Description and Affinities
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. 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 different water beetle families, whereas other analyses suggest rather that the Gyrinidae are a sister group to the rest of the Adephaga. Some of the Adephagan families seem to be polyphyletic themselves, so a definitive cladistic structure will have to await more advanced nucleic acid analyses.
Whirligig beetles are most conspicuous by reason of their bewildering swimming, but their coloration is not showy and commonly they can be quite hard to see if they are not moving or are under water. However, seen to best effect most species are handsomely coloured with a sombre lustre of steely grey or bronze. Their integument is finely sculpted with little pits; it is hard and elastic and produces a water repellent waxy outer layer, constantly supplemented. Among other functions, the lubricant layer and smooth outline make the beetles remarkably difficult to hold onto if caught; they slip from between one's fingers like a fresh orange pip.
The antennae are unusual among beetles, being short and plump, and placed about at water level. The compound eyes are remarkable for each being divided into a higher part that is above water level when a beetle is floating passively, and a lower part that is below water level. In this respect they recall the Four-eyed fish. The middle, and more especially the hind, legs are natatory, meaning adapted for swimming; they are greatly flattened and fringed with bristles that fold to aid swimming action. In contrast the front legs are long and adapted for grasping food or prey. In males the front tarsi have suckers, which they need for holding onto slippery females during mating.
Read more about this topic: Whirligig Beetle
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