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Chordate Phylogeny

Chordates are Bilaterian Deuterostomes. Chordate Phylogeny. Amphioxus. Phyl ogeny (cont.). Sea Squirt. 5 Classes (before tetrapods ) Agnatha Jawless fish; hagfish and lampreys Chrondrichthes Sharks, skates and rays Osteichthes Bony fish

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Chordate Phylogeny

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  1. Chordates are BilaterianDeuterostomes Chordate Phylogeny

  2. Amphioxus Phylogeny(cont.) Sea Squirt • 5 Classes (before tetrapods) • Agnatha • Jawless fish; • hagfish and lampreys • Chrondrichthes • Sharks, skates and rays • Osteichthes • Bony fish • Actinopterygii • Ray- finned fish • Sarcopterygii • Lobe-finned fish Hagfish Lamprey

  3. Chordate Origins Chordates developed during the Cambrian period, around 560 Ma Evolutionary issue There is a poor fossil record for the origin of chordates, since they were most likely soft-bodied creatures Primitive chordates (like the sea squirt) are studied closely, along with Hemichordates, to try and piece together their origins

  4. Chordate Basics Chordate characteristics: Dorsal, hollow nerve cord Notochord Pharyngeal slits Post-anal tail

  5. Embryonic Development • Egg becomes fertilized, then divides repeatedly (cleavage) • Cells arranged into a round, hollow ball (called ablastula) with a fluid filled cavity (called the coelom) • One side of the ball indents and grows inward (gastrulation) until an opening is formed (called the blastopore) • Indentation continues until it breaks through the wall on the other side, creating a second opening

  6. Embryonic Dev. (cont.) • The notochord forms out of the mesoderm • made up of a hard, fibrous material • The dorsal, hollow nerve cord is derived from the ectoderm (through ‘invagination’) • eventually forms the brain and spinal cord • The Pharyngeal slits develop after the mouth and pharynx form, creating holes or slits into the pharynx • may become gills for respiration • used to filter food or eject water while eating • The post-anal tail is created when the body elongates

  7. Includes subphylums: • Hemichordata • Urochordata (tunicates) • Cephalochordates Protochordata Considered to be “primitive” chordates (“proto” means first) Larvae are generally planktonic, while adults may be sessile, benthic or they may burrow into the substrate May be solitary or colonial, and feed by means of cilia and mucus Male and female gonads are either found in a single individual (monoecious) or in separate individuals (dioecious)

  8. Hemichordata • Thought to be an intermediate group of species between the echinoderms and the chordates • Acorn Worm • Pterobranch • Graptolites (extinct) • Has pharyngeal slits and a dorsal nerve cord (may not be hollow). However, they do not appear to have a notochord (merely a stomochord) and have no post-anal tail

  9. Acorn Worms (Enteropneusts- Hemichordata) • # Species: 75-80 • Evolved: 500-540 Ma • Size: can reach over 1 meter • Nutrition: Filter feeders or normal ingestion • Lifestyle: Planktonic larvae, burrowing adults • Support: Stomochord • Musculature: Circular or longitudinal orientation • Non-segmented muscles • Reproduction: Dioecious or segmentation • Chordate Characteristics: Pharyngeal slits and dorsal nerve cord

  10. Acorn Worms (cont.) (Enteropneusts- Hemichordata)

  11. Pterobranch (Hemichordata) • # Species: about 20 • Evolved: 500-435 Ma • Size: can reach 1 mm • Nutrition: Filter feeders (ciliated tentacles) • Lifestyle: Planktonic larvae & sessile, colonial adults • Support: Stomochord and rigid, tube housing • Musculature: Circular or longitudinal orientation • Non-segmented muscles • Reproduction: Dioecious or asexual • Chordate Characteristics: Pharyngeal slits and dorsal nerve cord

  12. Graptolites EXTINCT (Graptolithina - Hemichordata ) • # Species: thought to be hundreds • Evolution: 490-545 Ma (extinct 298-354 Ma) • Lifestyle: Colonial and sessile or benthic • These were tiny, tubular creatures, which when fossilized may resemble a saw blade.

  13. Subphylum Urochordata Over 20,000 species - thought to be the oldest living chordates Includes: Tunicates (aka Sea Squirts; Ascidiacea) Larvacea Thaliacea

  14. Tunicates (Sea Squirt) (Ascidiacea- Subphylum Urochordata) • # Species: about 2,000 • Evolved: 540 Ma • Size: (small) • Nutrition: Filter feeders (complex straining apparatus); eat mostly plankton • Lifestyle: Planktonic larvae & sessile adults • Support: Notochord and tunic • Musculature: • Reproduction: hermaphroditicorasexual

  15. Tunicates (cont.) (Ascidiacea- Subphylum Urochordata)

  16. Larvaceaand Thaliacea (Subphylum Urochordata) • Larvacealook more like tunicates during adulthood • Thaliacearetain their tadpole-like body plan from larval state to their plankton-like adulthood (benthic) • Some are sexual and others are asexual, skipping the larval state altogether • May live solitary or colonial lives

  17. Subphylum Cephalochordata About 25species This is the first group of chordates to retain all 4 traits into adulthood Includes: Lancelets (or Amphioxus)

  18. Lancelets (Amphioxus) (Subphylum Cephalochordata) • # Species: about 20 • Evolved: 520 Ma • Size: up to 2 inches • Nutrition: Filter feeders - plankton and algae • Lifestyle: Burrowing adults • Support: Notochord (extends all the way to snout) • Musculature: Segmented (myotomes) • Reproduction: Dioecious

  19. Evolution of VertebratesDebate DNA confirms neither of these diagrams are feasible Why? Larval Development basis Pharyngeal slit development basis

  20. Class Craniata The evolution of heads! The evolution of the head (or skull) occurred around the same time that vertebrates evolved. All species in the Subphylum Vertebrata convert their notochord into a backbone (except for the hagfish)

  21. Subphylum Vertebrata The notochord is now converted to vertebral plates. With the inclusion of a head (or skull), species developed a brain, eyes and more complex nervous systems (the nerve cord becomes the spinal cord). Includes: Hagfish Lampreys Cartilaginous, lobe-finned and bony fish

  22. Hagfish (Subphylum Vertebrata) • # Species: about 72 • Evolved: 330 Ma • Size: about 30 inches • Nutrition: Parasitic or scavengers; eat mainly worms or dead creatures • Lifestyle: Live in the muddy bottom of the ocean • There is no known larval state • Support: Notochord • Reproduction: Dioecious (has both male and female gonads, but not hermaphroditic)

  23. Lampreys (Subphylum Vertebrata and Craniata) • # Species: approx. 3 • Evolved: approx. 330 Ma • Size: 5-40 inches • Nutrition: Filter feeders as larvae & parasitic adults (feeds on the blood of prey) • Lifestyle: Burrowing larvae & free swimming adults • Support: Cartilaginous skeleton • Reproduction: Dioecious (has both male and female gonads, but not hermaphroditic)

  24. Questions?

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