Chemoreception in four species of water mites (Acari: Hydrachnida): behavioural and morphological evidence

Silver nitrate staining of the solenidial and eupathidial sensilla on the palpi, tarsi and tibiae of legs I and II of Arrenurus acutus, Geayia ovata, Mideopsis reelfootensis and Albia caerulea, along with ultrastructural studies, showed that these setae have a porous shaft cuticle. These setae are hollow and contain dendrites in their lumens and more than one neuron is associated with each setae. Behavioural experiments supported the involvement of these sensilla in the perception of chemical cues from prey and sexual partners.     

Role of the male claw sensilla in perception of female mounting sex pheromone in Dermacentor variabilis,Dermacentor andersoni and Amblyomma americanum

The foreleg claw sensilla of male D. variabilis, D. andersoni and A. americanum ticks indlude the receptors that perceive the female contact mounting sex pheromone (MSP). In all three tick species, the foreleg claw sensilla comprise six anteriorly-directed setae arranged in three symmetrical pairs, two each on the opposite sides of the apotele of the claw and one on the ventral side. Morphological study and behavioral bioassays of these setae revealed that only the dorsal and middle (=lateral) pairs of claw sensilla are mechanogustatory. While the ventral pair are strictly mechanoreceptors. The dorsal and middle sensory setae exhibit a single pore-like structure located at or near their tip, a feature characteristic of mechanogustatory sensilla. These setae are similar to those found on the palps that are believed to function as pheromone receptors. In all three tick species, male mounting and postmounting behaviors were suppressed only when the dorsal and middle pairs of claw sensilla were ablated or covered with gelatin; normal behavior was restored when the gelatin was removed. Doscresponse bioassays were conducted with D. variabilis males to authenticate the results of the gelatin tests. The results of these bioassays demonstrated that the gelatin coat was impervious to the pheromone. The characteristics of the ixodid tick mating system that distinguish it from mating processes in other arthropods are discussed.     

Flagellar setae of the second antennae in decapod shrimps: sexual dimorphism and possible role in detection of contact sex pheromones

Summary

The antenna 2 (antennal) flagella of decapod shrimps are chemotactile, and their setae are proposed as sensilla involved in recognition of females by males via a contact sex pheromone on the surface of the female. Male recognition of females receptive to mating occurs in many caridean species upon contact of male antennal flagella with the surface of a newly molted parturial female. The hypothesis of sexual dimorphism in the number and kind of setae on the antennal flagella of four caridean and one penaeid shrimp species was tested with setal counts and observations on setal morphology. Unique male antennal setae (“male-specific sensilla”) were not identified in any of the species investigated. However, the abundance of antennal setae was significantly greater in males than in breeding females in the palaemonid carideans Palemonetes pugio and Macrobrachium ohione. In the hippolytid caridean Thor manningi and alpheid caridean Alpheus normanni, no sexual dimorphism in setal abundance was demonstrated. In the penaeoid Rimapenaeus similis, males had a higher abundance of antennal setae than the larger breeding females but so did juvenile females, similar in size to males. The sexual dimorphism in antennal sensilla in the palaemonid species and its absence in A. normanni might be related to their different mating systems, but no such association is suggested for T. manningi and R. similis. Setal morphology suggestive of chemoreceptive function (a terminal pore) was observed in all species.     

Surface structures of the antennular flagella of the hermit crab Pagurus alaskensis (Benedict): A light and scanning electron microscopy study

The surface structures of the antennular flagella of Pagurus alaskensis are described in detail. Attention is directed towards the surface morphology of two types of possible sensilla: (1) exoskeletal pores (1.0–3.0 μm in diameter); (2) setae of various kinds. In addition, small (0.1–0.2 μm) pits occur in the exoskeleton which are not considered to be sensory in function. The exoskeletal pores are found at fairly specific locations on both the inner and outer flagella, particularly on the short segments of the outer flagella. Neither the inner nor the outer flagella are bilaterally symmetrical with respect to their setal armature. On the outer flagellum six groups of setae may be distinguished: lateralmesial; dorsal; ventral; accessory; aesthetasc; setae of the distal segment. On the inner flagellum setae of the mesial and lateral rows form distinctive groups. The morphology, orientation and locations of all the flagellar setae are defined and where possible the numbers of the various morphological types within the specific setal groups are given. It is noteworthy that many setal types have obvious apical pores and yet no pores could be found in the chemoreceptive aesthetasc setae. The functions of the various setae are discussed in relation to their topographical position and to existing electrophysiological and behavioral data. Some suggestions are made about future experiments to demonstrate the central connections of specific sensilla or groups of sensilla and to show their significance in the whole animal.     

