Osmotic eel
From Memory Alpha, the free Star Trek reference.
The osmotic eel is a small aquatic lifeform resembling a starfish, that is useful in medicine for cleaning and healing wounds.
Doctor Phlox kept an osmotic eel aboard during his assignment to Enterprise, and it could often be seen in sickbay in a container of water. During their first mission in April 2151, it was used to cauterize Captain Archer's leg wound. (ENT: "Broken Bow").
Doctor Phlox's osmotic eel was a female, and he offered to give her to E'lis, a doctor on a deuterium mining colony in 2152, but she joked she wouldn't know what to feed her. Phlox then explained to E'lis that the eels feeding needs are relatively modest, as it only requires a nutrient broth every three or four days. He further noted that while they were working, they required their nutrient broth even less, as they usually ingested a little blood while healing an injured artery. (ENT: "Marauders")
Hoshi Sato fed Phlox's osmotic eel with Vulcan root leaf in 2153. (ENT: "Exile")
In 2154, she was used to remove the Xindi neural parasites that the Xindi-Reptilians had injected into Hoshi Sato to force her compliance. (ENT: "Countdown")
