Download Introduction to Animal Evolution

Animal Evolution
The Basics
 Animals = multicellular, heterotrophic
 Life history:
– Sexual w/ flagellated sperm/nonmotile egg
– Development: cleavage, blastula, gastrula,
some have larval stage, metamorphosis
 Probably evolved from a flagellated protist
1st Major Division:
Parazoa/Eumetazoa
 Parazoa:
– No true tissues
– Phylum Porifera (sponges)
 Eumetazoa:
– Have true tissues
2nd Major Division:
Radiata/Bilateria
 Radiata:
– Have radial symmetry
– Top and bottom sides
 Oral: mouth side
 Aboral: other side
– Only ecto/endoderm = diploblastic
– 2 phyla: Cnidaria (ex: jelly fish) & Ctenophora
 Bilateria:
– Bilateral symmetery
– 3 axes: Dorsal/ventral, anterior/posterior, right/left.
– 3 germ layers = triploblastic-ectoderm, mesoderm,
endoderm
Radial symmetry:
Symmetry around a
central point
Asymmetry:
No planes of
symmetry
Bilateral symmetry:
Symmetry across the
sagittal plane
dorsal
posterior
sagittal
plane
anterior
ventral
Bilateral symmetry:
 Associated w/ cephalization
– Concentration of sensory organs @ anterior end
– Many animals have CNS in head & a nerve cord
extending posterior
– Adaptation for movement/predation
Acoelomates,
Pseudocoelomates, Coelomates
 Acoelomates: 3 layers, but no body cavity
– Ex: Platyhelminthes (flatwoms)
 Psedocoelomates: cavity, but not
completely lined by mesoderm
– Ex: Phylum Nematoda, Rotifera
 Coelomates: True fluid-filled cavity,
completely lined by mesoderm
– Have mesentaries: connect layers, suspend
organs
No coelom (acoelomate)
ectoderm
mesoderm
flatworm
Pseudocoel
endoderm (gut)
ectoderm
mesoderm
pseudocoel
(mesoderm on one side only)
roundworm
Coelom
endoderm (gut)
ectoderm
mesoderm
coelom
(surrounded by mesoderm)
endoderm (gut)
earthworm
4th Major Division:
Protostomes/Deuterostomes
 Protostomes:
– Cleavage: Spiral, determinate
– Coelom formation: schizocoelous
– Blastopore: becomes mouth
 Deuterostomes:
– Cleavage: Radial, indeterminate
– Coelom formation: enterocoelus
– Blastopore: becomes anus
LE 32-9b
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Schizocoelous: solid
masses of mesoderm
split and form coelom
Blastopore
Mesoderm
Enterocoelous:
folds of archenteron
form coelom
LE 32-9c
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Mouth
Anus
Digestive tube
Mouth
Mouth develops
from blastopore
Anus
Anus develops
from blastopore
Fate of the blastopore
a Early embryo
b Adult
dorsal heart
anus
invagination
blastopore
mouth
invagination
mouth
blastopore
ventral
nerve cord
anus
mouth
dorsal nerve cord
anus
mouth
ventral
heart
anus