Transcript six key transitions in body plan

EVOLUTION OF THE
ANIMAL PHYLA
CHAPTER 19
GENERAL FEATURES OF ANIMALS
• Animals share many important
characteristics, such as they:
•
•
•
•
•
•
•
are heterotrophs
are multicellular and lack cell walls
can move from place to place
have diverse forms and habitats
reproduce, mostly by sexual reproduction
have a common pattern of development
have unique tissues
THE ANIMAL FAMILY TREE
• Animals consist of 35 very different phyla.
• To judge which phyla are more closely related,
taxonomists traditionally have compared
anatomical features and aspects of
embryological development.
• The end result are phylogenies, which are
basically like family trees.
THE ANIMAL FAMILY TREE
• The kingdom Animalia is traditionally divided
into two main branches based on tissue
presence.
• Parazoa possess neither tissues nor organs and
have no discernible symmetry.
• They are represented mostly by the phylum
Porifera, the sponges.
• Eumetazoa have a definite shape and symmetry
and, in most cases, tissues organized into organs
and organ systems.
• Although very different, the Parazoa and
Eumetazoa are thought to have evolved from a
common ancestor.
THE ANIMAL FAMILY TREE
• Eumetazoans are divided into two groups:
• Radiata have radial symmetry and two
embryological layers, an outer ectoderm and an
inner endoderm.
• This body plan is called diploblastic.
• Bilateria have bilateral symmetry and a third
embryological layer, the mesoderm, that occurs
between the ectoderm and the endoderm.
• This body plan is called triploblastic.
THE ANIMAL FAMILY TREE
• Traditionally, the Bilateria have been
subdivided based on traits that were
important to the evolutionary history of
phyla.
• For example, the presence or absence of a body
cavity.
• The traditional animal phylogeny relies on
the either-or nature of categories.
THE ANIMAL FAMILY TREE: THE
TRADITIONAL VIEWPOINT
No coelom Pseudocoel
No
tissues
Parazoa
Radial
symmetry
Radiata
Acoelomates
Pseudocoelomates
Protostomes
Coelom forms from
mesoderm cell mass
Mix of
characteristics
Coelom forms from
embryonic gut
Coelomates
Mix of
characteristics
Deuterostomes
Sponges Cnidarians Ctenophorans Flatworms Nematodes Mollusks Annelids Arthropods Lophophorates Echinoderms
Chordates
THE ANIMAL FAMILY TREE
• The traditional animal phylogeny is being
revised because some of the important
characters may not be conserved to the
extent previously thought.
• Molecular systematics offers a means to construct
phylogenic trees using unique gene sequences as
means to detect relatedness.
• New molecular data has resulted in a variety of
new phylogenies, most of which divide
protostomes into:
• Lophotrochozoans
• Ecdysozoans
THE ANIMAL FAMILY TREE: A NEW LOOK
Grow by increasing body mass,
locomotion is ciliary, trochophore larvae
No
tissues
Parazoa
Radial
symmetry
Radiata
Lophotrochozoa
Grow by molting
Coelom forms from
embryonic gut
Ecdysozoa
Protostomes
Sponges Cnidarians Ctenophorans Lophophorates Flatworms Mollusks
Annelids
Deuterostomes
Nematodes Arthropods
Echinoderms
Chordates
SIX KEY TRANSITIONS IN BODY
PLAN
•
The evolution of animals is marked by six
key transitions in body plan:
1.
2.
3.
4.
5.
6.
tissues
bilateral symmetry
body cavity
segmentation
molting
deuterostome development
SIX KEY TRANSITIONS IN BODY
PLAN
• The presence of tissues is the first key
transition in the animal body plan.
• Only the Parazoa, the sponges, lack defined
tissues and organs.
• These animals exist as aggregates of cells with
minimal intercellular coordination.
• All other animals, the Eumetazoa, possess tissues.
SIX KEY TRANSITIONS IN BODY
PLAN
• Virtually all animals other than sponges have
a definite shape and symmetry.
• Radial symmetry is a body plan in which all parts
of the body are arranged around a central axis.
