A sea urchin shell is a masterpiece of natural engineering based on a few basic rules:

A Five-Part Design: Just like its cousin the starfish, the shell is built around a perfectly balanced five-pointed star pattern.

Sunflower Spirals: The tiny bumps on the shell spiral outward from the center. Nature uses this exact same spacing trick in pinecones and sunflowers because it packs everything together tightly without wasting a single drop of space.

A Super-Strong Dome: The whole shell is pieced together from tiny interlocking plates, much like the patches on a soccer ball. This curved design spreads out physical stress, making the delicate-looking shell surprisingly tough against ocean pressure.

Also see:
Vintage Nikon D3 & Carl Zeiss Milvus 50mm f/2