The Evolution of Animal
Diversity
Dr. Stephen J. Salek
Biology 130
Fayetteville State University
Create your own animal?
• Start with a basic plant. Make the plant into a
simple animal such as a worm. Consider:
• Body form, cell types, feeding, reproduction,
movement, lifespan, size, growth, development
What is an animal?
• Multicellular, ingestive heterotrophs
without cell walls
• Many have flagella and cilia
• Have unique intercellular junctions
• Digestion in an internal space or tract
• Dominant diploid phase
• Unique embryonic phases sometimes
including larva
Animal Phyla
Phyla
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Porifora
Cnidaria
Platyhelminthes
Nematoda
Annelida
Arthropoda
Mollusca
Echinodermata
Chordata
Example
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Sponges
Jellyfish
Flatworms
Roundworms
Segmented worms
Crabs, insects
Snails, squid, clams
Starfish, sand dollars
Mammals, birds etc.
Some animals alternate
generations
• Diploid adult is
dominant
• Sperm or eggs
produced by
meiosis
Campbell 18.1
Development and Evolution
Campbell 18.2
• Animals go through stages of development
• Zygote - blastula - gastrula- larvae
Animals
• Digest food inside multicellular
bodies
• Composed of diploid cells except
gametes
Animals evolved from
Choanoflagellate Ancestors
Campbell Fig. 18.3 D
• nucleic acids match
• large colonies of
choanoflagellates, turned
outside-in, would
resemble sponges
small choanoflagellate colony
Porifera
Sponges, the
Simplest
Animal
Design
Choanocyte of a Sponge
Campbell 18.3C
• Sponges are simple
multicellular
animals
• Have porous bodies
• Filter feed using
chonaocytes and
phagocytosis
Main Cell Types
Campbell 18.3C
• Choanocytescreate water flow
and trap food
• Amoebocytes- pick
up food, digest it,
carry it to other
cells
Sponges exhibit radial
symmetry
• Radial symmetry– Mirror images
around a central
axis
– Campbell 18.3B
Other Sponge Body Forms
Spicules
• mineral needles
• may be calcium carbonate
or silica (glass)
• for skeletal support and
defense
Phylum Cnidaria
Radially symmetrical animals
that sting
Cnidarians
Major Characteristics
• Radial symmetry
• Have two body types and a larval form
– Polyp, medusa, and planula body forms
• Two tissue layers
– epidermis and gastrodermis,
• Incomplete gut - “gastrovascular cavity”
• Cnidocytes - stinging cells
Two Types of Bodies
Campbell Fig. 18.4 A-C
polyp
(attached, mouth-up)
medusa
(free-drifting, mouth-down)
Tissue layers and
gastrovascular cavity
food in
gastrovascular
cavity
epidermis
gastrodermis
cnidocytes
Cnidocyte
Campbell Fig. 18.4 D
nucleus
cnidocil or
trigger
Pop Quiz
• List 3 distinguishing characteristics
of the following two animal phya
• A) Porifera
• B) Cnidaria
Phylum Platyhelminthes
Flatworms - the Simplest
Bilateral Animals
Bilateral Body Design
• cephalized
– sensory organs concentrated in head
• body directions:
Simplest Bilateral Animals
• Move through
environment headfirst
not drifting like radial
symmetric animals
• Gastrovascular cavity
• Free living, parasitic
flukes, tapeworms
Campbell 18.6A
adults
(unusual because diecious)
eggs
cercaria
Schistosome
Fluke Life
Cycle
Campbell Fig. 18.6B
miracidium
sporocyst
reproduces asexually
Tapeworm Adult Anatomy
compare Campbell 18.6
Scolex -anchors worm,
buds asexually
Gravid Proglottids break off and
release eggs
testes
uterus
gonopore
ovaries
Proglottid reproduces sexually
acoelomate
pseudocoelomate
(muscles, not
peritoneum)
eucoelomate
peritoneum
Eucoelomate
Body Design
compare Campbell
Fig. 18.7C
ectoderm
mesoderm
endoderm
Coelom: fluid-filled cavity
between gut and body wall
that is lined with mesodermal
cells (peritoneum).
Most animals have a body cavity
• Solid, no body cavity
except for gastro
vascular cavity
flatworms, cnidaria
• Pseudocoelomateinternal space in
contact with digestive
tract, roundworms
• True coelom - internal
space lined by tissue all other animals