I've always been a bit disappointed by the spider enemy's absence.
Thanks to TheDoctorPoo, it can now be used in custom campaigns.
How much work would it take to add the spider to SOMA? (Disclaimer: I have no modding experience.) One question is where it would fit. I think it belongs near the WAU, for two reasons. First, it looks more "alien" and artificial than other enemies in the game; second, partly due to the teaser, it meshes well with Giger-esque environments.
Unfortunately, Alpha is too cramped to accommodate the spider. (Evasion would be impossible.) The only other location I can think of is the abyssal trench between Tau and Alpha, but I don't know how well it would work underwater.