Navicula exigua is a small diatom species characterized by elliptical valves with slightly protracted ends, giving them a fusiform shape. The valves display fine, parallel, punctate striae, which can be observed as single or biseriate arrangements. Like other Navicula species, N. exigua features a central raphe running longitudinally along the valve. Typically ranging from 5 to 20 micrometers in length, Navicula exigua thrives in freshwater environments, particularly in benthic habitats such as sediments and submerged vegetation. Its morphology and habitat preferences make it an important component of aquatic ecosystems, contributing to nutrient cycling and primary production.