Arachnoid is an alien encountered in Osiris: New Dawn.
A particularly nasty sight on a planet's surface, the arachnoid is an alien resembling a cross between a human and a monkey, with a bit of scorpion thrown in. In other words, not something you want to encounter at night outside your habitat.
The arachnoid tends to spawn at night and where there is one, more will usually be found. It attacks by rushing the player and also has a ranged spitting attack, where the arachnoid buckles and spits a blue acid. The effects of the attack are so far unknown. If you are holed up inside of a building it will sometimes circle the building at high speed. Like the Gnat, it can find the player even at great distances and through objects.