Unusual sensory setae of the raptorial Branchinecta gigas (Branchiopoda: Anostraca)

In many vernal pools, visibility is very poor because of the turbidity from suspended clay particles. For predatory species like Branchinecta gigas, these conditions can be detrimental to successful prey capture. In vernal lakes in central California, B. gigashave developed specialized hunting modes to capture anostracan prey in pools of low visibility. The position of their body, the kinematics of their locomotion, and their reduced eye size suggested the possibility of novel sensory structures on their antennae and/or their cercopods designed to enhance their prey capture abilities. Using Scanning Electron Microscopy, we investigated the presence and design of sensory setae on the antennae and cercopods of B. gigas. On both males and females, there are dense patches of sensilla along the length of the antennae. They are oriented ventrally and slightly anteriorly. These antennal setae appear to be chemosensory in structure and position; they resemble antennal setae of other branchiopods. However, the setae of the cercopods are unusual in their morphology and location on the appendage. The cercopods, which are bent over the head in the hunting position, have a linear arrangement of specialized setae on their ventral side. They are jointed setae with an anterior crown of protective spines. The setal joint only permits limited abduction either toward the head in the hunting position or ventrally when swimming. These setae appear to be mechanosensory in function and may be adaptations to a raptorial lifestyle. They correlate well with the behavioral components of hunting in B. gigasand their complex prey capture mechanism.     

Composition of external setae during regeneration and transformation of the bilaterally asymmetric claws of the snapping shrimp,Alpheus heterochelis

The paired thoracic chelipeds or claws of adult snapping shrimp, Alpheus heterochelis, are bilaterally asymmetric, consisting of an enlarged and elaborate, sound-producing major (snapper) claw and a much smaller minor (pincer) claw. These paired claws vary in the composition of their external sensilla. Both possess long serrulate and simple short setae but the snapper also have plumose setae and long serrulate setae on the plunger. The pincers differ in having short serrulate setae and, in males alone, a prominent fringe of plumoserrate setae. During regeneration of each claw type, these setal structures are gradually added over three molts to reach the pristine condition. The long serrulate and simple short setae appear first, being seen in intermolt limb buds and commonly in both claws. Setae exclusive to each claw, i.e., plumoserrate and short serrulate in the pincer and plumose and long serrulate on the plunger in the snapper, appear sparsely in either the regenerated 1st or 2nd postmolt claw, they proliferate in the subsequent 2nd or 3rd postmolt claw. Transformation of the pincer claw to the snapper type begins in the 1st postmolt stage with the loss of pincer setae and addition of snapper setae and is completed by the 3rd postmolt stage. Since changes in composition of the external sensilla are restricted to postmolt stages, the underlying hypodermis is presumably being remodeled during proecdysis.     

A new species of the genus Pergalumna Grandjean, 1936 from Iran (Acari: Oribatida: Galumnidae)

A new species of galumnid mite (Acari: Oribatida: Galumnidae), Pergalumna persica sp. n., is described from Fars province, southern Iran. The new species is characterised by a pointed rostrum, minute interlamellar setae, medium long, setiform sensilla, with finely barbed, slightly dilated head, complete dorsosejugal suture, large, nearly elongate-triangular areae porosae Aa, absence of median pore, and large body size.     

