This document defines key terms related to the animal kingdom, including invertebrates, vertebrates, feedback inhibition, blastula, protostomes, deuterostomes, radial symmetry, bilateral symmetry, and more. It describes animals as multicellular, eukaryotic heterotrophs and outlines their essential functions of feeding, respiration, circulation, excretion, response, movement, and reproduction. Complex animals are noted to have high cell specialization, internal organization, bilateral symmetry, a head with sense organs, and a body cavity.

1. 26.1 Introduction to the Animal
Kingdom

2. Invertebrate
• Animal that does not have a backbone, or
vertebral column.

3. vertebrate
• Animal that has a vertebral column, or
backbone

4. Feedback inhibition
• Process in which the product or result stops or
limits the process.

5. blastula
• Hollow ball of cells formed when a zygote
undergoes a series of divisions.

6. protostome
• Animal whose mouth is formed from its
blastopore.

7. deuterostome
• Animal whose anus is formed from the
blastopore of a blastula.

8. anus
• Opening through which wastes leave the
digestive tract.

9. endoderm
• Innermost germ layer of most animals;
develops into the linings of the digestive tract
and much of the respiratory system.

10. mesoderm
• Middle germ layer of most animals; gives rise
to muscles and much of the circulatory,
reproductive, and excretory systems.

11. ectoderm
• Outermost germ layer of most animals; gives
rise to outer layer of the skin, sense organs,
and nerves.

12. Radial symmetry
• Body plan in which body parts repeat around
the center of the body; characteristic of sea
anemones and sea stars.

13. Bilateral symmetry
• Body plan in which only a single, imaginary
line can divide the body into two equal halves;
characteristics of worms, arthropods, and
chordates.

14. cephalization
• Concentration of sense organs and nerve cells
at the front of an animal’s body.

15. Key Concept
• Animals, members of the kingdom Animalia,
are multicellular, eukaryotic heterotrophs
whose cells lack cell walls.

16. Key Concept
• Animals carry out the following essential
functions: feeding, respiration, circulation,
excretion, response, movement, and
reproduction.

17. Key Concept
• Complex animals tend to have high levels of
cell specialization and internal body
organization, bilateral body symmetry, a front
end or head with sense organs, and a body
cavity.