Development of the venom ducts in the centipede Scolopendra: an example of recapitulation

In contrast to previous claims that (a) there is a law of recapitulation and, conversely, (b) recapitulation never happens, the evolutionary repatterning of development can take many forms, of which recapitulation is one. Here, we add another example to the list of case studies of recapitulation. This example involves the development of the venom claws (forcipules) in the centipede Scolopendra subspinipes mutilans, and in particular the development of the duct through which venom flows from the gland that produces it (proximal) to the opening called the meatus (distal) through which it is injected into prey. Most of the information we present is from early postembryonic stages—these have been neglected in previous work on centipede development. We show that the venom ducts arise from sutures that are invaginations of the cuticle. In S. s. mutilans, the invagination in each forcipule forms into a tubular structure that detaches itself from the exoskeleton and moves toward the center of the forcipule. This is in contrast to extant Scutigera, and also, probably, Scolopendra's extinct Scutigera‐like ancestors, where the duct remains attached to the cuticle of throughout development. Thus, S. s. mutilans exhibits a recapitulatory repatterning of development.     

Variation and specialisation of the forcipular apparatus of centipedes (Arthropoda: Chilopoda): A comparative morphometric and microscopic investigation of an evolutionary novelty

The forcipules of centipedes are the only known example in the animal kingdom of an evolutionary transition from walking legs to venom-injecting appendages. They provide a classic case of an evolutionary novelty under most (but not all) definitions of that concept. Although there is a reasonable literature on forcipules, and on the forcipular segment more generally, it is fragmentary and scattered. Also, many previous studies have been based on a single species and hence have no comparative component. Here, we build on this earlier literature by providing detailed qualitative and quantitative information on the forcipular segments of representatives of the five extant orders of centipedes. Our results reveal notable differences between the orders – as well as considerable variation within some of them. The pattern of inter-group differences can be used to infer, albeit cautiously, a major evolutionary trend from a presumed scutigeromorph-like last common ancestor (LCA), in which the forcipules were probably leg-like (as in present-day scutigeromorphs) to a more specialized claw-like structure with movement restricted to the horizontal plane. This morphological trend may reflect an ecological trend from open-habitat ambush predation to leaf-litter and subterranean predatory opportunism.     

Morphology and ultrastructure of the venom glands of the northern pacific rattlesnake Crotalus viridis oreganus

The venom gland of Crotalus viridis oreganus is composed of two discrete secretory regions: a small anterior portion, the accessory gland, and a much larger main gland. These two glands are joined by a short primary duct consisting of simple columnar secretory cells and basal horizontal cells. The main gland has at least four morphologically distinct cell types: secretory cells, the dominant cell of the gland, mitochondria-rich cells, horizontal cells, and “dark” cells. Scanning electron microscopy shows that the mitochondria-rich cells are recessed into pits of varying depth; these cells do not secrete. Horizontal cells may serve as secretory stem cells, and “dark” cells may be myoepithelial cells. The accessory gland contains at least six distinct cell types: mucosecretory cells with large mucous granules, mitochondria-rich cells with apical vesicles, mitochondria-rich cells with electron-dense secretory granules, mitochondria-rich cells with numerous cilia, horizontal cells, and “dark” cells. Mitochondria-rich cells with apical vesicles or cilia cover much of the apical surface of mucosecretory cells and these three cell types are found in the anterior distal tubules of the accessory gland. The posterior regions of the accessory gland lack mucosecretory cells and do not appear to secrete. Ciliated cells have not been noted previously in snake venom glands. Release of secretory products (venom) into the lumen of the main gland is by exocytosis of granules and by release of intact membrane-bound vesicles. Following venom extraction, main gland secretory and mitochondria-rich cells increase in height, and protein synthesis (as suggested by rough endoplasmic reticulum proliferation) increases dramatically. No new cell types or alterations in morphology were noted among glands taken from either adult or juvenile snakes, even though the venom of each is quite distinct. In general, the glands of C. v. oreganus share structural similarities with those of crotalids and viperids previously described.     

