Xindi-Arboreals were members of the multi-species Xindi race. They were one of the most peaceful of the six species, which shared a common genetic ancestry.
In appearance, Arboreals were covered with hair and had long sharp fingernails, dark eyes, and a ridge running from their noses to the back of their heads.
As the third species of Xindi discovered by the crew of Enterprise, it was believed by Doctor Phlox that this species probably evolved from some sort of arboreal primate. (ENT: "Extinction")
Arboreals were afraid of the water. They were considered to be lethargic by the other Xindi species. They were also extremely calm, even when taken hostage. (ENT: "The Shipment")
Culture and technology
Arboreals wore belts that seemed to indicate their rank. For example, Gralik Durr's assistants wore two belts while he himself wore three. Jannar wore five belts.
Relatively speaking, Xindi-Arboreal starships were not very powerful; a Xindi-Reptilian starship patrol could easily destroy three Arboreal ships.
In the final draft script of third season Star Trek: Enterprise premiere "The Xindi", the Xindi-Arboreals are commonly referred to as "Xindi-Sloths". This was changed by the end of that season, as scripts for installments such as "Countdown" and "Zero Hour" instead refer to them as Xindi-Arboreals.
Executive Producer Rick Berman once commented that, of all the Xindi species, he thought "the Xindi-Sloth" looks especially good. (Star Trek: Communicator issue 147, p. 16)
The novelization of the episode "The Xindi" refers to the Xindi-Arboreals as "Xindi-Marsupials."