Species: narehate

From the works and manga series of Akihito Tsukushi (made_in_abyss)

Narehates (or "hollows") are beings who have survived the 6th layer's curse and whose bodies have become deformed as a result. They can take many different forms depending on the circumstances of their transformation. Their exact properties as a species are unknown.

While many of the narehate at Ilblu seem to be somewhat amorphous, most of them retain at least some sense of their humanity and are able to communicate with one another using Ilblu's language or gesticulation compared of those abandoned in the Miniature Garden Of the Dawn on the 6^th layer.

The word "narehate" comes from the term "nare no hate" (成れの果て) which means "the shadow of one's former self".
Source: https://madeinabyss.fandom.com/wiki/Narehate