• Any plane passing through the central axis
divides the organism in halves that are
approximate mirror images.
• Bilateral symmetry is a body plan with distinct
right and left halves that are mirror images.
• The plan allows for specialization among body
regions and more efficient movement.
SIX KEY TRANSITIONS IN BODY
PLAN
• The evolution of a body cavity was an
important step in animal evolution.
• This internal space allowed for the support of
organs, distribution of materials, and coordination
of development.
• For example, the digestive tract can be larger
and longer.
SIX KEY TRANSITIONS IN BODY
PLAN
• Bilateral animals can be divided into two
groups based on differences in the basic
pattern of development.
• Protostomes include the flatworms, nematodes,
mollusks, annelids, and arthropods.
• Deuterostomes include the echinoderms and the
chordates.
• Deuterostomes evolved from protostomes more
than 630 million years ago.
SIX KEY TRANSITIONS IN BODY
PLAN
• The subdivision of the body into segments is
another key transition in the animal body
plan.
• In highly segmented animals, each segment can
develop a more or less complete set of adult
organ systems.
• Each segment can function as a separate
locomotory unit.
Parazoa
Eumetazoa
Radiata
Bilateria
Coelomates
Pseudocoelomates
Deuterostomes
Protostomes
Echinodermata
Jointed appendages
exoskeleton, molting
Lophophorates
Segmented
Arthropoda
Annelida
Mollusca
Rotifera (rotifers)
Nematoda (roundworms)
Platyhelminthes (flatworms)
Porifera (sponges)
EVOLUTIONARY
TRENDS AMONG
THE ANIMALS
Radiata (Cnidaria and Ctenophora)
Segmented
Chordata
Acoelomates
Notochord,
segmentation,
jointed
appendages
Segmentation
Molting
?
Deuterostome development,
endoskeleton
Pseudocoel
Coelom
Body cavity
Radial symmetry
Bilateral symmetry
No true tissues
Tissues
Multicellularity
Ancestral protist
TABLE 19.2
THE MAJOR ANIMAL PHYLA
Approximate
Number of
Named Species
Phylum
Typical Examples
Key Characteristics
Arthropoda
(arthropods)
Insects, crabs,
spiders, millipedes
Most successful of all animal phyla; chitinous exoskeleton
covering segmented bodies with paired, jointed appendages;
most insect groups have wings; nearly all are freshwater or
terrestrial
Mollusca
(mollusks)
Snails, clams,
octopuses,
nudibranchs
Soft-bodied coelomates whose bodies are divided into three
parts: head-foot, visceral mass, and mantle; many have shells;
almost all possess a unique rasping tongue called a radula; most
are marine or freshwater but 35,000 species are terrestrial
110,000
Chordata
(chordates)
Mammals, fish,
reptiles, birds,
amphibians
Segmented coelomates with a notochord; possess a dorsal nerve
cord, pharyngeal pouches, and a tail at some stage of life; in
vertebrates, the notochord is replaced during development by the
spinal column; most are marine, many are freshwater, and 20,000
species are terrestrial
56,000
Platyhelminthes
(flatworms)
Planaria,
tapeworms,
flukes
Segmented coelomates with a notochord; possess a dorsal nerve
cord, pharyngeal pouches, and a tail at some stage of life; in
vertebrates, the notochord is replaced during development by the
spinal column; most are marine, many are freshwater, and 20,000
species are terrestrial
20,000
Nematoda
(roundworms)
Ascaris, pinworms,
hookworms, Filaria
Pseudocoelomate, unsegmented, bilaterally symmetrical worms;
tubular digestive tract passing from mouth to anus; tiny; without
cilia; live in great numbers in soil and aquatic sediments; some are
important animal parasites
20,000
Annelida
(segmented worms)
Earthworms,
marine worms,
leeches
Coelomate, serially segmented, bilaterally symmetrical worms;
complete digestive tract; most have bristles called setae on each
segment that anchor them during crawling; marine, freshwater,
and terrestrial
12,000
1,000,000
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
