protostomes 1

protostomes 1 - Flatworms (last lecture) are acoelomate: no...

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Flatworms (last lecture) are acoelomate : no body cavity. The rest of the phyla we discuss do have body cavities: Porifera Cnidaria Platy- Nematoda Annelida Arthropoda Mollusca Echino- Chordata helminthes dermata fundamental symmetry and number of germ layers development pattern the nature of the body cavity presence or absence of a body cavity Protostoma Deuterostoma Eucoelomates Pseudocoelomates other Bilateria Acoelomates Protistan ancestor Eumetazoa Parazoa Bilateria Radiata First, Pseudocoelomates (Nematodes, or roundworms) Porifera Cnidaria Platy- Nematoda Annelida Arthropoda Mollusca Echino- Chordata helminthes dermata fundamental symmetry and number of germ layers development pattern the nature of the body cavity presence or absence of a body cavity Protostoma Deuterostoma Eucoelomates Pseudocoelomates other Bilateria Acoelomates Protistan ancestor Eumetazoa Parazoa Bilateria Radiata • Most successful of several pesudocoelomate phyla; 80- 100,000 described species, probably > 500,000 total. • Found in most habitats (marine, freshwater, terrestrial, free living and parasitic); abundant and important ecologically All very similar in body plan: • Organ system level of organization Motile and cephalized -- ‘skeleton’ is hydrostatic and viscoelastic External cuticle -- protection, support, etc. -- key to the success of this group; molted ~ 4 times during maturation Internal cavity : pseudocoelom , formed from blastocoel Pseudocoelomates: phylum Nematoda Blastocoel Blastula Pseudocoelomates: phylum Nematoda Internal cavity : pseudocoelom , formed from blastocoel early in development:
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Gastrulation Blastopore, forms mouth Early mesodermal Cells, near blastopore Pseudocoelomates: phylum Nematoda Internal cavity : pseudocoelom , formed from blastocoel early in development: Blastocoel Blastopore, forms mouth Mesoderm grows around outside of blastocoel Gastrulation Pseudocoelomates: phylum Nematoda Internal cavity : pseudocoelom , formed from blastocoel early in development: Blastocoel Internal cavity : pseudocoelom , formed from blastocoel early in development: Blastopore, forms mouth Anus forms secondarily Mesoderm lines outer border of blastocoel Pseudocoelomates: phylum Nematoda Blastocoel Adult body plan of nematodes, with pseudocoelom , no mesodermal tissue around gut. Other major features: Eutely (constant cell number) to varying degrees -- important ‘model animals’ ectoderm mesoderm pseudocoel gut (no muscle) gut lumen cross-section Pseudocoelomates: phylum Nematoda Chaenorhabditis elegans: adult has 959 somatic cells, plus reproductive cells (gonads)
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Adult body plan of nematodes, with pseudocoelom , no mesodermal tissue around gut. Other major features: Eutely (constant cell number) to varying degrees -- important ‘model animals’ Complete gut with mouth and anus Longitudinal cross-section:
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This note was uploaded on 04/17/2008 for the course BIO 005b taught by Professor Chappel during the Spring '07 term at UC Riverside.

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protostomes 1 - Flatworms (last lecture) are acoelomate: no...

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