Download ANIMAL EVOLUTION AND DIVERSITY

Introduction
ƒ Most octopuses rely on nonaggressive defense
mechanisms such as camouflage.
ƒ The blue-ringed octopus is an exception, with
– a toxin 10,000 times more lethal than cyanide (氰化物)
and
– sapphire-blue (寶藍色) circles that proclaim (宣示) its
identity.
Blue-ringed octopus
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Big Ideas
ANIMAL EVOLUTION
AND DIVERSITY
Animal Evolution
and Diversity
Invertebrate Diversity
Animal Phylogeny and
Diversity Revisited
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What is an animal?
Figure 18.1A
ƒ Animals are
– eukaryotic,
– multicellular heterotrophs, and
– have cells that lack cell walls.
ƒ Animals also use ingestion, the eating of food.
ƒ Fungi absorb nutrients after digesting food outside
their body.
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Ingestion, the animal way of life
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What is an animal?
What is an animal?
ƒ Most adult animals are diploid and reproduce
sexually.
ƒ One side of the blastula folds in and cells become
rearranged to form a gastrula that establishes
three embryonic layers.
– The eggs and sperm
– Endoderm forms a lining of the future digestive tract.
– are produced by meiosis,
– Ectoderm forms an outer layer that will give rise to the
skin and nervous system.
– are the only haploid cells, and
– fuse during fertilization to form a zygote.
– The zygote divides by mitosis to form a hollow ball of
cells called a blastula (囊胚).
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– Mesoderm forms a middle layer that will give rise to
muscles and most internal organs.
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What is an animal?
Sperm
ƒ After the gastrula stage, many animals develop
directly into adults.
ƒ Other animals, such as the sea star, develop into
one or more larval stages.
1
Meiosis
Key
Haploid (n)
Diploid (2n)
Egg
Adult
– A larva is an immature individual that looks different from
the adult animal.
– A larva undergoes a major change in body form, called
metamorphosis, and becomes a reproductively mature
adult.
ƒ Clusters of master control homeotic (同源) genes
control transformation of the zygote into an adult
animal.
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Sperm
Sperm
2
2
1
1
Meiosis
Key
Haploid (n)
Diploid (2n)
Egg
Meiosis
Zygote
(fertilized egg)
Adult
Key
Haploid (n)
Diploid (2n)
Egg
Zygote
(fertilized egg)
Adult
3
Eight-cell stage
2
Sperm
Sperm
2
2
1
1
Meiosis
Egg
Meiosis
Key
Haploid (n)
Diploid (2n)
Adult
Egg
3
Zygote
(fertilized egg)
3
Zygote
(fertilized egg)
Key
Haploid (n)
Diploid (2n)
Adult
Eight-cell stage
Eight-cell stage
4
4
Blastula
(cross section)
Blastula
(cross section)
5
Early gastrula
(cross section)
Sperm
Sperm
2
2
1
1
Meiosis
Egg
Meiosis
3
Zygote
(fertilized egg)
Key
Haploid (n)
Diploid (2n)
Adult
Egg
3
Zygote
(fertilized egg)
Key
Haploid (n)
Diploid (2n)
Adult
Eight-cell stage
Eight-cell stage
4
4
Blastula
(cross section)
Blastula
(cross section)
Digestive tract
5
5
Larva
Ectoderm
Ectoderm
7
Endoderm
Internal sac
Early gastrula
(cross section)
6
Future mesoderm
Later gastrula
(cross section)
Internal sac
2
Egg
3
Zygote
(fertilized egg)
Adult
Eight-cell stage
8
Metamorphosis
4
Blastula
(cross section)
Digestive tract
5
Larva
Ectoderm
7
Endoderm
Internal sac
6
Early gastrula
(cross section)
ƒ The oldest generally accepted animal fossils that
have been found are 575–550 million years old.
1
Key
Haploid (n)
Diploid (2n)
6
Future mesoderm
Later gastrula
(cross section)
Animal diversification began more than half a
billion years ago
Sperm
Meiosis
Endoderm
Early gastrula
(cross section)
Future mesoderm
Later gastrula
(cross section)
ƒ Animal diversification appears to have accelerated
rapidly from 535 to 525 million years ago, during the
Cambrian (寒武紀) period, known as the Cambrian
explosion.