Ultrastructure of the venom gland of the scorpion,Centruroides sculpturatus (Ewing)

The venom apparatus of the scorpion, C. sculpturatus (Ewing) was studied with light and electron microscopy. Each of the paired glands is lined by secretory epithelium made up of a single layer of columnar cells. Extensive folding in the epithelial layer creates a primitive acinar gland. The secretory products are either membrane-bound or unbound vesicles with discrete morphologies and are observed in the extruded venom, within the lumen of the gland, and within single secretory cells. The venom apparatus, including connective tissues, nerve cells, and muscle tunic is described and correlations are made with observations in other Athropods.     

Anatomical correlates of venom production in Conus californicus

Like all members of the genus, Conus californicus has a specialized venom apparatus, including a modified radular tooth, with which it injects paralyzing venom into its prey. In this paper the venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy. The general anatomy of the venom apparatus resembles that in other members of the genus, but several features are described that have not been previously reported for other species. The proximal (posterior) quarter of the venom duct is composed of a complex epithelium that may be specialized for active transport rather than secretion. The distal portion of the duct is composed of a different type of epithelium, suggestive of holocrine secretion, and the cells display prominent intracellular granules of at least two types. Similar granules fill the lumen of the duct. The passageway between the lumen of the venom duct and pharynx is a flattened branching channel that narrows to a width of 10 micro m and is lined by a unique cell type of unknown function. Granular material similar to that in the venom duct was also found in the lumen of individual teeth within the radular sac. Mass spectrometry (MALDI-TOF) demonstrated the presence of putative peptides in material derived from the tooth lumen, and all of the more prominent species were also evident in the anterior venom duct. Radular teeth thus appear to be loaded with peptide toxins while they are still in the radular sac.     

Venom apparatus of the Brazilian tarantula <Emphasis Type="Italic">Vitalius dubius</Emphasis> Mello-Leitão 1923 (Theraphosidae)

Tarantula venoms are a cocktail of proteins and peptides that have been increasingly studied in recent years. In contrast, less attention has been given to analyzing the structure of the paired cephalic glands that produce the venom. We have used light, electron, and confocal microscopy to study the organization and structure of the venom gland of the Brazilian tarantula Vitalius dubius. The chelicerae are hairy chitinous structures, each with a single curved hollow fang that opens via an orifice on the anterior surface. Internally, each chelicera contains striated muscle fiber bundles that control fang extension and retraction, and a cylindrical conical venom gland surrounded by a thick well-developed layer of obliquely arranged muscle fibers. Light microscopy of longitudinal and transverse sections showed that the gland secretory epithelium consists of a sponge-like network of slender epithelial cell processes with numerous bridges and interconnections that form lacunae containing secretion. This secretory epithelium is supported by a basement membrane containing elastic fibers. The entire epithelial structure of the venom-secreting cells is reinforced by a dense network of F-actin intermediate filaments, as shown by staining with phalloidin. Neural elements (axons and acetylcholinesterase activity) are also associated with the venom gland. Transmission electron microscopy of the epithelium revealed an ultrastructure typical of secretory cells, including abundant rough and smooth endoplasmic reticulum, an extensive Golgi apparatus, and numerous mitochondria.     

Histology,histochemistry, and emptying mechanism of the venom glands of some elapid snakes

The venom glands of several species of elapid snakes are described. The main venom gland consists of many tubules which usually contain large amounts of secretion product. The accessory gland surrounds the entire venom duct and is usually composed of uniform mucous epithelium. The epithelium lining the tubules of the accessory gland of Naja naja is composed of two distinct types of cells. Histochemical tests indicate that the main venom gland reacts with mercury bromphenol blue and PAS but not with alcian blue. The accessory gland reacts with PAS and alcian blue, and not with mercury bromphenol blue. Treatment of sections with sialidase demonstrates the presence of a sialomucin in the accessory gland. Stimulation of the muscles associated with the venom gland offers an indication of the venom expulsion mechanism of Bungarus caeruleus. A comparison of the venom apparatus of elapid and viperid snakes emphasizes marked differences in the internal anatomy of the venom glands, muscles associated with the gland, and arrangement of glandular components. The morphological differences and dissimilar venom expulsion mechanisms support the recent view of the polyphyletic origin of venomous snakes.     

