Ward_Lect26A_Development_Sponges_ppt

Ward_Lect26A_Development_Sponges_ppt - BIS2C Winter 2010...

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Unformatted text preview: BIS2C Winter 2010 (Ward) Lecture 26. Animal development (contd) & Sponges Todays lecture (24 February) animal development sponges (Porifera) Fridays lectures Cnidaria & Ctenophora introduction to Bilateria Animal Development Zygote Blastula Gastrula Cleavage : early stages of cell division after zygote formation, resulting in multiple cells (blastomeres) and establishment of a longitudinal axis (animal-vegetal axis) Animal Development Cleavage : early stages of cell division after zygote formation Patterns of cleavage vary among different animal groups, especially as a function of how much yolk (stored nutrient) is in the egg. In invertebrates we can distinguish two fundamental kinds of cleavage: radial cleavage and spiral cleavage . Animal Development Cleavage : early stages of cell division after zygote formation Radial cleavage : cells divide parallel to, or at 90 to, the animal- vegetal axis, and accumulate in even, symmetrical layers Spiral cleavage : cells divide at an oblique angle to the animal- vegetal axis, and new cells lies in furrows between existing ones Animations available at: http://learning.ucdavis.edu/DevBio/ Animal Development Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Animal Development Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Diploblastic animals: two cell layers formed, ectoderm and endoderm Animal Development Animal Development Gastrulation: formation of cell layers by invagination (in-pocketing) of blastula to form gastrula Triploblastic animals: three cell layers formed, ectoderm , endoderm and mesoderm blastula blastula gastrula diploblasty blastula gastrula diploblasty triploblasty Which of the following statements is false ? 1. Animals exhibiting a blastula stage of development form a monophyletic group. 2. Animals exhibiting a gastrula stage of development form a paraphyletic group. 3. Animals with diploblastic development form a paraphyletic group. 4. Animals with triploblastic development are a clade. Major lineages of metazoans Major lineages of metazoans Sponges (Porifera) According to your textbook ( Life, 8 th Edition ) sponges are a paraphyletic group comprising three clades: 1. glass sponges (Hexactinellida) 2. demosponges (Demospongiae) 3. calcareous sponges (Calcarea) What does this suggest about the features observed in sponges? Pick the best answer....
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Ward_Lect26A_Development_Sponges_ppt - BIS2C Winter 2010...

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