   Although there are many rows of teeth, only the outer
    row or two is functional. The inner rows are
    replacement teeth, which move forward when outer
    teeth break off. Unlike ours, the upper jaw is not
    rigidly connected to the braincase and can be moved
    to open the jaws.

•   Although most sharks are predatory or scavengers,
    the largest sharks (whale sharks and basking sharks)
    feed on planktonic organisms they filter from the sea.

•   The outer skin layer is the epidermis, beneath which
    a thick, fibrous dermis can be seen. The outer, hard
    portion of the scale is enameloid, one of the toughest
    materials produced in the animal kingdom.
Class Osteicthyes
              •   The bony fish (Osteon = "bone";
                  "icthys" = "fish") are the most
                  diverse and numerous of all

              •   They differ from most of the
                  cartilaginous fishes in having a
                  terminal mouth and a flap
                  (operculum) covering the gills.

              •   In addition, most have a swim
                  bladder, which is ordinarily used to
                  adjust their buoyancy, although
                  among the air-breathing fishes it is
                  attached to the pharynx and serves
                  as a simple lung.
Class Osteicthyes
•   The skin has many mucus glands
    and is usually adorned with dermal

•   Their jaws are well developed,
    articulated with the skull, and
    armed with teeth.

•   They have a two-chambered heart
    built on the same plan as the

•   The sexes are separate, most are
    oviparous, and fertilization is
    usually external.
Class Osteicthyes
• There are two subclasses:
Subclass Actinopterygii       Subclass Sarcopterygii
   (ray-finned fishes)          (lobe-finned fishes)
Subclass Actinopterygii
• The Actinopterygii is the
  larger of the two subclasses
• These animals have slender fin
  rays suporting their fins and
  lack the odd appendages of the
  lobe-finned fish.
• Most have a symmetrical
  caudal fin (homocercal tail) and
  a swim bladder.
• This group includes most of the
  fishes with which you are
  familiar (bass, goldfish,
  guppies, sea horses,
  sturgeons, and tuna).
Subclass Sarcopterygii
                 •   Sarcopterygians have a fleshy lobe at
                     the base of their fins that is leg-like in
                 •   They include fossil forms that are
                     ancestors of the amphibians, the true
                     lungfishes, and the coelacanth.
                 •   Today's coelacanths are "living fossils,"
                     represented by a single species
                     (Latimeria) found near the coast of
                 •    Until 1938, when a coelacanth was first
                     captured by chance, they were known
                     only from the fossil record. Since then
                     several dozen have been captured and
                     some of their behavior has been filmed
                     using robotic cameras.
                 •   Latimeria is important because it
                     provides an opportunity to compare
                     observations from the fossil record with
                     a living animal.
Superclass Tetrapoda
              • Tetrapoda means "four feet",
                and the group was so-named
                as its members primitively had
                four limbs, as opposed to fins.

              • This taxon includes about 3000
                extant species of amphibians
                (frogs, salamanders, and
                caecilians) and approximately
                18100 extant species of
                amniotes (mammals, reptiles,
                and birds).
Superclass Tetrapoda
• Superclass Tetrapoda has four major class
    •   Class Amphibia
    •   Class Reptilia
    •   Class Aves
    •   Class Mammailia
Class Amphibia
             •   The ancestors of today's
                 amphibians were the first
                 chordates to venture onto land

             •   Although many changes in the
                 anatomy, physiology, and behavior
                 were required for terrestrial
                 colonization, several pre-
                 adaptations among the early
                 amphibians eased their
                 colonization of terrestrial habitats.

