This story is, more or less, Philippine version of Cinderella.
The myth was told that the crab was the spirit of Maria’s mother who died when Maria was still young. Maria’s father remarried to the widow with two daughters. Just like Cinderella, Maria was forced to do all the works and the two daughters envied her beauty.
Maria met the crab for the first time when she was crying in the lake. The crab, then, always taking cares of her such that, gave her food.
The step mother found this little secret, and being the evil being she was, she ate the crab making Maria miserable and crying in misery. While in this situation, Maria heard the crab’s voice in her head, telling her to bury the shells in the yard. The morning after, the spot grew a tree with golden fruits.
And this is when the prince charming came into the picture…
A handsome man came to their house, interested with the golden fruits. The two evil sisters, who try to get it for him, were unable to come close to the tree. The handsome man fell in love with Maria at the first sight.
They married…and live happily ever after.
Source:
Crabs Folklore 