Arthropods Are

capability of flight. (No other invertebrate possesses the ability to fly!)

The combination of physical characteristics that distinguish arthropods are:

a chitinous exoskeleton

paired, jointed appendages adapted for walking, swimming, jumping, feeding,

reproduction, defense, sense perception and even sound production, depending on the species 3) segmented body divided into regions (head, thorax, abdomen) or 2 regions (cephalothorax, abdomen)

protostome coelomates

complete digestive system with anterior appendages modified to form mouthparts

highly organized nervous system with complex sense organs; and corresponding complex

behaviors, even social organization in some

The Phylum Arthropoda is so large it has been subdivided into three extant subphyla, Crustacea, Uniramia, and Chelicerata, plus one extinct subphylum Trilobita. The trilobites, Class Trilobita, (fossils on demonstration in lab and pictured on Buschbaum p.523) have been extinct, as far as we know, for 250 million years. However, they and other arthropods are abundant in the fossil record dating back 600 million years and more.

Most of our focus will be on the living arthropod classes. Keep in mind the characteristics shared by all arthropods while you examine the modifications that distinguish the various subphyla and classes. The appendages vary the most between classes. Do take note, however, that though they may look and function in different ways, all the appendages are homologous across all the arthropod groups. The appendages of a single individual are referred to as serially homologous. Read Buschbaum pp. 323-324 for a discussion of this topic.

As the name implies, the first pair of appendages of the two classes within Subphylum Chelicerata are modified into pincerlike mouthparts called chelicerae. They have no antennae. The head and thorax are fused into a single cephalothorax bearing