| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 2778578 | Arthropod Structure & Development | 2015 | 9 Pages |
•The larva of the dragonfly Onychogomphus forcipatus has a burrowing lifestyle.•This is the first ultrastructural investigation (SEM, TEM) on its antennal sensilla.•Numerous mechanoreceptors and one possible chemoreceptor are described.•The mechanoreceptors are mostly filiform hairs presumably for current detection.•This is the first report of an antennal gland in palaeopteran insects.
The larva of the dragonfly Onychogomphus forcipatus (Anisoptera, Gomphidae) has a burrowing lifestyle and antennae composed of four short and broad segments (scape, pedicel and a two-segmented flagellum). The present ultrastructural investigation revealed that different sensilla and one gland are located on the antenna. There is a great diversity of mechanoreceptors of different kinds. In particular club-shaped sensilla, sensilla chaetica, and tree-like sensilla show the typical structure of bristles, the most common type of mechanoreceptors, usually responding to direct touch, while numerous long thin thorny trichoid sensilla show a morphology recalling the structure of filiform hair mechanoreceptors. The latter ones are presumably important in larval Odonata for current detection and rheotactic orientation, especially in a burrowing species. On the smooth apical cuticle of the second flagellar segment, three structures are visible: (1) a small ellipsoidal pit hosting a convoluted peg, the morphology of which resembles that of a typical chemoreceptor (even if pores are lacking), (2) a couple of small pits (not investigated under TEM), and (3) one wide depression with spherical structures, the internal morphology of which lets us assume that it is a gland with unknown function. This is the first report of an antennal gland in palaeopteran insects.
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