Distribution patterns and morphology of sensilla on the apical segment of the antennae and palpi of Hydradephaga (Coleoptera: adephaga)

Abstract

The sensilla on the terminal antennomere of selected Hydradephagans (Coleoptera) are modified in several distinct ways as compared to the sensilla on the terminal antennomere of Geadephagans (Coleoptera). There are no long sensilla of any type on antennae of Hydradephagans, the sensilla are either short, peg-like sensilla that may be recessed in the antennal surface or they are multiporous plate-like sensilla. Multiporous plate-like sensilla have not been found on the antennae of Geadephagans. A pit sensillum occurs on the antennae of one family, Gyrinidae, in the Hydradephaga whereas it is found on the antennae of several species from the families of Geadephaga. The sensilla on the terminal antennomere of Hydradephaga are often grouped into sensory fields that could be located on a particular area of the antennomere. Sensory fields are also located on the apices of the maxillary and labial palps and the most unique sensory fields occur in the Noteridae. The maxillary palpal apex of Hydrocanthus oblongus (Noteridae) is bifurcate and a sensory field with several types of sensilla is at the apex of each branch. The terminal labial palpomere is greatly enlarged and has a long, slender sensory field at the apex and a secondary sensory field on a thumb-like projection. The sensilla on the palpal apices are more diverse and complex in form as compared to the sensilla on the palps of Geadephaga. The most complex sensillum has a cuticular collar and a dome that is divided into six or seven triangular sections. The dome may be opened or closed and a peg-like sensillum with a very wide apical pore is situated beneath the dome.

Morphology and distribution of sensilla on head appendages in the water beetle Hygrobia hermanni (Coleoptera: Adephaga: Hygrobiidae)

“…hermanni (visible in Figure 2g) against two in Dytiscidae (Baker, 2001;Jensen & Zacharuk, 1992;Song et al, 2017) and a single one in Noteridae and Haliplidae (Baker, 2001), as well as in Gyrinidae and Amphizoidae (although in the latter two families, there is no anterior sensory field and the sensilla placodea are located at the apex of antennomere XI, Baker, 2001). Furthermore, of the three antennal subtypes of multiporous sensilla placodea observed in H. hermanni, one shows no trace of an encircling groove (pla3 MPp, Figures 2g, 2q, 3), i.e., its process is continuous with the surrounding cuticule (Figure 8, character 2).…”

“…Macleay, 1825), subfamily Colymbetinae). In Haliplidae, Meruidae, Noteridae and Amphizoidae, apical sensory fields of palps are simple (they cannot be subdivided into distinct units or clusters; Baker, 2001;Spangler & Steiner, 2005).…”

“…Chemosensory sensilla are particularly concentrated on the antennae and both pairs of palps, and are recognisable by their cuticular process perforated with pores and/or slits (Zacharuk, 1985)—even if some chemosensory sensilla in aquatic insects may lack cuticle perforations (Gaino & Rebora, 1999). In beetles of the suborder Adephaga, there are considerable differences in terms of the morphology and distribution of sensilla on adult antennae and palps between terrestrial and aquatic families, as well as amongst the latter (Baker, 2001). However, to date, chemosensory sensilla on head appendages have never been described using electron microscopy in a member of the family Hygrobiidae despite its key phylogenetic position.…”

“…In beetles of the suborder Adephaga, there are considerable differences in terms of the morphology and distribution of sensilla on adult antennae and palps between terrestrial and aquatic families, as well as amongst the latter (Baker, 2001). However, to date, chemosensory sensilla on head appendages have never been described using electron microscopy in a member of the family Hygrobiidae despite its key phylogenetic position.…”

The Chemosensory Transcriptome of a Diving Beetle

“…They are predaceous animals, like most other members of the Coleoptera suborder Adephaga, and chemical senses may play a prominent role in prey detection (Culler et al, 2014). Morphological studies have indicated that porous sensilla at the surface of antennae and palps of Dytiscidae differ from those of their closest terrestrial cousins, the Carabidae (Baker, 2001). In diving beetles, there is experimental evidence suggesting that the antennae play a role in chemoreception both underwater and in the air, whereas the palps detect chemical stimuli in the liquid medium only (Hodgson, 1953).…”