A topographical and typological comparison of the rodlike setae of ambulatory dactylopodites in decapod crustaceans

The arrangement and external morphology of the rodlike setae and associated structures located on the dactylopodites of the walking legs of six species of decapod crustaceans are compared. The dactyls of littoral species, represented by the rock crab, Cancer antennarius, and the spiny lobster, Panulirus interruptus, have dense tufts and bands of rodlike setae, as is typical of many decapods, and additionally only a few small plumed setae. The arrangement of setae on the dactyls of the recently discovered Galapagos vent crab, Bythograea thermydron, closely resembles that of C. antennarius. Rodlike and long plumed setae occur in about equal numbers on the dactyls of the pelagic anomuran, Pleuroncodes planipes. The dactyls having the fewest rodlike setae are those of the terrestrial hermit crab, Coenobita perlatus, and those of the kelp crab, Pugettia producta, where flat setae typical of Majidae have replaced most rodlike setae. The presence and structures of the terminal pores in rodlike setae vary intra- and interspecifically, possibly as a function of molt stage. Variations in some features of rodlike setae, such as tip acuity and presence of microsetae and surface sculpting, appear to be related to development. Serrated setae occur on the dactyls of megalopal P. producta but not in later stages. The topography and typology of setae located on the ambulatory dactyls of decapod crustaceans are considered in light of recent interest in using setal characteristics to determine the sensory functions of sensilla and to clarify the phylogeny of arthropod groups.     

Structure of dactyl sensilla in the kelp crab,Pugettia producta

In the kelp crab, Pugettia producta, flat plate setae cover all but the ventral surfaces of the walking leg dactyls. Dendrites enter the setal shaft located inside the plate superstructure, and extend to a region of the setal tip that contains a system of minute pores resembling the pore systems found in chemosensory sensilla of insects. Presumably, much of the chemosensitivity of the dactyls in the kelp crab is mediated by the plate setae. In the interior of the dactyl, supporting cells and the neurons innervating plate setae, other types of setae, and other presumptive sensilla form scolopidia. Large scolopidia, containing as many as 12 dendrites, appear to innervate some of the plate setae and also large ventral rodlike setae that might be chemosensory. Two of the dendrites of large scolopidia usually have more densely packed microtubules, longer ciliary axonemes, slightly larger rootlets, and dark A fibers with arms, characteristics indicative of mechanosensory function. Some dactyl setae, therefore, could be both mechanosensory and chemosensory. Small scolopidia containing two or three dendrites that exhibit mechanosensory characteristics appear to innervate small, rodlike setae, which presumably are strictly mechanosensory. The two types of structures located on the epicuticular cap, elliptical structures resembling campaniform sensilla and small cones in pits resembling CAP organs, appear to be dually innervated and presumably are mechanosensory, although other functions are possible. The internal positions of the scolopidia, together with the support afforded by an extracellular dendritic sheath, by the scolopale, and by desmosomelike and septate junctions, may serve to protect internal portions of setal dendrites, some of which appear to remain functional in nonmolting adults that have abraded setae.     

Zahl und Verteilung antennaler Sensillen bei der Honigbiene (Apis mellifera L.)

Zusammenfassung An Totalpräparaten der Antennengeißel von Arbeiterin und Drohne vonApis mellifera carnica wurden Zahl und Verteilung aller Sensillen und Setae ermittelt. Dabei ließen sich anhand des cuticularen Baues folgende Sensillentypen unterscheiden: S. placodeum, S. ampullaceum, S. coeloconicum, S. campaniforme und 5 Haarsensillen S. trichodeum A, B1, B2, C, D, sowie 4 Setatypen (A 1–3, B), die wahrscheinlich nicht innerviert sind. Die Benennungen der Sensillen wurde den bisher gebrauchten Bezeichnungen gegenübergestellt. Sensillenzahl und -Verteilung, Sinneszellzahl und Funktion der Sensillen wurden anhand von Literaturangaben zusammengestellt und diskutiert. Bemerkenswert ist der starke Dimorphismus zwischen Arbeiterin und Drohne in der relativen Sensillenzahl für die einzelnen Sensillentypen und in der Gesamtzahl der Sinneszellen. So sind bei der Arbeiterin die wahrscheinlich olfaktorischen S. trichodea A und die mechanorezeptorischen S. trichodea B 1 wesentlich stärker vertreten. Die Drohne hat keine S. basiconica und im übrigen wesentlich mehr S. placodea als die Arbeiterin. Insgesamt hat die Drohne eine ca. 2-fach größere Geißeloberfläche und etwa 5-mal soviele Sinneszellen wie die Arbeiterin. Die Arbeiterinnengeißel hat auf ihrer Rückseite eine porenplattenfreie Zone, die dicht mit nichtinnervierten Setae besetzt ist. Bei der Drohne findet man stattdessen eine porenplattenärmere Zone mit einer geringeren Zahl von Setae. Charakteristische Verteilungsmuster bestehen auch für alle anderen Sensillen und Setae.

