Diving beetles in the family Dytiscidae mate underwater. The male has elaborate prolegs that allow it to grip the elytra of the female during mating. Tarsomeres of the male prolegs (but not the female) are expanded and serve as a platform for suckers, hairs and other attachment devices. The area of the female elytra where a male attaches typically has a surface that is much rougher than the rest of the cuticle, features noted by Charles Darwin in The descent of man and selection in relation to sex.
One of the *2015 Nikon Small World Top 20 award winners is this image by Frank Reiser. The image was made using stacking software to get focus throughout the depth of field. Note that the suckers reside in a field of hairs. The hairs have an important role in the attachment and release of the male.