title: The antenna of a burrowing dragonfly larva, Onychogomphus forcipatus (Anisoptera, Gomphidae).
abstract: 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.
authors.affiliation: Dipartimento di Chimica, Biologia e Biotecnologie, University of Perugia, 06121, Italy. Electronic address: manuela.rebora@unipg.it.
authors.forename: Manuela
authors.initials: M
authors.lastname: Rebora
authors.affiliation: Dipartimento di Chimica, Biologia e Biotecnologie, University of Perugia, 06121, Italy.
authors.forename: Silvana
authors.initials: S
authors.lastname: Piersanti
authors.affiliation: Dipartimento di Scienze Agrarie, Alimentari e Ambientali, University of Perugia, 06123, Italy.
authors.forename: Gianandrea
authors.initials: G
authors.lastname: Salerno
authors.affiliation: Department Functional Morphology and Biomechanics, Zoological Institute of the University of Kiel, Am Botanischen Garten 1-9, 24098 Kiel, Germany.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Gorb
mesh_terms: D000818:Animals; D057506:Arthropod Antennae / Q000648:ultrastructure; D002628:Chemoreceptor Cells / Q000648:ultrastructure; D007558:Italy; D007814:Larva / Q000254:growth & development / Q000648:ultrastructure; D008465:Mechanoreceptors / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009758:Nymph / Q000254:growth & development / Q000648:ultrastructure; D063191:Odonata / Q000254:growth & development / Q000648:ultrastructure*; D058618:Sensilla / Q000648:ultrastructure
keywords: Aquatic insects; Chemoreceptors; Mechanoreceptors; Odonata; Sensilla; Ultrastructure