Transparency is useful for avoidance of visual predators in sunlit open water habitats that lack shelter. This is particularly important for delicate gelatinous creatures since the absence of hard body plates and the relatively poor swimming ability renders most quite susceptible to predation. While medusae, comb jellies and pelagic molluscs may have limited escape responses, they are still slow compared to fishes and turtles that are seeking a meal. Only the cnidarian jellies with their stinging nematocysts can mount any serious defense against predators. With their capable defenses, many scyphomedusae such as purple-stripe jellies and sea nettles have abandoned the transparency strategy.
Many gelatinous animals are also bioluminescent.
Production of intense flashes of light are thought to provide some defense against visual predators, who can be confused or startled by the display. Although most gelatinous animals are capable of some type of locomotion, their long-distance travels are generally under the control of currents and other patterns of water movement. For this reason they are regarded as having a drifting lifestyle. The disadvantage is that they may be carried into areas that present multiple dangers, such as near shore. The upside is that with little expenditure of energy they can be dispersed over wide areas.