Chapter 26, Problem 31A

Summary Introduction

To write:The earliest and recently developed group of arthropods

Introduction:Arthropods are grouped into classes based on common characteristics, such as body segment form, appendages and mouthparts. The naming of arthropods is still questioned by taxonomists. Arthropods have joint-appended exoskeletons that allow them to move in diverse ways.

Explanation of Solution

The order of appearance of the features from oldest to most modern is- segmentation, body divided into two regions, chelicerae, and mandible.

Trilobites are a class of extinct arthropods of the marine arachnomorph which comprise the Trilobita class. Trilobites represent one of the oldest recognized arthropod groupings.Trilobites, like some existing arthropods, were circular, rounded, and divided into three body parts. Among modern arthropods, the vast number of similar segments of these ancestral arthropods changed to more advanced appendages and fewer segments.

Arachnids have a pair of appendages called pedicalps that are used to identify and retain prey. The most anterior pair of appendages of an arachnid is changed to mouthparts called chelicerae.An arachnid has two body parts- a cephalothorax and an abdomen.

Crustacea is made up of around 35,000 species. Many of them are marine and have two pairs of antennae, two compound eyes which are sometimes on the ends of slender horizontal stalks, and mandibles to chew.

Conclusion

Thus, it concludes thattrilobites are the earliest group of arthropods and insects are the recently developed group of arthropods.