INTRODUCTION TO
ANIMAL DIVERSITY
Chapter 32
Our Kingdom
We are Animals
Animals Are




Species-rich
Morphologically diverse lineage of multicellular organisms on the
tree of life
Distinguished by two traits


they eat
they move
The largest and most abundant predators, herbivores, and
detritivores
Animals Are


Multicellular, heterotrophic eukaryotes
Heterotrophs





Animal cells lack cell walls
Distinguished by two tissues


ingest food
find food by tunneling, swimming, filtering, crawling, creeping, slithering,
walking, running, or flying.
Dominant consumers in both aquatic and terrestrial habitats
Nervous tissue and muscle tissue
Most animals reproduce sexually with the diploid stage usually
dominating the life cycle
Methods in the Study of Animals



Analyzing Comparative Morphology
 The Evolution of Tissues
 Symmetry and Cephalization
 Evolution of a Body Cavity
 The Protostome and Deuterostome Patterns of
Development
 The Tube-within-a-Tube Design
 A Phylogeny of Animals Based on Morphology
Using the Fossil Record
Evaluating Molecular Phylogenies
Themes in the Diversification of Animals

Suspension (Filter) Feeding
Deposit Feeding
 Herbivory
 Predation
 Parasitism
 FeedingMovement
 Types of Limbs: Unjointed and Jointed
 Are All Animal Appendages Homologous?
 Reproduction and Life Cycles

Key Lineages of Animals


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Choanoflagellates (Collar Flagellates)
Porifera (Sponges)
Cnidaria (Jellyfish, Corals, Anemones, Hydroids, Sea
Fans)
Ctenophora (Comb Jellies)
Acoelomorpha
Monophyletic and Very
Diverse
The animals are a monophyletic group
Animals are very diverse


34 major animal phyla are recognized
Analyzing Comparative
Morphology
Most morphological diversity in animals is
based on


differences in mouths and limbs
Basic Architecture
Four features define an animal's body
plan

1.
2.
3.
4.
the number of tissue types in embryos
the type of body symmetry
the presence or absence of a fluid-filled
cavity
the way in which the earliest events of
embryo development proceed
The Evolution of Tissues

All animals other than sponges have tissues
tightly
cells.

integrated structural and functional units of
Diploblasts
embryos



have two types of tissues or germ layers
Ectoderm
Endoderm
Triploblasts
embryos
have three types of tissues
Ectoderm
 Endoderm
 Mesoderm
germ layers develop into distinct adult tissues

Symmetry and Cephalization
A basic feature of a multicellular body is the
presence or absence of a plane of symmetry

radial
at
symmetry
least two planes of symmetry.
bilateral
a

symmetry
single plane of symmetry
face their environment in one direction.
Cephalization

Bilateral symmetry allowed
Evolution of a head, or anterior region, where
structures for feeding, sensing the environment, and
processing information are concentrated

Evolution of a Body Cavity
Animals may or may not have an internal,
fluid-filled body cavity

coelom
forms
from within the mesoderm
 lined with cells from the mesoderm
Advantages of a Coelom



Creates a medium for circulation
Makes space for internal organs
A hydrostatic skeleton
fluid-filled chamber
 allows movement


even without fins or limbs.
The Protostome and Deuterostome
Patterns of Development

Coelomates are bilaterally symmetric



except echinoderms
three embryonic tissue layers
Bilatera

protostomes


arthropods, mollusks, and segmented worms
deuterostomes

vertebrates and echinoderms
Differences in Early Development
Three events in early development differ in
protostomes and deuterostomes

Cleavage
Gastrulation

coelom formation
Cleavage

Rapid series of mitotic divisions

Spiral cleavage
mitotic spindles of dividing cells orient at
an angle to the main axis of the cells
 resulting in a helical arrangement


Radial cleavage
mitotic spindles of dividing cells orient
parallel or perpendicular to the main axis of
the cells
resulting in a pattern of cells stacked
directly on top of each other

The Tube-within-a-Tube Design
The basic animal body plan is a
tube-within-a-tube design in which
the outer tube forms the body wall
and the inner tube forms the gut

Ancestor?

The animal kingdom all developed from a common
ancestor ( monophyletic) probable during the
Precambrian era.



