12 Chordata


Published on

I borrowed and downloaded the ppt for my class.
Description of the chordate group.

Published in: Technology, Education
  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

12 Chordata

  1. 1. Introduction to Phylum Chordata By : Kent Simmons
  2. 2. <ul><li>Unifying Themes </li></ul><ul><li>1. Chordate evolution is a history of innovations that is built upon major invertebrate traits </li></ul><ul><li>They display many of the basic traits that first evolved in the invertebrates: bilateral symmetry, cephalization, segmentation, coelom, &quot;gut&quot; tube, etc. </li></ul>
  3. 3. <ul><li>2. Chordate evolution is marked by physical and behavioral specializations </li></ul><ul><li>For example the forelimb of mammals has a wide range of structural variation, specialized by natural selection </li></ul><ul><li>3. Evolutionary innovations and specializations led to adaptive radiations - the development of a variety of forms from a single ancestral group </li></ul>
  4. 4. Characteristics of the Chordates <ul><li>Notochord, dorsal hollow nerve cord, pharyngeal gill slits, blocks of muscle, postanal tail </li></ul>
  5. 5. <ul><li>Characteristics of the Chordates </li></ul><ul><li>The notochord </li></ul><ul><li>All chordate embryos have a notochord, a stiff but flexible rod that provides internal support </li></ul><ul><li>Remains throughout the life history of most invertebrate chordates; among, present only in the embryos of vertebrate chordates </li></ul>
  6. 6. <ul><li>Characteristics of the Chordates cont. </li></ul><ul><li>Dorsal Hollow Nerve Cord (=Spinal Cord) </li></ul><ul><li>A fluid-filled tube of nerve tissue that runs the length of the animal, dorsal to the notochord </li></ul><ul><li>Present in chordates throughout embryonic and adult life </li></ul>
  7. 7. <ul><li>Characteristics of the Chordates cont. </li></ul><ul><li>Pharyngeal gill slits </li></ul><ul><li>Pairs of opening through the pharynx </li></ul><ul><li>Invertebrate chordates use them to filter food </li></ul><ul><li>Juvenile fishes use them to them for breathing </li></ul><ul><li>In adult fishes the gill sits develop into true gills </li></ul><ul><li>In reptiles, birds, and mammals the gill slits are vestiges, occurring only in the embryo </li></ul>
  8. 8. <ul><li>Characteristics of the Chordates cont. </li></ul><ul><li>Blocks of Muscle - Myotomes </li></ul><ul><li>Surrounding the notochord and nerve cord are blocks of muscle - myotomes </li></ul><ul><li>Postanal Tail </li></ul><ul><li>The notochord, nerve cord, and the myotomes extend to the tail </li></ul><ul><li>Found at some time during a chordate's development </li></ul>
  9. 9. Invertebrate Chordates
  10. 10. <ul><li>SubPhylum Urochordata </li></ul><ul><li>Marine animals; some species are solitary, others are colonial. </li></ul><ul><li>Sessile as adults, but motile during the larval stages </li></ul><ul><li>Possess all 5 chordate characteristics as larvae </li></ul><ul><li>Settle head first on hard substrates and undergo a dramatic metamorphosis (e.g., tail, notochord, muscle segments, and nerve cord disappear) </li></ul>
  11. 11. <ul><li>SubPhylum Urochordata cont. </li></ul><ul><li>Adult body is covered by an outer envelope or tunic; composed of fibers of tunicin embedded in a mucopolysaccharide matrix </li></ul><ul><li>Tunic encloses a basket-like pharynx, that is perforated by gill slits </li></ul><ul><li>Tunicates are filter feeders; plankton is trapped in a sheet of mucus and cilia later direct the food-laden mucus to the stomach </li></ul><ul><li>Water leaves the animal via an excurrent siphon </li></ul>
  12. 12. <ul><li>Chordate Metamerism </li></ul><ul><li>Body segmentation (i.e. metamerism) appears to have evolved in two lineages of the chordates: the Cephalochordates and the Vertebrates; probably occurred after divergence from the Urochordates </li></ul><ul><li>However, segmentation in the chordates does not involve the coelom </li></ul><ul><li>The cephalochordates and the chordates movement is accomplished by contraction of muscle fibers that are arranged in segmented blocks - myotomes </li></ul><ul><li>Presumably, segmentation of muscles developed as an adaptation for undulatory swimming and rapid burrowing </li></ul>
  13. 13. <ul><li>SubPhylum Cephalochordata </li></ul><ul><li>Exclusively marine animals </li></ul><ul><li>Although they are capable of swimming, they usually are buried in the sand with only their anterior end being exposed </li></ul>
  14. 14. <ul><li>SubPhylum Cephalochordata cont. </li></ul><ul><li>All chordate characteristics are present throughout their life history </li></ul><ul><li>They are filter feeders: inside of the oral hood is lined with cilia - wheel organ </li></ul><ul><li>These cilia, plus cilia in the pharynx help generate a water current </li></ul><ul><li>Water and suspended food particles pass through the oral hood , equipped with projections called cirri that strain larger particles </li></ul><ul><li>Feed by secreting a mucous net across the gill slits to filter out food particles that are present in the water. </li></ul>
  15. 15. Subphylum Vertebrata
  16. 16. <ul><li>General Characteristics </li></ul><ul><li>Exhibit all 5 chordate characteristics at sometime in their life history </li></ul><ul><li>Usually well cephalized, including a well developed brain and a number of anterior sensory structures </li></ul><ul><li>Brain is usually encased in a skull, made of hard bone or a cartilage. </li></ul><ul><li>In most vertebrates, the embryonic notochord is replaced by a vertebral column. </li></ul><ul><li>Possess a distinctive endoskeleton consisting of vertebral column, limb girdles, two pairs of jointed appendages, and a head skeleton </li></ul><ul><li>Muscles are attached to the skeleton to provide movement </li></ul><ul><li>Often have a muscular perforated pharynx </li></ul><ul><li>Closed circulatory system with a well developed muscular heart; blood is oxygenated as it flows through vascularized skin, gills or lungs. </li></ul>
  17. 17. <ul><li>Evolutionary Relationships of the Vertebrates </li></ul><ul><li>Earliest vertebrate fossils (jawless ostracoderm fishes; 500 mya) share many of the novel structures observed in the living vertebrates </li></ul><ul><li>Q. When and from where did these vertebrate characteristics evolve? </li></ul><ul><li>May have evolved from an invertebrate chordate lineage </li></ul><ul><li>This idea is supported by the discovery of a fossilized mid-Cambrain invertebrate chordate from the Burgess Shale formation - Pikaia </li></ul><ul><li>A ribbon shaped, somewhat fish-like creature about 5 cm in length </li></ul><ul><li>It possessed a notochord and the V-shaped myomeres </li></ul><ul><li>Resembles Amphioxus, and may very well be an early cephalochordate </li></ul>
  18. 18. <ul><li>Evolutionary Relationships of the Vertebrates cont. </li></ul><ul><li>Speculations regarding vertebrate ancestry have focused on living cephalochordates and tunicates </li></ul><ul><li>One hypothesis on the evolution of the vertebrates is Garstang's Hypothesis </li></ul><ul><li>It suggests that sessile tunicates were an ancestral stock that evolved a motile larval stage </li></ul><ul><li>Garstang speculated that at some point larvae failed to metamorphose into an adult, but developed gonads and reproduced in the larval stage </li></ul><ul><li>And with continued larval evolution a new group of free swimming animals evolved </li></ul><ul><li>Garstang called this process paedomorphosis, a term that describes the presence (or evolutionary retention) of juvenile or larval traits in the adult body </li></ul>