Ultrastructure of sensilla on the maxillary and labial palps of three species (Coleoptera: Staphylinidae: Staphylininae)

Most species of Staphylinidae are predators in an agroecosystem. They acquire prey information from their environment through receptors. In this study, the sensilla on maxillary and labial palps of Philonthus kailiensis, Philonthus lewisius and Quedius robustus were examined with scanning electron microscopy to identify and analyse the external morphology and distribution of the sensilla to enhance our knowledge of the sensilla of Staphylinidae and provide a rationale of taxonomical studies on the two genus. Results showed that the sensilla are classified into six types: Böhm bristles, sensilla chaetica, sensilla furcate, sensilla coeloconica, sensilla placodea and sensilla basiconica. No sexual dimorphism exists among the three species. The relationships and functions of sensilla on maxillary and labial palps were also speculated. There may be a certain correlation between the sensilla on maxillary and labial palps of the staphylinid and its habitat.     

Ultrastructure and distribution of sensilla on the maxillary and labial palps of Chlorophorus caragana (Coleoptera: Cerambycidae)

Chlorophorus caragana is a species of long‐horned beetle that damages Caragana davazamcii Sancz. (Fabales: Papilionaceae) bushes in desert areas in China. The beetles cause substantial damage to local forestry plantations and the environment. Sensilla on the maxillary and labial palps of coleopterans a allow the insects to recognize their host plants. We used scanning and transmission electron microscopy to study the ultrastructure, distribution, and abundance of various sensilla on the maxillary and labial palps of C. caragana. We found four types of sensilla including ten subtypes: one of Böhm's bristles, three of sensilla chaetica, one of digitiform sensilla, and five of sensilla twig basiconica. The types and distribution of the sensilla on the maxillary and labial palps were highly similar between males and females. Finally, this article discusses the functions of the sensilla of related species in recognizing hosts and the significance of gustation studies in the context of the control of C. caragana.     

兴安落叶松鞘蛾触角及其感器的扫描电镜观察

应用扫描电镜对兴安落叶松鞘蛾Coleophora obducta(Meyrick)触角及其感器进行观察和研究。结果表明,兴安落叶松鞘蛾触角为丝状,其上共有8种感器:板形感器、锥形感器、腔锥形感器、栓锥形感器、毛形感器、鳞形感器、叉形感器和Bhm氏鬃毛,对各种感器的形态、分布特点进行描述,推测其可能具有的功能。雌雄蛾触角有明显的性二型现象,表现为雌雄触角大小不同,触角感器类型、大小、数量、分布不同。     

Morphological and ultrastructural characterization of olfactory sensilla in Drosophila suzukii: Scanning and transmission electron microscopy

Drosophila suzukii is a serious horticultural and quarantine pest, damaging various berry crops. Although the active use of olfactory communication in D. suzukii is well-known, their olfactory sensory system has not been comprehensively reported. Therefore, the present study was carried out to understand the morphology, distribution and ultrastructure of olfactory sensilla present in the antennae and maxillary palps of D. suzukii, through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The olfactory sensilla on the antennae of D. suzukii in both sexes could be classified into three major morphological types, basiconic, trichoid and coeloconic sensilla, according to their shapes. The antennal basiconic sensilla were further divided into three subtypes and the antennal trichoid sensilla into two subtypes, respectively, according to the size of individual sensillum. In contrast to the antennal olfactory sensilla showing diverse morphology, basiconic sensilla was the only type of olfactory sensilla in the maxillary palps of D. suzukii. The basiconic sensilla in the maxillary palps could be further classified into three subtypes, based on their size. Our SEM and TEM observations indicated that multiple nanoscale pores are present on the surface of all types of olfactory sensilla in the antennae and maxillary palps, except coeloconic sensilla. The difference in the morphological types and the distribution of olfactory sensilla suggests that their olfactory functions are different between antennae and maxillary palps in D. suzukii. The results of this study provide useful information for further studies to determine the function of olfactory sensilla in D. suzukii and to understand their chemical communication system.     

