A metamorph was a lifeform that was able to alter its body to take on the characteristics and appearance of another species (and then change back).
Biological metamorphs Edit
Some metamorphs had the ability to take on a wide variety of forms, with few limitations. These included Aubertides (PROSE: Human Nature), Brancheerians (COMIC: Meteorite Meeting), Gizou (COMIC: Agent Provocateur), Gwanzulum (COMIC: Planet of the Dead), Kymbra Chimeras (COMIC: Changes) and Whifferdills (COMIC: The Shape Shifter).
Other metamorphs seemed to be only able to take on humanoid forms, such as multi-forms (TV: The Eleventh Hour), Nostrovites (TV: Something Borrowed) and members of the Rutan Host (TV: Horror of Fang Rock).
Still other metamorphs were limited to shifting between a default form and an alternate form. These included Axons (TV: The Claws of Axos), Carrionites (TV: The Shakespeare Code), Vardans (TV: The Invasion of Time) and Vespiforms (TV: The Unicorn and the Wasp). Werewolves could change from humans into wolves, while some vampires could change into bats.
Although most metamorphs changed form voluntarily, others could not. Time Lords changed form whenever they regenerated (TV: The Tenth Planet), as did Kastrians (TV: The Hand of Fear). The Solonians changed form when they went through their natural life cycle. (TV: The Mutants) The Yend became involuntary shapeshifters after exposure to radiation from the rogue star Mortain. (PROSE: The Sons of the Crab)
Technological metamorphs Edit
Some species were only able to change their shape through the use of advanced technology.
Cell 114 sleeper agents were apparently modified to resemble the native species of the planets they invaded, and could change back and forth once they were activated. (TV: Sleeper) The Chameleons used technology to assume the identities of other beings after losing their own. (TV: The Faceless Ones) Usurians exposed themselves to particle radiation to assume humanoid form. (TV: The Sun Makers) Zolfa-Thurans could change the appearance of any humanoid they possessed, but only to a similarly shaped being. (TV: Meglos) Zygons used body-print technology to augment their limited natural shapeshifting abilities. (TV: Terror of the Zygons)