A new alien species, or two.

The hospitassimion is a species that takes over other organisms and turns them into members of its own species. They come in a variety of shapes and sizes depending on what species the organism originally belonged to before being taken over. The organism loses any memories of its former self but retains its personality and temperament.

Sorquines are simply hospitassimions who used to belong to another particular species - although it could be argued they still do, since their reproductive systems are fully functional. Their newborns are born as the original species but get turned into sorquines after birth by one of their parents as a matter of routine.