This has been bothering me for quite a while. This is a movie I saw as a kid back in the 80's, but it could easily have been produced in the 70's (I vaguely remember actors with 70's hair). I'll try to list everything I can remember.
- Crew of a spaceship lands on an alien planet and head for a human base there (responding to an SOS maybe?). I think there were two women and three or four guys.
- Everyone in base is found dead.
- The culprit is an alien monster that looks like a rock and can thus disguise its presence.
- It (of course) systematically starts to kill the members of the newly arrived crew.
- A scene I remember distinctly is the survivors climbing out of a trapdoor running away from the monster below. Token black guy is too slow and gets pulled down screaming.
- Only one guy and one girl manage to reach their spaceship and escape.
- Movie closes with a shot of one of the body bags aboard the ship starting to move (implying an Alien-like offspring inside the body)