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Abstract
Hannaea superiorensis sp. nov. is formally described from benthic and tychoplanktonic locations in the North American (Laurentian) Great Lakes, primarily from Lake Superior. This taxon has previously been reported as Ceratoneis arcus (Ehrenb.) Kütz., Hannaea arcus (Ehrenberg) Patrick or Hannaea arcus var. linearis (Holmboe) Ross in Hartley; however, significant morphological and ecological differences support the separation of Hannaea superiorensis as a new species. Length-width-curvature triplots demonstrate the greater length and length: width ratio of this taxon compared with other Hannaea populations. Morphologically, H. superiorensis most closely resembles H. arcus var. linearis. Finally, the habitat preferences of H. superiorensis are distinctive compared to the riverine nature of H. arcus and its varieties; Hannaea superiorensis is primarily found as epilithon in the littoral wave zone of Lake Superior. This species can also be found secondarily in the tychoplankton of Lake Superior and is occasionally transported as tychoplankton to other Laurentian Great Lakes. Hannaea superiorensis does not appear to be sympatric with H. arcus in the modern Great Lakes, but it may have speciated from local river populations of H. arcus during the Late Pleistocene-Early Holocene to become adapted to the cold, high-energy wave zone of Lake Superior.