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Animal Kingdom:
Evolution and Diversity
Characteristics of Animals
• Multicelled
• Aerobic heterotrophs
• Sexual reproduction
– Some also reproduce asexually
– Embryos produce primary tissues
• Motile at some stage
Animal Lineages
• Vertebrates (single phylum: Chordata)
– Mammals
– Birds
– Reptiles
– Amphibians
– Fishes
• Invertebrates (many phyla)
– No backbone
Sponges
No true tissues
Cnidarians
Radial symmetry
Ancestral
protist
Molluscs
Flatworms
Tissues
Annelids
Roundworms
Arthropods
Bilateral symmetry
Echinoderms
Chordates
Figure 17.5
Evolutionary Tree
sponges
cnidarians
flatworms
coelom lost
annelids mollusks roundworms
coelom
reduced
pseudocoel
arthropods
echinoderms
chordates
coelom
reduced
molting
radial ancestry, two
germ layers
true tissues
multicelled
body
PROTOSTOMES
mouth from blastopore
DEUTEROSOMES
anus from blastopore
bilateral, coelomate ancestry,
three germ layers
Fig. 16-1, p.260
Animal Origins
• Monophyletic group
• Ediacarans
– Oldest date to 610 million years ago
– Variety of forms
Animal Origins
• Cambrian explosion of diversity
Animal Diversity
Many characteristics are used to group animals
and determine evolutionary links
• Body Plans
– Symmetry
– Segmentation and cephalization
– Body cavities
• Digestive systems (none, incomplete, complete)
• Embryonic Development (protostome vs
deuterostome)
Body Plans
• Radial symmetry
– Parts arrayed around a central point
• Bilateral symmetry
– Two halves that mirror each other
• Cephalization
– Concentration of nerve and sensory cells
at anterior end
Symmetry
Radial
Bilateral
Segmentation
• Repeating series of body units
• Units may or may not be similar to
one another
– Earthworms: segments appear similar
– Insects: segments may be fused and/or
have specialized functions
Body Cavities
• Coelom– Space between the gut and body wall that
allows internal organs to expand and
operate freely
– A “true” coelom is a body cavity lined with
peritoneum.
Body Cavities: Acoelomate
epidermis
gut cavity
no body cavity; region between gut
and body wall packed with organs
Body Cavities: Pseudocoel
epidermis
gut cavity
unlined body cavity
(pseudocoel) around gut
Body Cavities: Coelom
gut cavity
lined body cavity
(coelom)
peritoneum
Digestive Systems
• Region where food is digested and
then absorbed
• No digestive system- intracellular (in
cell) digestion (e.g. sponges)
• Incomplete digestive system ( saclike gut)
– One opening for taking in food and
expelling waste (e.g. flatworms, sea anemones)
• Complete digestive system
– Opening at both ends, mouth and anus
Sponges
• No symmetry, tissues, or organs
• Filter feeders
• Reproduce sexually
• Microscopic swimming larva
Sponges
water out
glasslike
structural
elements
amoeboid
cell
pore
semifluid
matrix
central
cavity
flattened
surface
cells
water in
Fig. 16-4, p.262
Cnidarians
• Only animals that produce nematocysts
• Epithelial tissues
• Nerve net
• Hydrostatic skeleton
• Saclike gut
• Medusa and polyp forms
• Jellyfish, corals, sea anemones, hydras
Nematocyst
lid
capsule's
trigger
(modified
cilium)
barbs on
discharged
thread
exposed
barbed
thread in
capsule
nematocyst (capsule at free surface of epidermal cell)
Fig. 16-5, p.262
Cnidarian Body Plans
Cnidarian Body Plans
outer epithelium
(epidermis)
mesoglea
(matrix)
inner epithelium
(gastrodermis)
Fig. 16-6a,b, p.263
Protostome vs Deuterostome
• Two animal lineages distinguished by
embryonic development
• Protostome (first mouth)- blastopore
develops into mouth
– (e.g.) insects, snails, worms
• Deuterostome (second mouth)
blastopore develops into anus
– (e.g.) seastars, vertebrates
Sperm
FERTILIZATION
MEIOSIS
Egg
MITOSIS
Zygote
(fertilized egg)
Eight-cell stage
Adult
Blastula
(cross section)
Digestive tract
Outer cell layer
(ectoderm)
Larva
Inner cell layer
(endoderm)
Internal sac
Early gastrula
(cross section)
Later gastrula Future middle
(cross section) layer of cells
(mesoderm)
Key
Haploid (n)
Diploid (2n)
Figure 17.2-7
Protostome vs Deuterostome
Flatworms
• Bilateral, cephalized, no body cavity
• Most are hermaphrodites
• Include
– Turbellarians (including planarians)
– Flukes (including schistosomes)
– Tapeworms
Fig. 16-7, p.263
Schistosomes
• Parasitic worms
• Complicated life
cycle
– Larval stage
infects a mollusk
– Adult infects a
vertebrate
Worms mate in
human host.
