Bilateral symmetry, metameric segmentation, coelom, and an open circulatory system characterize the phylum Arthropoda.

Bilateral Symmetry:
Bilateral symmetry refers to the organization of body parts into two similar halves, divided by a single plane. This means that the body of an arthropod can be divided into two equal halves along its longitudinal axis. Examples of bilateral symmetry in arthropods include insects, spiders, and crustaceans.

Metameric Segmentation:
Metameric segmentation, also known as serial segmentation, is the division of the body into a series of repeated segments. Each segment typically contains a similar set of organs and structures. Arthropods exhibit metameric segmentation, with their bodies divided into distinct segments. This segmentation allows for specialization and efficient movement, as each segment can perform specific functions.

Coelom:
A coelom is a fluid-filled body cavity that is completely lined with mesoderm. Arthropods have a coelom, although it is reduced compared to other phyla. The coelom in arthropods is often filled with blood and serves as a space for internal organs and as a hydrostatic skeleton for movement.

Open Circulatory System:
Arthropods have an open circulatory system, which means that their circulatory fluid, called hemolymph, is not confined to blood vessels. Instead, it directly bathes the organs and tissues. The hemolymph is pumped by a heart-like structure called a dorsal vessel, which pumps the fluid into the body cavity. From there, it flows through the tissues, exchanging nutrients and waste products. The hemolymph eventually returns to the heart for recirculation.

Other characteristics of the phylum Arthropoda include jointed appendages, a chitinous exoskeleton, and a well-developed nervous system. Arthropods are the largest phylum in the animal kingdom and include insects, spiders, crustaceans, and millipedes. They are highly diverse and can be found in almost every habitat on Earth.