Final answer:
Echinoderms have radial symmetry as adults, although their larvae initially display bilateral symmetry before undergoing metamorphosis to form the adult radial symmetry.
Step-by-step explanation:
Echinoderms, members of the phylum Echinodermata which includes sea stars, sand dollars, and sea urchins, exhibit radial symmetry as adults. This type of symmetry means that the arrangement of their body parts is centered around a central axis. It is important to note that while adult echinoderms display radial symmetry, their larval stages show bilateral symmetry, which is a symmetry that can be seen in many other animal phyla where the body can be divided into equivalent halves along one particular plane. This transition from bilateral symmetry in the larval stage to radial symmetry in the adult form is known as secondary radial symmetry.
Radial symmetry is particularly advantageous for certain lifestyles in the animal kingdom, as it allows an organism to interact with its environment from all directions equally, which is beneficial for sedentary or slow-moving organisms.