Ultrastructure and distribution of sensilla on the antennae of female fig wasp Eupristina sp. (Hymenoptera: Agaonidae)

In the species‐specific and obligate mutualism between the fig (Moraceae: Ficus spp.) and its pollinator (Hymenoptera: Agaonidae), the continuity of lifecycle of both partners completely depends on the female pollinator's ability to detect receptive figs. To better understand the chemical location mechanism, we examined the antennae and their sensilla of the female fig pollinator Eupristina sp. using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The antennae of female Eupristina sp. are geniculated, and in total, there were seven types of sensilla found on the antennae: two types of multiporous placoid sensilla (type 1 is sausage‐like and type 2 is rounded), sensilla trichodea (ST), basiconic sensilla (BS), chaetica sensilla (ChS), coeloconic sensilla (CoS), and one specialized sensillum classified as sensillum obscurum (SO). We described external morphology, abundance, distribution, ultrastructure and discussed putative functions. We inferred from their ultrastructures as chemoreceptors that two types of multiporous placoid sensilla, BS and CoS, were innervated by sensory neurons. The aporous type ST, ChS, and SO were not innervated by dendrites which may function as mechanoreceptor/proprioceptor. These results were also discussed in relation to the interaction between Eupristina sp. and its host fig.     

Organization of the olfactory system of the Indian major carp <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.): A scanning and transmission electron microscopy study

Catla catla, Labeo rohita, and Cirrhinus mrigala represent important alimentary fish in India. Their reproduction/breeding depends on seasons. Fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in central regulation of reproduction. However, no electron microscopy data are available on organization of olfactory components of these fish. We studied organization of the olfactory organ in male L. rohita using scanning (SEM) and transmission electron microscopy (TEM). This organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The olfactory organ is ovoid in shape and consists of about 47–52 lamellae in adults and about 14–20 lamellae in fingerlings. These lamellae originate from the midline raphe. By SEM, microvillar sensory and ciliated non-sensory cells were observed in the lamellae. TEM revealed microvillar receptor cell with rough endoplasmic reticulum and Golgi apparatus towards apical end. Basal cells were present at the base of receptor cell, supporting cells were located adjacent to the olfactory receptor neurons, while epithelial cells—in the nonsensory part of olfactory epithelium. Mast, blastema, and macrophage cells were also found at the basement membrane. This work is the first publication on ultrastructural organization of the olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of the olfactory system and opens new avenues for further investigation of chemical neuroanatomy, sensory signal processing, and neural regulation of reproduction in the Indian major carp.     

桔小实蝇雄成虫联系性嗅觉学习

【目的】为了探究桔小实蝇 Bactrocera dorsalis (Hendel)雄成虫的嗅觉学习能力。【方法】本研究采用经典性嗅觉条件反射训练法（classical olfactory conditioning）在室内对固定的羽化后14-17日龄的桔小实蝇雄成虫进行气味与食物的联合学习训练, 即薄荷精油和10%蔗糖溶液联合的奖赏性训练（appetitive conditioning）以及甲基丁香酚(methyl eugenol, ME)和饱和盐溶液联合的惩罚性训练（aversive conditioning）,并以伸喙反射行为（proboscis extension reflex, PER）作为学习与否的判定标准。【结果】经过奖赏性训练后,桔小实蝇雄成虫对薄荷精油的伸喙反射率可从0%增加至68%;而经过惩罚性训练后,桔小实蝇对甲基丁香酚的伸喙反射率可从100%降低至36.54%,且这种伸喙反射率的变化是通过气味条件刺激（conditioned stimulus）和食物非条件刺激（unconditioned stimulus）的对称性联合而产生的。【结论】结果表明,桔小实蝇雄性成虫具有较强的联系性嗅觉学习能力,并且两种刺激的联合是形成学习记忆的必要条件。     

Adhesion of Plasmodium gallinaceum Ookinetes to the Aedes aegypti Midgut: Sites of Parasite Attachment and Morphological Changes in the Ookinete

Plasmodium gallinaceum ookinetes adhered to Aedes aegypti midgut epithelia when purified ookinetes and isolated midguts were combined in vitro. Ookinetes preferentially bound to the microvillated luminal surface of the midgut, and they seemed to interact with three types of structures on the midgut surface. First, they adhered lo and migrated through a network-like matrix, which we have termed microvilli-associated network, that covers the surface of the microvilli. This network forms on the luminal midgut surface in response to blood or protein meals. Second, the ookinetes bound directly to the microvilli on the surface of the midgut and were occasionally found immersed in the thick microvillar layer. Third, the ookinetes associated with accumulations of vesicular structures found interspersed between the microvillated cells of the midgut. The origin of these vesicular structures is unknown, but they correlated with the surface of midgut cells invaded by ookinetes as observed by TEM. After binding to the midgut. ookinetes underwent extensive morphological changes: they frequently developed one or more annular constrictions, and their surface roughened considerably, suggesting that midgut components remain bound to the parasite surface. Our observations suggest that, in a natural infection, the ookinete interacts in a sequential manner with specific components of the midgut surface. Initial binding to the midgut surface may activate the ookinete and cause morphological changes in preparation for invasion of the midgut cells.     

