Venom Delivery System Research Articles

Mesozoic larva in amber reveals the venom delivery system and the palaeobiology of an ancient lineage of venomous insects (Neuroptera)

The larvae of Neuroptera are predators that feed by injecting bioactive compounds into their prey and then suctioning the fluids through modified mouthparts. We explore the evolutionary history of this feeding structure through the examination of a new fossil larva preserved in Late Cretaceous Kachin amber, which we describe as new genus and species, Electroxipheus veneficus gen et sp. nov. X-ray phase-contrast microtomography enabled us to study the anatomy of the larva in 3D, including the structure of the mouthparts and that of the venom delivery system. The specimen exhibited a unique combination of morphological traits not found in any known fossil or extant lacewing, including an unusual structure of the antenna. Phylogenetic analyses, incorporating a selection of living and fossil larval Neuroptera and enforcing maximum parsimony and Bayesian inference, identified the larva as belonging to the stem group Mantispoidea. The larva shows that the anatomy of the feeding and venom-delivery apparatus has remained unchanged in Neuroptera from the Cretaceous to the present. The morphology of the specimen suggests that it was an active predator, in contrast with the scarcely mobile, specialized relatives, like mantispids and berothids.

Highly conserved and extremely variable: The paradoxical pattern of toxin expression revealed by comparative venom-gland transcriptomics of Phalotris (Serpentes: Dipsadidae)

Although non-front fanged snakes account for almost two-thirds of snake diversity, most studies on venom composition and evolution focus exclusively on front-fanged species, which comprise most of the clinically relevant accidents. Comprehensive reports on venom composition of non-front fanged snakes are still scarce for several groups. In this study, we address such shortage of knowledge by providing new insights about the venom composition among species of Phalotris, a poorly studied Neotropical dipsadid genus. Phalotris are known for their specialized venom delivery system and toxic venoms, which can cause life-threatening accidents in humans. We evaluate the venom-gland transcriptome of Phalotris, comparing the following three South American species: P. reticulatus for the Araucaria Pine forests, P. lemniscatus for the Pampa grasslands, and P. mertensi for the Brazilian Cerrado. Our results indicate similar venom profiles, in which they share a high expression level of Kunitz-type inhibitors (KUNZ). On the other hand, comparative analyses revealed substantial differences in the expression levels of C-type lectins (CTL) and snake venom metalloproteinases (SVMP). The diverse set of SVMP and CTL isoforms shows signals of positive selection, and we also identified truncated forms of type III SVMPs, which resemble type II and type I SVMPs of viperids. Additionally, we identified a CNP precursor hosting a proline-rich region containing a BPP motif resembling those commonly detected in viperid venoms with hypotensive activity. Altogether, our results suggest an evolutionary history favoring high expression levels of few KUNZ isoforms in Phalotris venoms, contrasting with a highly diverse set of SVMP and CTL isoforms. Such diversity can be comparable with the venom variability observed in some viperids. Our findings highlight the extreme phenotypic diversity of non-front fanged snakes and the importance to allocate greater effort to study neglected groups of Colubroidea.

A Comparative Analysis of the Venom System between Two Morphotypes of the Sea Anemone Actinia equina.

The current study investigates the venom-delivery system of green and red morphotypes of the sea anemone Actinia equina to disclose its potential as a source of bioactive compounds. We compared the two morphotypes using electron and optical microscopy, proteomics, and toxicity assessment on zebrafish embryos. Specialized venom-injecting cells (nematocysts) are equally distributed and found in the tentacles of both varieties. Proteomics revealed proteins of interest in both red and green Actinia, yielding the three most abundant Gene Ontology (GO) terms related to the biological processes "proteolysis", "hemolysis in another organism" and "lipid catabolic process". Neurotoxins and cytolytic toxins similar to known cnidarian toxins like PsTX-60A and AvTX-60A, for instance, were identified in both types. Extracts from green and red anemones were toxic to zebrafish embryos, with green anemone venom appearing to be more potent. The findings highlight the presence of proteinaceous toxins in A. equina and the potential for different varieties to possess distinct bioactive compounds. Notably, pore-forming toxins are suggested for molecular probes and immunotoxins, making them valuable assets for potential biotechnological and biomedical purposes.