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Number and distribution of the sensilla on the antennal flagellum of the honeybee (Apis mellifera L.)

Summary Number and distribution of sensilla and setae on the antennal flagellum of the honeybeeApis mellifera carnica were determined on whole antennal preparations. The following types of sensilla were distinguished according to their cuticular structure: Sensillum placodeum, S. ampullaceum, S. coeloconicum, S. basiconicum, S. campaniforme and 5 hair sensilla S.trichodeum A, B1, B2, C, D, as well as 4 types of probably non-innervated setae (A1–3, B). The names used here for the different types were compared with the previously used terms. Number and distribution of sensilla, the number of sensory cells and the function of the sensilla were discussed with respect to the data available from the literature. There is a notable dimorphism between the worker and drone with respect to the relative number of sensilla of each type and to the total number of sensory cells. The worker has far more of the presumably olfactory S. trichodea A and of the mechanoreceptive S. trichodea B1. The drone lacks the S. basiconica and has far more S. placodea than the worker. The flagellum surfarce of the drone is twice as large as that of the worker and has 5 times as many sensory cells. The worker flagellum has a poreplate-free zone on the side facing the head which is densely packed with non-innervated setae. In the corresponding zone the drone has a lower density of poreplates than elsewhere on its antennal flagellum. All other sensilla and setae are also characteristically distributed.

     

A new genus and species of oribatid mites <Emphasis Type="Italic">Scarabacarus longisensillus</Emphasis> gen. et sp. n. (Acariformes,Liacaridae) from the Caucasus

A new genus and species, Scarabacarus longisensillus gen. et sp. n., of the family Liacaridae are described from the Caucasus (Azerbaijan and Abkhazia): The new genus Scarabacarus is characterized by the highly convex body, straight anterior margin of the notogaster, narrow fusiform sensilla, the lamellae situated on the lateral margins of the prodorsum, the absence of interlamellar and notogastral setae (besides one posterior pair), presence of four pairs of genital setae, and tridactylous leg tarsi.     

Morphology and ultrastructure of the antennal chemoreceptors and mechanoreceptors of worker Coptotermes formosanus Shiraki

Summary Three types of setae were found on the antenna of workers of C. formosanus. Sensilla basiconica function as chemoreceptors. They are non-socketed, with fixed plate base, thin walled, and perforated. Pore tubules are contained within the cuticular pores of s. basiconica. The pore tubules have direct contact with the dendritic branches within the sensilla. The other sensilla are tactile mechanoreceptors. The longest setae (sensilla trichodea) are thick walled, socketed, mononeuronic, and non-perforated. The shorter mechanoreceptors (sensilla chaetica) have the same characteristics as s. trichodea, exept that they are sometimes dineuronic. The numbers and distribution of the sensilla were established.Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and in part by the M.U.C.I.A. program, the National Science Foundation Grant No. 36700, and the U.S.D.A., Forest Service Cooperative Project 12-13. The authors also acknowledge the SEM and TEM assistance of S. D. Carlson, M. Garment, and G. Gaard, respectively     

Agnetina den, a new species of perlid stonefly (Plecoptera: Perlidae) from Vietnam

A new species of perlid stonefly, Agnetina den, is described from Vietnam. Male adults of this species can be easily distinguished by their black body color pattern, submedian patches of sensilla basiconica on hemitergites 7–8, and clusters of long dense fine setae on the inner sides the abdominal tergites. Illustrations of habitat and diagnostic characters are presented.     

Morphology and histology of secretory setae in terrestrial larvae of biting midges of the genus Forcipomyia (Diptera: Ceratopogonidae)

Apneustic larvae of the genus Forcipomyia possess unique secretory setae located on the dorsal surface along the body in two rows, one pair on each thoracic and abdominal segment and two pairs on the head. Morphological and histological studies of secretory setae in fourth instar larvae of Forcipomyia nigra (Winnertz) and Forcipomyia nigrans Remm indicate they are modified mechanoreceptors (sensilla trichodea) in which the trichogen cell is a glandular cell producing a hygroscopic secretion. The cytoplasm of the glandular trichogen cell fills the lumen of a secretory seta, which shows one or more pores on the apex. The cytoplasm contains numerous microtubules responsible for transportation of proteinaceous vesicles, and an extremely large polyploid nucleus typical of gland cells. The main role of the hygroscopic secretion is to moist the body and thus facilitate cuticular respiration.     

