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Chapter 11: Animal Diversification
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Learning Objectives

Define an animal and the key evolutionary branchpoints that divide the phyla.

Describe the major events in animal evolution, including
early human lifestyles and human evolution.

Define and describe the invertebrates, including
echinoderms, arthropods, molluscs, annelids,
flatworms, cnidarians, and sponges.

Define and describe the vertebrates, including
terrestrial vertebrates: amphibians, reptiles, birds, and
mammals.
11.1 What is an animal?
Three Key Characteristics
Animals are Heterotrophs.
Direct vs. Indirect Development
• When lots of nourishing yolk is present, embryos develop into a
miniature adult.
– Direct development
• When little yolk is present, young develop into larval stages that can
feed.
– Indirect development
• Mammals have little yolk, but nourish the embryo via the placenta.
11.2 Four key distinctions divide the
animals.
 Four
key distinctions divide the animals:
1) tissue or not
2) radial or bilateral symmetry
3) protostome or deuterostome development
4) growth through molting or not
1) Does the animal have defined
tissues, with specialized cells?
2) Does the animal develop with radial
symmetry or bilateral symmetry?
A body structured like a pie
or
A body with a left and right side,
which are mirror images
3) During development, does the animal’s
gut develop from front to back or back to
front?
Protostomes (first mouth)
Deuterostomes (second mouth)
4) Does growth occur by molting or by
adding continuously to the skeletal
elements?
A branch within the Protostome
group…
Arthropods and Roundworms grow
through molting – shedding the
exoskeleton and replacing it with a larger
one.
Let’s follow the history of animal evolution from
the simplest animals to the most complex…
Look for key evolutionary innovations...
Recall the major phyla of the Animal
Kingdom...
Invertebrates are the largest and most
diverse group of animals.
Invertebrates comprise 96% of all the living
species of animals.
11.20
Sponges
(Phylum
Porifera) are
animals that
lack tissues
and organs.
A sponge
consists of a
hollow tube with
pores in its wall, it
has no tissues or
organs, and only
three kinds of
cells.
Sponges
reproduce
sexually, but
asexual
reproduction is
common through
budding.
Sponges reproduce asexually (by budding) and sexually by
producing eggs and sperm. (sponges_reproduction)
11.19
Jellyfish and
other
cnidarians
are among
the most
poisonous
animals in the
world.
Coral Cnidarians exist in a mutual symbiosis
with their algal partners.
How is global warming affecting the
coral reefs of the world?
https://www.youtube.com/watch?v=_Zf
GIKiSwwQ
you tube
Cnidarians
 Two
types of cnidarian bodies:
• a sessile polyp
• a free-floating medusa.

Reproduce both
sexually and
asexually
Although all cnidarians possess cnidocytes
(stinging cells), there is great diversity among the
three major groups.

Jellyfish - medusa

Sea anemones - polyp

Corals – polyp, generally has mutual symbiosis
with photosynthetic protists.
The Portuguese Man O War is a complex Cnidarian
predator. (Portuguese_Man_O War )
End
11.18
Segmented
worms
(Annelida),
flatworms
(Platyhelminthes), and
roundworms
(Nematoda),
come in all
shapes and
sizes.
The first
phylum to
exhibit
cephalization,
the
concentration
of neural
elements in a
head-like
region
Flatworms
• Phylum Platyhelminthes
– Is represented by the simplest bilateral animals
– Includes tapeworms, flukes, and free-living
forms such as planarians
(Planaria)
Roundworms
First
organisms to
have a
complete
digestive
tract (closed
from mouth
to anus), can
process food
more
efficiently
Roundworms
• Phylum Nematoda
– Includes the most diverse
and widespread of all
animals (~ 90,000 species)
– Occurs in aquatic and moist
terrestrial habitats
– First organisms to have a
complete digestive tract
(closed from mouth to
anus), can process food
more efficiently
Annelids: Polychaetes
 Marine
worms
 “Many
bristles”
 Some
are burrowing
 Some
are tube dwelling
Annelids: Earthworms
 “Few
 Bulk
bristles”
feeders
• consume particles of soil and organic material
 Castings
are valued by gardeners
Annelids: Leeches

The saliva of bloodsucking leeches contains
an anticoagulant
substance that prevents
blood from clotting.

