Sub-functionalization of dorsal and ventral eyes in a whirligig beetle (Coleoptera: Gyrinidae)

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

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.

Retracted: A new aquatic beetle (Adephaga: Coptoclavidae) from the Middle Jurassic Daohugou Biota

Tigrivia baii gen. et sp. nov. (Coleoptera: Adephaga: Coptoclavidae) is described and named based on a fossil specimen from the Middle Jurassic Daohugou Biota, Nincheng County, Inner Mongolia of China. The fossil is very similar in morphology with the adult Coptoclava longipoda Ping 1928 (Laiyang Formation of Nanligezhuang Village, Laiyang City, Shandong Province, China, Lower Cretaceous, 121 ~ 120 Ma), but differs from C. longipoda by the adjacencies of two procoxae and two mesocoxae. T. baii gen. et sp. nov. differs from Daohugounectes primitinus Wang et al. 2010 by the absence of striae on the elytra and the absence of ventral eyes under the head. The new beetle species shows developed aquatic adaptions, such as specialized raptorial forelegs, and swimming middle and hind legs. Furthermore, it is speculated to lead a similar lifestyle as extant Dytiscoidae, according to the two eyes on the side of head and the absence of spiracles on ventrites. This new fossil expanded our knowledge of the diversity of the Middle Jurassic Coptoclavid beetles in Daohugou Biota and improved our understanding of their paleoecological significance.