Evolution of Animal Diversity What is an animal?
• multicellular _______________________, and
• have cells that lack cell walls.
Animals also use _______________, the eating of food.
_____________________absorb nutrients after
digesting food outside their body.
© 2012 Pearson Education, Inc. • _________________________is much larger than
• The large majority of phyla are invertebrates
• All vertebrates are chordates … but not all chordates
• _________________________________________ Animal diversification began more than half a
billion years ago
The oldest generally accepted animal fossils that have
been found are __________________________years old.
Animal diversification appears to have accelerated rapidly
from then, during the Cambrian period, known as the
The most celebrated source of Cambrian fossils is the
Burgess Shale containing a cornucopia of perfectly
preserved animal fossils.
© 2012 Pearson Education, Inc. Figure 18.2B_1 Animals can be characterized by basic features of
their “body plan”
Animal body plans vary in
• number of ________________________________________,
• presence of a ___________________________, and
• details of their ___________________________________.
© 2012 Pearson Education, Inc. What is an animal?
After the gastrula stage, many animals develop
__________________________ into adults.
Other animals, such as the sea star, develop into one or
• A larva is an ___________________________ individual that
looks different from the adult animal.
• A larva undergoes a major change in body form, called
____________________________ , and becomes a
reproductively mature adult.
In vertebrates and insects metamorphosis is regulated
by hormones – __________________________
© 2012 Pearson Education, Inc. Figure 18.3A Animals can be characterized by basic features of their “body plan”
• Animals that have ____________________have a top and bottom
but lack back and front or right and left sides. An imaginary slice
through the central axis divides them into mirror images.
• Animals with ________________________________have mirror-
image right and left sides and a
– distinct head, or anterior end,
– tail, orposterior end,
– back, or dorsal, surface, and
– bottom, or ventral, surface.
© 2012 Pearson Education, Inc. Animals can be characterized by basic features of
their “body plan”
Animals with three embryonic layers may have a
______________________________, a fluid-filled space
between the digestive tract and outer body wall that
• cushions internal organs and that
• enables them to grow and move independently of the body
• In soft-bodied animals, fluid in the body cavity forms a
• A _____________________________is completely lined by
tissues derived from mesoderm.
• A _____________________________is a body cavity that is
not completely lined by tissues derived from mesoderm.
© 2012 Pearson Education, Inc. Animals with and without
• ________________: no
Coelom lined by
mesoderm only on the
body wall, not around