Some unusual types of sea animals include the siphonophores, colonies of animals that superficially resemble jellyfish; sea anemones, animals that look like flowers; and the sea mouse, which is a bristly worm. Siphonophores are especially notable as among the longest creatures on earth.
The siphonophores group contains about 175 species. Although a colony of siphonophores looks like an individual jellyfish, complete with tentacles and other organs, colonies are actually composed of many specialized smaller animals called zooids. Colonies are very fragile, but they go grow to great lengths, some as long as 130 feet.
Sea anemones are plant-like creatures whose tentacles resemble flower petals. Although they also have a system of gene expression that is more like that found in plants, they are still considered animals. Like siphonophores, they belong to the group Cnidaria.
Sea mice are marine worms that are covered in bristly setae. These hollow tubes of chitin cover the top side of the worm, obscuring its body segments. The worm swims by swinging its legs back and forth. Although usually drably colored, under certain kinds of lights sea mice can appear iridescent.