管氏肿腿蜂毒液器官超微结构观察

应用透射电镜技术,观察了管氏肿腿蜂Scleroderma guani毒液器官的超微结构.毒腺由基膜层、分泌细胞层、导管细胞层和内膜层构成,分泌细胞内含内质网、末端附器、分泌囊泡、分泌颗粒、液泡等细胞器,其内合成的毒液由末端附器输送至毒腺的腔体.毒囊由肌肉鞘层、上皮细胞层和内膜层组成,肌肉鞘内的肌纤丝规则排列不交错,上皮细胞层内细胞器稀少,内膜层呈波浪状均匀加厚.     

Comparative morphology of the venom apparatus in the braconid wasp subfamily Rogadinae (Insecta, Hymenoptera, Braconidae) and related taxa

Zaldivar‐River ó n, A., Areekul, B., Shaw, M. R. & Quicke, D. L. J. (2004). Comparative morphology of the venom apparatus in the braconid wasp subfamily Rogadinae (Insecta, Hymenoptera, Braconidae) and related taxa. —Zoologica Scripta, 33, 223–237. The morphology of the venom apparatus intima in representatives of 38 genera of the problematic braconid wasp subfamily Rogadinae and other cyclostome braconids was investigated and a preliminary phylogenetic analysis for the group was performed with the information obtained. Despite the limited number of characters, the data suggest several relationships at various taxonomic levels. The venom apparatus in the Clinocentrini and the Stiropiini is relatively unmodified and similar to that found in other genera previously placed within a broader concept of the Rogadinae (e.g. genera of Lysitermini, Pentatermini, Tetratermini, Hormiini) and also to that of the Betylobraconinae. The presence of a cone of filaments located inside the secondary venom duct near to its insertion on the venom reservoir/primary venom duct is proposed as a synapomorphy for the tribe Rogadini to the exclusion of Stiropiini, Clinocentrini and Yeliconini. Other features of the secondary venom duct and its insertion on the venom reservoir/primary venom duct support a number of relationships between the genera of the Rogadini and also within the large genus Aleiodes. A clade containing 15 Rogadini genera (Bathoteca, Bathotecoides, Bulborogas, Canalirogas, Colastomion, Conspinaria, Cystomastacoides, Macrostomion, Megarhogas, Myocron, Pholichora, Rectivena, Rogas, Spinaria and Triraphis) is supported by the presence of a thickened and short secondary venom duct, whereas the different members of Aleiodes (excluding members of the subgenus Heterogamus) and Cordylorhogas are distinguished by having a recessed secondary venom duct with well‐defined and numerous internal filaments. New World Rogas species exhibit a unique venom apparatus and may not be closely related to the Old World ones. Features of the venom apparatus of the enigmatic genus Telengaia and the exothecine genera Shawiana and Colastes suggest that the Telengainae and Exothecinae are both closely related to the Braconinae, Gnamptodontinae, and possibly to the Opiinae and Alysiinae. An unsculptured venom reservoir was found in one specimen of the type species of Avga, A. choaspes, which is consistent with it occupying either a very basal position within the cyclostome braconids or belonging to a recently recognized ‘Gondwanan’ clade that also includes the Aphidiinae.     

Ultrastructural investigations of the salivary glands in adults of the microtrombidiid mite Platytrombidium fasciatum (C. L. Koch, 1836) (Acariformes: Microtrombidiidae)

The organization of the salivary glands in ad libitum-fed adult females of the microtrombidiid mite Platytrombidium fasciatum (C. L. Koch, 1836) was observed using transmission electron microscopy. In all, four pairs of large simple alveolar salivary glands were determined, which have been named due to their position as posterior, ventral, medial and dorsal. These glands occupy a body cavity behind, around the base and partly inside the gnathosoma. The posterior glands are largest and possess large nuclei with greatly folded nuclear envelope. Secretory granules are electron-light, containing fine granular material and are partly provided with various lamellar inclusions inside the granules. The latter tend to be placed predominantly in the middle parts of the gland around the central (intra-alveolar) cavity. The remaining glands, conversely, are typically filled with tightly packed electron-dense secretory granules, except for the ventral glands, the granules of which may show a compound organization. The nuclei of all these glands occupy a peripheral position and are mostly pressed between the granules. No prominent endoplasmic reticulum or conspicuous Golgi bodies were observed within the salivary glands. The salivary glands are provided with a complex apparatus of the intra-alveolar cavity (acinar lumen) with the excretory duct base provided by a system of branched special cells producing the duct walls. The ventral glands open by separate ducts into the most posterior part of the subcheliceral space. Ducts of the posterior glands immediately fuse with the ducts of the tubular (coxal) glands. The common duct of each side of the body joins with the ducts of the medial and dorsal glands respectively, and opens into the subcheliceral space far anterior to that of the ventral glands.     