Not all leeches are blood
suckers.
• More than half the species
of leeches are predators.
Summary: Worms
Worms fall into 3 different phyla:
Platyhelminthes, Nematoda, and Annelida
 All are bilaterally symmetrical protostomes
with defined tissue.
 The segmented worms (Annelida) and
flatworms (Platyhelminthes) do not molt,
whereas the roundworms (Nematoda) do.
 Earthworms play an important role in
recycling dead plant material.
 Roundworms and Flatworms are often
parasites of plants or animals.

11.16
Most
molluscs
live in
shells.
Example of Predator-Prey
(nudibranch_man_of_war)
The Three Major Groups of Molluscs
1) Gastropods – “stomach foot”
•
i.e. Snails, slugs
2) Bivalve molluscs – bi = two (two shells)
•
i.e. Clams, oysters
3) Cephalopods – “head foot”
•
•
i.e. octopus, squid
Cephalization – larger brain, more active
predators, remarkable camouflage ability
Gastropods
 Snails
and slugs are called gastropod
molluscs.
 Found
in both aquatic and terrestrial
environments, snails and slugs account for
three-quarters of all molluscs.
 Recall
the sea slug that was a predator of
the Portuguese Man O War.
Bivalve Molluscs
 Clams,
scallops, oysters, and mussels
have a pair of shells that clamp together.
 Roughly 8000 species of bivalve—most of
them live in the ocean.
 Filter
feeders.
Cephalopods
Cephalization: the concentration of
neural elements in a head-like region.
Octopi are very intelligent, and have
shown remarkable learning abilities.
Summary: Molluscs
 Molluscs
are protostome invertebrates that
do not molt.
 Including the snails and slugs, clams and
oysters, and squid and octopuses, the
molluscs are the second most diverse
phylum of animals.
 Most feature a shell for protection, a
muscular foot, and a specialized tongue
called a radula.
11.14 An
external
skeleton and
metamorphosis
produced the
greatest
adaptive
radiation ever.
In incomplete
metamorphosis,
the nymph stage
replaces the
larva and pupa
stages. The
nymph
resembles the
adult, and the
metamorphosis
is less dramatic.
Arthropoda Overview
The arthropods are protostome invertebrates,
including insects.
 The life cycle of most insects includes a larval
stage, which is devoted to feeding and growth,
and an adult stage, in which the insect
reproduces.
 This separation of life stages has contributed to
the enormous ecological diversity of insects.
 It has also produced remarkable specializations
among the nearly 1 million species of insects
that have been named.

Honey bees have evolved a very sophisticated defense!
(bee_hive_defence)
Insects generally have a three-part body
Insects outnumber all
other animals combined.
Figure 17.25
11.15. Other arthropods include arachnids,
crustaceans, millipedes, and centipedes.
Dragonfly nymphs look more like the adult than butterfly larvae.
(dragonfly_larvae)
Caterpillar – ant mutualism (Different insects and life stages)
(ant_caterpillar_mutualism)
Arachnids
 Land-dwelling
arthropods
 Include
spiders, scorpions, mites, and ticks
 Usually
have four pairs of walking legs
• and a specialized feeding apparatus
 Only
have legs on the thorax
Venom/Poison
 Arachnids
are predators
 Black
widow spider
 Brown recluse spider
 Being
stung by most scorpions is no worse
than being stung by a bee
 Nocturnal
predators of insects
The Crustaceans
• Lobsters, crayfish, crabs, and shrimps
• All have five pairs of appendages extending
from their heads
• Many pairs of legs modified for many
purposes
• Most are aquatic
Millipedes and Centipedes
• Long segmented bodies
• “A thousand feet” (2 pairs of legs per body segment) and
“a hundred feet” (1 pair of legs per body segment).
• Millipedes feed on decaying plant material
• Centipedes are predators—use venomous fangs to kill
insects and even small mammals
End
11.13 Echinoderms are vertebrates'
invertebrate relatives
Sea stars, sea
urchins, and
sand dollars
Both
Echinoderms
and Chordates
use an
endoskeleton
for support and
movement.
Echinoderms
Radial symmetry in adults – some resemble
sponges
 Bilateral symmetry in larvae
 An evolutionary specialization – tube feet
associated with their locomotor mode and
feeding specializations
 Echinoderms are deuterostomes like chordates
and possess and endoskeleton, but they lack
backbones.
 Echinoderms and chordates are each other’s
closest relatives.

