Transcript evolution of a body cavity

Essentials of the Living World
Second Edition
George B. Johnson
Jonathan B. Losos
Chapter 19
Evolution of Animals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
19.1 General Features of Animals
• Animals are a diverse group that are characterized by
several features
 animals are heterotrophs
 all animals are multicellular and lack cell walls
 animals are able to move from place to place
 most animals reproduce sexually
 animals have a characteristic pattern of development and
possess unique tissues
19.2 Five Key Transitions in Body
Plan
•
The evolution of animals is marked by five key
transitions to the body and are branchpoints of
the animal evolutionary tree
1. evolution of tissues
•
•
only the sponges (Parazoa) lack both defined
tissues and organs
all other animals (Metazoa) have true tissues
19.2 Five Key Transitions in Body
Plan
2.
evolution of bilateral symmetry

sponges also lack any definite symmetry and grow as irregular
masses

virtually all of the Eumetazoa have a definite shape and
symmetry
•
radial symmetry means the parts of their bodies are arranged
around central axis
•
bilateral symmetry means that body only has left and right mirror
images
–
permits different organization patterns in localized different organs in
different parts of the body
19.2 Five Key Transitions in Body
Plan
3. evolution of a body cavity
•
a body cavity makes possible the evolution
of efficient organ systems
•
•
•
supports organs, distributes materials, and
fosters complex developmental interactions
allows the digestive tract to be larger and longer
provides space within which the gonads (ovaries
and testes) can expand
19.2 Five Key Transitions in Body
Plan
4. the evolution of deuterostome
development
•
bilateral animals can be divided into two
groups based on differences in the basic
pattern of development
•
•
protostomes include flatworms, nematodes,
mollusks, annelids, and arthropods
deuterostomes include echinoderms and
chordates
19.2 Key Transitions in Body Plan
5. the evolution of segmentation
•
embryonic segmentation is advantageous
for two reasons
•
each segment may go on to develop a more or
less complete set of adult organ system
•
•
damage to any one segment need not be fatal to the
entire individual
locomotion is more effective when each segment
can move independently
Figure 19.1 Evolutionary trends among
the animals
19.3 Sponges and Cnidarians: The
Simplest Animals
• Sponges are members of the phylum Porifera
 as parazoans, they lack true tissues and organs but
are comprised of masses of specialized cells
embedded in a gel-like matrix
 the body of a sponge is perforated by tiny holes
• unique flagellated cells, called choanocytes, line the body
cavity of the sponge and draw water in through the pores
• the sponge is a “filter-feeder” that ingests any suspended
food particles trapped by the choanocytes as the water flows
by
Figure 19.2 Sponges
19.3 Sponges and Cnidarians: The
Simplest Animals
• Other than the sponges, all other animals
are eumetazoans and form distinct
embryonic layers
 in radially symmetrical eumetazoans, there
are two embryonic layers
• an outer ectoderm, which gives rises to the
epidermis
• an inner endoderm, which gives rise to the
gastrodermis
• a jellylike layer, called the mesoglea, forms
between the epidermis and gastrodermis
19.3 Sponges and Cnidarians: The
Simplest Animals
• Two primitive phyla of eumetazoans exhibit
radial symmetry and are organized around an
oral-aboral axis
 the oral side of the animal contains the “mouth”
