All species that I have encountered have armor on their shoulders and wrists indicating a high intelligence. They seem to live in underground tunnels networked all over the planet which they can use to ambush prey.
From what I've briefly seen they seem to enjoy song and dance.
Lemurians are one of the first enemies you'll meet in the game, and can be knocked back by basic abilities. They are possibly one of the easiest enemies in the game to defeat on their own, but as the difficulty scales it is important to conduct crowd control, as they are more formidable in groups than on their own.
Lemurians are described as intelligent seeming bipedal species, and that the author of the field notes (presumed to be the commando) spend much of their time imagining what the caverns that they live in look like.