Predation of the oriental fruit fly,Bactrocera dorsalis puparia by the red imported fire ant,Solenopsis invicta: role of host olfactory cues and soil depth

Predation by red imported fire ants, Solenopsis invicta on oriental fruit fly, Bactrocera dorsalis puparia was evaluated. No significant olfactory response of the workers was observed at 0, 2 and 4 days after fly pupation, whereas the workers were significantly attracted by the 6th day old puparia. We found S. invicta that predated on puparia of B. dorsalis in the field. The predation rate was negatively correlated with the depth of puparia in the soil. The predation rate was 70% at 4 cm depth; whereas, zero predation rate was observed at 6 cm depth. The predation rate was also significantly affected by soil moisture. The predation rate was 66.5% and 72.1% at soil moisture values of 40% and 80%, respectively, and no predation occurred at soil moisture value of 0%.     

Molecular and functional characterization of the flightin gene in the Oriental fruit fly,Bactrocera dorsalis

Flightin is a protein in flight muscles and is crucial for the flight capacity. Flightin also has been proposed as a protein with deep ancestry and functions outside of flight muscles. However, functional and molecular characterization of flightin achieved so far is mainly in flight muscles of Drosophila. Here, we cloned the flightin (Bd-flightin) gene and tested its expression and function in Bactrocera dorsalis, an important migratory pest. Phylogenetic analysis based on flightin orthologs revealed that the divergence of flightin is consistent with the taxonomic classification of insects. Motif analysis indicated obvious variations in flightin orthologs, which may have occurred during speciation and functional differentiation. The expression is quite low during egg and larval stages, which largely increased during pupal stage and then peaked at the beginning of the adult stage. Bd-flightin also showed tissue- and age-specific expression patterns during adult stage. The relative expression level is low in wing, head, ovary and testis, which is relatively higher in leg and abdominal wall and much higher in thorax. Injection of late pupae and newly eclosed adults with 1 μg flightin dsRNA per insect both significantly reduced the expression of flightin and the flight capacity in males and females. In addition, silencing the expression of flightin also decreased the weight ratio of thorax and whole-body. These results suggested that flightin plays important roles in flight muscle development and flight function in B. dorsalis, which can potentially be used to control the flight behaviour of the fruit fly.     

Microscopic analysis and seasonality of gemma production in the freshwater red alga Hildenbrandia angolensis (Hildenbrandiales, Rhodophyta)

The development and release of the unique vegetative propagules of the freshwater encrusting alga Hildenbrandia angolensis Welwitsch ex West et West, gemmae, were studied using several different microscopic and histochemical techniques. In addition, the seasonality of gemma production was monitored bimonthly over a 12‐month period in two spring‐fed streams in Texas, USA. Gemmae differentiate within the thallus and are subsequently released from the surface of the crust. Release of the gemmae most likely occurs by digestion of surrounding cells, as suggested by the presence of starch granules and lipid globules in the region between the released gemma and the thallus. The initial separation of the gemmae from the thallus occurs from the sides of the gemma or the bottom, or possibly simultaneously. Contrary to previous studies, we have observed that gemma production occurs endogenously within the thallus of freshwater Hildenbrandia, rather than on the surface of the crust in raised structures. Histochemical tests and electron microscopic examination indicate that the cells of the gemmae contain a large amount of floridean starch. The starch granules frequently form rings surrounding the nuclei of both gemma and thallus cells; a feature infrequently reported for florideophyte red algae. Our seasonality investigations indicate that large fluctuations in gemma production occur over 1 year, but at least some gemma production continues year‐round in the streams examined.     