TABLE 19.2
(CONTINUED)
Approximate
Numberof
NamedSpecies
Phylum
Typical Examples
Key Characteristics
Cnidaria
(cnidarians)
Jellyfish, hydra,
corals, sea
anemones
Soft, gelatinous, radially symmetrical bodies whose digestive
cavity has a single opening; possess tentacles armed with
stinging cells called cnidocytes that shoot sharp harpoons called
nematocysts; almost entirely marine
10,000
Echinodermata
(echinoderms)
Sea stars, sea
urchins, sand
dollars, sea
cucumbers
Soft, gelatinous, radially symmetrical bodies whose digestive
cavity has a single opening; possess tentacles armed with
stinging cells called cnidocytes that shoot sharp harpoons called
nematocysts; almost entirely marine
6,000
Porifera
(sponges)
Barrel sponges,
boring sponges,
basket sponges,
vase sponges
Asymmetrical bodies without distinct tissues or organs; saclike
body consists of two layers breached by many pores; internal
cavity lined with food-filtering cells called choanocytes; most
marine (150 species live in freshwater)
5,150
Lophophorates
(Bryozoa, also called
moss animalsor
Ectoprocta)
Bower bankia,
Plumatella, sea
mats, sea moss
Microscopic, aquatic deuterostomes that form branching
colonies, possess circular or U-shaped row of ciliated tentacles
for feeding called a lophophore that usually protrudes through
pores in a hard exoskeleton; Bryozoa are also called Ectoprocta
because the anus, or proct, is external to the lophophore; marine
or freshwater
4,000
Rotifera
(wheel animals)
Rotifers
Small, aquatic pseudocoelomates with a crown of cilia around the
mouth resembling a wheel; almost all live in freshwater
2,000
SPONGES: ANIMALS WITHOUT
TISSUES
• Sponges are members of the Phylum
Porifera.
• Their bodies a little more than masses of
specialized cells embedded in a gel-like matrix.
• Clumps of cells disassociated from a sponge can
give rise to new sponges.
SPONGES: ANIMALS WITHOUT
TISSUES
• The body of a sponge is perforated by many pores.
• Choanocytes are flagellated cells that line the
body cavity of the sponge and draw in water
through the pores.
• The sponge is a filter feeder which traps any food
particles.
CNIDARIANS: TISSUES LEAD TO
GREATER SPECIALIZATION
• Radiata are radially symmetrical and
include two phyla.
• Cnidaria comprises the hydra, jellyfish, corals, and
anemones.
• Ctenophora comprises the comb jellies.
• The members of the Radiata have a body
plan that allows them to interact with their
environment on all sides.
CNIDARIANS: TISSUES LEAD TO
GREATER SPECIALIZATION
• A major evolutionary advance in the
Radiata is extracellular digestion of food.
• Digestion begins outside of cells in a gut cavity
called the gastrovascular cavity.
• This form of digestion allows animals to digest an
animal larger than itself.
CNIDARIANS: TISSUES LEAD TO
GREATER SPECIALIZATION
• Cnidarians (phylum Cnidaria) are carnivores that
capture prey with tentacles that ring their mouths.
• These tentacles and, sometimes, the body surface bear
stinging cells called cnidocytes.
• Within each cnidocyte is a harpoonlike barb, called a
nematocyst, which cnidarians use to spear prey and retract
it towards the tentacle
• The nematocyst can discharge so explosively that it is
capable of piercing the hard shell of a crab
CNIDARIANS: TISSUES LEAD TO
GREATER SPECIALIZATION
• Cnidarians have
two basic body
forms:
• Medusae are a
floating form.
• Polyps are a sessile
form.
Gastrovascular
cavity
Epidermis
Mesoglea
Medusa
Gastrodermis
Tentacles
Mouth
Polyp
Gastrovascular
cavity
CNIDARIANS: TISSUES LEAD TO
GREATER SPECIALIZATION
• Medusae are often called “jellyfish,”
because of their gelatinous interior, or
“stinging nettles,” because of their
nematocysts.
• Polyps are pipe-shaped animals that usually
attach to rock.
• In corals, the polyps secrete a deposit of calcium
carbonate in which they live.
