BIOL1131 Lecture Notes - Lecture 1: Arthropod, Chordate, Body Cavity
7 Jun 2018
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The Advent of Animals
• Animal life evolved first, in the sea ~600mYa
• Cambrian Explosions 545-510mYa
o Large, diverse fauna of many phyla, especially arthropods
o Exoskeletons easily fossilized
• Life started with Eukaryotes before evolving to Prokaryotes
• There are three theories of animal multicellularity:
o Ciliate protist in which partitioned cytoplasm gave rise to an
organism resembling a flatworm
o Flagellate protist similar to choanocytes of sponges
o Two-layered organism similar to Trichoplax
o The second theory is the most supported
• 90% of animals are in these nine phylum
• Symmetry
o Bilateral Symmetry
▪ Animals have anterior and posterior ends
▪ Promotes cephalization, locomotion and concentration of
sensory organs
o Radial Symmetry
o No Symmetry
• Germ Layers and Tissues
o Germ layers form during embryological development
▪ Endoderm – inner layer
▪ Mesoderm – middle layer
▪ Ectoderm – outer layer
o Develop into tissues – aggregations of similar cells connected by
an extracellular matrix, e.g. muscle, blood, bone
• Body Layers
o Animals may have
▪ Layers of cells but no tissues
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