Fig 1.
Overview of the general morphology and five types of sensilla distribution on the antenna of male C. japonicus Sharp.
(A) External morphology of the male antenna under the light micrograph; the schematic distribution of various types of sensilla on the dorsal side (windward side) (B) and ventral side (lee side) (C). Sc: scape, Pe: pedicel, F1-F9: flagellum 1–9.
Fig 2.
Scanning electron microscope (SEM) of general structure of the antenna in male diving beetle C. japonicus Sharp.
(A) External morphology of the antenna under SEM; (B) Flagellum 9 of the antennae under SEM, and the area in the red rectangle is enlarged at higher magnification in (C), showing round s. placodea (round dot), elongated s. placodea (triangle), type I s. coeloconica (pentagram), type II s. coeloconica (arrow), and type III s. coeloconica (diamond).
Fig 3.
The sensilla distribution (A) and length of each segment (B) between males and females of diving beetle C. japonicus Sharp.
Sc: scape, Pe: pedicel, F1-F9: flagellum 1–9. * indicates significant differences between sexes according to student’s t-test (P<0.05).
Table 1.
The morphological feature and number of sensilla on the antennae of adult C.japonicas Sharp.
Fig 4.
Scanning electron microscope (SEM) of round s. placodea in male diving beetle C. japonicus Sharp.
(A) Flagellum 9 of the antennae under SEM showing round s. placodea in red rectangle. (B, C) Close-up view of the round s. placodea on the dorsal side of antennal flagellum. (D) Pores on the surface of the round s. placodea, with density of 60 pores/μm2.
Fig 5.
The morphology and ultrastructure of the elongated s. placodea of diving beetle C. japonicus Sharp.
(A) SEM of the elongated s. placodea, showing many pores on the surface that perforate the outer cuticle. (B) The multiple pores under the SEM with density of 170 pores/μm2. (C) Longitudinal section through the elongated s. placodea, showing three dendrites enclosed in the dendrite sheath. (D) Ultrastructure of the enlongated s. placodae under TEM showing the intercuticular space between the inner and outer cuticles, where the dendrites lose their arrangement, with the dendritic branches occupy the whole space, and the cuticular wall of these sensilla is around 0.5 μm. p: pore, d: dendrite, db: dendritic branches.
Fig 6.
The morphology and ultrastructure of the type I s. coeloconica.
(A) SEM of the type I s. coeloconica of male diving beetle C. japonicus Sharp, which is characterized as a flame-like peg, sitting inside a chamber. Longitudinal (B) and cross section (C) of the sensilla under TEM showing the thick cuticular wall and two sensory neurons, tightly embedded by a thick dendrite sheath, are presented inside each peg. Cw: cuticle wall, ds: dendritic sheath, d: dendrite.
Fig 7.
The morphology and ultrastructure of the type II s. coeloconica of male diving beetle C. japonicus Sharp.
(A) SEM of the type II s. coeloconica, containing a peg with flower-slit on the flat surface. Longitudinal (B) and cross section (C) of the sensilla under TEM showing it contains two bipolar neurons. According to (B), both dendrites reach the tip of the sensillum peg. The cross section in (C) showed two sensory dendrites are tightly embedded by the dendrite sheath. cw: cuticle wall, d: dendrite, ds: dendrite sheath.
Fig 8.
The morphology and ultrastructure of the type III s. coeloconica of male diving beetle C. japonicus Sharp.
(A) SEM of the type III s. coeloconica showing this type of sensillum is characterized externally by a smooth peg, with about 10μm in height. (B) Four dendrites are located in two separated cavities, and three of them reach the tip of the peg, which was shown at higher magnification in (C), while one of them ends in a tubular body beneath the base of the peg (D), shown at higher magnification in (E). d: dendrite, tb: tubular body, ds: dendritic sheath.
Fig 9.
Longitudinal section of the round s. placodea of female diving beetle C. japonicus Sharp under transmission electron microscope (TEM).
The dendrites are clustered into a group, containing 2 bipolar neurons (A). Numerous pores on the surface of sensilla that perforate the outer cuticle (B). p: pore, d: dendrite, db: dendritic branches, cw: cuticle wall.