Spiral-shelled mollusk

NAUTILUS

This deep-sea creature, often called a "living fossil," has a chambered shell that inspired early submarine designs.

The clue "Spiral-shelled mollusk" directly points to the nautilus, a marine creature known for its distinctive coiled shell. The word "spiral" highlights the shell’s logarithmic shape, while "mollusk" narrows it down to this specific deep-sea cephalopod. Unlike squid or octopus, the nautilus is famous for its chambered shell, often called a "living fossil" because it’s changed little over millions of years.