             •   Two barriers, however, keep most
                 amphibians from a totally terrestrial
                 lifestyle: respiration and
Class Amphibia
•   Today's amphibians have a moist,
    glandular skin with no scales (with a
    few exceptions).
•   Most have two pair of limbs adapted for
    walking and/or swimming. Their hearts
    have three chambers (two auricles and
    one ventricle)
•   Respiration is by the skin, lining of the
    mouth, gills, and/or lungs, depending
    on the species or stage in their life
    history. Most cannot survive away from
    water for very long because they lose
    too much moisture through their thin
    respiratory surfaces.
•   In addition, most amphibians require
    water for reproduction and have an
    aquatic larval stage. Fertilization may
    be internal or external and most are
Class Amphibia
• There are three surviving orders:
  – Order Caudata (newts and salamanders)

  – Order Anura (frogs and toads)

  – Order Gymnophiona (caecilians)

                                            (Extinct Euryops)
Order Caudata
                • Caudatans (salamanders and
                  newts) have poorly developed
                  limbs and retain a tail as adults
                  (the name Caudata refers to
                  the presence of a tail).
                • They prey on worms, insects,
                  and small mollusks. Some
                  species have no lungs and
                  depend entirely on cutaneous
                  respiration. Others, such as the
                  mudpuppy (Necturus) and the
                  axolotl (Ambystoma), retain the
                  larval gills as adults.
Order Anura
• Frogs and toads belong to the
  order Anura ("Anura" refers to
  the lack of a tail in adults).
• They differ from the caudates
  by having a more complex
  skeletal system with stronger
  limbs and developmental
  metamorphosis (from a tailed
  and limbless polliwog to a
  tailless limbed adult).
• Of all the amphibians, anurans
  have been most successful in
  their occupation of terrestrial
  habitats (including trees).
Order Gymnophiona
              •   Caecilians, as they are more
                  commonly called, are wormlike
                  creatures found in tropical forests.
                  They make their livings by
                  burrowing through the soft soil
                  searching for worms and other tasty
              •   Several adaptations are related to
                  their subterranean habits: They
                  have no legs, are almost totally
                  blind (atrophied eyes are hidden
                  under the skin), and have sensory
              •   Their skin is annulated, and some
                  have minute dermal scales. This
                  combination of characteristics
                  makes them look very much like
                  overgrown earthworms.
Class Reptilia
            • Reptiles have acquired several
              advances over amphibians that have
              allowed them to move successfully into
              terrestrial habitats.
            • Their skin, for example, is more heavily
              thickened and is protected with surface
              scales that are impervious to water.
            • A reptile's scales are very different in
              structure from that of fish. The outer
              layer of skin is a thick layer of dead,
              keratin-filled cornified cells. These cells
              are organized into horny scales
              covering the entire outer surface.
            • Since reptiles have internal fertilization,
              water isn't even needed for mating.
Class Reptilia
•   There are two major subclasses:
         • Subclass Anapsida – Turtles; Tortoises; some dinosaurs
         • Subclass Diapsida – Crocodiles; Snakes; Lizards; most dinosaurs

•   This is based on the presence or
    absence of certain temporal openings:
Subclass Anapsida
• The term Anapsida ("no
  arch") refers to all those
  reptile groups that lack
  skull openings behind the

• Subclass Anapsida
  contains most of the
  extremely primitive
  ancestral reptiles as well
  as turtles and tortoises
Subclass Diapsida
               • Most all other reptiles are
                 diapsids (including lizards,
                 crocodiles, snakes, and most

               • The main diagnostic physical
                 character for a diapsid is the
                 presence of two openings on
                 each side of the skull; the
                 upper and lower temporal

               • Birds even exhibit this
                 temporal arrangement
Class Aves
• Birds are endothermic (warm-blooded)
  vertebrates with feathers. Their anterior
  limbs are modified as wings for flight,
  while the posterior pair is adapted for
  walking, swimming, or perching.

• Other adaptations related to flight include
  changes in the skeletal, respiratory,
  circulatory, reproductive, digestive, and
  excretory systems.

• Today's birds still retain many reptilian
  characteristics such as similarities in
  behavior, skull structure, and scales on
  their beak, legs, and feet.
Class Aves
             •   The long hollow and porous bones of birds are
                 thin and slender to aid in flight. Many bones
                 overtime have fused together to give support.

             •   Teeth have been lost and replaced by a light

             •   Feathers are cornified epidermal appendages
                 that are probably related to scales. They are
                 used for thermoregulation, communication, and
                 as a flight surface.