The perspective of fish venom: An overview of the physiology, evolution, molecular and genetics

Fish venom has several biological activities, including enzyme activity, cytotoxicity, neurotoxicity, muscular toxicity, haemolytic, and cardiotoxicity, when they enter other species or a human being, they disrupt the physiological systems. Transcriptomic analysis of the fish venom glands revealed a large number of proteins relevant to the pharmacological activity even though they are not well-studied. The limitations in studying fish venoms also have an impact on their molecular characterization. This is partly because of the nature of fish venoms, as they are extremely unstable at normal ambient temperatures making them difficult to study. Venomous fish inhabit both marine and freshwater environments, they have specialized venom-delivery apparatuses. Venom delivery systems have evolved in a various animal species, originally for different purposes including defense, competition, as well as predation. In coastal areas, fish stings are a major problem because they have a serious toxic effect on fishermen, local communities, and visitors. In this study, we have discussed the general perspective of fish venom from marine and freshwater species in different aspects basically in their molecular evolution, physiology, diversity, transcriptome, and proteomic studies. We expect that this paper will provide readers with a unique perspective on understanding the current status of fish venom research as well as working for future studies. Therefore, the gap of knowledge acquired from this study will play as a baseline for researchers discovering new studies and using fish venom in a broader range of biomedical applications, and their biological information that can be used to develop drugs for pharmaceutical uses.

Phylogenetic and morphological evidence reveals the association between diet and the evolution of the venom delivery system in Neotropical goo-eating snakes

Advanced endoglyptodont snakes share a complex but homologous venom delivery system associated with the upper jaw and its dentition. Recently, a remarkable novel lower jaw venom delivery system was described for the Neotropical dipsadine radiation of goo-eating snakes. While most dipsadines are opistoglyphous and exhibit large, mainly serous venom glands associated with the upper jaw and supralabial glands, goo-eating dipsadine snakes are aglyphous and lack serous upper labial venom glands. Here, we provide new morphological and histological information on the oral glands and maxillary dentition of representatives of the major lineages of dipsadines that help trace the evolutionary steps that shaped the venom delivery system of dipsadines. We performed a maximum likelihood analysis on a molecular dataset that includes 443 terminals and seven loci. Our results show that goo-eating dipsadines form a monophyletic assemblage that includes the genus Adelphicos for the first time, along with Geophis, Atractus, Ninia, Chersodromus, Tropidodipsas, Sibon, and Dipsas. We also provide the first evidence of a complete shift from an upper jaw to a lower jaw venom delivery system associated with their specialized feeding behaviour. Unlike other dipsadines who exhibit typical endoglyptodont anteroposteriorly ridged posterior maxillary teeth, goo-eating dipsadines have uniform lateromedially ridged teeth throughout their maxilla. Our results indicate that the loss of the endoglyptodont venom delivery system occurred in the most recent common ancestor of goo-eating dipsadines, probably resulting from the loss of the embryonic posterior maxillary lamina responsible for the development of the venom delivery system.

Shedding Light on the Dentition and Venom Delivery System of the Rear-Fanged Snake, Galvarinus chilensis chilensis (Serpentes: Dipsadidae: Tachymenini) from Chile.

Although the rear-fanged snake Galvarinus chilensis chilensis (formerly named Tachymenis ch. chilensis) causes ophidian accidents with clinical importance in Chile, the anatomical and histological characterizations of the venom delivery system (venom gland and fang) of this species still remain unknown. This study describes the dentition and characteristics of fangs and their ontogenetic variations in G. ch. chilensis. Moreover, histological and histochemistry analyses of the venom glands of this species are presented. Using micro-computed tomography and scanning electron microscopy, the dentitions of neonates, juveniles, and adults were analyzed, and no ontogenetic variations in teeth length and number present in the dentary and maxilla were observed. Moreover, we found three types of basic teeth, with distributional patterns conserved in all ontogenetic categories. The fangs exhibited a groove from the base to the middle. At the end of the groove, prominent ridges are formed. The fang and groove lengths were significantly distinct between ontogenetic categories. No differences between females and males were observed. Histologically, we found that the venom gland is close to the fangs and has a seromucous composition. Our results describe, for the first time, the distributional pattern and characteristics of the dentition and venom delivery system of the poorly studied snake G. ch. chilensis.