THE LIFE CYCLE OF OBELIA, A MARINE
COLONIAL HYDROID
Medusae
Testis
Ovary
Feeding
polyp
Sexual
reproduction
Medusa bud
Eggs
Sperm
Reproductive
polyp
Zygote
Blastula
Free-swimming
planula larva
Mature
colony
Young colony and
asexual budding
Settles down to
start new colony
SOLID WORMS: BILATERAL
SYMMETRY
• Body symmetry differs
among the
Eumetazoa.
• Radial symmetry means
that multiple planes
cutting the organism in
half will produce mirror
images.
• Bilateral symmetry
means that only one
plane can cut the
organism in half to
produce mirror images.
SOLID WORMS: BILATERAL
SYMMETRY
• Most bilaterally symmetrical animals have
evolved a definitive head end.
• This process is termed cephalization.
SOLID WORMS: BILATERAL
SYMMETRY
• The bilaterally symmetrical eumetazoans
produce three embryonic layers.
• Ectoderm will develop into the outer coverings of
the body and the nervous system.
• Mesoderm will develop into the skeleton and
muscles.
• Endoderm will develop into the digestive organs
and intestine.
SOLID WORMS: BILATERAL
SYMMETRY
• The solid worms are the simplest of all
bilaterally symmetrical animals.
• The largest phylum of these worms is the
Phylum Platyhelminthes, which includes the
flatworms.
• Flatworms lack any internal cavity other than
the digestive tract.
• This solid condition is called acoelomate.
• Flatworms are the simplest animals in which
organs occur.
SOLID WORMS: BILATERAL
SYMMETRY
• Most flatworms are parasitic but some are
free-living.
• Flatworms range in size from less than a millimeter
to many meters long.
SOLID WORMS: BILATERAL
SYMMETRY
• There are two classes of parasitic flatworms:
• Flukes
• Tapeworms
• The parasitic lifestyle has resulted in the eventual
loss of features not used or needed by the parasite.
• For example, parasitic flatworms do not need
eyespots.
• This loss of features that lack adaptive purpose for
parasitism is sometimes called degenerative
evolution.
LIFE CYCLE OF THE HUMAN LIVER FLUKE,
CLONORCHIS SINENSIS
Raw, infected fish
is consumed by
humans or other
mammals
3
Metacercarial
cysts in fish
muscle
Flukes often
require two or
more hosts to
complete their
life cycles
Liver
Adult fluke
Bile duct
2
1
Egg containing
miracidium
Miracidium hatches
after being eaten
by snail
Cercaria
Redia
Sporocyst
SOLID WORMS: BILATERAL
SYMMETRY
• Tapeworms are a classic example of
degenerative evolution.
• The body of a tapeworm has been reduced to
two primary functions.
• Eating
• Reproduction
SOLID WORMS: BILATERAL
SYMMETRY
• Those flatworms that have a digestive
cavity, have an incomplete gut, one with
only one opening.
• The gut branches throughout the body and is
involved in both digestion and excretion.
• The parasitic flatworms lack a gut entirely
and absorb food directly through their body
walls.
SOLID WORMS: BILATERAL
SYMMETRY
• Flatworms lack a
circulatory system and all
cells must be within
diffusion distance of
oxygen and food.
• Flatworms have a simple
nervous system, either a
nerve net or longitudinal
nerve cords with cross
connections.
• Free-living forms have
eyespots to distinguish light
from dark.
ROUNDWORMS: THE EVOLUTION OF
A BODY CAVITY
• A key transition in the evolution of the
animal body plan was the evolution of the
body cavity.
• The evolution of an internal body cavity
helped improve the animal body design in
three areas:
• circulation
• movement
• organ function
ROUNDWORMS: THE EVOLUTION OF
A BODY CAVITY
• There are three basic
kinds of body plans
found in bilaterally
symmetrical animals:
• Acoelomates have no
body cavity.
• Pseudocoelomates have
a body cavity (called a
pseudocoel) located
between the mesoderm
and the endoderm.
• Coelomates have a body
cavity (called a coelom)
that develops entirely
within the mesoderm.