             •   There are two subclasses of Aves:
                  – Subclass Archaeornithes (Extinct Archaeopteryx)
                  – Subclass Neornithes (All other birds)
Subclass Archaeornithes
•   The Archaeornithes, are
    represented by a single extinct
    species (Archaeopteryx).
•   The first Archaeopteryx specimen
    was discovered during the
    nineteenth century. It was about
    the size of a crow, had a long
    reptilian tail and a reptilian skull
    with no beak. It had three fingers
    on its wings, each bearing a claw.
    Because of its small sternum and
    flexible trunk, it's unlikely that
    Archaeopteryx was a strong flier.
•   Its characteristics are so reptilian
    that, were it not for the feathers
    fossilized with the specimen, it
    would not be recognizable as a
    potential ancestor of birds.
Subclass Neornithes
           • All birds other than
             Archaeopteryx belong to the
             subclass Neornithes.

           • While most neornithes fly, ratites
             can not. Examples of living
             ratites include emus, rheas,
             ostriches, and penguins.

           • Neornithes that fly are carinates
             (they have a large carina).
Class Mammalia
          • Members of the class Mammalia
            possess both hair and mammary glands.

          • Their integument is complex and has
            many glands used for a variety of
            purposes: thermoregulation and
            excretion (sweat glands), communication
            (scent glands), care of the hair and skin
            (sebaceous oil glands), and for feeding of
            the young (mammary glands).
Class Mammalia
•   They are thermic and have relatively
    high rates of metabolism. In keeping
    with their higher metabolic rates,
    adaptations for efficient feeding include
    heterodont teeth in most species and a
    secondary palate to separate the
    respiratory and food passages (so they
    can breathe and chew at the same

•   The circulatory systems are efficient,
    and they have a four-chambered heart
    with separate pulmonary and systemic

•   Their brains are highly developed,
    fertilization is internal, and most have
    placental attachment of the young.
Class Mammalia
             • There are three subclasses
               based on birthing systems:

                 – Subclass Prototheria
                   (egg-laying monotremes)

                 – Subclass Metatheria

                 – Subclass Eutheria
Subclass Prototheria
•   Members of the subclass Prototheria are so
    different from placentals that they may have
    developed from a different theriapsid species

•   Today's monotremes are found in Australia,
    Tasmania, and New Guinea. The only living
    monotremes are the duckbill platypus and
    echidna (spiny anteater).

•   Monotremes have several primitive
    characteristics: They lack teeth as adults, the
    braincase and other skeletal elements are
    reptilian in structure, they have a single
    ventral orifice (connected to a cloaca), and
    they are oviparous.

•   In these ways they are reptilian in their
    structure, reproduction, and physiology.
    Nonetheless, monotremes do possess hair
    and feed their young milk, so they do qualify
    as mammals
Subclass Metatheria
       •   Metatherians are the marsupial
           mammals (kangaroos, koalas,
           opossums, Tasmanian wolves, and

       •   Like the placental mammals,
           marsupials start their lives attached
           by a placenta to the maternal
           circulation. Marsupial placental
           development, however is short-
           lived; and following their birth the
           embryos attach to a nipple within a
           skin pouch (marsupium) where
           they continue their development.

       •   They are nocturnal in their habits
           and are often found in association
           with humans
Subclass Eutheria
                    • Eutherian mammals
                      are placental beasts.
                    • The number and
                      arrangement of the
                      teeth are important in
                      the classification of
                      these mammals
                    • All of these animals
                      give live birth and
                      place heavy
                      importance on raising
                      their young
Subclass Eutheria
 You need to know the Eutherian orders:
   Artiodactyla (deer, goat, pig)    Macroscelidea (elephant shrews)
   Carnivora (bears, wolves)          Perissodactyla (horses, rhinos)
   Cetacea (whales, dolphins)         Pholidota (the pangolin)
   Chiroptera (bats)                  Primates (monkeys, apes)
   Edentata (armadillo, sloth)        Proboscidea (elephants)
   Hyracoidea (hyraxes)              Rodentia (rats, mice)
   Insectivora (shrew, hedgehog)     Sirenia (manatees)
   Lagomorpha (rabbits)              Tubulidentata (aardvarks)
                  Pinnipedia (seal, walrus)