2011L Lec5 Platyhelminthes Spr08

2011L Lec5 Platyhelminthes Spr08 - Phylum Platyhelminthes...

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Unformatted text preview: Phylum Platyhelminthes The flatworms http://www.waterworxbali.com/Images/Photos/Large/pseudoceros-ferrugineus.jpg http://struggle.net/history/images/flatworm.gif http://www.scuba-equipment-usa.com/marine/AUG04/images/Cycloporus_sp.jpg http://www.islandream.com/wakatobi/flatworm02.jpg http://www.kingsnake.com/westindian/bipaliumkewense2.JPG The major lineages of evolution in animals Fundamental evolutionary divergence among Eumetazoa, but based on what? if you dont move , radial symmetry is useful (e.g., cnidarian polyps) however, if you do move , its an advantage to put sense organs on the end that encounters the new environment first (i.e., anterior ); this provides an anterior-posterior axis which leads inexorably to bilateral symmetry with movement comes the need for musculature specializations to coordinate movement there is a need for a better nervous system specialization in some sectors fosters specialization in others, leading to division of labor and development of organ systems Becoming bilateral QuickTime and a TIF (Uncompres ed) decompres or are needed to see this picture. a n im a l-tr e a n im a l-tr e a n im a l-tr e The Bilateria (acoelomate) Acoelomate Bilateria simplest (earliest) animals with bilateral symmetry bilateral symmetry in acoelomate ancestors probably arose from a benthic, creeping planula-like form solid body with no coelom (that comes later) they are protostomes with spiral determinate cleavage The major lineages of evolution in bilateral animals indeterminate & radial cleavage (blastopore becomes anus) Echinodermata, Hemichordata, Chordata determinate & spiral cleavage (blastopore becomes mouth) Platyhelminthes, Nemertea, Annelida, Mollusca, Arthropoda RECALL: Three coelomic architectures Recall: Acoelomate Bilateria - lack body cavity; region around gut filled in by mesodermal parenchymal cells (todays Platyhelminthes and Nemertea) Pseudocoelomate Bilateria - cavity derived from blastocoel (not from mesoderm), so not enclosed entirely by mesoderm Eucoelomate Bilateria - true coelom derived from mesoderm and lined with mesodermal peritoneum acoelomates- development of a third tissue layer i.e., triploblastic (ectoderm, mesoderm, & endoderm)- mesoderm fills and obliterates blastocoel- meso. does not split and form a coelom Acoelomate Bilateria (contd) development of complex organs: different tissues come together as a single unit (organ-system level of organization) circular (outer) and longitudina l (inner) body wall muscles act antagonistically to facilitate movement and locomotion compartmentalization: internal fluid-filled cavities fully enclosed & under control of the organism; compartments may take on specific functions (house gonads, locomotion) beginnings of a ladder-type of nervous system excretory organs: large body size requires an excretory system - wastes transported out of body via a system of protonephridia have either a blind-ending gut or none at all; the somewhat more...
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This note was uploaded on 04/08/2008 for the course BIO bsc2011L taught by Professor Spears during the Spring '08 term at FSU.

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2011L Lec5 Platyhelminthes Spr08 - Phylum Platyhelminthes...

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