(Ctenophores also have musculature in their in-between layer, the mesoderm, but it likely evolved separately from the mesoderm found in bilaterians like people.) Both have two major cell layers: the external epidermis and the internal gastrodermis. While jellyfish and comb jellies have several anatomical differences, the basics are the same. Invasive jellies have also wreaked havoc in some parts of the world. Whatever the reason, huge explosions in jelly numbers (a jelly bloom) can disrupt fisheries, make for unpleasant swimming, or foul up the works of power plants that use seawater for cooling. As seawater temperature rises, predators of jellies are removed by fishing, more structures are built in seawater, and more nutrients flow into the ocean, some types of jellyfish and comb jellies may be finding it easier to grow and survive. And, in the modern age, they are having similar effects on ecosystems. Yet though they look similar in some ways, jellyfish and comb jellies are not very close relatives (being in different phyla-Cnidaria and Ctenophora, respectively) and have very different life histories.īoth groups are ancient animals, having roamed the seas for at least 500 million years. They are both beautiful-the jellyfish with their pulsating bells and long, trailing tentacles, and the comb jellies with their paddling combs generating rainbow-like colors. Jellyfish and comb jellies are gelatinous animals that drift through the ocean's water column around the world.
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