31. Invertebrates

A land snail, a clam, and an octopus all share

a. A mantle

b. A radula

c. Gills

d. Distinct cephalization

The genes for the traits that Mendel worked with are either all located on different chromosomes or behave as if they were. How did this help Mendel recognize the principle of independent assortment?

a. Otherwise, his dihybrid crosses would not have produced a 9 : 3 : 3 : 1 ratio of F2 phenotypes.

b. The occurrence of individuals with unexpected phenotypes led him to the discovery of recombination.

c. It led him to the realization that the behavior of chromosomes during meiosis explained his results.

d. It meant that the alleles involved were either dominant or recessive, which gave 3 : 1 ratios in the F1 generation.

What is a lophophore?

a. A specialized filter-feeding structure

b. The single opening in species with a blind gut

c. A distinctive type of larva with a band of cilia

d. A synapomorphy that defines lophotrochozoans

Brachiopoda is a phylum within the Lophotrochozoa. Even though they are not closely related to bivalve mollusks (such as clams or mussels), brachiopods look and act like bivalve mollusks. Specifically, brachiopods suspension feed, secrete calcium carbonate shells with two valves that hinge together in some species, and attach to rocks or other hard surfaces on the ocean floor. How is it possible for brachiopods and bivalves to be so similar if they did not share a recent common ancestor?

One trait that is shared by humans and protostomes is __________.