Probably a colonial choanoflagelate that lived
about700 million years ago. Modern choanoflagellates
are tiny, have a stalk and live in ponds and lakes)
A hypothesis of animal origin from flagellated
protists says that the colony of cells in the protist
evolved into a sphere and then differenciated and
especialized creating two layers of cells.
The common ancestor of living animals


May have lived 1.2 billion–800 million years ago
May have resembled modern choanoflagellates,
protists that are the closest living relatives of
animals
Single cell
Stalk
Figure 32.3
closest living relatives of animals

a colonial, flagellated protist
Digestive
cavity
Somatic cells
Reproductive cells
Colonial protist,
an aggregate of
identical cells
Figure 32.4
Hollow sphere of
unspecialized
cells (shown in
cross section)
Beginning of cell
specialization
Infolding
Gastrula-like
“protoanimal”
A Phylogeny of Animals Based on
Morphology
The phylogenetic tree indicates
that a group of protists called the
choanoflagellates are the closest
living relatives of animals and that
the Porifera (sponges) are the most
ancient animal phylum.

Phylogeny Based
on Morphology
Radially symmetric phyla are placed
on the tree next because their
tubelike body plans are relatively
simple. Among the bilaterally
symmetric phyla, the acoelomates
and pseudocoelomates appeared
first, followed by the coelomates.

Two major events occurred after
the coelomates split into the
protostomes and deuterostomes

radial
symmetry evolved
 segmentation evolved independently in
both lineages of coelomates.
Using the Fossil
Record
Most major groups of animals appear in
the fossil record starting about 580 million
years ago

The
fossil record is generally consistent
with the morphological phylogeny.
Neoproterozoic Era (1 Billion–524 Million
Years Ago)

Early members of the animal fossil record are known as the
Ediacaran fauna( first fossils of animals about 575 mya). Simple
radial forms and segmented bodies with legs.
Figure 32.5a, b
(a)
(b)
Paleozoic Era (542–251 Million Years Ago)

The Cambrian explosion marks the earliest fossil
appearance of many major groups of living animals
 Is described by several current hypotheses such
as predator- prey relationships, oxygen increase
and evolution of the hox genes
Figure 32.6
Mesozoic Era (251–65.5 Million Years Ago)

During the Mesozoic era



Dinosaurs were the dominant terrestrial
vertebrates
Coral reefs emerged, becoming important marine
ecological niches for other organisms
The first mammals appeared (tiny, nocturnal insect
eaters
Cenozoic Era (65.5 Million Years Ago to the
Present)

The beginning of this era


Followed mass extinctions of both terrestrial and
marine animals
Modern mammal orders and insects
diversified during the Cenozoic
 Also flowering plants appeared
Points of Agreement

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All animals share a common ancestor
Sponges are basal animals (branch from the base
of tree, no tissues)
Eumetazoa is a clade of animals with true tissues
Most animal phyla belong to the clade Bilateria
Vertebrates belong to the clade Deuterostomia
Disagreement over the Bilaterians

The morphology-based tree


Divides the bilaterians into two clades:
deuterostomes and protostomes
In contrast, recent molecular studies

assign two sister taxa to the protostomes rather
than one: the ecdysozoans and the
lophotrochozoans
Important Observations Emerge
From the Data
1.
2.
3.
4.
The most ancient triploblasts lacked a
coelom;
The major event in the evolution of the
Bilateria was the split between
protostomes and deuterostomes
Segmentation evolved independently in
the annelids and the arthropods; and
Pseudocoeloms arose from coeloms twice
in evolutionary history
Phylogenetic trees are best described as
1.
2.
3.
4.
5.
true and inerrant statements about evolutionary
relationships.
hypothetical portrayals of evolutionary relationships.
the most accurate possible representations of genetic
relationships among taxa.
theories of evolution.
the closest things to absolute certainty that modern
systematists can produce.
Themes in the Diversification of
Animals

Within the phylum
basic
features of the body plan do not vary from
species to species

Diversity arose
mostly
because of the evolution of innovative
methods for feeding and moving
Feeding

