This document summarizes key characteristics of animals. It notes that animals are multicellular, heterotrophic eukaryotes whose cells lack cell walls. It describes two main modes of animal development - protostome and deuterostome. Protostome development involves spiral, determinate cleavage and schizocoelous coelom formation, resulting in the blastopore developing into the mouth. Deuterostome development involves radial, indeterminate cleavage and enterocoelous coelom formation, with the blastopore developing into the anus.

2.  Extends far beyond humans and other
animals we may encounter
Figure 32.1

3.  Animal are multicellular, heterotrophic
eukaryotes with tissues that develop from
embryonic layers
 Several characteristics of animals
◦ Sufficiently define the group

4. • Animals are heterotrophs
– That ingest their food

5. • Animals are multicellular eukaryotes
• Their cells lack cell walls

6. • Most animals reproduce sexually
– With the diploid stage usually dominating the
life cycle
• After a sperm fertilizes an egg
– The zygote undergoes cleavage, leading to
the formation of a blastula
• The blastula undergoes gastrulation
– Resulting in the formation of embryonic
tissue layers and a gastrula

7. Blastocoel
Cleavage Cleavage
Eight-cell stage Blastula Cross section
Zygote of blastula
Blastocoel
Endoderm
Ectoderm
Gastrula Gastrulation
Blastopore

8. • Early members of the animal fossil record
– Include the Ediacaran fauna

9. • The Cambrian explosion
– Marks the earliest fossil
appearance of many major groups
of living animals
– Is described by several current
hypotheses

10. • During the Mesozoic era
– Dinosaurs were the dominant terrestrial
vertebrates
– Coral reefs emerged, becoming important
marine ecological niches for other organisms

11. • The beginning of this era
– Followed mass extinctions of both
terrestrial and marine animals
• Modern mammal orders and insects
– Diversified during the Cenozoic

12. • Animals can be categorized
– According to the symmetry of their bodies, or
lack of it
• Some animals have radial symmetry
– Like in a flower pot
Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum
Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the
animal into mirror images.

13.  Bilateral symmetry. A bilateral
animal, such as a lobster (phylum Arthropoda), has a left side and a
right side. Only one imaginary cut divides the animal into mirror-
image halves.

14. • Based on certain features seen in early
development
– Many animals can be categorized as having
one of two developmental modes:
protostome development or deuterostome
development

15.  In protostome development
◦ Cleavage is spiral and determinate
 In deuterostome development
◦ Cleavage is radial and indeterminate
Protostome development Deuterostome development
(examples: molluscs, annelids, (examples: echinoderms,
arthropods) chordates)
(a) Cleavage. In general, protostome
Eight-cell stage Eight-cell stage development begins with spiral,
determinate cleavage.
Deuterostome development is
characterized by radial,
indeterminate cleavage.
Spiral and determinate Radial and indeterminate

16.  In protostome development
◦ The splitting of the initially solid masses of
mesoderm to form the coelomic cavity is
called schizocoelous development
 In deuterostome development
◦ Formation of the body cavity is described as
enterocoelous development
Coelom (b) Coelom formation. Coelom
formation begins in the gastrula
stage. In protostome
Archenteron
development, the coelom forms
from splits in the mesoderm
Coelom (schizocoelous development). In
Mesoderm Blastopore Mesoderm deuterostome development, the
Blastopore
coelom forms from mesodermal
Schizocoelous: solid Enterocoelous: outpocketings of the archenteron
masses of mesoderm folds of archenteron (enterocoelous development).
split and form coelom form coelom
Figure 32.9b

17.  In protostome development
◦ The blastopore becomes the mouth
 In deuterostome development
◦ The blastopore becomes the anus
Anus Mouth
Digestive tube
Mouth Anus
Mouth develops Anus develops
Figure 32.9c from blastopore from blastopore