Animal EvolutionAnimal Evolution

The BasicsThe 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

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/Eumetazoa1st Major Division:

Parazoa/Eumetazoa Parazoa:

– No true tissues– Phylum Porifera (sponges)

Eumetazoa:– Have true tissues

Parazoa:– No true tissues– Phylum Porifera (sponges)

Eumetazoa:– Have true tissues

2nd Major Division:Radiata/Bilateria

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

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 acentral point

Asymmetry:No planes ofsymmetry

Bilateral symmetry:Symmetry across thesagittal plane

dorsal

ventral

posterior

anterior

sagittalplane

Bilateral symmetry: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

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, 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

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

ectoderm

mesoderm

endoderm (gut)

No coelom (acoelomate)

Pseudocoel

Coelom

roundworm

earthworm

ectoderm

mesoderm

endoderm (gut)

pseudocoel(mesoderm on one side only)

ectoderm

mesoderm

endoderm (gut)

coelom(surrounded by mesoderm)

flatworm

4th Major Division: Protostomes/Deuterostomes

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

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 formationCoelom

Archenteron

Blastopore Mesoderm

Enterocoelous:folds of archenteronform coelom

Coelom

BlastoporeMesoderm

Schizocoelous: solidmasses of mesodermsplit and form coelom

LE 32-9c

Protostome development(examples: molluscs,

annnelids, arthropods)

Deuterostome development(examples: echinoderms,

chordates)

Fate of the blastoporeMouth

Anus developsfrom blastopore

AnusMouth

Mouth developsfrom blastopore

Anus

Digestive tube

blastoporeinvagination

mouth anus

a Early embryo

blastoporeinvagination

mouthanus

b Adult

mouth anus

anus mouth

dorsal heart

dorsal nerve cord

ventralheart

ventralnerve cord