ƒ The most celebrated source of Cambrian fossils is
the Burgess Shale (伯吉斯頁岩) containing a
cornucopia (聚寶盆) of perfectly preserved animal
fossils.
*伯吉斯頁岩：發現於加拿大西北方英屬哥倫比亞境內的洛磯山脈
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Dickinsonia costata (狄更遜水母)
(about 8 cm across)
Spriggina floundersi (斯普里格蠕蟲)
(about 3 cm long)
Animal diversification began more than half a
billion years ago
Chordate
Arthropod
ƒ The Cambrian explosion may have been caused by
Anomalocaris
– increasingly complex predator-prey relationships or
– an increase in atmospheric oxygen.
Hallucigenia
ƒ Much of the diversity in body form among the
animal phyla is associated with variations in where
and when homeotic genes are expressed within
developing embryos.
ƒ Of the 35 or so animal phyla, all but one are
invertebrates, named because they lack vertebra.
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Animals can be characterized by basic features of
their “body plan”
Animals can be characterized by basic features of
their “body plan”
ƒ Animal body plans vary in
ƒ Symmetry
– symmetry,
– presence of true tissues,
– number of embryonic layers,
– presence of a body cavity, and
– details of their embryonic development.
– Animals that have radial symmetry have a top and
bottom but lack back and front or right and left sides. An
imaginary (假想) slice through the central axis divides
them into mirror images.
– Animals with bilateral symmetry have mirror-image
right and left sides and a
– distinct head, or anterior end,
– tail, or posterior end,
– back, or dorsal, surface, and
– bottom, or ventral, surface.
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Figure 18.3A
Animals can be characterized by basic features of
their “body plan”
ƒ Tissues
Top
– Tissues are collections of specialized cells that perform
special functions.
Dorsal surface
Anterior
end
– Sponges are the only animals that lack true tissues.
Posterior
end
ƒ Embryonic layers
– Some animals have only ectoderm and endoderm.
Bottom
Ventral surface
– Most animals have
– ectoderm,
– mesoderm, and
– endoderm.
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Animals can be characterized by basic features of
their “body plan”
Animals can be characterized by basic features of
their “body plan”
ƒ Animals with three embryonic layers may have a
body cavity, a fluid-filled space between the
digestive tract and outer body wall that
ƒ Animals with three tissue layers can be separated
into two groups based on details of their embryonic
development. For example, the opening formed
during gastrulation develops into the
– Cushions (緩衝) internal organs and that
– enables them to grow and move independently of the
body wall.
– In soft-bodied animals, fluid in the body cavity forms a
hydrostatic skeleton.
– mouth in protostomes and
– anus in deuterostomes.
– A true coelom is completely lined (襯) by tissues derived
from mesoderm.
– A pseudocoelom is a body cavity that is not completely
lined by tissues derived from mesoderm.
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Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Body covering
(from ectoderm)
Muscle layer
(from mesoderm)
Digestive tract
(from endoderm)
Pseudocoelom
Pseudocoelom (a roundworm)
True coelom (a segmented worm)
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The body plans of animals can be used to build
phylogenetic trees
Body covering
(from ectoderm)
Tissue-filled region
(from mesoderm)
ƒ Because animals diversified so rapidly on the scale
of geologic time, it is difficult to sort out the
evolutionary relationships among phyla using the
fossil record.
Digestive sac
(from endoderm)
No body cavity (a flatworm)
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The body plans of animals can be used to build
phylogenetic trees
Cnidarians
– protostomes and deuterostomes.
ƒ Researchers are increasingly adding molecular
comparisons to the construction of these trees.
Nematodes
Annelids
Arthropods
Deuterostomes
Bilateral
symmetry
ƒ All phylogenetic trees are hypotheses for the key
events in the evolutionary history of animals.