Immunocytochemical localization and secretion process of the toxin CSTX-1 in the venom gland of the wandering spider Cupiennius salei (Araneae: Ctenidae)

Fluorescein and horseradish peroxidase-labeled monoclonal antibodies were used to localize the predominant toxic peptide CSTX-1 in the venom gland of the spider Cupiennius salei. There was no polarity of CSTX-1 expression in repleted glands, whereas the glands of previously milked spiders showed a decreasing immunofluorescent response from the distal to the proximal portion. Detailed investigation revealed a new structure in the venom-secreting epithelium, which is postulated to be an evolutionary adaptation to increasing gland volume. CSTX-1 was found to be synthesized and stored as a fully active toxin within complex units, composed of long interdigitating cells running perpendicular to the muscular sheath and extending into the central lumen of the gland. These venom-producing units were found in all sectors of the gland, including the transitional region between the main gland and the venom duct. The venom is liberated from the venom-producing units into the glandular lumen following the contraction of the surrounding muscle layer. Free nuclei or other cellular fragments, which would have provided evidence for a holocrine secretion process, were not found in the glandular lumen or in the crude venom obtained by electrical stimulation. The fine regulation of the spider's venom injection process is postulated to be the function of the bulbous ampulla, situated in the anterior third of the venom duct.     

腰带长体茧蜂毒液器官和卵巢的形态学及其超微结构

应用超薄切片和电镜技术,观察内寄生蜂腰带长体茧蜂Macrocentrus cingulum Brischke毒液器官和卵巢的形态结构。腰带长体茧蜂毒液器官由1个毒囊和2条毒腺组成,毒腺接于毒囊的顶端。毒腺由单层分泌细胞、退化的外胚层细胞和环腔的内膜构成,分泌细胞主要由1个明显的细胞核和1个较大囊状细胞器构成,囊状细胞器的功能是分泌毒液。毒囊由肌肉鞘和扁平细胞层构成,但没有分泌细胞。腰带长体茧蜂卵巢1对,每个卵巢由10条左右卵巢小管组成,与侧输卵管相接处略微膨大形成卵巢萼区。2条侧输卵管在产卵管基部会合形成1条总输卵管与产卵管相接。毒液器官通过毒囊的毒液导管附着在总输卵管上。对寄生蜂毒液器官的生物学、细胞学及在分类进化上的意义进行研究。     

Molecular cloning and characterization of a new cDNA sequence encoding a venom peptide from the centipede <Emphasis Type="Italic">Scolopendra subspinipes</Emphasis> mutilans

Many studies have been performed on venomous peptides derived from animals. However, little of this research has focused on peptides from centipede venoms. Here, a venom gland cDNA library was suc-cessfully constructed for the centipede Scolopendra subspinipes mutilans. A new cDNA encoding the precursor of a venom peptide, named SsmTx, was cloned from the venomous gland cDNA library of the centipede S. subspinipes mutilans. The full-length SsmTx cDNA sequence is 465 nt, including a 249 nt ORF, a 45 nt 5′ UTR and a 171 nt 3′ UTR. There is a signal tail AATAAA 31 nt upstream of the poly (A) tail. The precursor nucleotide sequence of SsmTx encodes a signal peptide of 25 residues and a mature peptide of 57 residues, which is bridged by two pairs of disulfide bonds. SsmTx displays a unique cysteine motif that is completely different from that of other venomous animal toxins. This is the first reported cDNA sequence encoding a venom peptide from the centipede S. subspinipes mutilans.     