 the two phyla are
• phylum Cnidaria
– jellyfish, corals, and sea anemones
• phylum Ctenophora
– comb jellies
 together, the two phyla constitute the Radiata
19.3 Sponges and Cnidarians: The
Simplest Animals
• Cnidarians are carnivores that capture
their prey with tentacles that ring their
mouth
 the tentacles and, sometimes the body
surface, bear stinging cells called cnidocytes
• inside each cnidocyte is a harpoon called a
nematocyst
Figure 19.3 A cnidarian
19.3 Sponges and Cnidarians: The
Simplest Animals
• Radiates, such as cnidarians, perform
extracellular digestion of food
 digestion begins outside of cells in a gut
cavity, called the gastrovascular cavity
 after the food is broken down into smaller
pieces, cells lining the cavity will complete
digestion intracellularly
 this is advantageous because it became
possible to digest an animal larger than
oneself
19.3 Sponges and Cnidarians: The
Simplest Animals
• Cnidarians have two basic body forms
 medusae are free-floating
 polyps are sessile
Figure 19.4 Two basic body forms of cnidarians
19.4 The Advent of Bilateral
Symmetry
• All eumetazoans other than cnidarians and
ctenophores are bilaterally symmetrical
 it allows different parts of the body to become
specialized in different ways
• cephalization means that an animal has a definite
head end where sensory organs are often
concentrated
 produce three embryonic layers
• mesoderm develops inbetween the ectoderm and
endoderm layers
– the skeleton and muscles develop from mesoderm
Figure 19.5 How radial and bilateral
symmetry differ
19.4 The Advent of Bilateral
Symmetry
• The simplest of all bilaterally symmetrical
animals are the solid worms
 the largest phylum is Platyhelminthes
• flatworms
 they lack any internal cavity other than the
digestive tract
• the gut is completed surrounded by tissues and
organs
• for this reason, this body type is called
acoelomate
Figure 19.6 Body plan of a solid
worm
19.4 The Advent of Bilateral
Symmetry
• The gut of flatworms with a digestive cavity is
incomplete (i.e., only has one opening)
 the flatworm cannot feed continuously
 other flatworms are parasitic and lack a digestive
tract, instead absorbing nutrients through the body
wall
• Flatworms have an excretory system comprised
of a network of fine tubules associated with
flame cells
 flame cells use cilia to move water and wastes into
the tubules and out exit pores in the epidermis
19.3 Sponges and Cnidarians: The
Simplest Animals
• Flatworms lack a circulatory system
 they are thin-bodied in order to keep within the limits
of diffusion distance for oxygen and food
• Flatworms have a simple nervous system
 most have a nerve cord and multiple sensory
structures
• Reproductive systems of flatworms are complex
 some are hermaphroditic (i.e., each individual
contains both male and female sexual structures)
 others are capable of asexual regeneration
19.5 The Advent of a Body Cavity
• The evolution of an internal body cavity was an important
improvement in animal body design for three reasons
 circulation
• fluids that move within the body cavity can serve as a circulatory
system
 movement
• fluid in the body cavity makes the animal’s body rigid permitting
resistance to muscle contraction
 organ function
• in a fluid-filled enclosure, body organs can function without being
deformed by surrounding muscles
19.5 The Advent of a Body Cavity
• iIn bilaterally symmetrical animals, there
are three basic kinds of body plans
 acoelomate
• no body cavity present
 pseudocoelomate
