Gill Slits: Paired openings that lead from pharynx to
the exterior which occur during the development of all chordates.
Notochord: A flexible, skeletal rod that lies above
the alimentary canal and below the nerve cord. It may be partially or
completely replaced by a vertebral column in majority of chordates. Example:
In vertebrates, the notochord is replaced by a vertebral column.
Bilateral Symmetry: Similarity between the right and left
sides of an animal. Considering the antero-posterior
axis from head to tail, the two sides present on either side of the axis are symmertrical. Example: Vertebrates are bilaterally
Triploblastic Condition: Having three
germinal layers called as ectoderm, endoderm and mesoderm. Example:
Vertebrates are triploblastic.
Heterocercal Tail: A tail that is
laterally compressed and slightly bent upwards. For example, in Scoliodon.
Lateral Line: A line that runs on either side of the body
extending from head to tail. It is found in fishes and marks the position of
an underlying canal that contains special receptor organs.
Poikilothermic (Cold-blooded): Having a body
temperature that fluctuates with the temperature of the surroundings.
Example: Amphibians are cold-blooded animals.
Homeothermic (Warm-blooded): Having a constant
body temperature irrespective of the changes in the temperature of
surroundings. Example: Birds and mammals are warm-blooded animals.
Vertebrates: Animals possessing backbone or vertebral