Just felt like writing this today may add further information to it in future, if you want add your own stuff but
I request you cite your source, whether it is an official one or yourself.
Stage I (Ovomorph) Egg.
Stage II (Manumala noxhydria) Facehugger.
Stage III (Plagiarus Preapotens) Chestburster.
Stage IV P. Praepotens (Drone) Lurker:
Bipedal adult, with a smooth chitinous translucent carapace, biomechanical exoskeleton and four symmetrical dorsal tube like protrusions with often a distinct pointed central fifth and a tail ending in a single blade, born from a human.
2.4 meters tall upright.
Spoiler
Also claims it is able to:
Cause ovomorphing with it's barb toxin.
P. Praepotens (Runner) Scout:
Quadrupedal adult, with a smooth chitinous translucent carapace, biomechanical exoskeleton and a tail ending in a large blade, born from a animal.
2.1 meters tall upright.
Spoiler
Also claims it does:
Traverse walls and ceilings faster with greater efficiency.
Stage V P. Praepotens (Warrior) Soldier:
Bipedal adult, with a ridged chitinous opaque carapace and developed extremities with nails replaced with claws, biomechanical exoskeleton and four symmetrical dorsal tube like protrusions with often a distinct pointed central fifth and a tail ending in a single blade, developed from a Lurker.
2.4 meters tall upright.
Spoiler
Also claims it is able to:
Cause paralysis with it's barb toxin.
P. Praepotens (Defender) Sentry:
Quadrupedal adult, with a ridged chitinous opaque carapace and developed extremities with nails replaced with claws, biomechanical exoskeleton and a tail ending in a large blade, developed from a Scout.
2.1 meters tall upright.
Spoiler
Also claims it does:
Now develop dorsal tube like protrusions, with no description of their appearance or number, though whether visible by Stage five or Stage six remains unknown.
Stage VI (P. Praepotens) Praetorian Guard: Bipedal Praetorian, developed from a Soldier.
(P. Praepotens) Praetorian Charger: Quadrupedal Praetorian, developed from a Sentry.
(P. Praepotens) Queen.
Source: Alien The RPG.