It Waits Below — Eric Red

It waits no more!
In the 1800s, an asteroid carrying an extraterrestrial life form crashed to earth and sunk a Spanish treasure ship. Now, a trio of salvage experts dives a three-man sub to the deepest part of the ocean to recover the sunken gold. There, they confront a nightmarish alien organism beyond comprehension, which has waited for over a century to get to the surface. It finally has its chance.

As their support ship on the surface is ambushed by deadly modern-day pirates, the crew of the stranded sub battles for their very lives against a monster no one on Earth has seen before.