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Phylum Chordata

Phylum Chordata . Chapter 23. Amphioxus. Along the more southern coasts of NA, half buried in sand on the sea floor lives a small fishlike translucent animal quietly filtering organic particles from seawater One of the famous animals of classic zoology Exhibits 5 characteristics of chordates

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Phylum Chordata

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  1. Phylum Chordata Chapter 23

  2. Amphioxus • Along the more southern coasts of NA, half buried in sand on the sea floor lives a small fishlike translucent animal quietly filtering organic particles from seawater • One of the famous animals of classic zoology • Exhibits 5 characteristics of chordates • Considered by many to resemble closely the direct ancestor of vertebrates

  3. 5 Chordate Hallmarks • Supportive Notochord • Dorsal tubular nerve cord • Pharyngeal pouches • Endostyle for filter feeding • Postanal tail for propulsion All of these characteristics are found at some embryonic stage, although they may be altered or disappear in later stages of life

  4. Notochord • A flexible, rod-like structure, extending the length of the body • It is the first part of the endoskeleton to appear in the embryo

  5. Dorsal Tubular Nerve Cord • Tube dorsal to notochord • Anterior end enlarged to form the brain

  6. Pharyngeal Pouches and Slits • Pharyngeal slits are openings that lead from the pharyngeal cavity to the outside • Led to the evolution of internal gills

  7. Endostyle or Thyroid Gland • Derivative of the thyroid gland (which is only found in chordates and no other animals) • Secretes mucus that traps small food particles brought into the pharyngeal cavity

  8. Postanal Tail • Provides motility for free-swimming existence • Tail is evident in humans only as a vestige

  9. Subphylums • Urochordata: “tail chordates”; tunicates • Cephalochordata: lancelets • Vertebrata: more accurately described as having a braincase (because some jawless fish lack vertebrae)

  10. Urochordates • Include about 200 species • Found in all seas from near shoreline to great depths • Most are sessile as adults • Named for the nonliving tunic, or test, that surrounds the animal and contains cellulose • Larval stage has all 5 hallmarks (look like a tadpole)

  11. Tunicates • Often called “sea squirts” because some species forcefully discharge a jet of water from the excurrent siphon when irritated

  12. Cephalochordates • Lancelets are slender, laterally compressed, translucent animals about 5 to 7 cm in legth • Inhabit sandy bottoms of coastal waters such as Tampa Bay • Also called Amphioxus

  13. Internal structure of a lancelet

  14. Vertebrates • Earliest known vertebrate fossils, were armored jawless fish called ostracoderms

  15. Earliest Jawed Vertebrates • Upper and lower jaw developed from structures that originally functioned as gill supports

  16. Earliest Jawed Fish • Of Devonian period, 400 million years ago

  17. Questions? • The urochordates are A. Called tunicates B. Marine animals C. Sessile as adults, but tadpole-like as larvae D. All of the choices are correct • Lancelets are found A. Very rarely and are about extinct B. Are parasites inside the tracts of fish C. Commonly in the sandy bottoms of coastal waters such as Tampa Bay D. Near deep ocean thermal vents

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