Chapter 25: Q4ITD (page 523)

Propose a hypothesis to explain the differences in longevity of snail species with planktonic and nonplanktonic larvae.

Short Answer

Expert verified

The offspring produced by species of nonplanktonic larvae is less than the offspring produced by species of planktonic larvae. The nonplanktonic larvae exhibit limited distribution than the planktonic larvae. The survival rate of species with planktonic larvae is lesser than the species with nonplanktonic larvae.

Step by step solution

Volutidae

The family of sea snails is known as volutid or Volutidae. The operculum is absent in the members of volutids. In the given case, the fossils of the snails are found in North America's Gulf coast in outcrops of sedimentary rocks. The members Volutidae have planktonic as well as nonplanktonic larvae.

Planktonic and nonplanktonic larvae

The ocean contains a tiny group of afloat animals due to spines and feathery projections, and such organisms are called planktons. The larva of some organisms develops drifting in plankton.The species of nonplankton larva develop into adults without the swimming stage.

Hypothesis that explains the difference in planktonic and nonplanktonic in terms of longevity

The planktonic larvae develop with the swimming stage; therefore, they show more distribution than the nonplanktonic larvae. The dispersion also brings predatory risk. Thus, the nonplanktonic larvae's survival rate is higher because they do not swim like the planktonic larvae.

More dispersal increases the relative fitness of the snails; therefore, snails are produced at a higher rate for planktonic larvae than nonplanktonic larvae.