Coalescent Organism

Coalescent Organism is a designation given to a life form which survives by absorbing other creatures and taking up their appearance and memories, remaining in that form until the need to feed again. Essentially, they become a copy of the organism that they just consumed.

Biology
The Coalescent Organism mimics not only the form of its victims, but their cellular and genetic structure as well. Even a DNA test will fail to identify them. Their natural form appears as a brown, gelatinous mass which moves in amoeboid fashion.

History
Most known Coalescent Organisms are microscopic, and change form by absorbing new cells every few seconds. However, a man-sized specimen attacked and absorbed Human Starfleet officer Keith Rocha during a mission in the Triona System.

Being much larger and more complex than others, this particular Coalescent Organism could remain in Rocha's form for several days, during which he was transferred to Relay Station 47 and behaved in a more antagonistic manner than the real Rocha was known to. When the time came for the creature to change form again, it tried to absorb Haliian officer Aquiel Uhnari, but she managed to fight the alien with a phaser and escape in a shuttlecraft.

Due to the effect of the coalescing process, Aquiel suffered from a form of amnesia and couldn't remember the details of what had happened. The organism, meanwhile, turned its attention towards Aquiel's dog Maura, absorbing it and taking its place for several days, during which the dog behaved in a seemingly normal fashion, with only a few episodes of atypical behavior such as destroying Geordi La Forge's shoes. Later, when it came time to change again, the Organism tried to attack Geordi, but was ultimately destroyed by a phaser discharge.

Appearances

 * Star Trek: The Next Generation, s06e13, "Aquiel" (1993)