Final answer:
Brachiopods spread throughout the ocean by larval dispersal via ocean currents, and post-mortem movement of their shells. This allows these sessile organisms to cover a wide range of ocean habitats despite being anchored as adults.
Step-by-step explanation:
Brachiopods are marine organisms that produce their own shells and spend most of their lives attached to the ocean floor. However, they can still be found spread throughout the ocean due to several factors. Although brachiopods are sessile, meaning they typically do not move from their anchored spot, their larvae are free-swimming. After brachiopods reproduce, their larvae can be carried by ocean currents to different locations before settling down to form new shells. This larval dispersal is a common way for sessile marine species to distribute themselves over wider areas. In addition to currents, the movement of brachiopod shells can occur post-mortem. Once the organism dies, the empty shell can be moved by oceanic forces like currents, waves, or animals, further aiding in their distribution throughout various habitats in the ocean.