26_Ward_Development+_+Sponges+Outline

26_Ward_Development+_+Sponges+Outline - BIS2C W2011 Animal...

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BIS2C W2011 Lecture 26 (18 February 2011) 1 Animal development; Sponges Animal development Zygote blastula gastrula Cleavage : the early stages of cell division after formation of the zygote Radial cleavage (ancestral condition) versus spiral cleavage Gastrulation : formation of cell layers, by in-pocketing of blastula to form gastrula. Diploblastic construction : only two cell layers (ectoderm and endoderm) Triploblastic construction: three cell layers (ectoderm, endoderm and mesoderm). Gastrulation: synapomorphy of Eumetazoa. Triploblasty: synapomorphy of Bilateria. Map these conditions on the metazoan tree. Sponges (Porifera) According to textbook ( Life, 9 th Edition ) sponges are a monophyletic group comprising three lineages: glass sponges (Hexactinellida) demosponges (Demospongiae) calcareous sponges (Calcarea) In previous edition ( Life, 8 th Edition ) they were considered paraphyletic. Consider implications of this for inferring the ancestral metazoan condition. Sponge features
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This note was uploaded on 03/09/2011 for the course BIS 2 taught by Professor Coolprof during the Spring '11 term at Bank Street College of Education.

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26_Ward_Development+_+Sponges+Outline - BIS2C W2011 Animal...

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