The relationship between reef-building coral animals and zooxanthellae is classified as:

A) mutualism.
B) commensalism.
C) Batesian mimicry.
D) parasitism.
E) character displacement.

Reef-Building Coral

Marine invertebrates in the order Scleractinia that produce calcium carbonate skeletons, forming the structure of coral reefs.

Mutualism

refers to a symbiotic relationship between two different species where both species benefit from the interaction, enhancing each other's growth, survival, or reproduction.

Zooxanthellae

Symbiotic algae that live inside corals and other marine organisms, providing nutrients through photosynthesis, which is essential for reef building.