Kingdom Animalia- Phylum Chordata
All Chordates look
alike at Some Point
in their
Development
Key Points
Phylum is built off invertebrate traits:
• Display basic traits that first evolved in invertebrates: bilateral symmetry,
cephalization (concentration of sense organs), segmentation, coelom, "gut"
tube, etc.
Chordate evolution has physical and behavioral specializations
• Ex: forelimb of mammals specialized by natural selection
Evolution led to ADAPTIVE RADIATIONS (variety of forms from a single ancestral
group)
4 Major Characteristics of Chordates
• Notochord, dorsal hollow nerve cord, pharyngeal gill slits, postanal
tail
The Notochord
• All chordate embryos have a notochord,
• Stiff flexible rod that provides support
• Remains throughout the life history of most invertebrate chordates;
present only in the embryos of vertebrate chordates
Dorsal Hollow Nerve Cord (=Spinal Cord)
• fluid-filled tube of nerve tissue that runs the length of the animal,
above the notochord
• Present in chordates throughout embryonic and adult life
Pharyngeal Gill Slits
• Pairs of opening through the pharynx
• Invertebrate chordates use them to filter food
• Fish gill sits develop into true gills
• In reptiles, birds, and mammals the gill slits only occur in the embryo
Postanal Tail
• The notochord, nerve cord, and the myotomes extend to the tail
• Found at some time during a chordate's development
Endotherms VS Ectotherms
Endotherm:
-Organisms that are able to maintain a constant body temperature.
-Rely on heat from internal bodily functions.
Ectotherm:
-Organisms that are not able to maintain a constant body temperature.
-Rely on ambient heat (heat from environment)
ACTIVITY
DRAW A CHORDATE AND LABEL ITS 4 CHARACTERISTIC CHORDATE STRUCTURES