A Pseudoscorpion's Promising Pinch: The venom of Chelifer cancroides contains a rich source of novel compounds

With pedipalps modified for venom injection, some pseudoscorpions possess a unique venom delivery system, which evolved independently from those of other arachnids like scorpions and spiders. Up to now, only a few studies have been focused on pseudoscorpion venom, which either identified a small fraction of venom compounds, or were based on solely transcriptomic approaches. Only one study addressed the bioactivity of pseudoscorpion venom. Here, we expand existing knowledge about pseudoscorpion venom by providing a comprehensive proteomic and transcriptomic analysis of the venom of Chelifer cancroides. We identified the first putative genuine toxins in the venom of C. cancroides and we showed that a large fraction of the venom comprises novel compounds. In addition, we tested the activity of the venom at specific ion channels for the first time. These tests demonstrate that the venom of C. cancroides causes inhibition of a voltage-gated insect potassium channel (Shaker IR) and modulates the inactivation process of voltage-gated sodium channels from Varroa destructor. For one of the smallest venomous animals ever studied, today's toolkits enabled a comprehensive venom analysis. This is demonstrated by allocating our identified venom compounds to more than half of the prominent ion signals in MALDI-TOF mass spectra of venom samples. The present study is a starting point for understanding the complex composition and activity of pseudoscorpion venom and provides a potential rich source of bioactive compounds useable for basic research and industrial application.

Sharp and fully loaded: 3D tissue reconstruction reveals how snake fangs stay deadly during fang replacement.

Snake venom is produced, transported and delivered by the sophisticated venom delivery system (VDS). When snakes bite, the venom travels from the venom gland through the venom duct into needle-like fangs that inject it into their prey. To counteract breakages, fangs are continuously replaced throughout life. Currently, the anatomy of the connection between the duct and the fang has not been described, and the mechanism by which the duct is reconnected to the replacement fang has not been identified. We examined the VDS in 3D in representative species from two families and one subfamily (Elapidae, Viperidae, Atractaspidinae) using contrast-enhanced microCT (diceCT), followed by dissection and histology. We observed that the venom duct bifurcates immediately anterior to the fangs so that both the original and replacement fangs are separately connected and functional in delivering venom. When a fang is absent, the canal leading to the empty position is temporarily closed. We found that elapid snakes have a crescent-shaped venom reservoir where venom likely pools before it enters the fang. These findings form the final piece of the puzzle of VDS anatomy in front-fanged venomous snakes. Additionally, they provide further evidence for independent evolution of the VDS in these three snake taxa.

Tentacle Morphological Variation Coincides with Differential Expression of Toxins in Sea Anemones.

Phylum Cnidaria is an ancient venomous group defined by the presence of cnidae, specialised organelles that serve as venom delivery systems. The distribution of cnidae across the body plan is linked to regionalisation of venom production, with tissue-specific venom composition observed in multiple actiniarian species. In this study, we assess whether morphological variants of tentacles are associated with distinct toxin expression profiles and investigate the functional significance of specialised tentacular structures. Using five sea anemone species, we analysed differential expression of toxin-like transcripts and found that expression levels differ significantly across tentacular structures when substantial morphological variation is present. Therefore, the differential expression of toxin genes is associated with morphological variation of tentacular structures in a tissue-specific manner. Furthermore, the unique toxin profile of spherical tentacular structures in families Aliciidae and Thalassianthidae indicate that vesicles and nematospheres may function to protect branched structures that host a large number of photosynthetic symbionts. Thus, hosting zooxanthellae may account for the tentacle-specific toxin expression profiles observed in the current study. Overall, specialised tentacular structures serve unique ecological roles and, in order to fulfil their functions, they possess distinct venom cocktails.

