Fumarole worm

A fumarole worm was an animal lifeform found Priors 5d, a class P moon of Priors World in Priors system, located in the galaxy's Beta Quadrant. The fumarole worm was a worm species. 

Biology and environment
Cocytan beasts shared their body plan with with Aehallh worms, including their behavior, size and abilities. Like them, they roamed underground and only pushed a part of their body aboveground. When defeated, they retreated into the ground and their hole collapsed back to even ground.

The tubular body was propelled by digit-like attachments to the ventral armor plating. While the back was covered in teal-colored armor, the ventral plates were shaded light brown. The head lacked noticeable eyes, and was dominated by a three-pronged maw, from which the worm could spit venom.

When emerging from underground, the fumarole worm towered over average-sized humanoids, which it would slam with its upper body, or cover with venom.

The fumarole worm emerged from its hole one at a time, although several worms would live in close proximity. On Priors 5d, these worms lived in a fumarole pit. Cocytan beasts kept away from the fumaroles. 

History
Fumarole worms attacked survivors from a crash when they navigated the scalding pools of fumarole geysers on their way to a cave for shelter. Phaser fire forced each worm to retreat back underground.

On Day 3, the Starfleet crash survivors fought attacking Klingons near the fumaroles, so the geysers and worms would inadvertently aid them.