Elementals normally refers to what is called “chungpo” in Tibetan or “bhuta” in Sanskrit, a type of harmful spirit in the preta realm.
The 84000 project actually just published a new Sutra translation this week listing all the 31 realms and the lifespans of beings in each, called the Limit of Life Sutra.
Another source on the 31 realms is here: https://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html. This lists each of them together with sources from the Pali Canon.
Hope this helps.