Contemporary Biological Problems Lab 17.1 Evolution of Animals oday, molecular d

Question

Contemporary Biological Problems Lab 17.1 Evolution of Animals oday, molecular data are used in addition to comparative anatomy to trace animals. These data tell us that all animals share a common ancestor. This common ancestor was most likely a choanoflagellate, a protist consisting of a colony of flagellated cells. All but one of the phyla depicted in the tree (Fig. 17.1) consist of only invertebrates-the chordates contain a few invertebrates as well as the the evolutionary history of vertebrates. Certain anatomical features of animals are used in the tree. The first feature of interest is ormation of tissue layers. Sponges have no true tissue layers. Which phyla in the tree have only two tissue layers? The other phyla have three tissue layers. Another feature of interest is symmetry. Asymmetry means the animal phyla have radial symmetry, in which, as in a wheel, two identical halves are obtained no matter how The other Which the animal is longitudinally sliced? have bilateral symmetry, which means the adult animal has a definite right half and left half Finally, complex animals are either protostomes (first opening during development is the mouth) or deuterost omes (second opening during development is the mouth [the first one is the anus). Which pattern of development do the flatworms, rotifers, and nematodes (also called roundworms) have? Figure 17.1 A modern look at the animal evolutionary tree The relationships in this diagram are based on research into the developmental biology of each group, as molecular studies of DNA, RNA, and protein similarity. Pareos cauans

Explanation / Answer

1.Which phyla in the tree have only two tissue layers?
Ans- Phylum Cnidarians has two layers that include endoderm and ectoderm.
2.Which phyla have radial symmetry, in which, as in a wheel, two identical halves are obtained no matter how the animal is longitudinally sliced?
Ans- Cnidarians. They are radially symmetrical and organized circularly, just as a wheel and two identical halves are obtained, no matter how the animal is sliced longitudinally.
3. Which pattern of development do the flatworms, rotifers, and nematodes have?
Ans- The flatworms, rotifers, and nematodes have Protostome pattern of development
Protostome pattern of development is the developmental process in which the first opening of the embryo is the mouth.

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