11.4 All vertebrates are members of
the phylum Chordata.
Four distinct
features of
chordates:
Gill slits
These traits are
always present in
the chordate
embryo.
The Notochord

A rod of tissue extending from the head to the
tail

Stiffens the body when muscles contract
during locomotion

In advanced chordates
• Present only in early embryos
• Develops into the vertebral column (backbone)
A Dorsal Hollow Nerve Cord
from head to tail – dorsal to the
notochord
 Extends
 In
vertebrates, develops into the central
nervous system (spinal cord and brain)
 In
other animals, lies in lower portion of
ventral part of body (and is solid instead of
hollow)
Pharyngeal Gill Slits
 Pharyngeal
region
• the area between the back of the mouth and
the top of the throat
 Pharyngeal
slits are present in the
embryos of all chordates.
• Originally used for breathing and feeding
vertebrates – develops into parts of the
face (jaw and inner ear)
 In
A Post-Anal Tail
 extends
back beyond the end of the trunk
The
lancelet
retains
all 4
features
as an
adult.
Phylum Chordata contains three sub-phyla:
Lancelets and tunicates do not have a
backbone, but they have all 4 chordate
features.
An overview
of chordate
phylogeny
by
evolutionary
innovations
The Hagfish is a type of Jawless Fish. (hagfish)
The evolution of fins paralleled the evolution of
jaws because the two structures work together.
Ray-finned and Lobe-finned
are sometimes grouped
together – Bony fish
• Bony fish
– Have a skeleton
reinforced by
hard calcium
salts
– Have a lateral
line system, a
keen sense of
smell, the swim
bladder, and
The operculum covers a chamber
excellent
housing the gills.
eyesight
Some Bony Fish also evolved parental care.
(cichilid_mouth_brooding)
Catfish walking using lobed fins…
11.6 The movement onto land required lungs, a
rigid backbone, four legs, and eggs that resist
drying.
11.7 Amphibians live a double life.
The Desert Frog has adapted to very dry conditions.
(desert_frog)
• Reptiles
– Include snakes, lizards, turtles, crocodiles, and
alligators (alive today)
– Evolved to be more independent of water
• Adaptations for living on land include:
– Scales to prevent dehydration (keratin)
– More well-developed lungs
– The amniotic egg (a water containing egg
with a tough shell).
Frilled Lizard uses a bluffing defense. (frilled_lizard)
The Horned Lizard uses poison.
(horned_lizard_and_coyote)
Flying Lizard can glide to escape predators.
(flying_lizard)
11.8 Birds are reptiles in which
feathers evolved.
All amniotic vertebrates use keratin for
water-proofing. Analogous or Homologous
structure?
11.9 Mammals
are animals that
have hair and
produce milk.
Placental mammals have a
placenta that provides oxygen and
nutrients to embryos.
Marsupial babies are tiny and vulnerable
when they are born – shorter gestation
period.
END
Sea cucumber’s movement facilitates feeding
(sea_cucumber_feeding)
Fungus gnat larvae spin silk to capture prey.
(fungus_gnat_larvae)
11.3 Everything that is not extinct is
evolutionarily successful.
• Which species evolve quickly enough to
survive changing environmental pressures?
One hypothesis
emphasizes
increasingly
complex
predator-prey
relationships.
Another focuses
on the evolution
of genes that
control
development.
Widespread Diversification during the Cambrian Period…
• Most animals
reproduce
sexually. Human
reproduction is an
example of direct
development.
• Indirect
development:
proceed through
a series of unique
developmental
stages
2
1
3
7
4
6
5
Body cavity (coelom)
– A body cavity is a fluidfilled space separating
the digestive tract from
the outer body wall
– May be a pseudocoelom
or a true coelom