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Chordata
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The Major Groups• Invertebrate Chordates
• Fishes
– Class: Agnatha
– Class Condrichthyes
– Class Osteichthyes
• Class: Amphibia
• Class: Reptilia
• Class: Aves
• Class: Mammalia
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Body Plan of the Chordates
• Notochord, dorsal hollow nerve cord, pharyngeal gill slits, blocks of muscle, post-anal tail
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• notochord –reinforces body shape
• dorsal hollow nerve cord—modified into brain and spinal cord
• pharynx (feeding “basket”) with pharyngeal gill slits -at least in embryo
– develop into true gills in fishes, are vestigial (not found in adult form—leftover from evolution) segmented musculature and post-anal tail
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Lower Chordates
• Several subphyla are invertebrates (i.e. lack a skeleton)
• Probably evolved from ancient sea anemones
– Urochordates
• Tunicates
– Cephalochordates
• Lancets
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Tunicates• “tail chordates”
– notochord only in tail
• Example: sea squirts
• adult loses chordate body plan and becomes a sessile filter feeder or predator
• Breathe using gill slits
• Closed circulatory system with vanadium-rich blood
• Full digestive system with an endostyle for waste
• Hermaphrodites, External
Adult Larva
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Cephalochordates• “head chordates”
• Example: amphioxus
• adults can swim
• Feeding: filter food endostyle secretes mucus into gills
• breathe using gill slits
• excretion = kidneys
• Circulation = closed, but no heart or blood cells
• external fertilization
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Phylum: Chordates
Examples/Habitat Invertebrates (Tunicates, Cephalochordates, Urochordates), Fish,
amphibians, reptiles, birds, mammals
Body Plan(symmetry, special cells)
Notochord, dorsal hollow nerve cord, pharyngeal gill slits (at some
point in life), blocks of muscle, post-anal tail
Feeding All groups
Respiration Gills, skin, some times lungs used for breathing
Circulation Closed system, aortic arches, dorsal and ventral vessels
Excretion Digestive waste excreted through anus—complete digestive tract
Movement and
Response
All have dorsal nerve cords, some have simple eyes and chemical
receptors, many have very complex systems
Muscles and skeleton allow directional movement
Reproduction Most have male and female sexual reproduction, some are
hermaphroditic
Human Concerns
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Subphylum Vertebrata
Fill all habitats and all feeding types
Fossilized skeleton of Diplodocus carnegii
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Vertebrate Chordates• Follow basic developmental pattern
of chordate anatomy
• Have a backbone made up of
vertebrae which protects the
notochord
• Endoskeleton for support & growth
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Body Plan
•Usually well cephalized, including a well developed brain and a number of anterior sensory structures
• Brain is usually encased in a skull In most vertebrates
• the embryonic notochord is replaced by a vertebral column.
• endoskeleton consisting of vertebral column, limb girdles
•two pairs of jointed appendages, and a head skeleton
• Muscles are attached to the skeleton to provide movement
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Evolutionary Relationships of the Vertebrates
• Earliest vertebrate fossils (jawless ostracoderm fishes; 500 mya) share many of the novel structures observed in the living vertebrates•Fosslized mid-Cambrian invertebrate chordate from the Burgess Shale formation - Pikaia• A ribbon shaped, somewhat fish-like creature about 5 cm in length• It possessed a notochord and the V-shaped muscles
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• Well-developed sensory organs
• Brain enclosed in a skull (cephalization)
• Closed circulatory system, with a multi-chambered heart
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Circulation in Fish• Two chambered heart
• Three chambered heart
• Four chambered heart
Bulbus ArteriosusVentricle
AtriumSinus Venosus
Body
muscle
circulation
Digestive
system
circulation
Gills
Heart
Brain and
head
circulation
Oxygen-rich blood
Oxygen-poor blood
Oxygen-poor blood
from the veins collects
in the sinus
venosus.
Blood enters the
atrium and flows
to the ventricle.
The ventricle pumps
blood into the bulbus
arteriosus.
The bulbus arteriosus
moves blood into the
ventral aorta and toward
the gills.
Fish have a two-chambered heart
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Circulation in Amphibians, Reptiles & Mammals
• Three-chambered
heart
– Amphibians +
some reptiles
• Four-chambered
heart
– Birds + mammals
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Respiratory Strategies• External Gills
– Fish, some Amphibians
• Internal Lungs
– Amphibians, Reptiles,
Birds, Mammals
Salamander Lizard PigeonPrimate
Nostrils, mouth & throat
Trachea
Lung
Air sac
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Temperature Regulation
• Temperature is regulated by their external environment
• Ex. Fish, Amphibians, Reptiles
• Temperature is regulated by internal processes
• Ex. Birds, Mammals, possibly Dinosaurs
Ectotherms Endotherms
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Reproductive Strategies• External Fertilization
– Oviparous (hatch from egg)
– Requires aquatic environment
Ex. Fish, Amphibians
• Internal Fertilization
– Oviparous or Ovoviviparous (eggs hatch inside mother ex: snakes)
– Hard, water-resistant shell (does not require aquatic environment)
Ex. Reptiles, Birds
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Reproductive Strategies (cont.)• Viviparity = “live birth”
• Fully internal reproduction
• Embryo gets food from mother
• Live birth
–Ex. Mammals + Marsupials
Monotremes = mammals that lay eggsDuck-Billed Platypus!
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Evolutionary Relationships
Nonvertebrate
chordates
Fishes
AmphibiansReptiles
Birds
Mammals
Invertebrate ancestor