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S. waters and receives just enough light to support photosynthetic organisms. tants of extreme situations, such as hot underwater geothermal vents or extremely salty lakebeds. Another kingdom of one-celled organisms, Protista, includes amoeba, euglena, and diatoms. Unlike monerans, protists are large, complex cells that are structurally like the cells of multicellular organisms. Members of the Protista kingdom are a diverse group varying in mobility, size, shape, and feeding strategies. A number are autotrophs, some heterotrophs, and others are mixotrophs, organisms that can make their own food and eat other organisms, depending on the conditions dictated by their environment.

Since water in the ocean is always moving, the bodies of marine plants are flexible, permitting them to go with that movement. Some marine plants secrete mucus to make their surfaces slick, further reducing their drag or resistance to water movement. Mucus also helps keep animals from eating them. A plant that grows on land is described with terms such as leaf, stem, and root. Seaweeds are made up of different components. The parts of seaweed that look like leaves are termed blades, or fronds. Some are equipped with small, gas-filled sacs, or bladders, that help keep them afloat and close to the sunlight.

Organisms such as dinoflagellates and fish support lightemitting bacteria. 3 Sponges, Cnidarians, and Worms r Animals of the Ocean Surface and Seafloor he largest portion of the ocean is the open, deepwater area beyond the edges of the continental shelf. 6 km). The open sea and the deep seafloor are difficult environments that pose unique problems to living things. At the surface of the open ocean, marine animals have no place to hide from predators or seek protection from the Sun. In addition, nutrients in the upper levels of water are patchy, with only a small percentage of ocean area capable of supporting colonies of phytoplankton.