Chordates

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Chordates

• By Eduardo Alexander Becerra and Caleb Jennings
  Staurseth

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What Defines a Chordate?

• Its..
• Notochord
• Dorsal Nerve Chord
• Pharyngeal Slits
• Post-Anal Tail

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Chordate Embryos and Tissues

• Chordates have 3 layers of tissue
• Deutersomes
• Anus forms first, then the mouth forms
• Coelomates
• Bilaterial symmetry
• Endoskeleton
• Complete digestive system

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• Notochord A flexible rod-like structure that is
  similar to a spine

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• Dorsal Nerve Chord The nervous system in
  chordates.

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• Pharyngeal Slits Gill like structures that are
  located on the pharynx

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• Post-Anal Tail A tail that extends beyond the
  anus.

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The 3 Branches

• The three subdivisions or clades of chordates
• Craniates
• Lancelets
• Tunicates

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Tunicates(subphylum Urochordata)

• The deepest branching lineage of chordates.
• Resembles other chordates most intensely during
  larval stages
• Larva tunicate settles down, and goes through
  metamorphasis
• Many chordate characteristics disappear
• Tail and notochord go away, nervous system is
  destroyed
• Often called sea squirts as they shoot out
  water from their anus to jet away when attacked

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Tunicate
Tunicate lifecycle
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Polycarpa Auruta
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Lancelet(subphylum cephalochordata)

• Named after their bladelike shape
• Lancelet Larvae
• Devolop a notochord, dorsal, hollow nervecord,
  pharyngeal slits, and post-anal tail
• Food source is plankton
• Post metamorphasis
• Spend most of their time in the sand, leaving
  their mouth exposed, catching their food.
• Segmented muscle developed from somites - found
  in all chordate embryos

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Adult Lancelet
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Craniates

• craniates (literally means cranium/skull) are
  unique from their other chordate relatives in a
  number of characteristics
• Possess 2 clusters of Hox genes
• Neural Crest - collection of cells at the dorsal
  margins in an embryo which give rise to a variety
  of structures
• Teeth
• Many bones and cartilage of the skull
• Inner layer of skin (dermis) on the facial region
• Sensory capsules in which sense organs such as
  eyes develop.

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• Craniates are seperated into 2 major Clades
• Myxini/Hyperotreti (hagfish)
• Vertebrata

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Myxini
-Pacific Hagfish-

• These bad boys have a
• skull made of cartilage, and
• swim in a snake-like motion
• They Also have a small brain, eyes, ears, and a
  nasal opening which connects to their pharynx

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Vertebrata Craniates
Lampreys (Cephalaspidomorphi) are the oldest
living lineage of vertebrates, and lack a jaw
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Vertebrata Craniates

• Conodonts (cone teeth)
• Early, slender, soft-bodied verebrates with
  advanced eyes, and lacked a jaw

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Vertebrata Craniates
Ostracoderms Additional vertebrates stemmed from
the same period. Ostracoderms -- had paired fins,
inner ear and sense of balance, a muscular
pharynx, and armored bodies
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Vertebrata Craniates

• Gnathostomes (jaw mouth) jawed vertebrates
• The jaw enabled animals to grip food and chew it
  
• up for digestion
• 4 Hox Genes
• Enhanced sense of smell and vision resulted in a
  larger forebrain
• Have lateral line systems, which detected
  vibrations
• Consisted of placoderms plate-skinned and
  acanthodians, which are closely related to
  ray-finned fish and lobe-finned fish
• Went extinct around 360 million years ago

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Vertebrata Craniates

• Chondrichthyans
• Consists of Sharks, rays, and their close
  relatives
• Have skeleton made mostly of cartilage and loads
  of calcium, developed mostly in embryonic stages
• Sharks
• have a spiral valve, which makes up for the
  sharks short digestive tract
• Have noses meant only for smelling, not
  breathing
• Eggs fertelized internally
• Some species are oviparous
• Some species are ovoviviparous
• Rays
• Bottom-dwellers, whiplike tails, venomous barbs

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JAWS - Great White
Large Stingray
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Vertebrata Craniates

• Osteichthyes (Bony Fish)
• Bony endoskeletaon
• Breathe through gills
• protected by bony flaps called operculum
• Buoyancy controlled with an air sac called a
  swim bladder

Common fish
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Vertebrata Craniates

• Osteichthyes continued
• Ray-Finned Fishes
• Majority of aquatic osteichthyans
• Bass, trout, perch, tuna, herring
• Fins allow for increased
• maneuverability
• defense

Blue-Fin Tuna
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Vertebrata Craniates

• Osteichthyes continued
• Lobe-Fins
• Fins have a thick muscle layer in pectoral and
  pelvic fins
• Used to walk across the sea floor
• Only three lineages left today
• Coelacanths, lungfishes, and tetrapods

Coelacanths
lungfish
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Vertebrata Craniates

• Tetrrapods -- gnathostomes with feet
• Have 4 feet with digits
• Able to support weight on land
• No gill slits
• in embryonic development, what would have
  developed into gill slits creates ears and glands
  
• Overall, adaptions making organisms fit for land

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Vertebrata Craniates

• First Group of Tetrapods Amphibians
• 4,800 species today
• Comprising of salamanders, frogs and caecilians
• Live on land and in water
• Scientists believe that the earliest tetrapods
  were heavily tied to water

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Tadpole Life Cycle
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Sources

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