Spirilla are a type of bacteria characterized by their spiral or corkscrew shape. They belong to the group of prokaryotes, which means they lack a nucleus and other membrane-bound organelles. Spirilla can be found in various environments, including soil and water, and some species are known to be pathogenic, causing diseases in humans and animals. These bacteria move using a unique structure called a flagellum, which acts like a tail, allowing them to swim through liquids. Spirilla play important roles in ecosystems, contributing to nutrient cycling and decomposition. Understanding their biology is essential for studying microbiology and environmental science.