Few animals wear their identity so plainly in their name: Hexarthra fennica belongs to a genus whose name means "six joints," a reference to the six movable, paddle-like appendages this microscopic animal uses to swim through open water.
Hexarthra fennica is a species of rotifer, a group of microscopic invertebrates in the phylum Rotifera. It sits within the class Eurotatoria, order Flosculariaceae, and family Hexarthridae, placing it among the animal kingdom's smallest multicellular organisms. Despite its size, it is worth knowing because of how it moves, feeds, and disperses across freshwater and brackish habitats, using the very appendages that give the genus its name.
Distribution and Habitat
Occurrence records for Hexarthra fennica show a distinct seasonal pattern, with a pronounced peak of 72 recorded observations in April against a backdrop of far lower counts in the surrounding months, ranging from just 3 in June and December up to 24 in August. This spike suggests the species is detected far more often in spring than at other times of year, though the underlying cause, whether a true rise in numbers or simply more sampling effort during that period, cannot be determined from occurrence counts alone.
The remaining months show a more irregular pattern, with modest counts in January (16), July (20) and September (21), and noticeably fewer records in February, March, May, June, October, November and December. As the GBIF data represent presence observations rather than measures of abundance or a complete picture of the species' native range, these fluctuations should be read as an indication of when Hexarthra fennica has been most frequently reported rather than as a reliable seasonal population curve.
