necto-, nect-, nekto-, nek- +

Characterized by having a foot, or feet, used for swimming: Certain aquatic organisms are nectopodic in that they can use such appendages or limbs for moving independently in water.

The region of a siphonophore colony that bears nectophores (medusae specialized for propulsion).

A nectosome is an order of Hydrozoa (various simple and compound polyps and jellyfish) consisting of various free-swimming or floating pelagic, mostly delicate and transparent, and often colored forms that are usually regarded as compound animals composed of zooids modified to perform various functions for the colony. Examples are feeding, defense, and locomotion which sometimes have two or more zooids in the form of a bell so that, by their contractions, they cause the colony to swim, and which often have a hollow float which keeps the colony afloat.

An organism that inhabits the middle depths of the sea: The nectozooids are neither the benthos, which are animals and plants living on the bottom of a sea or lake, nor the plankton or the animal and plant life, mostly microscopic, which generally floats and drifts near the surface of a lake, river, or sea.

The form of marine life that exists just above the ocean bottom and occasionally rests on it: The nektobenthos is typically associated with the benthos that swim actively in the water column at certain periods.

1. Animals of the pelagic zone of a sea, or lake, that are free-swimming and independent of tides, currents, and waves: Examples of nektons are fish, whales, squids, crabs, and shrimps.
2. An organism that swims and is not simply carried passively by currents: Nektons are capable of counteracting currents through various swimming mechanisms.

Nekton are limited in distribution by temperature and nutrient supplies, and they decrease with the increasing depth of the sea.

Uncounted myriads of little plants, together with the great numbers of tiny animals that feed on them, and on each other, form the plankton.

The term "plankton" is the name applied in 1887 by Victor Hensen, a German professor of zoology, with reference to the great company of marine creatures that drift at the mercy of the currents, as distinguished from the nekton, animals like fish and whales which are able to swim against the moving waters, and from the "benthos", the plants and animals attached to the bottom of the sea or crawling on it.

There is no clear-cut dividing line between planktonic and nektonic creatures because some of the fish and other marine animals belong to the plankton during the early stages of their lives, and then to the nekton later.

A reference to organisms that swim actively in open water: Such nektonic creatures can move in water independent of water currents as opposed to drifting, floating, or being attached to other creatures.

Concerning an organism that swims on its back: The family of Notonectidae, aquatic carnivorous insects, is considered to be notonectal and generally swims back downwards using its long hind legs which resemble oars.