A marsupial kept by Doctor Phlox, whose droppings contain an exceptionally high concentration of regenerative enzymes and are therefore, to his delight, medically valuable.
The Altarian marsupial is a small animal valued by Denobulan medicine for an unglamorous reason: its droppings hold the greatest concentration of regenerative enzymes known to Doctor Phlox.
Phlox explains this to a startled Captain Archer in Broken Bow, as he settles his cages of animals into the ship's sickbay before the voyage to Qo'noS. The doctor's enthusiasm for the creature sets the tone for his whole approach to healing.
The marsupial travels with him aboard Enterprise NX-01 as part of the sickbay menagerie that also includes a Pyrithian bat and an osmotic eel.