Accumulation,localisation, and toxic effects of cadmium in the liverwort Lunularia cruciata

Summary. Accumulation, tissue and intracellular localisation, and toxic effects of cadmium were investigated in the liverwort Lunularia cruciata. The results of analyses carried out by atomic absorption spectrometry on single plants showed that the cadmium accumulation was dose- and time-dependent. Cadmium localisation was assessed by X-ray scanning electron microscopy microanalysis in gemmalings and in the different tissues of the thallus and by X-ray transmission electron microscopy microanalysis at the cellular level. The metal preferentially accumulated in the hyaline parenchyma and at the base of the gemma cups. Inside the cell, cadmium accumulated in the vacuoles and the cell wall. Metal accumulation was accompanied by a concomitant increase in sulphur content within the vacuoles of stressed cells. Gel-permeation chromatography showed that most of the cadmium was associated with a low-molecular-mass fraction eluting at a ratio of elution volume to void volume corresponding to that of phytochelatins. The excess of sulphur deposited in the vacuoles may well have been caused by the stress-induced synthesis of phytochelatins. At the ultrastructural level, sublethal concentrations of cadmium caused alterations of the fine structure of the cells, inducing marked alterations of the chloroplast structure. Cadmium also induced a dose-dependent inhibition of apical thallus growth and gemma germination.Correspondence and reprints: Department of Plant Biology, University Federico 11, via Foria 223, 80132 Naples, Italy.     

Larval competition within and between insecticide resistant and susceptible individuals in the oriental fruit fly,Bactrocera dorsalis

Insecticide resistance is a serious issue in agriculture. Ecological interactions may be used to manage the spread of resistance, but little information is currently available. In particular, virtually none is known about interactions between resistant and susceptible individuals. This study investigated competition between resistant and susceptible oriental fruit fly larvae (Bactrocera dorsalis). Competition in the larval stage was examined with an explicit consideration of individual identity (resistant or susceptible). Guava fruits were inoculated with eggs of susceptible and/or resistant flies, and their development and survival were monitored. Egg density influenced the time that larvae stayed in fruits as well as their survival. In addition, susceptible flies survived better when interacting with resistant flies than with other susceptible flies, indicating that susceptible flies are competitively superior to resistant flies. The results suggest that artificially creating environments that induce competition between susceptible and resistant flies can be useful for the management of insecticide resistance.     

Role of a tachykinin-related peptide and its receptor in modulating the olfactory sensitivity in the oriental fruit fly,Bactrocera dorsalis (Hendel)

Insect tachykinin-related peptide (TRP), an ortholog of tachykinin in vertebrates, has been linked with regulation of diverse physiological processes, such as olfactory perception, locomotion, aggression, lipid metabolism and myotropic activity. In this study, we investigated the function of TRP (BdTRP) and its receptor (BdTRPR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis. BdTRPR is a typical G-protein coupled-receptor (GPCR), and it could be activated by the putative BdTRP mature peptides with the effective concentrations (EC₅₀) at the nanomolar range when expressed in Chinese hamster ovary cells. Consistent with its role as a neuromodulator, expression of BdTRP was detected in the central nervous system (CNS) of B. dorsalis, specifically in the local interneurons with cell bodies lateral to the antennal lobe. BdTRPR was found in the CNS, midgut and hindgut, but interestingly also in the antennae. To investigate the role of BdTRP and BdTRPR in olfaction behavior, adult flies were subjected to RNA interference, which led to a reduction in the antennal electrophysiological response and sensitivity to ethyl acetate in the Y-tube assay. Taken together, we demonstrate the impact of TRP/TRPR signaling on the modulation of the olfactory sensitivity in B. dorsalis. The result improve our understanding of olfactory processing in this agriculturally important pest insect.     

Pollen morphology of Xanthium L. (s.l.) (Asteraceae,Asteroideae, Heliantheae,Ambrosiinae) in the Iberian Peninsula - a palynotaxonomic approach to a poisonous,allergenic and invasive genus

Abstract

The pollen morphology of the Iberian taxa of the genus Xanthium s.l. and of the non-Iberian species X. ambrosioides was studied to help to identify these poisonous, allergenic and invasive taxa and clarify their taxonomic relationships. In addition, the question of the existence and structure of a mesoaperture in the apertural system of Xanthium was also considered. The pollen grains of sections Acanthoxanthium and Xanthium clearly differ by their characters, which supports the separation of both taxa and allows for their distinction based on pollen morphology. It is suggested that the morphological and palynological differences between Xanthium and Acanthoxanthium, together with the lack of hybridisation between the two sections and the monophyly of Acanthoxanthium, could lead to the elevation of the latter to the generic status. The two species of section Xanthium present in the Iberian Peninsula (X. orientale and X. strumarium) and of section Acanthoxanthium are well separated by their palynological features. Likewise, the Iberian subspecies of Xanthium, X. orientale subsp. orientale and X. orientale subsp. italicum are palynologically distinguishable. However, no significant difference could be found between the pollen of X. strumarium subsp. strumarium and of X. strumarium subsp. brasilicum. The pollen data do not support the hypotheses of a hybrid origin for X. strumarium subsp. brasilicum. A mesoaperture intersecting the foot layer and the upper part of the endexine is present in both sections, which is congruent with the results already found for other Asteroideae.     

