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.
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.
