Undersea (adjective)

Situated or occurring beneath the sea.

Origin:

Late 19th century: from under- (expressing sub-) + sea.

Examples:

1. The undersea volcano erupted and created a new island.
2. The undersea cable was cut and communication was disrupted.
3. The undersea environment is unique and often still unexplored.
4. The undersea cave was filled with a variety of exotic sea life.
5. The undersea mountain range was home to a diverse ecosystem.