• has a body cavity called the pseudocoel located
between the mesoderm and endoderm
 coelomate
• has a body cavity called a coelom located
completely within the mesoderm
Figure 19.8 Three body plans for
bilaterally symmetrical animals
19.5 The Advent of a Body Cavity
• The different phyla of pseudocoelomates form
two groups that do no appear to be closely
related
 in all pseudocoleomates, the pseudocoel serves as a
hydrostatic skeleton
• the muscles work against the rigid fluid that fills the cavity
 two phyla are noteworthy
• phylum Nematoda
– roundworms
• phylum Rotifera
– rotifers
Figure 19.9 Pseudocoelomates
19.5 The Advent of a Body Cavity
• Nematodes are unsegmented worms with
a cylindrical (i.e., round) body
 development is simple and the adults consist
of very few cells
• nematodes are important subject for genetic and
development studies
– Caenorhabditis elegans is the only animal whose
complete developmental cellular animal is known and it
was the first animal whose genome was fully sequenced
19.5 The Advent of a Body Cavity
• About 50 species of nematodes regularly
parasitize human beings
 Trichinella causes trichinosis after
consuming raw or undercooked pork
 Ascaris lumbricoides infects the intestines and
is spread to their eggs through feces
19.5 The Advent of a Body Cavity
• The bulk of the animal kingdom consists of
coelomates
 a major advantage of the coelomate body
plan is that it allows contact between
mesoderm and endoderm during
development
 this permits localized portions of the digestive
tract to be developed into complex, highly
specialized regions, such as the stomach
19.5 The Advent of a Body Cavity
• The only major phylum of coelomates without
segmented bodies are the mollusks (phylum
Mollusca)
 mollusks have a basic body design
• a foot
– this structure is muscular and may function in locomotion,
attachment, food adaptation, etc.
• a central visceral mass
– contains the body’s organs
• a mantle
– a heavy fold of tissue that surrounds the visceral mass
– gills are positioned on the inner surface of the mantle
19.5 The Advent of a Body Cavity
• The three major groups of mollusks are
 gastropods
• use the muscular foot to crawl and their mantle often
secretes a single, hard protective cell
• all terrestrial mollusks are gastropods
 bivalves
• secrete a two-part shell with a hinge and filter-feed by
drawing water into their shell
 cephalopods
• have a modified mantle cavity that permits jet propulsion and,
in most groups, the shell is reduced or absent
Figure 19.10 Three major groups
of mollusks
19.5 The Advent of a Body Cavity
• One of the most characteristic features of
mollusks is the radula
 the radula is a rasping, tongue-like organ
• In mollusks with shells,
 the outer layer of the shell consists of horny material
that is rich in protein
 the inner layer of the shell consists of pearly material
that is used as mother-of-pearl
• pearls are formed in clams and oysters when a foreign
objects are lodged between the mantle and the inner shell
• the mantle coats the foreign object with layer upon layer of
shell material to reduce irritation
19.5 The Advent of a Body Cavity
• Segmentation is the building of a body
from a series of similar segments
 a small change in an existing segment can
produce a new kind of segment with a
different function
• The first segmented individuals to evolve
were the annelid worms (phylum
Annelida)
19.5 The Advent of a Body Cavity
•
The basic body plan of annelid is a tube within a tube:
a digestive tract is suspended within the coelom