The divergent genome of Scorpion Group 1 (SG1) intracellular bacterium from the venom glands of Vaejovis smithi (Scorpiones: Vaejovidae)

Scorpions were among the first animals on land around 430 million years ago. Like many arachnids, scorpions have evolved complex venoms used to paralyze their prey and for self-defense. Here we sequenced and analyzed the metagenomic DNA from venom glands from Vaejovis smithi scorpions. A metagenome-assembled genome (MAG) of 624,025 bp was obtained corresponding to the previously reported Scorpion Group 1 (SG1). The SG1 genome from venom glands had a low GC content (25.8%) characteristic of reduced genomes, many hypothetical genes and genes from the reported minimal set of bacterial genes. Phylogenomic reconstructions placed the uncultured SG1 distant from other reported bacteria constituting a taxonomic novelty. By PCR we detected SG1 in all tested venom glands from 30 independent individuals. Microscopically, we observed SG1 inside epithelial cells from the venom glands using FISH and its presence in scorpion embryos suggested that SG1 is transferred from mother to offspring.     

Ultrastructure of the Feeding Apparatus of Rhabdodemania minima Chitwood, 1936 (Enoplida: Rhabdodemaniidae)

The feeding apparatus of the marine nematode Rhabdodemania minima Chitwood, 1936 has been examined with light and transmission electron microscopy. The buccal capsule consists of a posterior region with smooth walls bearing three sets of three minute denticles at its posterior end and three large onchia in its mid region; a middle region with grooved walls; and an anterior region with costae and six odontia. The anterior and middle portions of the buccal capsule are enveloped by the cephalic cuticle, whereas the posterior region, which is set off from the middle region by a buccal seam, is partially enveloped by the anterior end of the esophagus. Two subventral esophageal glands open into the lumen of the esophagus. Secretions of each of three paraesophageal glands are conveyed through a duct in each of the three corresponding corners of the buccal wall to an opening between labia. A pair of wing-like thickenings, termed pterons, embraces the duct of each paraesophageal gland in the posterior and middle regions of the buccal capsule. A model of how the buccal capsule operates is proposed and tested. Morphological and functional aspects of the buccal apparatus and cephalic cuticle are compared with those of other taxa of the Enoplida, and their phylogenetic implications are discussed.     

Ultrastructural identification of the antennal gland complement in Siagona europaea Dejean 1826, a myrmecophagous carabid beetle

We examined antennal exocrine glands in adults of a myrmecophagous carabid beetle, Siagona europaea Dejean 1826 (Coleoptera, Carabidae), by light and electron microscopy and we identified two types of integumentary glands. The first type includes glands formed by three cells (a secretory cell, an intercalary cell and a duct cell) known as class 3 of Noirot and Quennedey (1991). The secretory cell has several large multivesicular electron‐lucent bodies, indicating a glycoprotein product associated with lipids. We hypothesize that this secretion protects the surface of antennae and sensilla from wear. The second group of glands includes unicellular glands known as oenocytes (class 2 of Noirot and Quennedey, 1991), which secrete epicuticular hydrocarbons through epidermal cells.     

Bioweapons synthesis and storage: The venom gland of front-fanged snakes

A paradoxical task of the venom gland of snakes is the synthesis and storage of an instantly available suite of toxins to immobilize prey and the protection of the snake against its own venom components. Furthermore, autolysis of the venom constituents due to the action of venom metalloproteases is an additional problem, particularly among viperid venoms, which are typically rich in lytic enzymatic proteins. To address questions concerning these problems, the structure of the venom gland was investigated using light microscopy, SEM and TEM. The composition of the venom originating from the intact venom apparatus or from the main venom gland alone was analyzed by electrophoresis, and the pH of freshly expressed venom as well as pH optima of several representative enzymes was evaluated. Results from several species of rattlesnakes demonstrated that the venom gland is structurally complex, particularly in its small rostral portion called the accessory gland, which may be a site of activation of venom components. Secreted venom is stable in extremes of temperature and dilution, and several proximate mechanisms, including pH and endogenous inhibitors, exist which inhibit enzymatic activity of the venom during storage within the venom gland but allow for spontaneous activation upon injection into prey. Whereas acid secretion by the parietal cells activates digestive enzymes in the stomach, within the venom gland acidification inhibits venom enzymes. We propose that the mitochondria-rich cells of the main venom gland, which are morphologically and histochemically very similar to the parietal cells of the mammalian gastric pit, play a central role in the stabilization of the venom by secreting acidic compounds into the venom and maintaining the stored venom at pH 5.4. Hence, our results indicate yet another trophic link between the processes of venom production and of digestion, and demonstrate that the venom glands of snakes may represent an excellent model for the study of protein stability and maintenance of toxic proteins.     

