Final answer:
Entoprocts retract their feeding tentacles when disturbed, using them for both feeding and sensing, which is a common defense mechanism among aquatic organisms with tentacles.
Step-by-step explanation:
When entoprocts are disturbed, they typically react by retracting their feeding tentacles. These tentacles are not only for feeding but also for sensing the environment. Similar to other marine organisms that have specialized features for feeding and defense, entoprocts retract their tentacles to protect themselves from potential harm or predators. This behavior can be compared with how some polychaetes retreat into their tubes, or how cephalopods may eject a stream of water for quick escape. Though not specifically mentioned in the reference material, retracting tentacles is a common defense mechanism among many aquatic organisms that bear tentacles.