Structure and Ultrastructure of the Acrotrichis grandicollis (Coleoptera: Ptiliidae) Compound Eyes and the Eye Features Related to Miniaturisation.

Here is the first description of the visual organ of Acrotrichis grandicollis, a member of Ptiliidae family that includes the smallest free-living insects. The apposition eyes of A. grandicollis have the acone-type crystalline cone; a fused rhabdom is formed by eight retinula cells and surrounded by primary pigment cells. Secondary pigment cells are located only in the distal part of the ommatidium under the lens. The eye consists of about 50 facets about 12 μm in diameter. The A. grandicollis ommatidium ultrastructure has been compared with that of large Coleoptera. The results obtained enabled us to emphasize the compound eye specific features associated with the small body size.