[Again, I am assured that the name means "goes both ways" and is another name for the (mythical) amphisbaena].
Dobleandadorids are small, bipedal predators most closely related to [that big yellowish theropod analogue in the Snaiad group pic, I'll wager].
In this family, the forelimbs have been lost entirely. The animal moves about on modified hindlimbs, which include three toes, all opposable to the others. This group obviously evolved in the "trees", given their propensity for climbing. On land, they move on tiptoes in "bipod" stance.
The second head and the tail are prehensile, muscular, and well-developed. They are used together to aid in climbing, balance, and catching food. Since they tend to resemble each other, they are also used in confusing enemies about which end is which.
Dobleandadorids are predators, skulking about in the undergrowth or contortionistically climbing trees in search of prey. In this sense, they are close to Terran mustelids. They are often brightly colored and patterned, and can be very aggressive if cornered. At least one species has cells analogous to nematocysts in its second head and tail, producing a terrible electric shock on contact.
Snaiad and all related indicia are copyright Ramjet, Ramjet, and Co. All inquiries to be directed to Mr. Ramjet, who still has total control over his world.
Perhaps it could be derived from an odd part, like the infamous panda's thumb?