Chapter 27, Problem 18STP

Summary Introduction

To write: The idea that it was not a large evolutionary jump for aquatic arthropods to move onto land.

Introduction:

Arthropod, any member of the phylum Arthropoda, the biggest phylum in the animal kingdom, which consists such familiar forms as lobsters, crabs, spiders, mites, insects, centipedes, and millipedes. About 84 percent of all well known species of animals are members of this phylum. Arthropods are represented in each habitat on Earth and show a huge variation of adaptations. Several kinds live in aquatic environments, and others reside in terrestrial ones; few individuals are even adapted for flight.

Explanation of Solution

There are over 800,000 named species in the Phylum Arthropoda, together the familiar arachnids, crustaceans, and insects, collectively with a host of less familiar critters, like centipedes, millipedes and sea spiders. All arthropods have jointed appendages. This evolutionary innovation is might be the key to the great success of this diversified group. There are about 10 billion arthropods alive at any single time. Arthropods do everything with legs or modified legs. They walk, they swim, they creep and crawl, they use legs to sense with (the antennae), to bite and sting with, and even to chew with. That's the reason arthropods look so different when we see them up close. They chew sideways, and it is all done with legs. Their bodies are covered by a hard cuticle composed of proteins and chitin, a polysaccharide with added nitrogen groups. A cuticle is a hard outer cover of non living organic substance. The cuticle of arthropods functions as an exoskeleton. 

Conclusion

Aquatic arthropods respire with gills. Terrestrial arthropods depend on diffusion via tiny tubes known as trachea. Trachea is cuticle-lined air ducts that branch throughout the body, and open in small holes called spiracles, located along the abdomen. Arthropods excrete bvia way of means of malphigian tubules; projections of the digestive tract that help conserve water. Terrestrial arthropods eliminate nitrogen as uric acid, as do birds. Their waste is sort dry, a superb adaptation to life on land.