there are three further characteristics of this arrangement
1.
repeated segments
•
2.
specialized segments
•
3.
in each of the segments, the excretory and locomor organs are
repeated
the anterior segments contain sensory organs and a brain
connections
•
•
circulatory system is required because the segments are divided by
partitions
a nervous system allows for coordination
Figure 19.11 Representative
annelids
19.5 The Advent of a Body Cavity
• The evolutionary innovation of jointed
appendages led to the origin of the most
successful animal phylum of all,
Arthropoda
 the arthropod body plan involves a rigid
external skeleton, or exoskeleton, made of
chitin
 about two-thirds of all named species on earth
are arthropods
Figure 19.13 The body plan of an
insect
Figure 19.12 Arthropods are a
successful group
Figure 19.14 Insect diversity
19.6 Redesigning the Embryo
• In embryonic development, cell divisions
of the fertilized egg produce a hollow ball
of cells called a blastula
 the blastula then indents to form a two-layer
thick ball with a blastopore opening to the
outside
• in protostomes, the mouth develops from or near
the blastopore
• in deuterostomes, the anus develops from or near
the blastopore while the mouth develops on
another part of the blastula
Figure 19.15 Embryonic development
in protostomes and deuterostomes
19.6 Redesigning the Embryo
•
Deuterostomes differ from protostomes in
three other embryological features
1. they have radial cleavage instead of spiral
cleavage
•
cleavage is the progressive division of cells that forms the
blastula
2. the first cleavage divisions produce identical
daughter cells, any one of which can, if separated,
develop into a complete organism
3. the coelom is produced as outpockets of the
primitive gut, called the archenteron
19.5 The Advent of a Body Cavity
• Echinoderms (phylum Echinodermata) were the
first deuterostomes to evolve
 their name means “spiny skin,” which refers to an
endoskeleton composed of hard, calcium-rich plates
called ossicles
 all echinoderms are bilaterally symmetrical as larvae
but become radially symmetrical as adults
 a key innovation of echinoderms is a hydraulic system
that aids in movement called the water vascular
system
• it is a system of fluid-filled canals that extend into numerous,
hollow tube-feet
Figure 19.16 Diversity in echinoderms
19.5 The Advent of a Body Cavity
• Chordates (phylum Chordata) are
deuterostome coelomates characterized
by a flexible rod called a notochord that
develops along the back of the embryo
 this evolutionary innovation made possible an
internal point of attachment for muscles
 in addition to an endoskeleton, this led to truly
large animals
19.5 The Advent of a Body Cavity
•
Chordates are distinguished by four principal features
1.
notochord
•
2.
nerve cord
•
3.
a single dorsal hollow nerve cord
pharyngeal pouches
•
4.
a stiff but flexible rod that forms beneath the nerve cord in the
early embryo
a series of pouches behind the mouth that develop into slit in
some animals
postanal tail
•
a tail that extends beyond the anus, at least during embryonic
development
19.5 The Advent of a Body Cavity
• All vertebrates are chordates
 the only non-vertebrate chordates are the
tunicates and the lancelets
 vertebrates are distinguished by having
• backbone (comprised of a series of hollow bones)
that replaces the notochord
• head with a skull and brain
Non-vertebrate Chordates
Figure 19.17 A tunicate
Figure 19.18 Lancelets
A Vertebrate Chordate
Figure 19.19 A mouse embryo
19.7 Overview of Vertebrate
Evolution
• Scientists divide the earth’s past into large blocks of time
called eras
 each era is further divided into small blocks of time called
periods
• epochs make up some periods
– epochs can be subdivided into ages
• Virtually all of the major groups of animals that survive at
the present time originated in the sea at the beginning of
the Paleozoic era, during or soon after the Cambrian
period (545 - 490 MYA)
 the first vertebrates (jawless fishes) evolved about 500MYA
19.7 Overview of Vertebrate
Evolution
• The first organisms to invade land were fungi
and plants
 this occurred over 500 million years ago
• The first invasion by animals was accomplished
by arthopods
 this occurred about 410 million years ago
• Vertebrates invaded land during the
Carboniferous period (360-280 MYA)
 the first vertebrates to live on land were the
amphibians
19.7 Overview of Vertebrate
Evolution
• The history of life on earth has been marked by
periodic episodes of extinction, where the loss of
species outpaces the formation of new species
 particularly sharp declines in species diversity are
called mass extinctions
• mass extinctions left vacant many ecological opportunities
and, for this reason, they were followed by rapid evolution
among the relatively few plants, animals, and other
organisms that survived
19.7 Overview of Vertebrate
Evolution
• The most famous and well-studied
extinction occurred at the end of the
Cretaceous period (65 MYA)
 during this time, the dinosaurs and any other
organisms went extinct
 recent findings have supported the hypothesis
that this mass extinction was caused by an
asteroid impact
19.7 Overview of Vertebrate
Evolution
• We are living in a new mass extinction
event
 while the number of species is greater today
than it has ever been, the rate of extinction is
alarmingly high due to human activity
 some estimates say that as many as onefourth of all species will become extinct in the
near future
Figure 19.20 Vertebrate Family Tree
evolutionary advances allowed vertebrates to conquer first the sea and then
the land
19.8 Fishes Dominate the Sea
•
All fishes have in common four important characteristics
1.
gills

