Little is known about the Aquaman spinoff The Trench other than that it will be set in the kingdom of the Trench and will not feature the main cast of Aquaman.
The Trench creatures are rather recent arrivals to the Aquaman lore, having been introduced in the comics only in 2011 when DC did a revamp of its entire publishing line. They are revealed to be part of the kingdom of Atlantis but when it sunk, inhabitants who were cut off from other survivors and evolved into ravenous monsters.