Protomorphism is the term used to refer to a physical change in a descendant that doesn't complete changing and is not controllable, the descendants with protomorphism are referred to as protomorphs.
The difference between a protomorphism and a metamorphism is completeness and reversability. Metamorphs are able to control their change and return to a human form. Protomorphs are "stuck" part-way through their first metamorph change and cannot complete it or return to a human form.
Protomorphs may have abilities separate from their protomorphism, are as extensions of the protomorphism that they can control. Protomorphs are usually considered objects of pity as their power has permanently deformed them, however the protomorph form is not always one considered deforming, and protomorphs are often able to come to terms with their life.