Arthropods, the most diverse phylum of animals, are characterized by:

Question

Accepted Answer

An exoskeleton, segmented bodies, and jointed appendages. Arthropods are characterized by three key features: an exoskeleton (an external skeleton made of chitin), segmented bodies, and jointed appendages (the name "arthropod" literally means "jointed foot"). This phylum is the most species-rich group of animals on Earth, with an estimated 1-10 million species, including insects, arachnids, crustaceans, and myriapods. Their success is attributed to their versatile body plan, which allows for adaptation to nearly every terrestrial, freshwater, and marine habitat.

A backbone and internal skeleton are characteristics of vertebrates (a subphylum of Chordata), not arthropods. Arthropods are invertebrates with no internal bony skeleton; their exoskeleton provides structural support, protection, and attachment points for muscles. Moist skin used for gas exchange characterizes amphibians, which breathe partly through their permeable skin. A water vascular system for movement is unique to echinoderms (sea stars, sea urchins, and their relatives), which use hydraulic pressure in a system of canals and tube feet for locomotion and feeding.

Arthropods must periodically shed their exoskeleton through a process called molting (ecdysis) to grow, as the rigid exoskeleton cannot expand. This temporary vulnerability is one of the few disadvantages of having an exoskeleton. Insects, the most diverse class of arthropods, owe much of their success to adaptations including flight (the first animals to evolve flight), complete metamorphosis (allowing larvae and adults to exploit different ecological niches), and small body size. Understanding animal diversity, classification, and the key characteristics of major phyla is important for the CLEP Biology exam.

CLEP Biology: Question of the Day

Get a free CLEP Biology question every day

Ready for the full CLEP Biology? Earn 6 college credits.