This is an irregular feature - both in frequency and oddness - dedicated to a word I came across that I have never previously used.
nekton (NECK-tuhn) n. organisms that live in the water columns of oceans and freshwater lakes; free-swimming pelagic organisms whose movements are independent of the tides, currents and waves; all aquatic animals that can swim through the water against currents.
Some examples are of nekton include adult krill, small fish, whales, and tuna, all of which can egage in migratory behavior. By contrast, plankton are those organisms that drift passively with the current, although plankton are still capable of independent movement.
The largest group of nekton are known as chordates, and these animals possess bones or cartilage. This group includes most bony fish, whales, sharks, porpoises, dolphins and seals. Molluscate nekton include animals like octopus and squid, while arthropodic nekton include animals like shrimp.
The term nekton is derived from the Greek word nēktón ("the swimming"), and dates to the late nineteenth century. The study of swimming organisms is called nektology, while a person who studies swimming in all its forms is referred to as a nektologist.