Virturally unable to move Alexstraza is forced to breathe in the air provided by her captor. She quickly grows light headed and her struggles wane before she loses consciousness. The tentacles prove too strong for Yrel who soon vanishes inside the second creature. It burrows under the sand, fading from sight. Once inside she is further restrained by the creature which squeezes her with it's muscular stomach. Now barely able to move her face is covered by the strange, larger tentacle. Needing air as much as Alexstraza, she soon exhales and breathes in the strange air provided by the creature. Able to draw breath again she resumes her futile struggle but quickly succumbs to the anesthetic, slipping out of consciousness. Moments after the attack began little evidence remains that the women had ever been here; captured and held for an unknown purpose.
Really leaves you in awe. What's the point of knocking them out with gas (breathable no less) if they were drowning anyway? Too bad you don't plan on a follow up. Based on what we know, they weren't eaten and there was a purpose to keeping them alive. Possibilities:
1. The creatures serve a being that would benefit having them as captives or slaves
2. Because I'm getting Alien vibes, they reproduce by putting their eggs into other beings
3. They're gonna undergo transformation (Some sort of mermaid?)