31. Invertebrates

The arthropods superficially resemble earthworms in that both groups __________, yet the two are distinctly different because arthropods, but not earthworms, __________.

A major characteristic of arthropods is __________.

In most insects, gas exchange is accomplished by __________.

In arthropods, molting is necessary because __________.

Sowbugs are really crustaceans, not insects. Therefore, a sowbug does not have __________.

The majority of animal species are __________.

An unidentified species of animal displays the following characteristics: bilateral symmetry, a complete digestive system, an open circulatory system, distinct body segmentation, and a series of molting stages during growth. To which of the following animal phyla does this species most likely belong?

Complete metamorphosis __________.

Which of the following animals is most closely related to spiders?

What is the function of the arthropod exoskeleton? a. The presence of an exoskeleton has given arthropods a good fossil record, because hard parts fossilize more readily than do soft tissues. b. It has no well-established function. (Trilobites had an exoskeleton, and they went extinct.) c. It provides protection and functions in locomotion. d. It makes growth by molting possible.

One trait that is shared by the Lophotrochozoa and Ecdysozoa is                .

Which of the following groupings includes the largest number of species? (Explain your answer.) a. invertebrates b. arthropods c. insects d. vertebrates

Molecular comparisons place nematodes and arthropods in clade Ecdysozoa. What characteristic do they share that is the basis for the name Ecdysozoa? a. a complete digestive tract b. body segmentation c. molting of an exoskeleton d. bilateral symmetry

Suppose that a gene originally identified in nematodes (roundworms) is found to be homologous with a gene that can cause developmental abnormalities in humans. Would it be possible to use fruit flies as a model organism to study this gene? Explain.

One of the key characteristics of arthropods is their jointed appendages. Describe four functions of these appendages in four different arthropods.

SCIENTIFIC THINKING In one of the experiments described in researchers tested the hypothesis that the highly successful arthropod body plan resulted from new genes that originated in the arthropod lineage. Draw a diagram showing the evolutionary relationship between arthropods and velvet worms and use it to explain why velvet worms were a good choice to test this hypothesis. What results would have supported the hypothesis?