cnidaria - anemones collar cell of a sponge ... · cnidaria - jellyfishcnidaria - corals ctenophora...
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Choanoflagellata Porifera - sponges
Collar cell of a spongeCnidaria - anemones
Cnidaria - jellyfish Cnidaria - corals
Ctenophora - comb-jellies Brachiopoda - lamp shells
EchinodermataHemichordata - acorn
worms
Chordata - sea
squirts,
lancelets,
vertebrates
Platyhelminthes - flatworms
Nemertea - ribbon wormsMollusca
Annelida - segmented
worms Annelida - earthworm
Annelida - polychaetes Arthropoda - arachnids
Arthropoda - crustaceans Arthropoda - insects
Arthropoda - centipedes
and millipedes (myriapods)
Onychophora - velvet
worms
Nematoda - roundwormsSignificant evolutionary events
during the Cambrian explosion
! 1 - evolution of multicellularity - animals
can therefore become large
! 2 - evolution of true tissues
" The most primitive animals with true tissues
(the Cnidaria) are diploblastic -
" They have two embryonic (or germ) layers:
ectoderm and endoderm
Cnidarian cell typesSignificant evolutionary events
during the Cambrian explosion
! 3 - evolution of triploblastic animals
! 4 - evolution of HOX genes
HOX genesSponge
Flatworm
Earthworm
Velvet worm
Crustacean
Centipede
Fruit fly
Amphioxus
Mouse
Zebrafish
Figure 24.8
Foot
FinHoxd-11 expression
along long axis of limb
Hoxd-11 expression as in fish,
followed by expression toward head
Head TailHead Tail
(c) Hypothesis
(b) Later in
development
(a) Early in
development
FISH LIMB BUD MOUSE LIMB BUD
Figure 24.9
Hoxd-11 transcripts
in hind part of limb
bud
Head Tail
Later in
development
Early in
development
FISH LIMB BUD
Few Hoxd-11
transcripts, only
in hind part
Figure 24.9a,b left
Hoxd-11 transcripts
in hind part of limb
bud
Head Tail
MOUSE LIMB BUD
Hoxd-11 transcripts
along head-tail axis
Figure 24.9a,b right
Significant evolutionary events
during the Cambrian explosion
! 5 - the evolution of radial cleavage
Significant evolutionary events
during the Cambrian explosion
! 6 - the evolution of deuterostomatous
development
Significant evolutionary events
during the Cambrian explosion
! 7 - the evolution of a coelom(body cavity lined withmesoderm)
DeuterostomiaSignificant evolutionary events
during the Cambrian explosion
! 8 - the evolution of spiral cleavage
Significant evolutionary events
during the Cambrian explosion
! 9 - the evolution of protostomatous development
Protostomia
Significant evolutionary events
during the Cambrian explosion
! 10 - the evolution of a coelom (body cavity linedwith mesoderm)
Significant evolutionary events
during the Cambrian explosion
! 11 - the evolution ofsegmentation
Significant evolutionary events
during the Cambrian explosion
! 12 - the evolution of a calcified exoskeleton
Arthropod appendages