The feeding tactics observed in animals
can be broken into five general types:
1.
2.
3.
4.
5.
suspension feeding
deposit feeding
herbivory
predation
Parasitism
Many animals undergo a metamorphosis



a change in form during development
allows juveniles and adults to exploit
different sources of food
Suspension (Filter)
Feeding
Suspension feeders, or filter
feeders, capture food by filtering
out particles suspended in water or
air
This method is found in a wide
variety of animal groups and has
evolved many times independently

Deposit Feeding
Deposit feeders eat their way through a
substrate
 Food

soil-dwelling bacteria, protists, fungi, and archaea
 detritus—the dead and partially decomposed
remains of organisms


Depending on food
herbivores
(plant eaters), parasites, detritivores
(detritus eaters), or predators
Herbivory

Herbivores
animals
that digest algae or plant tissues
complex mouths with structures that make biting
and chewing or sucking possible
Predation
Sit-and-wait predators rarely move at all until
prey is captured
 stalkers pursue their prey

Parasitism
Parasites are much smaller than their victims
and often harvest nutrients without causing
death
 Endoparasites

live
inside their hosts
often wormlike in shape
can be extremely simple morphologically
Ectoparasites
live
outside their hosts
usually have grasping mouthparts
pierce the host’s exterior and suck the nutrient-rich
fluids inside
Movement
Many animals are sit-and-wait
predators, and some are sessile
throughout their adult lives. But the
vast majority of animals move under
their own power either as juveniles
or as adults.

Function of Movement

three functions in adult animals:
1.
2.
3.
Finding food
finding mates
escaping from predators.
Limbs

A major innovation in animals
made

highly controlled, rapid movement possible
Two types

Unjointed

saclike
Jointed
move when muscles that are attached to a skeleton
contract or relax

Homologous vs Non-Homologous
Biologists have argued that at least a few of
the same genes are involved in the development
of all appendages observed in animals
 Hypothesis is that all animal appendages have
some degree of genetic homology
that they are all derived from appendages
that were present in a common ancestor.
This hypothesis is controversial, however, and
research continues

Reproduction and Life Cycles
At least some species in most animal phyla can
reproduce asexually (via mitosis), as well as
sexually (via meiosis).

Sexual
reproduction can occur with internal or
external fertilization
Development
Eggs or embryos may be retained in the
female’s body during development


viviparous
May

be laid outside the body
oviparous
Female retains eggs inside her body during early
development

embryos are nourished by yolk inside the egg and not
by nutrients transferred directly from the mother
 ovoviviparous


Vast majority of animals are oviparous
Development

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

Early embryonic development in animals
.
2 Only one cleavage
1 The zygote of an animal
stage–the
eight-cell
undergoes a succession of mitotic
embryo–is
shown here.
cell divisions called cleavage.
3 In most animals, cleavage results in the
formation of a multicellular stage called a blastula.
The blastula of many animals is a hollow ball of cells.
Blastocoel
Cleavage
Cleavage
6 The endoderm of
the archenteron develops into the tissue
lining the animal’s
digestive tract.
Zygote
Eight-cell stage
Blastula
Cross section
of blastula
Blastocoel
Endoderm
5 The blind pouch
formed by gastrulation, called
the archenteron,
opens to the outside
via the blastopore.
Ectoderm
Gastrula
Blastopore
Figure 32.2
Gastrulation
4 Most animals also undergo gastrulation, a rearrangement of
the embryo in which one end of the embryo folds inward, expands,
and eventually fills the blastocoel, producing layers of embryonic
tissues: the ectoderm (outer layer) and the endoderm (inner layer).
Metamorphosis


The change from juvenile to adult body type
Larva
juvenile individual
 looks substantially different from the adult


Nymph
juvenile individual
 looks like a miniature adult

Pupation
When a larva has grown sufficiently, it
secretes a protective case and is now
known as a pupa

Into an Adult
During pupation, the pupa’s body is
completely remodeled into a new, adult form

Holometabolous

Complete metamorphosis
two-step process
from larva to pupa to adult
involving dramatic changes in
morphology and habitat use

Hemimetabolou

Incomplete metamorphosis
One-step process of sexual
maturation.

Limited
morphological difference
between juvenile and adult
Marine Animals
Complete metamorphosis
 extremely common in marine animals
most cnidarians have two distinct body types
during their life cycle

a
largely sessile form called a polyp
alternates with a free-floating stage called a medusa