The term 'Nautilus Shape' refers to the SPIRAL shape of the shell of a nautilus, a type of cephalopod mollusk. The crossword solution for this term is 'SPIRAL, ' which is an accurate description of the shell's shape. The nautilus shell is composed of a series of chambers connected by a tube-like structure that spirals outward from the center. This SPIRAL shape is a common feature of many mollusks and is thought to be an adaptation to increase the surface area of the shell while maintaining its strength.