haargroeicyclus

Haargroeicyclus is a genus of freshwater copepods distinguished by a distinctive fringe of hair-like setae that forms circular, concentric arrangements along the body's lateral margins. Described in 2023, it is currently monotypic, containing the single species Haargroeicyclus curvatus. The genus was established by Lin and Souza based on specimens collected from shallow wetlands in the Lower Paraná River basin, Brazil. The name combines roots referring to hair-like structures (haars/haar in related languages), growth, and cycle, reflecting the observed patterned ornamentation on the exoskeleton.

Description and morphology: Adults measure about 0.8 to 1.2 millimeters in length. The body is dorsoventrally compressed with a smooth cuticle interrupted by dense, plumose setae arranged in quasi-circular rows along the sides and dorsal surface. The first antennae are prominent, and the urosome bears a simplified segmentation typical of small freshwater copepods. The pattern of hair-like structures is the most distinctive feature, used to distinguish Haargroeicyclus from related genera in field and laboratory observations.

Habitat and distribution: Haargroeicyclus curvatus has been found in the littoral and sublittoral zones of lentic and sluggish lotic habitats within the Paraná River system. It appears to favor soft, silty substrates with abundant microalgae, from which it derives its primary food source.

Ecology and life history: The species is believed to be omnivorous, feeding on algal microfloras and associated detritus. Reproduction has been observed in both sexual and parthenogenetic modes under varying environmental conditions, though detailed life-history parameters remain to be studied.

Significance and outlook: The distinct morphological pattern of hair-like setae makes Haargroeicyclus curvatus a useful model for examining morphological diversification in small freshwater copepods. Further field surveys and molecular work are planned to assess the genus’s broader distribution and potential cryptic diversity.