A jar full of immunocytic gel worms
The immunocytic gel worm was a corkscrew-shaped organism that lived in a viscous pink fluid. Doctor Phlox kept a jar full of them in the sickbay on Enterprise for medical purposes.
Although Phlox allowed Captain Jonathan Archer, commanding officer of Enterprise, to observe the worms in 2151, Phlox told him not to shake them. (ENT: "Broken Bow")
The immunocytic gel worms were created using computer-generated graphics. Initially an exotic-looking tropical fish called Oliver was considered for the role, but it did not look strange enough. ("Broken Bow" text commentary, ENT Season 1 DVD)