Life in Water: Invertebrates - Locomomotion
Many marine invertebrates move about by pushing their way through the water, much as fishes do. When fishes contract their side muscles, their rigid internal skeleton causes their tail to swing from side to side with great power. But because invertebrates have no bones, they cannot generate nearly as much forward thrust. Consequently, invertebrates have evolved many different ways of moving through water.
Some, such as scallops, squids and octopuses, move by jet propulsion, sucking in water and squirting it out again to generate thrust. Leeches swim by undulating their bodies vertically—unlike fishes, which undulate from side to side. Some ocean invertebrates crawl and burrow in the mud; others simply float or drift wherever the currents take them; and some anchor themselves to the ocean floor and do not move around at all.
Other Ways of Moving
Some microscopic dinoflagellates move by waving tiny, whiplike flagella. O