MYSTERY ON MONSTER ISLAND (1981). Director: Juan Piquer Simon.
Jeff Morgan (Ian Sera) wants to see the world before settling down, and goes on a voyage arranged by his Uncle William (Peter Cushing). But the young man winds up shipwrecked on Spencer Island with all manner of beasties, the nervous-nellie instructor Prof. Artelect (David Hatton), and a fellow named Taskinar (Terence Stamp). They encounter everything from giant steam-snorting caterpillars to crazed kelp creatures, as well as phony rubber fish men. Most of the monsters are barely mobile, but for once there's an explanation for this, which I won't give away here. Very loosely based on the novel "L'École des Robinsons" by Jules Verne. There's some charming stuff in this, including a chimp who wears men's shoes, and a good sequence when the group uses primitive weapons to fight off some invaders.
Verdict: Not quite as awful as it could have been. **1/2.