| A | B |
|---|
| plankton | plants and animals that drift and move by surface currents |
| nekton | free-swimming animals |
| benthos | plants and animals that live on the ocean bottom |
| continental shelf | the underwater edge of a continent (is the gently sloping part of the continent covered by shallow ocean water) |
| continental slope | the steep slope leading down from the continental shelf toward the ocean floor (is the area that begins where the continental shelf suddenly drops) |
| continental rise | the zone of sand and mud that stretches from the continental slope to the deep-sea floor |
| abyssal plain | the vast flat lands that cover the bottom of the deep, open ocean |
| rift zones | systems of cracks in the ocean floor through which magma rises |
| mid-ocean ridges | mountain chains that form along the rift zones |
| vents | openings along the rift zones that let out very hot water |
| trench | a deep narrow valley in the ocean floor |
| sonar | an instrument that uses sound waves to locate objects in the water |