Bilaterians
True
tissues
Flatworms
Eumetazoans
Ancestral
colonial
protist
– sponges and eumetazoans (後生生物) (animals with true
tissues),
– animals with radial or bilateral symmetry (bilaterians),
and
Sponges
Radial
symmetry
Protostomes
ƒ One diagram of evolutionary relationships uses
morphology to construct a phylogenetic tree. This
tree distinguishes between
No true
tissues
Molluscs
Echinoderms
Chordates
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Sponges have a relatively simple, porous body
INVERTEBRATE DIVERSITY
ƒ Sponges (phylum Porifera) are simple, sedentary
animals without true tissues.
ƒ Water enters through pores in the body wall into a
central cavity and then flows out through a larger
opening.
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Sponges have a relatively simple, porous body
ƒ The body of a sponge consists of two layers of
cells separated by a gelatinous (凝膠狀) region.
– The inner layer of flagellated choanocytes filters food
and engulfs (吞噬) it by phagocytosis (吞噬作用).
– Amoebocytes wander through the middle body region
and produce skeletal fibers composed of
– flexible protein and
– mineralized particles called spicules.
A purple tube sponge
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Scypha
An azure vase sponge
Sponges have a relatively simple, porous body
Central
cavity
Skeletal fiber
Water flow
Choanocyte
in contact with
an amoebocyte
Choanocyte
Water
flow
ƒ Sponges are suspension feeders, filtering food
particles from water passed through food-trapping
equipment.
– To grow by 100 g, a sponge must filter roughly 1,000 kg of
water.
– Choanocytes trap food particles in mucus on the
membranous collars that surround their flagella.
Pore
Amoebocyte
Pores
Flagellum
Water flow
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Sponges have a relatively simple, porous body
Cnidarians are radial animals with tentacles and
stinging cells
ƒ Adult sponges are sessile and cannot escape from
predators. They deter (防阻) pathogens, parasites,
and predators by producing
ƒ Cnidarians (phylum Cnidaria)
– are characterized by radial symmetry and
– have only two tissue layers:
– defensive toxins and
– an outer epidermis,
– antibiotics.
– an inner cell layer lining the digestive cavity, and
– a jelly-filled middle region may have scattered (零落) amoeboid
cells.
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Cnidarians are radial animals with tentacles and
stinging cells
ƒ Cnidarians exhibit two kinds of radially symmetrical
body forms.
– The most sedentary (固生) polyp body is cylindrical with
tentacles projecting from one end.
– The more mobile medusa form is exemplified by a
marine jelly.
A sea anemone (about 6 cm in diameter)
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A hydra
(about 2–25 mm tall)
A marine jelly
(about 6 cm in diameter)
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Cnidarians are radial animals with tentacles and
stinging cells
ƒ Cnidarians are carnivores that use their tentacles to
capture prey and to push prey into their mouths.
– The mouth leads to the gastrovascular cavity, which
functions in digestion and circulation and as a hydrostatic
skeleton.
Tentacle
Prey
– Cnidocytes are unique stinging cells that capture prey
and function in defense.
Discharge
“Trigger” of thread
Coiled thread
Capsule
Cnidocyte
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Flatworms are the simplest bilateral animals
ƒ The vast majority of animal species belong to the
clade Bilateria, consisting of animals with bilateral
symmetry.
Gastrovascular
cavity
Nerve cords
ƒ Flatworms (phylum Platyhelminthes) are the
simplest bilaterians.
Mouth
Eyecups
ƒ Flatworms live in marine, freshwater, and damp (潮濕)
terrestrial habitats.
Nervous
tissue clusters
ƒ Some are parasitic and others are free-living.
Bilateral symmetry
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Flatworms are the simplest bilateral animals
ƒ There are three major groups of flatworms.
1. Free-living flatworms (planarians) have
– heads with light-sensitive eyespots,
Flatworms are the simplest bilateral animals
2. Flukes (吸蟲) are parasitic flatworms with
– complex life cycles and
– suckers to attach to their hosts.
3. Tapeworms
– flaps (類耳瓣) to detect chemicals,
– are parasitic,
– dense clusters of nerve cells that form a simple brain and a pair
of nerve cords that runs the length of the body, and
– inhabit the digestive tracts of vertebrates,
– a branched gastrovascular cavity with a single opening.
– have an anterior scolex armed with hooks and suckers that
grasp (攫住) the host,
– consist of a ribbonlike body with repeated units,
– have no mouth, and simply absorb nutrients across their body
surface.