Differential polymorphism in cutaneous glands of archaic Leiopelma species

Endemic New Zealand frogs of the genus Leiopelma are from a basal lineage of extant anurans that release defensive secretions onto their skin when disturbed. Here, we characterize the gross anatomy and microscopic structure of the skin of L. archeyi, L. hochstetteri, and L. pakeka using stereoscopic, light and transmission electron microscopy. The terrestrial L. archeyi and L. pakeka possess dimorphic granular glands, categorized as type I and II, based on their frequency and morphological traits, whereas the semi‐aquatic L. hochstetteri lacks type I glands. This is the first report of differential dimorphism in anurans of the same genus. This dimorphism could be interpreted as an adaptation to different physiological or ecological needs of these species. However, species within this ancient genus share similar general gland morphology with other anurans, namely, a secretory unit containing storage granules ensheathed by myoepithelial cells. Type I glands are ellipsoid, large and contain a homogeneous mass of electron‐dense granules (1.8 ± 0.08 μm in diameter). Type II glands are round and contain larger heterogeneous granules (4.06 ± 0.16 μm) of varying densities. Exposure to noradrenaline causes the contraction of myoepithelial cells, resulting in bulk discharge of type I glands through the epidermal duct onto the skin surface. Differential release of secretions from dimorphic glands may be indicative of their functional specialisation in antipredatory or regulative roles. Mass spectrometric techniques were used to de novo sequence peptides present in the skin secretions of Leiopelma species. A total of 30 previously undescribed peptides from Leiopelma species were fully or partially sequenced. These peptides exhibited no similarity to any known compounds. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Venom gland and reservoir morphology in cynipoid wasps

The venom apparatus morphology was examined in 25 species of Cynipoidea, representing 11 parasitoid taxa; 12 gall inducers and two inquilines. Typically the venom apparatus consists of an oval or bilobed reservoir connected to the ovipositor apparatus by a very short venom duct at the anterior end and to a single elongate unbranched venom gland at or near its posterior end. The Dufour's gland was not found in any of the examined species. The elongate unbranched venom gland and the absence of the Dufour's gland are putative cynipoid synapomorphies. The shape and size of especially the venom reservoir were found to vary considerably within the Cynipoidea. It is typically less prominent in the parasitoid taxa than in the gall inducers. Exceptions include the poppy gallers Barbotinia and Aylax, in which the venom reservoirs were remarkably small and in the rose galler Diplolepis, where only a rudimentary venom apparatus was found. Possible functional and phylogenetic implications of cynipoid venom apparatus features are discussed.     

Morphologic analysis of the venom gland of Apis mellifera L. (Hymenoptera: Apidae) in populations of Mato Grosso do Sul, Brazil

In Apis mellifera L. the venom gland (also called acid gland) is composed of secretory cells that surround a channel that opens into a reservoir devoid of musculature. This gland can present apical branching. In this study the frequency of branched venom glands in Africanized honeybee workers (A. mellifera) from eleven localities in the state of Mato Grosso do Sul was recorded. The relations among the length of the main duct, the length of the duct from the reservoir to the beginning of branching, the length of the branched segment (when present) and the total length of the gland were also analyzed. The frequency of branched glands varied from 50% to 83% in the workers, indicating that this characteristic is primitive in those bees. The results of the Analysis of Discriminant Functions indicated significant differences in the morphometrical segments of the venom gland (Wilks Lambda = 0.092; F (40, 55) = 3.43; P < 0.001), and permitted a differentiation of the populations studied. Using the Mantel test we verified that there does not exist a significant correlation between the morphologic characteristics and the geographical distance between the localities evaluated (Mantel r = -0.006, P = 0.48). The high frequency of workers with large venom gland in all the apiaries considered makes viable the development of a selection program in order to obtain bees with longer venom glands, aimed at the commercial production of venom by the beekeepers of those localities of Mato Grosso do Sul.