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Introduction to the
Animal Kingdom
Introduction to the Animal Kingdom
• Animals are multicellular eukaryotic heterotroph
whose cells lack cell walls, digestion is internal
• Vertebrates: 5% of animal species with
backbones
• Invertebrates: 95% of animal species WITHOUT
backbones
• Cell specialization – special shape, physical
structure, and chemical composition to perform a
special function in a multicellular organism
(Division of Labor)
Early Development
• Zygote (fertilized egg) undergoes divisions to
form blastula, or a hollow ball of cells
• Blastula flattens on one side and folds into itself
forming a single opening called a blastopore
• Blastopore leads into center tube running the
length of the developing embryo. This tube
becomes the digestive track
– Protostome – mouth formed first from blastopore
(most invertebrates)
– Deuterostome – anus formed first from blastopore
(echinoderms and all vertebrates)
Early Development
(continued)
• Cells then differentiate into three layers,
called germ layers
– Endoderm – innermost germ layer – forms
linings of digestive track and respiratory
system
– Mesoderm – middle germ layer – forms
muscles, circulatory, reproductive, and
excretory systems
– Ectoderm – outermost germ layer – forms
sense organs, nerves, and outer layer of skin
Early Development
(continued)
In Order to Survive, Animals Must:
• Feed –
– Carnivores – eat other animals
– Herbivores – eat plants
– Omnivores – eat other animals and plants
– Parasites – inside or on other organisms and
do them harm
– Filter feeders – strain food from water
– Detritus feeders – feed on dead organic
matter
In Order to Survive, Animals Must:
• Respire –
– Consume oxygen and give off CO2
– Skin, gills, lungs
In Order to Survive, Animals Must:
• Circulate/Internal Transport –
– Must carry O2, nutrients and waste products
to and from internal cells
– Heart and blood vessels in larger animals
– Smaller animals rely on diffusion
In Order to Survive, Animals Must:
• Excrete –
– Small animals – diffusion
– Larger animals – excretory systems (that can
include complex kidneys)
In Order to Survive, Animals Must:
• Respond –
– Nerve cells – brain
– Gather information from environment
– Varies greatly from phylum to phylum
In Order to Survive, Animals Must:
• Move –
– Sessile – one spot, no movement
– Motile – move, muscles and/or skeletons
In Order to Survive, Animals Must:
• Reproduce –
– Mainly sexual, but invertebrates can also
reproduce asexually
– Live birth or eggs
– Direct Metamorphosis – young look like adult
– Indirect Metamorphosis – young →
metamorphosis → adult
Direct Metamorphosis
– Direct – young look like adult
Indirect Metamorphosis
• Indirect – young → metamorphosis → adult
Early Animals and the Cambrian
Explosion
– Scientists hypothesize that animals evolved
from a colonial flagellated protist.
– The oldest animal fossils found are 550–575
million years old.
– The molecular data suggest a much earlier
origin for animals.
Early Animals and the Cambrian
Explosion
– Animal diversification appears to have
accelerated rapidly from 525-535 million years
ago, during the Cambrian period.
– Because so many animal body plans and new
phyla appear in the fossils from such an
evolutionarily short time span, biologists call this
episode the Cambrian explosion.
Early Animals and the Cambrian
Explosion
– The Cambrian explosion may have been ignited
by
• increasingly complex predator-prey relationships
and/or
• an increase in atmospheric oxygen.
– The genetic framework for complex bodies, a
set of “master control” genes, was already in
place.
Animal Evolution
• 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.
Cell Specialization
• Cell → tissue → organ → organ system →
organism
– Ex. Stomach cell → stomach tissue →
digestive system (mouth, stomach, intestines,
etc) → all organ systems put together
Body Symmetry
• Asymmetrical – no symmetry (sponges)
• Radial symmetry – body parts repeat around
center of body (simple animals – sea anemone
and starfish)
• Bilateral symmetry – body can be divided into
two equal halves – left and right sides
–
–
–
–
Anterior – front end
Posterior – back end
Dorsal – upper side
Ventral – lower side
Body Symmetry
Bilateral Symmetry
Radial Symmetry
Posterior end
Dorsal side
Anterior end
Plane of
symmetry
Planes of
symmetry
Body Cavity
– Animals also vary according to the presence
and type of body cavity, a fluid-filled space
separating the digestive tract from the outer
body wall.
– There are differences in how the body cavity
develops.
• If the body cavity is not completely lined by tissue
derived from mesoderm, it is called a
pseudocoelom.
• A true coelom is completely lined by tissue derived
from mesoderm.
Body
covering
Body Cavity
Tissue-filled
region
Digestive tract
(a) No body cavity
Body covering
Muscle
layer
Coelom
Body
covering
Pseudocoelom
Digestive tract
(b) Pseudocoelom
Digestive tract Tissue layer lining
coelom and
suspending
internal organs
(c) True coelom
Cephalization
• Complex animals concentrate sense
organs and nerve cells in the anterior end
of the body, this is called cephalization
– Ganglia – small clusters of nerve cells (simple
animals)
– Brain – clusters of ganglia (more complex
animals)
Introduction to Invertebrates