<human>:  What are the differences between a tortoise and a turtle?
<bot>: The primary difference between a tortoise and a turtle is in the shape of their shells. A tortoise has a high-domed shell that is squat and round, whilst a turtle's shell is flatter and has a more streamlined shape that helps them to move through water. Additionally, tortoises are mostly land-dwelling creatures, while turtles spend much of their time in water.