An arthropod lacks which of the following characteristics?

Arthropods are characterized by having true tissues, bilateral symmetry, and developing as protostomes. They are part of the ecdysozoans, which undergo molting (ecdysis) as they grow. The presence of true tissues means that arthropods have complex tissue organization, typically with layers that can specialize into organs and systems, allowing for diverse functions.

Bilateral symmetry in arthropods is evident as their body plan can be divided into two identical halves along a single plane, a feature common among many animal groups that facilitates movement and body coordination. Protostome development refers to the early embryonic development pattern where the mouth forms before the anus, a method observed in arthropods during their development.

In contrast, pseudocoelom refers to a body cavity that is not completely lined by mesoderm. Arthropods are characterized by having a true coelom, which is a body cavity fully enclosed within mesodermal tissue. This distinction is significant as it impacts the structural organization and functions within the body of the organism. Thus, the correct answer reflects that arthropods do not possess a pseudocoelom.