The term 'Nautilus Shapes' refers to the spiral shapes of the shells of the Nautilus, a type of cephalopod mollusk. The crossword solution for this term is 'SPIRALS, ' which is an accurate description of the shell's shape. The Nautilus shell is composed of a series of chambers connected by a spiral-shaped tube, and the shell grows in size as the animal grows. The Nautilus is a living fossil, meaning that it has remained relatively unchanged for millions of years.