What key features are shared by organisms placed in Phylum Arthropoda?
An exoskeleton, a segmented body, and jointed appendages
The Phylum Arthropoda is one of the most successful and diverse groups in the biological world, encompassing insects, spiders, and crustaceans. The defining synapomorphies—shared, derived characteristics—that place an organism into this phylum are highly specific. These include the presence of a hard, external skeleton, which is typically chitinous and provides structural support and protection. Furthermore, their bodies are characterized by segmentation, allowing for specialized functional regions. Finally, locomotion and interaction with the environment are facilitated by appendages that are articulated or 'jointed.' The woolly aphid exhibits all three of these fundamental arthropod traits, validating its placement here, distinct from soft-bodied worms or vertebrates.
