True or false? New major animal body plans have continued to evolve since the Cambrian about 550 million years ago.

In a tube-within-a-tube body plan, what is the interior tube derived from?a. ectodermb. mesodermc. the coelomd. endoderm

Which of the following was probably an important factor in bringing about the Cambrian explosion? (A) the movement of animals onto land (B) an increase in the concentration of atmospheric nitrogen (C) the emergence of predator-prey relationships (D) the origin of bilaterian animals

Which of the following was probably the least important factor in bringing about the Cambrian explosion?a. the emergence of predator-prey relationshipsb. an increase in the concentration of atmospheric oxygenc. the movement of animals onto landd. the origin of Hox genes

Bilateral symmetry in animals is best correlated witha. an ability to see equally in all directions.b. the presence of a skeleton.c. motility and active predation and escape.d. adaptation to terrestrial environments.

Which of the following combinations of phylum and description is correct? (A) Echinodermata—radial symmetry as a larva, coelom (B) Nematoda—roundworms, internal skeleton (C) Platyhelminthes—flatworms, gastrovascular cavity, no body cavity (D) Porifera—gastrovascular cavity, coelom

Based on the tree in Figure 32.11, which statement is false?a. The animal kingdom is monophyletic.b. Acoelomate flatworms are more closely related to echinoderms than to annelids.c. Sponges are basal animals.d. Bilaterians form a clade

Select True or False for each statement.T/FSister chromatids are homologous chromosomes.T/FNon-sister chromatids are found on two different homologs.T/FCrossing over occurs between sister chromatids.T/FA chiasma forms between two of the four molecules of double-stranded DNA on duplicated homologous chromosomes.

Why is it ecologically significant that animals are heterotrophic and multicellular?