Parasite (Puppet Master)
The creatures were quite intelligent and developed a type of space craft which they used to travel world to world. Once arriving on a planet, they would attempt to descreetly infiltrate the host society. The initial infectees would attempt to behave normally and attempt to trick new hosts into positions where they would infect them with new parasites. This process would continue until the parasites dominate the environment. Infiltration and implantation of new hosts being their primary strength in combating enemies by compromising military forces to serve the parasites goals.
The parasites were, as already mentioned, stingray shaped and would attach to the back of the host where a tongue-like tendril at its mouth would drill into the neck and two suckers would control the nervous system. The creatures possessed a complete control of the host and were capable of creating a heart attack or other means to threaten the host should it wish to do so. Their forms were aerodynamic allowing them to glide through the air and use their tendril-like tongues, that can shoot out and pierce rocks, to aid them in movement. They could wrap their bodies and form a ball like shape where it would hibernate until a host would approach. The creatures reproduced completely alone and had a genetic memory which it passed to its offspring.
Once implanted by the parasite, the host would serve as the creatures puppet and benefitted from improved strength due to a stimulation of the adrenaline gland. They are also capable of taking far more punishment and damage from outside attacks then a normal human could but this is all done on the parasites part with the human having no control on the matter. Should the host be trapped or wounded, then the parasite can abandon the host and use its small form to maneuver far better than a host could do. While the parasites work on a collective goal, they are individualistic and do not possess a hive-mind. Information is shared either verbally or chemically through 'feelers' on the back of the parasite which connect to the feelers of another parasite.
The creatures were vulnerable to neurological diseases as their bodies were dominated by neural tissue. This served as the basis of their failure to conquer Earth in the movie, however, a single member of the species managed to survive briefly as it had developed an immunity but it was destroyed before it could reproduce.
Despite their use of 'conventional' forms of warfare, the parasites were known to be quite advanced and had used an interstellar vessel to arrive on Earth. The internal chambers of their craft appeared organic in nature with incubation pools where the parasites would roam freely and grow. While organic isolation pods were created to encompass humans who were 'immune' from the parasites infection in an attempt to combat this immunity.