i call these the Cookie Monsters of the sea -- but they are better known as a Chocolate Chip Sea Cucumber. they are "detritivores", meaning, they feed by sifting through sand and mud (detritus) for food. in other words, they are nature's vacuum cleaners of the sea. they can eviscerate/expel their internal organs to deter predators, but i have never observed this behavior. the breathing-like motion you see in this video is in fact respiration, not feeding. that is the posterior end of the animal. this one is about 15 inches in length, they run from 4 to 20 inches.