Final answer:
a) Tentacle In invertebrates, a flexible appendage used as an organ of touch is called a tentacle, which is specialized for sensing and sometimes used for feeding.
Step-by-step explanation:
The "invertebrate's flexible appendage that serves as an organ of touch" is referred to as a tentacle. Invertebrates such as octopuses and squids have tentacles that they use for sensing their environment and for feeding. These tentacles are equipped with suction cups or hooks, which allow the animals to manipulate objects and capture prey. Unlike a tail or legs, which may be primarily for movement, or wings used for flight, tentacles are specialized for touch, and in many cases, taste. For instance, the feeding tentacles of some marine worms resemble a feather duster, which they use to capture food particles from the water.
The invertebrate's flexible appendage that serves as an organ of touch is referred to as a tentacle. Tentacles are commonly found in organisms such as worms and cephalopods like squids and octopuses. They are used for sensing their environment and capturing prey.