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  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  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  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 ventral posterior anterior sagittal plane

Bilateral symmetry:  Associated w/ cephalization –Concentration of sensory anterior end –Many animals have CNS in head & a nerve cord extending posterior –Adaptation for movement/predation  Associated w/ cephalization –Concentration of sensory 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  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  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 formation Coelom Archenteron Blastopore Mesoderm Enterocoelous: folds of archenteron form coelom Coelom BlastoporeMesoderm Schizocoelous: solid masses of mesoderm split and form coelom

LE 32-9c Protostome development (examples: molluscs, annnelids, arthropods) Deuterostome development (examples: echinoderms, chordates) Fate of the blastopore Mouth Anus develops from blastopore AnusMouth Mouth develops from blastopore Anus Digestive tube

blastoporeinvagination mouthanus a Early embryo blastoporeinvagination mouthanus b Adult mouth anus mouth dorsal heart dorsal nerve cord ventral heart ventral nerve cord