Ectoderm
Mesoderm
Endoderm
Acoelomate
Ectoderm
Mesoderm
Pseudocoelomate
Endoderm
Pseudocoel
Ectoderm
Mesoderm
Coelomate
Coelomic
cavity
Endoderm
ROUNDWORMS: THE EVOLUTION OF
A BODY CAVITY
• The largest pseudocoelomate phylum is
Nematoda, containing about 20,000 species.
• The members of this phylum include nematodes,
eelworms, and other roundworms.
• Nematodes are unsegmented, cylindrical worms
covered by a flexible cuticle that is molted as they
grow.
• Nematodes move in a whiplike fashion.
http://youtu.be/tp-O3LME3OU
ROUNDWORMS: THE EVOLUTION OF
A BODY CAVITY
• Some nematodes are parasitic in humans,
cats, dogs, and animals of economic
importance.
• Heartworm in dogs is caused by a nematode
• Trichinosis is an infection caused by the
nematode Trichinella and is transmitted to
humans who eat undercooked pork.
• Intestinal roundworms, Ascaris lumbricoides, live in
human intestines.
ROUNDWORMS: THE EVOLUTION OF
A BODY CAVITY
• Another
pseudocoelomate
phylum is Rotifera.
• Rotifers are small,
aquatic organisms
that have a crown of
cilia at their heads.
• The cilia help in both
locomotion and
feeding.
http://youtu.be/cYNJOVDQexA
MOLLUSKS: COELOMATES
• The body of a mollusk (Phylum Mollusca) is
comprised of three regions:
• a head-foot
• a visceral mass containing the body’s organs.
• a mantle that envelopes the visceral mass and is
associated with the gills.
MOLLUSKS: COELOMATES
• There are three major
groups of mollusks:
• Gastropods—include
the snails and slugs.
• Bivalves—include
clams, oysters, and
scallops.
• Cephalopods—include
the octopuses and
squids.
MOLLUSKS: COELOMATES
• Mollusks have a unique feeding structure, called a
radula.
• The radula is a rasping tonguelike organ that bears rows of
pointed, backward-curving teeth.
MOLLUSKS: COELOMATES
• In most mollusks, the outer surface of the
mantle secretes a protective shell.
• The shell has multiple layers comprised of protein,
calcium, and pearl.
ANNELIDS: THE RISE OF
SEGMENTATION
• One of the early innovations in body plan to
arise among the coelomates was
segmentation.
• Segmentation is the building of a body from a
series of similar segments.
• This body plan offers a lot of flexibility in that
small changes to segments can produce a new
kind of segment with different functions.
• The first segmented animals to evolve were the
annelid worms, Phylum Annelida.
ANNELIDS: THE RISE OF
SEGMENTATION
• The basic body plan of
an annelid is a tube
within a tube.
• The digestive tract is
suspended within the
tube of the coelom.
• There are three body
plan characteristics:
• Repeated segments
• Specialized segments
• Connections
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• The most successful of all animal groups is
the Phylum Arthropoda, consisting of the
arthropods.
• These animals have jointed appendages.
• In addition to joints, arthropods have an
exoskeleton made of chitin.
• The muscles of arthropods attach to the interior
of this outer shell.
• The shell offers protection against predators and
water loss.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Chitin cannot support much weight.
• Arthropod size is limited as a result.
• Arthropod bodies are segmented like annelids.
• Segments often fuse into functional groups in the
adult stage.
Antennae
Mouth
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Chelicerates are arthropods that lack jaws.
• They include spiders, mites, scorpions, and horseshoe
crabs.
• Mandibulates are arthropods with jaws, called
mandibles.
• They include the crustaceans, insects, centipedes,
and millipedes.
Antenna
Eye
Eyes
Pedipalp
Chelicera
Mandible
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• The chelicerate fossil record goes back 630
million years.
• A surviving type of chelicerate from this period is
the horseshoe crab.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• The class Arachnida has 57,000 named
species of arachnids, including spiders, ticks,
mites, scorpions, and daddy longlegs.
