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.