Development of the venom delivery system in Elapidae snake species: Naja siamensis and Oxyuranus microlepidotus

Many advanced snakes possess a unique venom delivery system which they utilise to subdue prey and for defence. Despite extensive efforts, the evolutionary differences in this key system between advanced snake families remains enigmatic. The current study has investigated the development of the venom delivery system using two oviparous Elapidae models, Naja siamensis and Oxyuranus microlepidotus. The development stages of the embryos in both models were detailed using previously standardised characterisation. Variations in the days post-oviposition between these stages was observed, despite a continuous development trajectory. These differences also translated to the development of the venom delivery system.

Fangs for the Memories? A Survey of Pain in Snakebite Patients Does Not Support a Strong Role for Defense in the Evolution of Snake Venom Composition.

Animals use venoms for multiple purposes, most prominently for prey acquisition and self-defense. In snakes, venom composition often evolves as a result of selection for optimization for local diet. However, whether selection for a defensive function has also played a role in driving the evolution of venom composition has remained largely unstudied. Here, we use an online survey of snakebite victims to test a key prediction of a defensive function, that envenoming should result in the rapid onset of severe pain. From the analysis of 584 snakebite reports, involving 192 species of venomous snake, we find that the vast majority of bites do not result in severe early pain. Phylogenetic comparative analysis shows that where early pain after a bite evolves, it is often lost rapidly. Our results, therefore, do not support the hypothesis that natural selection for antipredator defense played an important role in the origin of venom or front-fanged delivery systems in general, although there may be intriguing exceptions to this rule.

Reciprocal transplantation of the heterotrophic coral Tubastraea coccinea (Scleractinia: Dendrophylliidae) between distinct habitats did not alter its venom toxin composition.

Tubastraea coccinea is an azooxanthellate coral species recorded in the Indian and Atlantic oceans and is presently widespread in the southwestern Atlantic with an alien status for Brazil. T. coccinea outcompete other native coral species by using a varied repertoire of biological traits. For example, T. coccinea has evolved potent venom capable of immobilizing and digesting zooplankton prey. Diversification and modification of venom toxins can provide potential adaptive benefits to individual fitness, yet acquired alteration of venom composition in cnidarians is poorly understood as the adaptive flexibility affecting toxin composition in these ancient lineages has been largely ignored. We used quantitative high‐throughput proteomics to detect changes in toxin expression in clonal fragments of specimens collected and interchanged from two environmentally distinct and geographically separate study sites. Unexpectedly, despite global changes in protein expression, there were no changes in the composition and abundance of toxins from coral fragments recovered from either site, and following clonal transplantation between sites. There were also no apparent changes to the cnidome (cnidae) and gross skeletal or soft tissue morphologies of the specimens. These results suggest that the conserved toxin complexity of T. coccinea co‐evolved with innovation of the venom delivery system, and its morphological development and phenotypic expression are not modulated by habitat pressures over short periods of time. The adaptive response of the venom trait to specific predatory regimes, however, necessitates further consideration.

