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Exam 32: An Overview of Animal Diversity

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Question 21

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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, except Nematostella (of β-catenin fame) , which has three Hox genes. On the basis of these observations, some have proposed that the ancestral cnidarians were originally bilateral and, in stages, lost Hox genes from their genomes. If true, this would mean that

A) Radiata should be a true 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 Acoela as the basal bilaterians.
E) Two of the responses above are correct.

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Question 22

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The most recently discovered phylum in the animal kingdom (1995) is the phylum Cycliophora. It includes three species of tiny organisms that live in large numbers on the outsides of the mouthparts and appendages of lobsters. The feeding stage permanently attaches to the lobster via an adhesive disk, and collects scraps of food from its host's feeding by capturing the scraps in a current created by a ring of cilia. The body is sac-like and has a U-shaped intestine that brings the anus close to the mouth. Cycliophorans are eucoelomate, do not molt (though their host does) , and their embryos undergo spiral cleavage. -If harboring large populations of cycliophorans neither helps nor harms their lobster hosts, then cycliophorans can be properly considered to be 1) parasites. 2) mutualists. 3) commensals. 4) symbionts. 5) endosymbionts.

A) 1 and 4
B) 2 and 4
C) 3 and 4
D) 2 and 5
E) 3 and 5

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Question 23

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Some researchers claim that sponge genomes have homeotic genes, but no Hox genes. If true, this finding would

The previous figure shows a chart of the animal kingdom set up as a modified phylogenetic tree. Use the diagram to answer the following questions. -Which of these is the basal group of the Eumetazoa?

Placozoan evolutionary relationships to other animals are currently unclear, and different phylogenies can be created, depending on the character used to infer relatedness. Sponges have no tissues, but about 20 cell types. Tp (Trichoplax adhaerens) produces a neuropeptide almost identical to one found in cnidarians. The genome of Tp, though the smallest of any known animal, shares many features of complex eumetazoan (even human!) genomes. The next three questions refer to the phylogenetic trees that follow. I. II. III. -Cycliophorans have two types of larvae. One type of larva-the Prometheus larva-develops into a male. The male, which lacks a digestive system, attaches to the outside of a feeding stage (a female) and impregnates her digestive system, which develops into a different type of larva. What must be true of the digestive system of the feeding-stage female while she is still a virgin? 1) At least some of its cells are haploid. 2) It consists only of highly specialized cells. 3) It is the same size as the male.

Which of the following statements concerning animal taxonomy is (are) true? 1) Animals are more closely related to plants than to fungi. 2) All animal clades based on body plan have been found to be incorrect. 3) Kingdom Animalia is monophyletic. 4) Only animals reproduce by sexual means. 5) Animals are thought to have evolved from flagellated protists similar to modern choanoflagellates.

Protostome characteristics generally include which of the following?

According to the evidence collected so far, the animal kingdom is

You have before you a living organism, which you examine carefully. Which of the following should convince you that the organism is acoelomate?

Trichoplax adhaerens (Tp) 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. They move using cilia, and any "edge" can lead. Tp 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. Tp sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage. -In an experiment, several Tp individuals were stained different colors. The stained individuals were then passed through a strainer, disaggregated to the level of single cells, and collected into a common container of seawater. Which subsequent finding would be most surprising if the Tp individuals used in this experiment had been produced by sexual, rather than asexual, means?

What does recent evidence from molecular systematics reveal about the relationship between grades and clades?

A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the embryo seem to be rotated 45 degrees and to lie in the grooves between larger, underlying cells (i.e., spiral cleavage) . -This embryo may potentially develop into a(n)

A researcher is trying to construct a molecular-based phylogeny of the entire animal kingdom. Assuming that none of the following genes is absolutely conserved, which of the following would be the best choice on which to base the phylogeny?

Phylogenetic trees are best described as

Fossil evidence indicates that the following events occurred in what sequence, from earliest to most recent? 1) Protostomes invade terrestrial environments. 2) Cambrian explosion occurs. 3) Deuterostomes invade terrestrial environments. 4) Vertebrates become top predators in the seas.

Placozoan evolutionary relationships to other animals are currently unclear, and different phylogenies can be created, depending on the character used to infer relatedness. Sponges have no tissues, but about 20 cell types. Tp (Trichoplax adhaerens) produces a neuropeptide almost identical to one found in cnidarians. The genome of Tp, though the smallest of any known animal, shares many features of complex eumetazoan (even human!) genomes. The next three questions refer to the phylogenetic trees that follow. I. II. III. -Which phylogeny has been created by emphasizing a protein found in placozoans?

If the current molecular evidence regarding animal origins is well-substantiated in the future, then what will be true of any contrary evidence regarding the origin of animals derived from the fossil record?

Both animals and fungi are heterotrophic. What distinguishes animal heterotrophy from fungal heterotrophy is that only animals derive their nutrition by

What is true of the clade Ecdysozoa?

The most recently discovered phylum in the animal kingdom (1995) is the phylum Cycliophora. It includes three species of tiny organisms that live in large numbers on the outsides of the mouthparts and appendages of lobsters. The feeding stage permanently attaches to the lobster via an adhesive disk, and collects scraps of food from its host's feeding by capturing the scraps in a current created by a ring of cilia. The body is sac-like and has a U-shaped intestine that brings the anus close to the mouth. Cycliophorans are eucoelomate, do not molt (though their host does) , and their embryos undergo spiral cleavage. -Cycliophorans have two types of larvae. One type of larva is produced when the digestive system of a female is impregnated by a male. The digestive system then collapses and develops into a larva, which swims away in search of a new host after the surrounding female dies. Which is the embryonic tissue that is apparently most important in forming this type of larva?