Chapter 34: Phylum Chordata

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Chapter 34 Phylum Chordata
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Phylum Chordata

• all chordates are have true tissues (eumetazoans)
  a true coelom and exhibit bilateral symmetry
  deuterostome development
• 4 derived characters
• notochord a long, flexible rod that appears
  during embryonic development between the
  digestive tube and the dorsal nerve cord (present
  in all embryos but may be reduced in adults)
• dorsal, hollow nerve cord develops into the
  central nervous system (brain spinal cord)
• pharyngeal clefts grooves that separate a
  series of pouches along the sides of the pharynx
• muscular, post-anal tail

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Invertebrate Chordates

• chordates that lack a backbone

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Subphylum Urochordata

• aka tunicates
• resemble other chordates during larval stage
• larvae use tail muscles notochord to swim
• when larvae settle, they undergo metamorphosis
  lose many chordate characteristics
• adults filter-feed by bringing water in through a
  siphon, letting it pass through the pharyngeal
  slits into an atrium out through a second
  siphon (as a result, tunicates are often called
  sea squirts)

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Subphylum Cephalochordata

• aka lancelets
• bladelike shape
• adults retain chordate traits after metamorphosis
• first animals to show sign of a brain

• swollen tip at anterior end of dorsal nerve cord
• the cells of this region express the same Hox
  genes as the brain of vertebrate embryos

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Craniates

• chordates with a head
• consists of a brain, eyes, sensory organs, a
  skull
• derived characters
• increased genetic complexity (ex 2 clusters of
  Hox genes)
• neural crest
• pharyngeal clefts become gill slits
• higher metabolism more extensive muscular
  system
• heart with 2 chambers
• red blood cells hemoglobin
• kidneys

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Class Myxini

• aka hagfishes
• oldest living craniates
• invertebrates
• skull made of cartilage
• retain notochord in adulthood (used for movement)
• has a small brain, eyes, ears, nasal opening
  that connects with pharynx
• tooth-like formations
• slime glands

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Vertebrates

• craniates that have a backbone
• derived characters
• additional genetic complexity associated with
  advancements in nervous system skeleton
  development
• more extensive skull
• backbone composed of vertebrae that enclose the
  spinal cord have assumed the role of the
  notochord

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Class Cephalaspidomorphi

• aka lampreys
• oldest lineage of vertebrates
• most are parasites
• round, jawless mouth
• rasping tongue
• cartilage skeleton (contains no collagen)
• notochord persists as main axial skeleton but has
  a cartilaginous pipe around it
• live in marine fresh water

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Gnathostomes

• vertebrates that have jaws
• hinged jaws evolved from the modification of
  skeletal parts that had once supported the
  pharyngeal (gill) slits
• additional characteristics
• 4 clusters of Hox genes
• increased gene complexity
• enlarged forebrain
• lateral line system (in aquatic species) senses
  water vibrations
• mineralized endoskeleton
• appeared in fossil record 470 mya

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Class Chondrichthyes

• skeleton composed of cartilage
• streamlined bodies
• denser than water sink if stop swimming
• 3 methods of reproduction
• oviparous young do not develop w/in female
  female lays eggs that hatch outside the body
• ovoviviparous young develop w/in female w/out a
  placenta for nourishment
• viviparous young develop w/in female fed by a
  placenta
• (ex) sharks, skates, rays, ratfishes, chimaeras

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Class Osteichthyes

• aka bony fishes
• ossified endoskeleton
• bodies covered in scales
• breathe with gills
• swim bladder (to control buoyancy)
• mucus secreting glands in skin
• lateral line system
• most oviparous

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2 Subclasses of Bony Fishes

• Subclass Actinopterygii
• aka ray-finned fishes
• fins supported by long, flexible rays
• fins modified for maneuvering defense
• (ex) bass, trout, perch, tuna, etc.
• Subclass Sarcopterygii
• aka lobe-finned fishes
• rod-shaped bones surrounded by a thick layer of
  muscle in the pectoral pelvic fins
• (ex) coelacanths lungfishes

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Tetrapods

• gnathostomes that have limbs feet
• additional characteristics
• bones of pelvic girdle fused to backbone
• no gill slits
• ears detect airborne sounds

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Class Amphibia

• amphibian means 2 lives (aquatic terrestrial)
  which is a reference to the metamorphosis of many
  species
• depend on damp/wet habitats because gas exchange
  occurs through the skin
• eggs lack a shell fertilization is external so
  they depend on water to complete their life cycle
• 3 orders
• Order Urodela (tailed) salamanders
• Order Anura (tailless) frogs
• Order Apoda (legless) caecilians

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Amniotes

• tetrapods that have a terrestrially adapted egg
• amniotic egg
• has a shell that retains water
• has extraembryonic membranes that function in gas
  exchange, waste storage, the transport of
  nutrients to the embryo

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Reptiles

• waterproof scales (keratin)
• rely on lungs for gas exchange
• lay shelled eggs on land
• internal fertilization
• cold-blooded (ectothermic) regulate body
  temperature by absorbing heat from the
  environment (rather than via metabolism)
• extinct groups dinosaurs (land), pterosaurs
  (air), plesiosaurs (marine)
• living groups turtles, tuataras, lizards,
  snakes, alligators, crocodiles

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Birds

• lay amniotic eggs
• have keratin scales on legs
• bodies constructed for flight
• light, hollow bones
• few organs
• wings feathers
• endothermic (regulate body temperature
  internally)
• toothless
• acute vision
• efficient respiratory circulatory systems with
  a 4-chambered heart

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Class Mammalia

• mammary glands (produce milk for offspring)
• hair
• endothermic
• most born rather than hatched
• internal fertilization
• proportionally larger brains than other
  vertebrates
• teeth of different shapes sizes (adapted for
  different foods)
• efficient respiratory circulatory systems
  including a 4-chambered heart

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3 Groups of Mammals

• Monotremes (egg-laying mammals)
• have hair produce milk but lack nipples
• (ex) platypuses, echidnas (spiny anteaters)
• Marsupials (mammals with a pouch)
• embryos begin development in uterus but are born
  early complete development in a marsupium
  (pouch)
• (ex) opossums, kangaroos, koalas, wombats
• Eutherians (placental mammals)
• embryos complete development with the uterus
  are joined to the mother by placenta

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Primates

• hands (opposable thumb) feet adapted for
  grasping
• large brains short jaws
• forward-looking eyes
• digits with flat nails
• excellent eye-hand coordination
• well-developed parental care
• complex social behavior
• 3 subgroups
• lemurs, lorises, pottos
• tarsiers
• anthropoids (monkeys, apes, humans)

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Humans

• stand upright walk on 2 legs
  (bipedal posture)
• large brain
• reduced jawbones jaw muscles
• shorter digestive tract
• reduced size-difference between the sexes
• capable of language, symbolic thought, and the
  manufacture use of complex tools
• study of human origins paleoanthropology