Larvae bore
into human
skin.
Larvae form,
leave snail.
fertilized egg
Asexual reproduction
in intermediate host.
ciliated larva
Southeast Asian blood fluke
Tapeworm
proglottids
a Larvae, each
with inverted
scolex of future
tapeworm,
become encysted
in intermediate
host tissues
(e.g., skeletal
muscle)
scolex
b A human, a definitive
host, eats infected,
undercooked beef which
is mainly skeletal muscle
d Inside each fertilized egg, an
embryonic, larval form develops. Cattle
may ingest embryonated eggs or ripe
proglottids, and so become intermediate
hosts
c Each sexually mature
proglottid has female
and male organs. Ripe
proglottids containing
fertilized eggs leave
host in feces, which may
contaminate water and
vegetation.
Fig. 16-8, p.264
Annelids
• Segmented, coelomates
– Earthworms
– Leeches
– Marine polychaetes
• Some with rudimentary brains
and nerve cords
Setae
• Chitin-reinforced bristles for crawling
• Oligochaetes
– Few bristles per segment
– earthworms
• Polychaetes
– Many bristles per segment
– Marine worms
Earthworm
setae (bristles)
Fig. 16-9b, p.265
Earthworm
coelomic
chamber
seta
(retracted)
circular
muscles
longitudinal
muscles
Fig. 16-9c, p.265
Annelid Diversity
Marine polychaetes
Leeches
before
feeding
Feeding leech
after
feeding
Mollusks
• Bilateral, softbodied, coelomate
• Many have a shell
or reduced version
of one
• Mantle drapes
over body and
secretes shell
mantle
Mollusks
anus
gill
excretory organ
heart
mantle
cavity
digestive
gland
stomach
shell
mantle
radula
foot
Fig. 16-11a, p.266
Molluscan Diversity
• Gastropods (snails)
• Chitons
• Bivalves (clams, etc)
• Cephalopods (squids, octopuses)
Cephalopod Adaptations
• Closed circulatory system
– Increases oxygen
• Squids
– Fastest invertebrates
– Jet propulsion
• Octopuses
– Smartest invertebrates
– Largest brains
– Most complex eye among inverts.
Mollusks
Fig. 16-11c, p.266
Evolutionary Tree
sponges
cnidarians
flatworms
coelom lost
annelids mollusks roundworms
coelom
reduced
pseudocoel
arthropods
echinoderms
chordates
coelom
reduced
molting
radial ancestry, two
germ layers
true tissues
multicelled
body
PROTOSTOMES
mouth from blastopore
DEUTEROSOMES
anus from blastopore
bilateral, coelomate ancestry,
three germ layers
Fig. 16-1, p.260
Roundworms (Nematodes)
• Bilateral, cephalized
• Pseudocoelom
• Complete digestive system
• Most free-living
• Some parasitize plants, animals,
or humans
– Trichinosis
– Elephantiasis
Roundworms
Arthropods
• Invertebrate group with the greatest number of
species
• Five lineages:
–
–
–
–
–
Trilobites (extinct)
Chelicerates (spiders, mites, ticks, scorpions)
Crustaceans (crabs, shrimps, barnacles)
Insects
Myriopods (centipedes, millipedes)
Adaptations for Success
• Hardened exoskeleton
• Jointed appendages
• Fused and modified segments
• Respiratory structures
• Specialized sensory structures
• Specialized developmental stages
Exoskeleton
• Molting of the cuticle
Metamorphosis
• Division of labor between different
developmental stages
• Growth as embryo (caterpillar)
• Reproduction and dispersal as adult
(butterfly)
Chelicerates
• Marine chelicerates
– horseshoe crabs, sea spiders
• Arachnids (terrestrial chelicerates)
Spiders
Scorpions
“Daddy longlegs”
Mites
Chiggers
Ticks
Arachnids
Phylum Arthropods – Class Arachnids
from scorpions to spiders
Crustaceans
• Most are marine,
some freshwater, a
few terrestrial
Copepods
• Head has two pairs of
antenna, three pairs
of food-handling
appendages
Lobsters
Crayfish
Barnacles
Shrimps
Crabs
Isopods (pillbugs)
Crab Life Cycle
Larval and juvenile
stages molt repeatedly
and grow in size
egg
Crustaceans
Insects
• 3 Segments
– Head, thorax, abdomen
• The only winged invertebrates
• More than 800,000 known species
• High reproductive capacity
Insect Diversity
• The most successful animals in terms of
– Distribution
– Number of species
– Population size
– Competitive adaptations
