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Exam 32: An Overview of Animal Diversity

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Question 31

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The last common ancestor of all bilaterians is thought to have had four Hox genes. Most extant cnidarians have two Hox genes, though some have three Hox genes. On the basis of these observations, some have proposed that the ancestral cnidarian's were originally bilateral and, in stages, lost Hox genes from their genomes. If true, this would mean that ________.

A) all radially symmetric animals should be grouped together in one clade
B) the radial symmetry of extant cnidarians is secondarily derived, rather than being an ancestral trait
C) Hox genes play little actual role in coding for an animal's "body plan"
D) cnidaria may someday replace porifera as the basal bilaterians

E) C) and D)
F) None of the above

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Question 32

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The evolution of animal species has been prolific (current estimates of species numbers reach into the tens of millions) . Much of this diversity is a result of the evolution of novel ways to ________.

A) reproduce
B) arrange cells into tissues
C) sense, feed, and move
D) form an embryo and establish a basic body plan

E) B) and D)
F) A) and D)

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Question 33

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A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise 1 hemisphere of the embryo seem to be rotated 45° and to lie in the grooves between larger, underlying cells. If we were to separate these eight cells and attempt to culture them individually, then what is most likely to happen?

What do animals ranging from corals to monkeys have in common?

If you think of the earthworm body plan as a drinking straw within a pipe, where would you expect to find most of the tissues that developed from endoderm?

The larvae of some insects are merely small versions of the adult, whereas the larvae of other insects look completely different from adults, eat different foods, and may live in different habitats. Which of the following is most directly involved in the evolution of these variations in metamorphosis?

Use the information to answer the question. Trichoplax adhaerens is the only living species in the phylum Placozoa. Individuals are about 1 mm wide and only 27 μm high, are irregularly shaped, and consist of a total of about 2,000 cells, which are diploid (2n = 12) . There are four types of cells, none of which are nerve or muscle cells, and none of which have cell walls. Individual animals move using cilia, and any "edge" can lead. T. adhaerens feeds on marine microbes, mostly unicellular green algae, by crawling atop the algae and trapping it between its ventral surface and the substrate. Enzymes are then secreted onto the algae, and the resulting nutrients are absorbed. T. adhaerens sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage. T.adhaerens' body symmetry seems to be most like that of ________.

What is the probable sequence in which the following animal clades originated, from earliest to most recent?

Whatever its ultimate cause(s) , the Cambrian explosion is a prime example of ________.

The protostome developmental sequence arose just once in evolutionary history, resulting in two main subgroups-Lophotrochozoa and Ecdysozoa. What does this finding suggest?

At one time, sponges were lumped into one phylum. Then, they were separated into several different phyla. Now, they are considered one phylum again. These changes indicate which of the following?

While looking at some seawater through your microscope, you spot the egg of an unknown animal. Which of the following tests could you use to determine whether the developing organism is a protostome or a deuterostome? See whether the embryo ________.

The most ancient branch point in animal phylogeny is the characteristic of having ________.

Which of the following factors most likely contributed to the extinction of many Ediacaran life forms?

Among protostomes, which morphological trait has shown the most variation?

Use the table to answer the following question. $\begin{array}{c}\begin{array}{|l|}\hline \\\text {Organism}\\\hline \\\\\\\text {A}\\\hline \\\\\\\\\text {B}\\\hline \\\\\\\text {C} \\\hline \\\\\\\text { D }\\\hline\end{array}\begin{array}{l|}\hline \\\text {Appearance}\\\hline \\ \text {Microscopic,}\\ \text {unicellular, with a}\\\text { flagellum}\\\hline\text { Shaped like a}\\ \text { basketball, covered }\\\text { with purple}\\ \text { filaments,}\\ \text { multicellular }\\\hline\text {Hard and branched. }\\\text {multicellular,}\\ \text {covered in a sticky }\\\text {coating}\\\hline\\\\\text {Multicellular with }\\\text {cell walls}\\\hline\end{array}\begin{array}{l|}\hline \\\text {Habitat/Activity}\\\hline \\\\\text {Swims around in }\\\text {freshwater pools}\\\hline \\\\\\\text {Rolls slowly across }\\\text {grassy fields}\\\hline \\\\\text {Attached to rocky }\\\text {surfaces}\\\hline \\\\\\\text {Flies across fields}\\\hline\end{array}\begin{array}{l|}\hline\text {Nutrient}\\\text {Acquisition}\\\hline\text {Envelops and}\\\text {consumes other}\\\text {microscopic}\\\text {organisms}\\\hline\\\text {Thrives with access}\\\text {to only freshwater}\\\text {and sunlight}\\\hline\\\text {Traps insects in}\\\text {sticky coating and}\\\text {dissolves them}\\\hline\text {Constructs nets to}\\\text {trap flying}\\\text {organisms, and}\\\text {sucks out internal}\\\text {fluids}\\\hline\end{array}\begin{array}{l|}\hline \\\text {Reproduction}\\\hline\\\\\text {Mates with others; }\\\text {young bud off}\\\hline\text {Mates with others;}\\\text { young emerge from }\\\text {hardened spherical }\\\text {structures}\\\hline\text {No mating, releases }\\\text {winged young that }\\\text {fly off and affix to}\\ \text {bare rocks}\\\hline\\\\ \text {Mates with others, }\\ \text {and disperses }\\ \text {young ballistically}\\\hline\end{array}\end{array}$ As you are on the way to Tahiti for a vacation, your plane crash lands on a previously undiscovered island. You soon find that the island is teeming with unfamiliar organisms, and you, as a student of biology, decide to survey them (with the aid of the Insta-Lab Portable Laboratory you brought along in your suitcase) . You select four organisms and observe them in detail, making the notations found in the figure. In which of the organisms listed would you search for photosynthetic genes?

Which of the following statements comparing symmetry in sessile and swimming animals is most probable?

Which of the following is a feature of the "tube-within-a-tube" body plan in most animal phyla?

Which tissue type or organ is not correctly matched with its germ layer tissue?

What was an early selective advantage of a coelom in animals? A coelom ________.