The Significance of Comparative Genomics in Modern Evolutionary Venomics

Venoms evolved convergently in diverse animal lineages as key adaptations that increase the evolu-tionary fitness of species which are manifold employed for defense, predation and competition. They constitute complex cocktails of various toxins that feature a broad range of bioactivities. The majority of described venom proteins belong to protein families that are known to comprise housekeeping genes or harbor protein-domains, which are present in genes with non-venom related functions. However, the evolutionary processes and mechanisms that foster the origin of these venom proteins and triggered their recruitment into the venom delivery system are still critically discussed. In most instances single or combined proteomic and transcriptomic approaches are applied to de-scribe venom compositions and the biological context of venoms. For neglected species these studies represent crucial contributions to improve our understanding of venom diversity on a broader scale. Nonetheless, the inference of the evolutionary origin of putative toxins in these studies could be mis-leading without appropriate coverage of gene populations from different tissue samples (gene com-pleteness) or complementary genome data. Providing a valid backbone to correctly map transcriptome and proteome data, whole genome sequences facilitate a clear distinction between variability of venom proteins or toxins due to posttranslational modifications, alternative splicing and false-positive matches that stem from sequencing or read processing and assembly errors. High-quality whole genome sequence data of venomous species are still sparse and unevenly distrib-uted within taxon lineages. However, to reveal the evolutionary pattern of putative toxins in venom-ous lineages and to identify ancestral variants of venom proteins, the appropriate sampling of ge-nomes from venomous and non-venomous species is crucial. Nevertheless, larger comparative studies based on multiple whole genome data sets are still sparse to uncover processes of venom evolution. Here, we review the general potential of comparative genomics in venomics to unravel mechanisms and patterns of evolutionary origin of toxin genes. Finally, we discuss the benefit of whole genome data to improve transcriptomics and proteomics-only studies, in particular if datasets are applied to assess the evolutionary origin of venom proteins.

Unveiling toxicological aspects of venom from the Aesculapian False Coral Snake Erythrolamprus aesculapii

Most colubrid snake venoms have been poorly studied, despite the fact that they represent a great resource for biological, ecological, toxinological and pharmacological research. Herein, we explore the venom delivery system of the Aesculapian False Coral Snake Erythrolamprus aesculapii as well as some biochemical and toxicological properties of its venom. Its Duvernoy's venom gland is composed of serous secretory cells arranged in densely packed secretory tubules, and the most striking feature of its fang is their double-curved shape, exhibiting a beveled bladelike appearance near the tips. Although E. aesculapii resembles elapid snakes of the genus Micrurus in color pattern, this species produces a venom reminiscent of viperid venoms, containing mainly tissue-damaging toxins such as proteinases. Prominent hemorrhage developed both locally and systemically in mice injected with the venom, and the minimum hemorrhagic dose was found to be 18.8 μg/mouse; the lethal dose, determined in mice, was 9.5 ± 3.7 μg/g body weight. This work has toxicological implications that bites to humans by E. aesculapii could result in moderately severe local (and perhaps systemic) hemorrhage and gives insight into future directions for research on the venom of this species.

Venom collection and analysis in the pseudoscorpion Chelifer cancroides (Pseudoscorpiones: Cheliferidae)

Pseudoscorpions are very small arthropods with almost worldwide distribution. They possess a unique venom delivery system in the chelal hands of their pedipalps that has evolved independently from that of scorpions and spiders. Studies on the venom composition of pseudoscorpions are very rare. Recently, the potential venom composition of the pseudoscorpion Synsphyronus apimelus Harvey, 1987 (Pseudoscorpiones: Garypidae) has been studied by transcriptome analysis. However, a proteome analysis of venom to identify the genuine venom compounds of pseudoscorpions has not yet been performed. In our study, we have developed a non-invasive approach for extracting minute amounts of venom, which for the first time allowed collecting pure venom samples of pseudoscorpions with minimal contaminations and high reproducibility. These experiments first required a morphological investigation of the venom delivery system with a focus on the role of the lamina defensor in the release of venom. Likely, the venom delivery system of pseudoscorpions has a mechanism that prevents the release of venom if the prey is not successfully penetrated by a venom tooth. Electrical stimulation of a gland-containing chelal hand in combination with a mechanical stimulation of the lamina defensor at the base of the venom tooth resulted in an average of 5 nl of collected venom. The utility of the method was then validated by repeated venom extractions and subsequent analysis of the venom composition using MALDI-TOF mass fingerprinting. Subsequent proteomics analysis in combination with transcriptome analyses of chelal hand tissue has identified the first genuine venom compounds of pseudoscorpions with putative antimicrobial peptides. For our experiments, we used the house pseudoscorpion Chelifer cancroides (Linnaeus, 1758) (Pseudoscorpiones: Cheliferidae).

