Exam 32: An Overview of Animal Diversity

Which of the following genetic processes may be most helpful in accounting for the Cambrian explosion?

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 how many of the following ways is Tp unlike the typical animal? 1)Tp is multicellular. 2)Tp lacks muscle and nerve cells. 3)Tp has cilia. 4)Tp has a different place where digestion of food occurs. 5)Tp lacks cell walls.

Which of these, if true, would support the claim that the ancestral cnidarians had bilateral symmetry? 1)Cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects. 2)Cnidarians have fewer Hox genes than bilaterians. 3)All extant cnidarians, including Nematostella, are diploblastic. 4)β-catenin turns out to be essential for gastrulation in all animals in which it occurs. 5)All cnidarians are acoelomate.

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. -What is true of the feeding stage of cycliophorans? 1)It is chemoheterotrophic. 2)It is sessile. 3)It captures food in a manner similar to that of animals with lophophores. 4)It has radial symmetry.

The most ancient branch point in animal phylogeny is that between having

Soon after the coelom begins to form, a researcher injects a dye into the coelom of a deuterostome embryo. Initially, the dye should be able to flow directly into the

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 genomic features of placozoans?

At which developmental stage should one be able to first distinguish a diploblastic embryo from a triploblastic embryo?

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. -Tp's body symmetry seems to be most like that of

Among the characteristics unique to animals is

What distinguishes a coelomate animal from a pseudocoelomate animal is that coelomates

What is the probable sequence in which the following clades of animals originated, from earliest to most recent? 1)tetrapods 2)vertebrates 3)deuterostomes 4)amniotes 5)bilaterians

If a multicellular animal lacks true tissues, then it can properly be included among the

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. -If Tp sperm are observed by future researchers, how many chromosomes should be found in a Tp sperm nucleus?