Functional Anatomy of Split Compound Eyes of the Whirligig Beetles Dineutus mellyi (Coleoptera: Gyrinidae).

Simple Summary: Whirligig beetles inhabit both fresh and brackish waters and possess a pair of split compound eyes. The dorsal eyes are situated above the water surface, whereas the ventral eyes are submerged beneath the water. Due to the difference in optical environments between water and air, we expected a difference in visual features and signal processing between the dorsal and ventral eyes. Using scanning electron microscopy, transmission electron microscopy, and microcomputed tomography, we investigated the functional modifications of different features of the split compound eyes of Dineutus mellyi (Coleoptera: Gyrinidae). Both dorsal and ventral parts of the split compound eyes of D. mellyi are the superposition type, with the ommatidium of dorsal and ventral eyes comprised of a laminated corneal lens, bullet-shaped crystalline cone, upper distal rhabdom, a clear zone and lower distal rhabdom, a basal rhabdom, and an eight retinular cell just above the basement membrane. In contrast to the dorsal eyes, ventral eyes are characterized by a higher field of vision but exhibit similar spatial resolution. The functional anatomy of the split compound eyes of whirligig beetles Dineutus mellyi (Coleoptera: Gyrinidae) was examined by advanced microscopy and microcomputed tomography. We report the first 3D visualization and analysis of the split compound eyes. On average, the dorsal and ventral eyes contain 1913 ± 44.5 facets and 3099 ± 86.2 facets, respectively. The larger area of ventral eyes ensures a higher field of vision underwater. The ommatidium of the split compound eyes is made up of laminated cornea lenses that offer protection against mechanical injuries, bullet-shaped crystalline cones that guide light to the photoreceptive regions, and screening pigments that ensure directional light passage. The photoreceptive elements, made up of eight retinular cells, exhibit a tri-tiered rhabdom structure, including the upper distal rhabdom, a clear zone that ensures maximum light passage, and an enlarged lower distal rhabdom that ensures optimal photon capture. [ABSTRACT FROM AUTHOR]