Attack of the Crab Monsters

Attack of the Crab Monsters is a 1957 science fiction film directed by Roger Corman. Russell Johnson (The Professor on Gilligan's Island) stars with Mel Welles (The Little Shop of Horrors, The Silver Chalice) and Ed Nelson (Bucket of Blood). I love the art work over the opening credits.

It's online at youtube in 7 parts. Part 1:

part 2, part 3, part 4, part 5, part 6, part 7

1000 Misspent Hours says,

Attack of the Crab Monsters still suffers from uneven acting, irritating comic relief, and a monster origin story consisting of some of the most incomprehensible pseudoscientific gibberish ever uttered, but it’s a remarkably streamlined and fairly effective film— perhaps the earliest to give some indication of what its director would prove himself capable of during the following decade.