2.
vertebral column

3.
all fishes have a skeleton made of either bone or cartilage
single-loop blood circulation

4.
fish use gills to extract dissolved oxygen from water
blood is pumped from the heart to the gills, to the body, and then
back to the heart
nutritional deficiencies

fish are unable to synthesize the aromatic amino acids and must
consume them in their diet
19.8 Fishes Dominate the Sea
• The first fishes to evolve were jawless
 only one group of jawless fish, the
agnathans, survive today
• hagfish and lampreys
• Members of the class Chondrichthyes, the
sharks and rays, were the first jawed
fishes and have a flexible, cartilaginous
skeleton
Figure 19.21 Chondrichthyes
19.8 Fishes Dominate the Sea
• Bony fish have a heavy internal skeleton of bone
but are still buoyant because of a swim bladder
 the swim bladder is a gas-filled sac that allow fish to
regulate their buoyant density
• Bony fishes are the most diverse of all
vertebrates
 of the 30,800 living species of fish, about 30,000 have
swim bladders
Figure 19.22 Diagram of a swim
bladder
19.9 Amphibians and Reptiles
Invade the Land
• Amphibians are the direct descendant of fishes
 they evolved from the lobe-finned fishes
Figure 19.24 A key adaptation of amphibians: the evolution of legs
19.9 Amphibians and Reptiles
Invade the Land
•
Amphibians have five key characteristics that allowed them to
invade successfully land
1.
legs
2.
lungs
3.
cutaneous respiration

4.
pulmonary veins

5.
supplements the use of lungs
returns oxygenated blood from the lungs to the heart for repumping
partially divided heart

helps to prevent oxygenated blood deoxygenated blood
19.9 Amphibians and Reptiles
Invade the Land
• Reptiles initially replaced amphibians as the dominant
terrestrial vertebrates because of important features
 amniotic egg
• reptiles lay watertight eggs that are protected from drying out and
contain a food source called yolk
• it is comprised of four layers of membranes
–
–
–
–
chorion allows O2 to enter but not the exit of H2O
amnion is a fluid-filled cavity surrounding the embryo
yolk sac connects to the gut of the embryo and delivers food
allantois accumulates wastes from the embryo
Figure 19.25 A key adaptation of
reptiles: watertight eggs
19.9 Amphibians and Reptiles
Invade the Land
• Additional features of reptiles
 dry skin
• the skin of reptiles is covered by dry scales that
prevent water loss
 thoracic breathing
• reptiles expand and contract the rib cage to move
air in and out of the lungs
19.10 Birds Master the Air
• Birds evolved from bipedal dinosaurs
 modern birds lack teeth and have only
vestigial tails
 they lay amniotic eggs and have reptilian
scales on their feet and lower legs
 birds are unique from reptiles in having
• feathers are lightweight and adapted for flight
• flight skeleton is firm for attaching flight muscles,
the bones are thin and hollow
Figure 19.26 A key adaptation of
birds: feathers
19.11 Mammals Adapt to Colder
Times
• Mammals have three major characteristics
 mammary glands
• female mammals have mammary glands that produce milk to
nurse the newborns
 hair
• the primary function is insulation
• hair is made up of dead cells filled with the protein, keratin
 middle ear
• all mammals have three middle ear bones that evolved from
bones in the reptile jaw
Characteristics of Modern
Mammals
• Endothermy
 this allows mammals to be active at any time of the day or night and to
colonize severe environments
• Placenta
 in most mammal species, females carry their young in the uterus during
development
 the placenta provides nourishment to the young while it is in the uterus
• Teeth
 mammals have heterodont dentition, meaning that different types of
teeth are highly specialized to match eating habits
• Hooves and horns
 the same protein used to make hair is also used to make claws,
fingernails and hooves
Figure 19.27 The placenta
19.11 Mammals Adapt to Colder
Times
• Today’s mammals include
 monotremes
• monotremes are the only egg-laying mammals
• they include the duck-billed platypus and spiny
anteater (echidna)
 marsupials
• their young are nursed in a marsupial pouch
 placental mammals
• the young develop in the uterus for a long time
while being nourished by a placenta
Figure 19.28 Today’s mammals
Inquiry & Analysis
• Which of the two lines
best represents the
data?
• Is Van Halen’s
hypothesis supported
by this analysis?
Graph of Family Survivorship of
Echinoids