Here's another four 'creatures' for your collection:
Werewolf - With characteristics of DDEXXX where X is 'as alter-ego', you don't want one of these stalking your ship. Unlike 'Alien' or 'Predator', even an inch-by-inch search may reveal nothing but passengers and crew.
Supernatural? Jekyll & Hyde genetics gone wrong? Viral infection? The hapless players never found out!
Catapult Scorpion - a variant of the terrestrial scorpion, it can launch a barb over distances of a metre or two. The barb is loaded with a powerful nerve toxin that induces total paralysis whilst leaving the victim conscious. This keeps the food source both static and fresh for several days whilst the local nest devours it. If the victim is brought to a sickbay, the symptoms can be discovered and rectified without lasting harm, but a less reliable field diagnosis (he's dead, Jim) may lead to comrades disposing of the 'corpse' via less-than-pleasant traditions.
Related to today's 'flesh-eating bugs', Zombie Rot is the common name for a bacterium that causes the body to undergo decomposition whilst still alive. Around a thousand times faster than Leprosy in its effects, and with pain levels similar to gangrene, death occurs in around 7 to 14 days. The disease can be halted, but not reversed, by a medical facility of TL10+, but the symptoms may not be recognised for several hours or days. Generally, the victim will lose 1 point every four (or 1D6) hours from a random* statistic (all except Soc) All losses will be permanent and every time Int is rolled, roll less than CURRENT Int to avoid the victim going psycho. In the later stages, the victim is essentially a zombie and will become a NPC.
*Actually, the process is not quite random.
Having rolled for a random characteristic, roll less than that characteristic's current value for it to be affected, otherwise roll for another characteristic. Continue until a characteristic is affected. If Int is rolled but not affected, it may still make the victim homicidally psychotic, but in this case the effects will be temporary, lasting for 1D6 hours.
Rybecker's Disease is a virulent viral population-decimator emulating Poe's Red Death and Ebola. It has a disturbing history of escaping quarantine.