Figure 1.
Adhesive devices of male diving beetles. (a) Measurement of the body length (LB), body width (WB) and body area (AB; area enclosed by the red dashed line) of a male diving beetle. (b–f) In male C. rugosus, the proleg has an expanded palette (b,c) composed of protarsomeres bearing specialized adhesive setae on their ventral side. Each spatula seta connects to the palette with an off-centre stalk (d) and its ventral surface has an oval-shaped sucker (blue dashed line) from which parallel channels extend distally (e). Channel width (WC), channel height (HC) and channel wall thickness (TC) can be measured from (f). (g–j) By contrast, the proleg of male H. pacificus has one round palette with circular setae (g,h). Enlargements of white boxes in (h) show that the circular seta has a rim on its edge with thickness (TR) (i), although with a rough ventral surface it does not have distinct channels as found on spatula setae (j). Area of the palette (AP; red in b,g), seta (AST; black in d,g) or spatula sucker (ASK; blue in d) is the area enclosed by the dashed line. (a–d,g) Light micrographs; (e,f,h–j) Scanning electron micrographs.