The mushroom coral polyps have the largest tentacles of any coral in the ocean. why is it so important for coral at this depth to have large tentacles?

Tentacles are needed for night feeding

Explanation:

The mushroom coral is one of the most recognizable species of Hawaiian stony corals. It is named for its oval shape and the radiating skeletal walls (septa) that give this coral its mushroom-like appearance.

During the day, the mushroom coral provides nutrition for itself via photosynthetic activities with the aid of the zooxanthelae.

The tentacles are needed for night feeding, floating plankton are caught at night with the tentacles are dragged into the mouth of the coral for digestion.