Nongilled

Nongilled is an adjective used in biology to describe organisms or life stages that lack gills. It denotes the absence of gill-based respiration or the loss of gilled structures, and it is typically used descriptively rather than as a formal taxonomic term.

Its use spans several groups. In amphibians, many species have gills only during larval stages, and the adults are nongilled. In fishes and other aquatic animals, gill reduction or loss can occur in lineages adapted to air-breathing or terrestrial life, resulting in nongilled adults or life stages. Some invertebrates exchange gases primarily by diffusion through the body surface and lack true gills, and such organisms may be described as nongilled. The term can also appear in fossil and comparative anatomy to indicate absence or reduction of gill structures in specimens, though preservation bias must be considered.

Limitations: nongilled is imprecise without context. It should specify whether gills are absent, reduced, nonfunctional, or merely not used in a particular life stage.

Etymology: the term is formed from non- (not) + gilled (bearing gills).

See also: gill, respiration, amphibian metamorphosis, lungfish, diffusion.