What are the hollow tubes on the underside of a starfish called?

The hollow tubes on the underside of a starfish are referred to as tube feet. These structures are part of the starfish's water vascular system, which is crucial for movement, feeding, and respiration. Each tube foot is an extension of the coelomic cavity and is operated by hydraulic pressure, allowing the starfish to extend and retract them to facilitate locomotion across the ocean floor.

Tube feet also play a significant role in the starfish's ability to grasp and manipulate objects, aiding in feeding by prying open the shells of prey like clams and mussels. The coordinated movement of several tube feet allows for effective movement and stability as they navigate their environment.

The other terms listed refer to different structures: the arms refer to the radiating limbs of the starfish, tentacles are typically associated with different organisms such as jellyfish, and pincers are often referred to in the context of crustaceans or other invertebrates with claw-like appendages.