a kind of bivalve
蜊 centers on a specific kind of bivalve shellfish, likely a clam or similar mollusk.
蜊 combines 虫 (insect or shellfish) with 利, which likely contributes the sound. The character is used for a type of bivalve, but the exact historical development is uncertain.
The left side 虫 often relates to shellfish or small creatures, and the right side 利 suggests something sharp or useful. Picture a clam with a sharp-edged shell: 蜊 is that bivalve.
For リ, imagine a little clam named Lee: Lee -> リ, and Lee the clam is the bivalve 蜊.
Manila clam (Ruditapes philippinarum); Japanese littleneck clam