• Arachnids have a pair of chelicerae, a pair of
pedipalps, and four pairs of walking legs.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Crustaceans belong to
the subphylum Crustacea
and comprise a diverse
group of mandibulates.
• There a 35,000 species of
crustaceans described
including species of crabs,
shrimps, lobsters, crayfish,
water fleas, pillbugs, and
sowbugs.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Most
crustaceans
have two pairs
of antennae,
three pairs of
chewing
appendages,
and various
numbers of
legs.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Crustaceans
pass through a
larval stage
called the
nauplius.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Millipedes and
centipedes have
bodies that consist of
a head region
followed by numerous
similar segments.
• Centipedes have one
pair of legs per segment
while millipedes have
two.
• Centipedes are all
carnivorous while
millipedes are
herbivorous.
ARTHROPODS: ADVENT OF JOINTED
APPENDAGES
• Insects belong to the
Class Insecta and
are the largest group
of arthropods.
• They are the most
abundant eukaryotes
on the earth.
• Insects have three
body sections:
• Head
• Thorax
• Abdomen
PROTOSTOMES AND
DEUTEROSTOMES
• There are two major kinds of coelomate animals
representing two distinct evolutionary lines:
• Protostomes
• The mouth develops from or near the blastopore.
• Deuterostomes
• The anus forms from or near the blastopore; the
mouth forms on another part of the blastula.
Mesoderm
Protostomes
Archenteron Coelom Anus
Coelom
Mouth
1 cell
2 cells
4 cells
8 cells
16 cells
32 cells
Blastula
Deuterostomes
Blastopore Mesoderm splits Mouth forms from
blastopore
Archenteron Coelom
Mouth
Coelom
1 cell
2 cells
4 cells
8 cells
16 cells
32 cells
Blastula
Blastopore
Archenteron
outpockets to
form coelom
Anus
Anus forms
from blastopore
PROTOSTOMES AND
DEUTEROSTOMES
• Deuterostomes also differ from protostomes
in three other fundamental ways:
• The pattern of cleavage
• Protostomes have spiral cleavage while
deuterostomes have radial cleavage.
• Fating of cells
• Occurs later in deuterostome cleavage than in
protostome cleavage.
• Origin of the coelom.
ECHINODERMS: THE FIRST
DEUTEROSTOMES
• Echinoderms are deuterostomes
that belong to the phylum
Echinodermata.
• Echinoderm means “spiny skin” and
refers to the endoskeleton of
calcium-rich ossicles just beneath
the echinoderm’s skin.
• Entirely marine animals and include
sea stars, sea urchins, sand dollars,
and sea cucumbers.
• All are bilaterally symmetrical as
larvae but become radially
symmetrical as adults.
ECHINODERMS: THE FIRST
DEUTEROSTOMES
• A key adaptation of
echinoderms is the
water vascular system
that aids movement.
• This system is fluid-filled
and composed of a
central ring canal from
which five radial canals
extend out into the
http://youtu.be/8JOxiT5_zpc
arms.
• From each radial canal, tiny vessels extend through
short side branches into thousands of tiny, hollow tube
feet.
• Echinoderms can extend the tube feet, attach them to
the ocean floor, and pull against them to move.
CHORDATES: IMPROVING THE
SKELETON
• Chordates are deuterostomes that belong
to the phylum Chordata.
• They exhibit a truly internal endoskeleton with
muscles attached to an internal rod, called a
notochord.
• This innovation opened the door to large body
sizes not possible in earlier animal forms.
CHORDATES: IMPROVING THE
SKELETON
• The approximately 56,000 species of
chordates share four principal features:
•
•
•
•
Notochord
Nerve cord
Pharyngeal pouches
Postanal tail
• All chordates have
all four of these
characteristics at
some time in their
lives.
CHORDATES: IMPROVING THE
SKELETON
• Not all chordates are vertebrates.
• Tunicates and lancelets are chordates.
CHORDATES: IMPROVING THE
SKELETON
• Vertebrate
chordates differ
from tunicates and
lancelets in two
important respects.
• Vertebrates have a
backbone that
replaces the role of
the notochord.
• Vertebrates have a
distinct and welldifferentiated head.