It very interesting how lombriz (worm) was translated to clam in English. Literarydevices.net reports that the phrase “as happy as a clam” is derived from the full phrase “happy as a clam at high water.” Clams are collected during the low tide, so if I were a clam, then I would be definitely most “happy” at high tide when I was safe from fishermen.
English Translation
I am as happy as a clam.
My theory is that it’s lombriz in Spanish because it rhymes, and it’s a bit absurd. That is, no deeper meaning.