Wrigglers are a type of aquatic creature that can be found in both freshwater and saltwater environments. They are often referred to as worms or eels, depending on their size and shape. The term 'wriggler' is derived from the wriggling motion they make when swimming. Worms are typically four-letter words, while eels are three-letter words. Both worms and eels are wrigglers, making them an appropriate answer for this crossword puzzle.