Low-temperature electron microscopy for the study of polysaccharide ultrastructures in hydrogels. I. Theoretical and technical considerations

The high-pressure freezing (HPF) technique was applied to the cryo-immobilization of alginate gels and the quality of the freezing analyzed on a TEM by comparison of the segregation pattern of samples of decreasing thickness. Dynamic simulations of heat transfer within an idealized slab of pure water surrounded by two walls of aluminium were performed to illustrate the effect of the heat-transfer coefficient by convection on the cooling rate of the sample. Heat-transfer coefficients in liquid nitrogen and liquid propane at ambient pressure were measured using a carefully characterized thermocouple and the values incorporated as parameters in heat-transfer simulations to compare the efficiency of the plunge-freezing technique with the high-pressure freezing technique. Values of the heat-transfer coefficient in liquid nitrogen and liquid propane, calculated between 273 K and 173 K were 670 and 18420 W/m(2)/K, respectively. Based on TEM observations and the results of heat-transfer simulations, the HPF technique was adapted to the cryo-fixation of 50-microm-thick alginate gels. The occurrence of artifacts was rejected because no differences were observed in the pattern of cryo-fixed and freeze-substituted samples of various thickness, with and without ethanol as cryo-protectant. A sample thickness of 50 microm was found to ensure an adequate preservation of structures as small as a few nanometers, as verified by TEM and SEM observations. Finally, DSC measurements on alginate solutions and alginate beads revealed that under the experimental conditions (0-3%), alginate cannot be considered to be an efficient cryo-protectant.     

Extracellular complexation of Cd in the Hartig net and cytosolic Zn sequestration in the fungal mantle of Picea abies – Hebeloma crustuliniforme ectomycorrhizas

Compartmentation of heavy metals on or within mycorrhizal fungi may serve as a protective function for the roots of forest trees growing in soils containing elevated concentrations of metals such as Cd and Zn. In this paper we present the first quantitative measurements by X‐ray microanalysis of heavy metals in high‐pressure frozen and cryosectioned ectomycorrhizal fungal hyphae. We used this technique to analyse the main sites of Cd and Zn in fungal cells of mantle and Hartig net hyphae and in cortical root cells of symbiotic Picea abies – Hebeloma crustuliniforme associations to gain new insights into the mechanisms of detoxification of these two metals in Norway spruce seedlings. The mycorrhizal seedlings were exposed in growth pouches to either 1 mM Cd or 2 mM Zn for 5 weeks. The microanalytical data revealed that two distinct Cd‐ and Zn‐binding mechanisms are involved in cellular compartmentation of Cd and Zn in the mycobiont. Whereas extracellular complexation of Cd occurred predominantly in the Hartig net hyphae, both extracellular complexation and cytosolic sequestration of Zn occurred in the fungal tissue. The vacuoles were presumed not to be a significant pool for Cd and Zn storage. Cadmium was almost exclusively localized in the cell walls of the Hartig net (up to 161 mmol kg ^{? 1} DW) compared with significantly lower concentrations in the cell walls of mantle hyphae (22 mmol kg ^{? 1} DW) and in the cell walls of cortical cells (15 mmol kg ^{? 1} DW). This suggests that the apoplast of the Hartig net is a primary accumulation site for Cd. Zinc accumulated mainly in the cell walls of the mantle hyphae (111 mmol kg ^{? 1} DW), the Hartig net hyphae (130 mmol kg ^{? 1} DW) and the cortical cells (152 mmol kg ^{? 1} DW). In addition, Zn occurred in high concentrations in the cytoplasm of the fungal mantle hyphae (up to 164 mmol kg ^{? 1} DW) suggesting that both the cell walls and the cytoplasm of fungal tissue are the main accumulation sites for Zn in P. abies resulting in decreased Zn transfer from the fungus to the root.     

