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Chapter 32

Chapter 32. 0. Introduction to Animal Evolution. According to the grade-based animal phylogeny, the acoelomate condition is primitive and the acoelomates branched off before the origin of the coelom. is the first branch point, separating the acoelomates from the eumetazoa.

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Chapter 32

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  1. Chapter 32 0 Introduction to Animal Evolution

  2. According to the grade-based animal phylogeny, the acoelomate condition • is primitive and the acoelomates branched off before the origin of the coelom. • is the first branch point, separating the acoelomates from the eumetazoa. • arose secondarily as the coelom was lost during the evolution of the flatworms. • led to the origin of the lophophore as a feeding adaptation. • was associated with a sessile or planktonic lifestyle and thus linked with radial symmetry.

  3. The grade-based and molecular-based phylogenetic trees agree in which of the following ways? • the acoelomate condition as a branch point before the divergence of the two protostome clades • the placement of the three lophophorate phyla into the protostomes • parazoa as the probable ancestor of the animal kingdom • the deepest branch points of the parazoa–eumetazoa and radiata–bilateria dichotomies, and the deuterostomes as a monophyletic clade • the origin of the Hox complex as the probable cause of the Cambrian explosion

  4. The larvae of some insects are merely small versions of the adult, whereas the larvae of certain other insects look radically different from adults, eat different foods, and may even live in different environments. What condition should most directly favor the evolution of the more radical kind of metamorphosis? • limited resources • increasing oxygen content of the biosphere • the evolution of meiosis • volcanoes in the environment • the felt need to introduce variety into the species

  5. What should animals as diverse as corals and monkeys have in common? • body cavity between body wall and digestive system • number of embryonic tissue layers • type of body symmetry • presence of Hox genes • degree of cephalization

  6. Cephalization is primarily • a result of adaptation to dark environments. • an adaptation to the method of reproduction. • due to the fate of the blastopore. • the result of the type of digestive system. • an adaptation to movement.

  7. Phylogenetic trees are best described as • true and inerrant statements about evolutionary relationships. • hypothetical portrayals of evolutionary relationships. • the most accurate possible representations of genetic relationships among taxa. • theories of evolution. • the closest things to absolute certainty that modern systematists can produce.

  8. If each of the following traits evolved only once during animal evolution, then which traits were probably possessed by the most recent common ancestor of the Deuterostomia, Ecdysozoa, and Lophotrochozoa? * indeterminate development exoskeleton triploblastic cephalization segmentation 1, 2 1, 2, 5 1, 3, 4 3, 4, 5 all of these

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