Ch32 Protostome - 32 Protostome Animals 32 Protostome...

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32 Protostome Animals
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32 Protostome Animals 32.1 What Is a Protostome? 32.2 What Features Distinguish the Major Groups of Lophotrochozoans? 32.3 What Features Distinguish the Major Groups of Ecdysozoans? 32.4 Why Are Arthropods So Diverse?
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32.1 What Is a Protostome? There are two triploblastic clades, protostomes and deuterostomes. Protostomes have far more species and individuals. Two major clades of protostomes: Lophotrochozoans and ecdysozoans, mostly based on DNA sequences.
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Figure 32.1 Phylogenetic Tree of Protostomes (Part 1)
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Figure 32.1 Phylogenetic Tree of Protostomes (Part 2)
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32.1 What Is a Protostome? Protostomes are bilaterally symmetrical. They have an anterior brain that surrounds the entrance to the digestive tract They have a ventral nervous system with paired or fused longitudinal nerve cords
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32.1 What Is a Protostome? The common ancestor had a coelom , but some lineages have modifications: Flatworms are acoelomate (coelom has been lost) Some lineages have a pseudocoelom Arthropods—the body cavity became a hemocoel or blood chamber, part of the open circulatory system
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32.1 What Is a Protostome? Mollusks have an open circulatory system similar to the hemocoel; but retain vestiges of an enclosed coelom
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32.1 What Is a Protostome? Lophotrochozoans Several groups have a lophophore , a circular or U-shaped ridge around the mouth with two rows of hollow, ciliated tentacles. The lophophore functions in food collection and gas exchange.
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Figure 32.2 Bryozoans Use Their Lophophore to Feed
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32.1 What Is a Protostome? The lophophore appears to have evolved independently several times; or it is ancestral and has been lost by some groups. Nearly all animals with a lophophore are sessile as adults (bryozoans, brachiopods, phoronids).
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32.1 What Is a Protostome? Some lophotrochozoans have a larval form known as a trochophore that moves by beating a band of cilia. This also brings plankton closer where they can be captured and ingested. Mollusks, annelids, ribbon worms, and bryozoans have trochophore larvae. It is probably ancestral, but lost in some groups.
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32.1 What Is a Protostome? Some lophotrochozoans have spiral cleavage (flatworms, ribbon worms, annelids, mollusks). Many lophotrochozoans are wormlike ; good shape for burrowing into soft sediments. Mollusks have a very different body plan.
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32.1 What Is a Protostome? Ecdysozoans have a cuticle , secreted by the epidermis (outermost cell layer). For the animal to grow, the exoskeleton must be shed or molted , and replaced with a larger one. Molting evolved 500 Mya, apparently only once. All ecdysozoans have a single common ancestor.
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Figure 32.3 Molting: Past and Present
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32.1 What Is a Protostome? Before molting, the new cuticle is already
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This note was uploaded on 03/30/2011 for the course MATHMATICS 1101 taught by Professor Zhong during the Spring '11 term at Georgia State University, Atlanta.

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Ch32 Protostome - 32 Protostome Animals 32 Protostome...

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