– Exploitation of diverse foods
Evolutionary Tree
sponges
cnidarians
flatworms
coelom lost
annelids mollusks roundworms
coelom
reduced
pseudocoel
arthropods
echinoderms
chordates
coelom
reduced
molting
radial ancestry, two
germ layers
true tissues
multicelled
body
PROTOSTOMES
mouth from blastopore
DEUTEROSOMES
anus from blastopore
bilateral, coelomate ancestry,
three germ layers
Fig. 16-1, p.260
Echinoderms
• Marine group
• Calcium carbonate
spines or plates
Crinoids (sea lilies)
Sea stars
• No brain
Brittle stars
• Tube feet
Sea urchins
• Adults radial with
bilateral features
Sand dollars
Sea cucumbers
Echinoderms
Body Plan of a Sea Star
Body plan of a sea star
Chordates
• Chordate Features
– Notochord supports body
– Nervous system develops from dorsal
nerve cord
– Embryos have pharynx with slits
– Embryos have tail that extends
past anus
Chordate Evolution
ray-finned lobe-finned
cartilaginous
fishes
fishes
lungfishes amphibians “reptiles” birds mammals
tunicates lancelets hagfishes lampreys fishes
amniotes
tetrapods
vertebrates
ancestral
chordates
jawed
vertebrates lungs or swim bladder
craniates
Fig. 16-20a, p.273
Tunicates
• Notochord, tail and
nerve cord occur
only in larval stage
• (tadpole larval)
Neoteny
(paedomorphosis)
: sexual maturity
in larval stage
Lancelet:
An Invertebrate Chordate
Lancelet body plan
Craniates (Vertebrates)
• A chamber of cartilage or bone holds
the brain
Fishes
Amphibians
Reptiles
Birds
Mammals
Key Innovations
• Shift from notochord to vertebrae
• Nerve cord expanded into brain
• Evolution of jaws
• Paired fins evolved, gave rise to limbs
• Gills evolved, and eventually lungs
Evolution of Craniates
supporting structures
gill slit
jaw
Jawed Fishes
• Most diverse and numerous group of
vertebrates
• Cartilaginous fishes
Sharks and rays
• Bony fishes
Ray-finned fishes
Lungfishes
Lobe-finned fishes
Fig. 16-22d, p.274
Evolution of Jaws
Evolution of jaws
Cartilaginous Fishes
Fig. 16-23, p.275
Ray-Finned Bony Fishes
 Soft


ray fishes
Salmonids (salmon, trout)
Cyprinids (carp, gold fish, Koy)
 Spiny



ray fishes
Perciform (perch, bass, blue gill)
Scorpiniform (sculpin, rock fish, ling cod)
Scrombiform (tuna, sword fish, etc)
Ray-Finned Bony Fishes
Spiny ray fish (bass)
dorsal fins
pectoral
fin
caudal fin
anal fin
Soft ray fish (trout)
pelvic fin
dorsal fin
caudal fin
anal fin
pelvic fin (pair)
pectoral fin
Fig. 16-24a, p.275
Lobed Fins to Tetrapods
• Coelocanths and lungfishes
inside lobed fins, bony or
cartilaginous structures
undergoing modification
limb bones of an
early tetrapod
Fig. 16-25d, p.276
Early Amphibians
• Fishlike skull
and tail
• Four limbs
(tetrapods)
Ichthyostega
• Short neck
Acanthostega
Modern Amphibians
• Require water at some stage in life
cycle; most lay eggs in water
• Lungs are less efficient than those of
other vertebrates
• Skin serves as respiratory organ
• Frogs, toads, salamanders
Modern Amphibians
Rise of Amniotes
• Arose during Carboniferous
• Adaptations to life on land
– Tough, scaly skin
– Internal fertilization
– Amniote eggs
– Water-conserving kidneys
Amniote Egg
yolk sac
embryo
amnion
allantois
chorion
albumin
hardened
shell
Living Reptiles
• Not a monophyletic group
Crocodilians
Turtles
Snakes and lizards
Reptiles
Dinosaurs
• Descended from Triassic reptiles
• Several mass extinctions, ending with K-T
asteroid impact
• Some are now considered early birds
Birds
• Vertebrates with feathers
– Diverse
– Good learners
• Diverged from small dinosaurs during
Mesozoic
• Amniote eggs fertilized internally
Feathers and Flight
• Flight required full-body modification
– Bone structure, respiration, circulation
– Wings, feathers, musculature
Mammal Characteristics
• Hair
• Mammary glands
• Distinctive teeth
• Highly developed brain
• Extended care for young
Three Mammalian Lineages
• Monotremes
– Egg-laying mammals
• Marsupials
– Pouched mammals
• Eutherians
– Placental mammals
Mammals