The differences in the eyelids microstructure and the conjunctiva‐associated lymphoid tissue between selected ornamental and wild birds as a result of adaptation to their habitat

The aim of the study was to describe the morphology of the upper, lower and third eyelid and characterize the organized lymphoid follicles and diffuse lymphocytes from ornamental and wild birds. The goal of these examinations was also to identify avian conjunctiva‐associated lymphoid tissue (CALT) and lymphoid tissue that contained specialized high endothelial venules. The upper, lower and third eyelid from 30 species of ornamental and wild birds representing 21 families were examined under light microscopy and using scanning electron microscopy. The third eyelid in all of the examined birds was composed of a free margin, which was divided into two parts. The largest tarsal plate of the third eyelid was observed in the greater rhea (Rheimorphae), the white‐tailed eagle and steppe eagle (Accipitrimorphae) and was approximately 13–15 mm wide and 9–11 mm long, respectively. In all of the examined birds, the CALT was associated with a rich network of small vessels. In addition, the presence of characteristic high endothelial venules and roundish bright endothelial cells was confirmed in the upper and lower eyelids or only in the lower eyelid (Phoenicopterimorphae, Procellariimorphae and Strigimorphae).     

Study on the interaction between pelargonidin‐3‐O‐glucoside and bovine serum albumin using spectroscopic,transmission electron microscopy and molecular modeling techniques

The aim of this study is to evaluate the binding behavior between pelargonidin‐3‐O‐glucoside (P3G) and bovine serum albumin (BSA) using multi‐spectroscopic, transmission electron microscopy (TEM) and molecular docking methods under physiological conditions. Fluorescence spectroscopy and time‐resolved fluorescence showed that the fluorescence of BSA could be quenched remarkably by P3G via a static quenching mechanism, and there is a single class of binding site on BSA. In addition, the thermodynamic functions ΔH and ΔS were –21.69 kJ/mol and 24.46 J/mol/K, indicating that an electrostatic interaction was a main acting force. The distance between BSA and P3G was 2.74 nm according to Förster's theory, illustrating that energy transfer occurred. In addition, the secondary structure of BSA changed with a decrease in the α‐helix content from 66.2% to 64.0% as seen using synchronous fluorescence, UV/vis, circular dichroism and Fourier transform infrared spectroscopies, whereas TEM images showed that P3G led to BSA aggregation and fibrillation. Furthermore, site marker competitive experiments and molecular docking indicated that P3G could bind with subdomain IIA of BSA. The calculated results of the equilibrium fraction showed that the concentration of free P3G in plasma was high enough to be stored and transported from the circulatory system to its target sites to provide therapeutic effects. Copyright © 2015 John Wiley & Sons, Ltd.     

Morphology and histochemistry of the peripheral olfactory organ in the round goby,Neogobius melanostomus (Teleostei: Gobiidae)

This first comprehensive study of the peripheral olfactory organ from a representative of the large and economically important order of teleost fishes, the Perciformes, shows a compact structure with olfactory sensory neurons distributed widely throughout the olfactory chamber. The spatial organization of the nasal cavity in the bottom-dwelling round goby (Gobiidae, Neogobius melanostomus) was examined using impression material injection, immunocytochemistry, and transmission electron microscopy. The olfactory chamber contains a single olfactory lamella; prominent dorsocaudal lachrymal and ethmoidal accessory nasal sacs are situated ventrocaudal to the chamber. The location of the olfactory mucosa within the olfactory chamber is novel for teleost fish, as it extends beyond the ventral surface to the lateral and dorsal regions. Microvillar olfactory sensory neurons and ciliated olfactory sensory neurons were identified by transmission electron microscopy and the spatial distribution of these two cell types was assessed through immunocytochemistry against olfactory receptor coupled G-proteins. Both G(alphaolf)-immunoreactive ciliated olfactory sensory neurons and the G(alphao)-immunoreactive microvillar form were located throughout the olfactory epithelium. Ciliated crypt cells were G(alphao) immunoreactive and were found throughout the olfactory epithelium of some specimens. The widespread occurrence of olfactory sensory neurons in the olfactory chamber supports the idea that olfactory signaling is important to the survival of the round goby. The prominence of the lachrymal and ethmoidal accessory nasal sacs indicates the capacity to regulate the flow of odorant molecules over the sensory surface of the olfactory sensory neurons, possibly through a pump-like mechanism driven by opercular activity associated with gill ventilation.