– The units at the posterior end of tapeworms are full of ripe eggs
that pass out of the host’s body.
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Nematodes have a pseudocoelom and a complete
digestive tract
ƒ Nematodes or roundworms (phylum Nematoda)
are abundant and diverse, with an estimated
500,000 species. Nematodes have
A tapeworm, a parasitic flatworm
– bilateral symmetry,
Units with
reproductive
structures
Hooks
Sucker
Scolex
(anterior
end)
– three tissue layers,
– a nonliving cuticle (表皮) covering the body that
prevents them from drying out,
– a pseudocoelom body cavity that functions to distribute
nutrients and as a hydroskeleton, and
– a complete digestive tract with a mouth and anus.
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Nematodes have a pseudocoelom and a complete
digestive tract
ƒ Although about 25,000 species of nematodes have
been named, estimates of the total number of
species range as high as 500,000.
ƒ Humans host at least 50 species of parasitic
nematodes.
Mouth
A free-living nematode
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Diverse molluscs are variations on a common
body plan
ƒ Molluscs (phylum Mollusca) have
– a muscular foot that functions in locomotion,
– a visceral (內臟) mass containing most of the internal
organs,
– a mantle, which may secrete a shell that encloses the
visceral mass, and
– a true coelom and a circulatory system that pumps blood
throughout the body.
– Many molluscs feed with a rasping (刮) radula, used to
scrape (刮) up food.
A dog heart infested by heartworm, a parasitic nematode
– The life cycle of many marine molluscs includes a ciliated
larva called a trochophore (擔輪幼蟲).
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Visceral mass
Coelom
Kidney
Heart
Mantle
Mantle
cavity
Reproductive
organs
Digestive
tract
Shell
Radula
Digestive
tract
Mouth
Anus
Gill
Mouth
Foot
Nerve
cords
Anus
Diverse molluscs are variations on a common
body plan
ƒ Gastropods are the largest group of molluscs and
include the snails and slugs. Gastropods are
– found in fresh water, salt water, and terrestrial
environments,
– the only molluscs that live on land, using the mantle
cavity as a lung, and
– often protected by a single, spiral shell.
– Sea slugs have lost their mantle and shell and have
long colorful projections that function as gills.
A sea slug (about 5 cm long)
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Diverse molluscs are variations on a common
body plan
ƒ Bivalves
– include clams, oysters, mussels, and scallops and
– have shells divided into two halves that are hinged
together.
– Most bivalves are sedentary suspension feeders,
attached to the substrate by strong threads.
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Eyes
A scallop (about 10 cm in diameter)
Mussels (each about 6 cm long)
Diverse molluscs are variations on a common
body plan
ƒ Cephalopods
– include squids, octopuses, and nautiluses,
– are fast, agile (敏捷) predators,
– have large brains and sophisticated sense organs,
including complex image-focusing eyes, and
– a shell that is large in a nautilus, small and internal in a
squid, or missing in an octopus.
– Squid are fast, streamlined predators that use a
muscular siphon for jet propulsion.
– Octopuses live on the seafloor, where they creep about
as active predators.
A chambered nautilus (about 21 cm in diameter)
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Annelids are segmented worms
ƒ Annelids (phylum Annelida) have
– segmentation, the subdivision of the body along its length
into a series of repeated parts,
– a true coelom that functions as a hydrostatic skeleton,
– a nervous system that includes a simple brain and ventral
nerve cord, and
– a closed circulatory system in which blood remains
enclosed in vessels throughout the body.
A squid (internal shell)
– Many invertebrates, such as molluscs and arthropods,
have an open circulatory system in which blood is
pumped through vessels into open body cavities.
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Annelids are segmented worms
Anus
ƒ Annelids are found in damp soil, the sea, and most
freshwater habitats.
Segment
wall
ƒ The three groups of annelids are
– earthworms and their relatives,
– polychaetes, and
Bristles
– leeches.
ƒ Earthworms ingest soil and extract nutrients,
aerating (透氣) soil and improving its texture.
