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UNIT 8
Chapter 32: Introduction to Animal Evolution
Chapter 33: Invertebrates
Chapter 34: Vertebrate Evolution & Diversity
Features of Animals
Organisms that belong in Kingdom Animalia must satisfy
five requirements.
1. Animals are multicellular, eukaryotic and
heterotrophic
- Animals ingest preformed organic materials
2. Animal cells lack cell walls
- Multicellular bodies held together by
extracellular proteins, especially collagen
3. Animals have two unique tissue types: nervous
and muscle
- Nervous tissue involved with impulse (action
potential) conduction
- Muscle tissue for movement
4. Most animals reproduce sexually and the
diploid stage is dominant
- In most species, a flagellated sperm
fertilizes an egg
- Cleavage commences: succession of mitotic
divisions leading to the creation of a morula
then ultimately a blastula
- Gastrulation creates the gastrula: a blind
pouch with an opening called a blastopore
- Some animals possess larval stage and
undergo metamorphosis to become adult
5. Development from zygote to animal depends on
Hox genes (regulatory)
- Hox genes regulate the expression of other
genes
- Ultimately involved with the fate of cells
- Body form (anatomy)
Important Milestones in Animal Evolution
1. Tissues
- Parazoans lack true tissues
- Sponges are only extant parazoans
2. Symmetry
- Some animals possess radial symmetry,
while others are bilateral
- Most bilateral
animals are
cephalized:
sensory organs
at/in a head region
- the radiata are diploblastic (two germ
layers)
- ectoderm & endoderm
- the bilateria are triploblastic (three
germ layers)
- ectoderm, endoderm & mesoderm
3. Body Cavities
- Acoelomates have no
body cavity
- Mesoderm isn’t
lining digestive tract
in pseudocoelomates
- Coelomates have a
body cavity and a
digestive tract lined
by the mesoderm
- a coelom has numerous functions:
- fluid cushions internal organs
- organs can move/grow independent
of the body covering
- can serve as a hydrostatic skeleton
4. Protostomes vs. Deuterostomes
Table 32.1
END
Within this phylum, there animals lacking backbones
and animals possessing them. In either case, ALL
chordates have four features.
1. Notochord
2. Dorsal, hollow nerve cord
3. Pharyngeal gill slits
4. Post-anal tail
In order to be a “member” of Phylum Chordata, you
must have exhibited each of these characteristics at
some point in your development.
Notochord: flexible rod that runs longitudinally
through the animal
comprised of fluid-filled cells, encased in
fibrous tissue
provides skeletal support
in some, notochord is reduced in adult
ex. It’s the “disc” material in human
vertebrae
Dorsal, hollow nerve cord: nervous tissue that
develops from the embryonic ectoderm.
most non-chordates have a solid, ventrally
located, nerve cord
becomes the CNS in vertebrates
Pharyngeal gill slits: connect the animal’s pharynx to
the outside.
allows water to enter the animal’s mouth and
exit without entering the digestive system
used/modified in various ways: feeding,
respiration
Post-anal tail: muscular in most chordates and
extends past the anus
compare to non-chordates that have a full bodylength digestive system
contains skeletal and muscular elements
used for propulsion in many aquatic species
• Invertebrate chordates
Class Amphibia
• Undergo a metamorphosis from a swimming larval
tadpole stage to a terrestrial adult.
Even though adult amphibians are terrestrial, they
cannot venture far from water.
respiration
eggs would desiccate
• Amphibians usually similar anatomy to other
vertebrate chordates
• Huge difference is that their heart is threechambered (one ventricle, two atria)
Class Reptilia
• Success is due to the amniotic egg
• Extraembryonic
membranes provide
structures involved
with gas exchange,
waste storage, and
nutrient storage
• Desiccation is
prevented
• Reptiles are referred to as ectotherms
• Do not use metabolism to heat bodies
• Compare to endotherms
• Four-chambered heart first appears in some
reptiles
• TOTAL separation of oxygenated and
deoxygenated blood
• Scales rather than
skin
Class Aves
• Almost every aspect of a bird’s anatomy is adapted
for flight, including its feathers
• Feathers, made of
keratin, are very light
and strong
Class Mammalia
• Mammals are distinguished by
the presence of mammary
glands which produce milk to
nourish young
• MOST (almost all) have hair
made of keratin
• Most are born (not hatched)
and possess relatively large
brains making them capable of
learning
1. Monotremes – reptile-like egg, no nipples
(platypuses and echidnas)
2. Marsupials – born “early” and completes
development in the mother’s pouch
(kangaroos, koalas, etc.)
3. Eutherians – development “completed” in
placenta in mother
END