What is a "sucker"?

A sucker is a specialized organ or structure found in certain animals used to attach themselves to surfaces or other animals. Suckers are most commonly found in cephalopods, such as octopuses and squids, and in fish, such as catfish and lampreys. These animals use their suckers to hold onto prey, climb, or attach themselves to rocks or other objects in their environment. The suckers are typically composed of circular muscle fibers, which can contract and expand to create suction, as well as specialized tissues that secrete adhesive substances to increase grip.