Mucus-secreting
organ
Dorsal
Digestive
blood vessel
tract
Coelom
Brain
Mouth
Excretory
organ
Segment
wall
Ventral blood vessel
Nerve cord
Pumping segmental vessels
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Epidermis
Circular
muscle
Segment wall
(partition
between
segments)
Longitudinal
muscle
Dorsal blood
vessel
Excretory
organ
A giant Australian earthworm
Bristles
Intestine
Nerve cord
Ventral
blood vessel
Annelids are segmented worms
ƒ Polychaetes are the largest group of annelids.
– Each polychaete segment has a pair of fleshy
appendages with stiff bristles or chaetae.
Tube-building
polychaetes
– Polychaetes search for prey on the seafloor or live in
tubes and filter food particles.
ƒ Most leeches are free-living carnivores, but some
suck blood.
– Blood-sucking leeches use razor-like jaws, secrete an
anesthetic (麻醉) and an anticoagulant (抗凝血), and suck
up to 10 times their own weight in blood.
Polychaetes: tube-building polychaetes
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A freeswimming
polychaete
A sandworm
Arthropods are segmented animals with jointed
appendages and an exoskeleton
ƒ There are over a million species of arthropods
(phylum Arthropoda), including crayfish (螯蝦),
lobsters, crabs, barnacles, spiders, ticks, and
insects.
ƒ The diversity and success of arthropods are due to
their
– segmentation,
– a hard exoskeleton, and
– jointed appendages, for which the phylum is named.
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Arthropods are segmented animals with jointed
appendages and an exoskeleton
ƒ Arthropods have
– an open circulatory system and
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Thorax
Head
– an exoskeleton, an external skeleton that protects the
animal but must be shed in the process of molting to
permit growth.
Swimming
appendages
– The body of most arthropods includes a head, thorax,
and abdomen, although these segments may be fused.
Walking legs
Mouthparts (feeding)
Pincer (鉗) (defense)
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Arthropods are segmented animals with jointed
appendages and an exoskeleton
ƒ Living arthropods represent four major lineages.
1. Chelicerates (螯肢亞門動物) include horseshoe crabs
and arachnids, such as spiders, scorpions, mites, and
ticks.
– Most are terrestrial.
– Scorpions are nocturnal (夜行) hunters.
– Spiders are a diverse group that typically hunt insects or trap
them in webs of silk that they spin from specialized glands on
their abdomen.
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A black widow spider
(about 1 cm wide)
A scorpion
Arthropods are segmented animals with jointed
appendages and an exoskeleton
2. Millipedes and centipedes are identified by the number
of jointed legs per body segment.
– Millipedes are herbivores that have two pairs of short legs per
body segment.
– Centipedes are carnivores that have one pair of legs per body
segment.
A dust mite
(about 0.4 mm long)
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Arthropods are segmented animals with jointed
appendages and an exoskeleton
3. Crustaceans are nearly all aquatic. They include crabs,
shrimp, and barnacles, which feed with jointed
appendages.
4. Insects are the fourth lineage of arthropods, addressed
next.
Goose barnacles
(about 2 cm high)
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Insects are the most successful group of animals
A ghost crab
(body about
2.5 cm across)
ƒ 70% of all identified animal species are insects.
– There may be as many as 30 million insect species.
ƒ The body of an insect typically includes
– a head,
– thorax,
– abdomen,
– three sets of legs, and
– wings (with few exceptions).
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Insects are the most successful group of animals
Insects are the most successful group of animals
ƒ The extraordinary success of insects is due to
ƒ Insect life cycles often include metamorphosis,
during which the animal takes on different body
forms as it develops from larva to adult.
– body segmentation,
– an exoskeleton,
– More than 80% of insect species undergo complete
metamorphosis in which a free-living larva transforms
from a pupa into an adult.
– jointed appendages,
– flight,
– a waterproof cuticle, and
– a complex life cycle with short generations and large
numbers of offspring.
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– Other insect species undergo incomplete
metamorphosis in which the transition from larva to
adult is achieved through multiple molts, but without
forming a pupa.
