Chapter 26, Problem 20A

Summary Introduction

To write:

How the body form of aquatic crustaceans and terrestrial arachnids is adapted to their environment.

Introduction :

Arthopods make up the largest phylum in the animal kingdom. They include insects, butterflies, moths, etc. They have segmented body and have an exoskeleton with jointed appendage. Arthropods have complex organ systems that allow them to live in a variety of habitats. Adaptations to several organ systems, like the respiratory system and the nervous system, have contributed to the development of these animals.

Explanation of Solution

Crabs, lobsters, shrimps, water fleas, etc., are crustaceans. They are found terrestrial, marine and freshwater habitats. They have two pairs of antennae, two compound eyes and mandible for chewing. Most of the crustaceans like crayfish, crabs and lobsters have five pair of legs. The first pair of legs is known as chelipeds. It is adapted to catch and crush food and has large claws. The next four pairs of legs are walking legs known as swimmerets. They are used as flippers during swimming and also for reproduction.

Arachnids include spiders, scorpions, mites etc. Most arachnids have a cephalothorax, abdomen and two pairs of jointed appendages. They lack antennae. The most anterior region of the appendage is modified into a mouthpiece called chelicerae that is adapted to function as pincers or fangs. The second pair of appendages is used for sensing and holding prey and is known as pedipalps. In male spiders, the pedipalps are used for reproduction. The rest of the four pairs of appendages in arachnids are used for movement.

Conclusion

Crustaceans have appendages like swimmerets and chelipeds that are adapted for swimming and catching prey. The arachnids have appendages called pedipalps and chelicerae adapted for holding prey and attacking prey or defending itself against predators.