Ultrastructure of tarsal sensilla and other integument structures of two Pseudocellus species (Ricinulei, Arachnida)

Ricinuleids are one of the least investigated groups of Arachnida. In particular, knowledge of their ultrastructure is poor. Observations of the distal tarsomeres of ricinuleids show differences in their shape and equipment of surface structures. Legs I and II are used by the Ricinulei to explore their surroundings with tentative movements. The tarsomeres of these legs show similarities in shape and surface structures that distinguish them from those of legs III and IV. In this study, 11 different structures of the tarsomere surfaces of two cave-dwelling species, Pseudocellus pearsei and P. boneti from México, were investigated for the first time with scanning and transmission electron microscopy and discussed regarding their possible function: 1) a single treelike ramifying seta resembles a no pore single-walled (np-sw) sensillum; 2) setae occurring in a small number and possessing a bipartite shaft represent terminal pore single-walled (tp-sw) sensilla. The surface of the proximal half of the shaft shows small branches. The distal half has a smooth surface; 3) long setae with conspicuous longitudinal lamellae show characteristics of chemoreceptive wall pore single-walled (wp-sw) sensilla; 4) frequent small wp-sw sensilla with flat and irregular lamellae; 5) very short wp-sw sensilla occurring solitary or in groups; 6) a few short setae with smooth surface correspond to wp-sw sensilla; 7) a single short clubbed seta articulating in a flat pit is considered to be a np-sw sensillum; 8) common long setae with a pointed tip show characteristics of mechanoreceptive np-sw sensilla; 9) ventral setae with adhesive and mechanosensory function are accompanied by multicellular "class III" glands; 10) slit organs with mechanoreceptive function; and 11) dome-like tubercles with no indication of sensorial function. Several of these sensilla form a sensory field on the dorsofrontal surface which is particularly pronounced on the distal tarsomeres of legs I and II.     

Two new species of the orientalis group of Rheocricotopus (Psilocricotopus) from China (Diptera: Chironomidae)

Rheocricotopus (Psilocricotopus) calviculus sp. n. and R. (P.) villiculus sp. n. from China are described as male imagines. The species are closely related to the previously described R. (P.) orientalis Wang forming a new group, the orientalis group, which eventually may deserve the rank of subgenus or even genus. The group is distinguished by lacking a humeral pit, numerous sensilla clavata on third palpomere, cuneiform wings, no or few setae on squama, long legs, banded abdomen, very long inferior volsella, gonocoxite with apical extensions, and gonostylus with a median triangular projection.     

Antennal sensilla in five Psychodini moth flies (Diptera: Psychodidae: Psychodinae) pollinators of Arum spp. (Araceae)

The pollination of the genus Arum (Araceae) is mainly achieved by deception, the floral odour mimicking the pollinator ovipositing site. In order to discover the sensory organs involved in this attraction, we have studied the antennae of five species of psychodine moth-flies (former Psychoda sensu lato=Psychodini), pollinators of Arum spp. The antennae of the five Psychodini reveal seven types of sensilla: multiporous tribranched sensilla basiconica (sensilla ascoidea), multiporous sensilla basiconica, multiporous sensilla coeloconica, multiporous sensilla auricillica, uniporous sensilla basiconica, aporous sensilla chaetica, aporous Böhm’s sensilla. Each species possesses three, five or six of these sensillum types. All the multiporous sensilla are probably olfactory receptors while the uniporous sensilla basiconica must possess a contact chemoreceptive function. The multiporous tribranched sensilla basiconica (s. ascoidea), present in all the species, are the best candidates for the reception of the odours given off by the ovipositing sites and the inflorescences of Arum. The multiporous sensilla basiconica and the multiporous sensilla coeloconica may be involved respectively as CO₂ receptors or thermoreceptors. Psychoda phalaenoides, which is the main pollinator of A. maculatum, is the species which possesses the largest number of antennal sensilla. The sexual dimorphism, studied only in Psycha grisescens, as concerns the number of sensilla and the absence of a sensillum type which differ according to sex, is difficult to interpret.