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Larva (grub 蠐螬, up
to 12 cm length)
Head
Adult (up to 4
cm length)
Antenna
Thorax
Specialized
jumping legs
Abdomen
Wings
(extensions of cuticle)
Eye
Pupa
Mouthparts
Walking legs
Insects are the most successful group of animals
Insects are the most successful group of animals
ƒ Insect mouthparts are adapted for various types of
feeding, such as
ƒ Insects have three pairs of legs, which are adapted
for
– chewing (grasshoppers),
– walking,
– biting and tearing prey (mantids),
– jumping,
– lapping up fluids (houseflies), and
– grasping prey,
– piercing and sucking fluids of plants (aphids 蚜蟲) and
animals (mosquitoes).
– digging in soil, or
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– paddling on water.
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Insects are the most successful group of animals
ƒ Wings
– Most adult insects have one or two pairs of wings,
allowing dispersal and escape from predators.
– Because wings are extensions of the cuticle, insects
have acquired (獲致) flight without sacrificing any legs.
ƒ Protective color patterns
– Many insects have protective color patterns and
disguises, including modifications to antennae, wings,
and bodies.
A stick insect
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A leaf-mimic katydid
A caterpillar resembling
a bird dropping
A hawk moth (天蛾) caterpillar
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Echinoderms have spiny skin, an endoskeleton,
and a water vascular system for movement
Echinoderms have spiny skin, an endoskeleton,
and a water vascular system for movement
ƒ Echinoderms (phylum Echinodermata) are
ƒ Echinoderms have
– a diverse group including sea stars, sand dollars, and
sea urchins,
– an endoskeleton of hard calcareous plates under a thin
skin,
– slow-moving or sessile,
– all marine,
– a water vascular system based on a network of waterfilled canals that branch into extensions called tube feet,
and
– radially symmetrical, and
– the ability to regenerate lost arms.
– deuterostomes (along with the chordates).
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Anus
Spines
Tube foot
Stomach
Tube feet
Canals
Our own phylum, Chordata, is distinguished by
four features
ƒ Chordates (phylum Chordata) are defined by
– a dorsal, hollow nerve cord,
– a flexible, supportive notochord,
Spines
– pharyngeal slits, and
– a muscular post-anal tail.
Tube feet
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Our own phylum, Chordata, is distinguished by
four features
Excurrent
siphon
ƒ The simplest chordates are tunicates and lancelets
(文昌魚), which
Post-anal tail
Dorsal, hollow
nerve cord
– do not have a backbone and
Notochord
– use their pharyngeal slits for suspension feeding.
Pharyngeal
slits
– Adult tunicates are stationary and attached, while the
tunicate larva is a tadpole-like organism.
Mouth
Muscle
segments
– Lancelets are small, bladelike chordates that live in
marine sands.
Adult
(about 3 cm high)
Larva
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ANIMAL PHYLOGENY
AND DIVERSITY REVISITED
Head
Mouth
Pharynx
Pharyngeal slits
Notochord
Digestive tract
Water exit
Dorsal, hollow
nerve cord
Post-anal tail
Segmental muscles
Anus
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An animal phylogenetic tree is a work in progress
No true
tissues
Sponges
Radial
symmetry
True
tissues
Bilaterians
蛻皮動物
Ecdysozoans
Bilateral
symmetry
Lophotrochozoans
Deuterostomes
ƒ A slightly revised tree based on this new molecular
data.
Cnidarians
後生動物
ƒ Recently, scientists have accumulated molecular
data such as DNA sequences that shed new light
on these phylogenetic relationships.
Ancestral
colonial
protist
Eumetazoans
ƒ Biologists used evidence from the fossil record,
morphology, and embryology to make hypotheses
about the evolutionary history of animal groups.
Flatworms
Molluscs
Annelids
Nematodes
Arthropods
Echinoderms
Chordates
© 2012 Pearson Education, Inc.
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The genes that build animal bodies are ancient
ƒ Genes responsible for building animal bodies are
shared by virtually every member of the animal
kingdom.
ƒ These ancient genes are the master control genes
called homeotic genes.
ƒ Changes in the regulation of homeotic gene
expression have been significant factors in the
evolution of animal diversity.
Peripatus, a velvet worm
© 2012 Pearson Education, Inc.
Antenna
Appendages
Expression of homeotic genes in the embryos of a centipede (left)
and a velvet worm (right)
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