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Whirligig beetle
The whirligig beetles are a family (Gyrinidae) of water beetles that usually swim on the surface of the water if undisturbed, though they swim actively underwater when threatened. They get their common name from their habit of swimming rapidly in circles when alarmed, and are also notable for their divided eyes which are believed to enable them to see both above and below water. The family includes some 700 extant species worldwide, in 15 genera, plus a few fossil species. Most species are very similar in general appearance, though they vary in size from perhaps 3 mm to 18 mm in length. They tend to be flattened and rounded in cross section, in plan view as seen from above, and in longitudinal section. In fact their shape is a good first approximation to an ellipsoid, with legs and other appendages fitting closely into a streamlined surface.
==Taxonomy==
The Gyrinidae generally have been regarded as a family in the Adephaga, but there is a great deal of work underway to clarify the relationships both within the Adephaga and within the Coleoptera in general.〔Hebert, Paul D. N; Cywinska, Alina; Ball, Shelley L.; deWaard, Jeremy R. Biological identifications through DNA barcodes. Proc. R. Soc. Lond. B. Proc. R. Soc. Lond. B 7 February 2003 vol. 270 no. 1512 313-321〕 Within the Adephaga there is confusion as well, with various rival proposals in contention; for example some workers regard the Gyrinidae as being closely related to such families as the Dytiscidae and various other predacious water beetle families, whereas other analyses suggest rather that the Gyrinidae are a sister group to the rest of the Adephaga.〔Rolf G. Beutela, Ignacio Riberab, Olaf R.P. Bininda-Emondsa; A genus-level supertree of Adephaga (Coleoptera) Organisms, Diversity & Evolution 7 (2008) 255-269〕 Some of the Adephagan families seem to be polyphyletic themselves, so a definitive cladistic structure will have to await more advanced nucleic acid analyses.〔Whiting, Michael F.; Phylogeny of the holometabolous insect orders: molecular evidence Zoologica Scripta Volume 31, Issue 1, pages 3-15, February 2002 〕
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