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Bio2 Lecture 3 - Bio2 Lecture 3 Bilaterally symmetric...

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Bio2 Lecture 3 1/25/05 Bilaterally symmetric vertebrates - True coelo, body cavity completely lined with mesoderm - Mesocoelomate body cavity is partly covered with mesoderm - Acoelomate body cavity has no mesoderm covering Organization of digestion system - gastrovascular cavity, has 1 opening - Having 2 openings allows for specialization in digestive system, one way digestive system - Start with zygote, cell division occurs, gives you a ball of cells, then a hollow ball of cells called a blastocoel , then a second cavity can form which is the forerunner of the digestive track, now it looks like a horseshoe, the space in the middle is the archenteron (arch – old, primitive Enteron – gut), with an opening up at top above archenteron called blastospore . Whether it is the mouth or anus will determine which classification animal is in. - Protostome – blastospore develops into mouth - Deuterostomes –blastospore develops into anus, and mouth develops later - Protostomes if you take out 1 cell of the four in the fertilized egg, you will get ¾ of the actual developed organism, so you cannot have identical twins. Table 28-1 Subkingdom Eumetazoa (Branch bilateria) Ascoelomates Phylum Platyhelminthes (“flatworms”) o Class turbellaria (free-living) o Class Trematoda (all parasitic; flukes) o Class Cestoda (all parasitic; tapeworms) Turbellaria o small bit of cephalization o Noted for capacity of regeneration o No coelem or pseudocoelem Trematoda o aka “flukes” o
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