Lecture_10_Animals_I

Lecture_10_Animals_I - 6/15/2011 What is an animal? Animals...

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6/15/2011 1 Animals I LS1: Summer Session A July 15, 2011 What is an animal? Animals are characterized by several general features: Multicellularity Ingestive heterotrophy Internal digestion Movement But not all animals exhibit these traits at all times Animal monophyly Animal monophyly is well-supported Although very few features are shared by ALL animals, phylogenetic evidence supports their monophyly Animals also have unique junctions between the cells as well as unique extracellular matrices Evidence from the field of evo-devo also supports the unity of animals as a clade Say hello to your gajillionth cousin (twice removed) Animals are most likely descended from a colonial flagellated protist similar to the modern choanoflagellates. The origin of animals Originated during the Precambrian (1.2 billion - 670 million years ago) Descended from a choanoflagellate protistan ancestor Some species of choanoflagellates are colonial They produce signaling molecules and adhesion proteins, which are the basis for tissue differentiation and adhesion in modern animals
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6/15/2011 2 Animal phylogeny Animal lineages The phylogeny of animals represents an evolutionary history The organisms within a lineage share features due to shared ancestry As we progress through the different animal phyla, be aware of the features that unite the animals within a lineage What sort of features? Embryological features Cleavage Number of tissue layers Gastrulation Body plans Symmetry Body cavities Segmentation Appendages Guts and diet Life cycles Cleavage In early embryonic development, cell divisions are characteristically different in different animal groups. These patterns are referred to as cleavage patterns. Tissue layers During early embryonic development, distinct tissue layers form Diploblastic animals have two tissue layers: endoderm and ectoderm Triploblastic animals have an additional layer called mesoderm Gastrulation The fate of the blastopore differs between the protostomes and the deuterostomes . In protostomes, the blastopore develops into the mouth. In deuterostomes, it becomes the anus.
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6/15/2011 3 Symmetry Animals may be asymmetrical, but most exhibit one of two kinds of symmetry: Radial symmetry , where the body is arranged around a single, central axis; or Bilateral symmetry , in which the animal can be divided into a mirror image along a single plane Body cavities Acoelomate animals lack a body cavity Pseudocoelomate animals have a body cavity lined only on one side by mesoderm Coelomate animals have a
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This note was uploaded on 09/08/2011 for the course LS 1 taught by Professor Thomas during the Summer '05 term at UCLA.

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Lecture_10_Animals_I - 6/15/2011 What is an animal? Animals...

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