Assessment of the potential toxicological hazard of the Green Parrot Snake (Leptophis ahaetulla marginatus): Characterization of its venom and venom-delivery system

Snakes are the major group of venomous vertebrates, and the rear-fanged snakes represent the vast majority of species and occur worldwide; however, relatively few studies have characterized their venoms and evaluated their potential hazards for humans. Herein we explore the protein composition and properties of the venom of the rear-fanged Green Parrot Snake, Leptophis ahaetulla marginatus, the most common snake found in the Iguazu National Park (Argentina), as well as the main features of its venom delivery system. This species has venom reminiscent of elapid venoms, composed mainly of components such as 3FTxs, CRiSPs and AChE, but it shows low toxicity toward mammals (LD50 > 20 μg/g mouse). The histology of its Duvernoy's venom gland is similar to that of other colubrids, with serous secretory cells arranged in densely packed secretory tubules. The posterior end of its maxilla exhibits 1–3 blade-shaped and slightly recurved fangs but without grooves. This study provides an initial analysis of the biological role of venom in Leptophis, with implications for potential symptoms that might be anticipated from bites by this species.

A Histological Study on Venom Apparatus of Montivipera xanthina (Gray, 1849) (Serpentes, Viperidae)

This is the first report describing morphological and histological structure of venom apparatus in Montivipera xanthina. The venom gland apparatus of M. xanthina was composed of four distinct parts, main venom gland, primary duct, accessory gland and secondary duct. The main venom gland was composed of acini. The accessory gland was formed by long and ramified tubules. Nine fangs were detected in one half of the upper jaw each at different stage of development. Only one tooth was functional and the eight remaining fangs form a replacement series. The venom apparatus of viperid snakes are the most effective venom-delivery system among vertebrates and have been the focus of scientific interests for many years. Despite this interest, there are few studies including venom-delivery system of venomous snakes. The results presented here may be common among venomous snakes and model of the viperid design of the venom apparatus.

Cabinet of Curiosities: Venom Systems and Their Ecological Function in Mammals, with a Focus on Primates.

Venom delivery systems (VDS) are common in the animal kingdom, but rare amongst mammals. New definitions of venom allow us to reconsider its diversity amongst mammals by reviewing the VDS of Chiroptera, Eulipotyphla, Monotremata, and Primates. All orders use modified anterior dentition as the venom delivery apparatus, except Monotremata, which possesses a crural system. The venom gland in most taxa is a modified submaxillary salivary gland. In Primates, the saliva is activated when combined with brachial gland exudate. In Monotremata, the crural spur contains the venom duct. Venom functions include feeding, intraspecific competition, anti-predator defense and parasite defense. Including mammals in discussion of venom evolution could prove vital in our understanding protein functioning in mammals and provide a new avenue for biomedical and therapeutic applications and drug discovery.

Stingray Envenomation Treatment Recommendations

INTRODUCTION ach year, millions pursue work and leisure activities in the ocean. Thousands of people Eunknowingly step into the ocean for wading or swimming and receive a barbed sting from a normally docile, frightened stingray. This wellcamouflaged creature from the Chondrichthyes class, which includes sharks and skates, lives in temperate oceans around the world. Stingrays are also found in freshwater river systems. In the coastal waters of the United States there are approximately 11 species of stingrays and about 150 worldwide, which are divided into 2 superfamilies, the Dasytoidea, or true stingrays, and the Myliobatoidea. Their sizes range from the size one’s palm to 6.5 feet (2 meters) and weigh up to 800 pounds (350 kg). The longer the stingray spine and the more distally located the spine is on the whiplike tail, the greater the danger to humans from stingray spine injuries. Stingrays are not to be confused with the Manta Ray, which is harmless and does not have a barbed tail. Of these 2 families, the majority of venomous marine stings are from 2 species. From the West Coast there is the Urolophus halleri, also commonly known as the round stingray, with an average length of up to 24 inches, and along the South-East coast there is the southern stingray, Dasyatis Americana, with lengths up to 79 inches. Scuba divers and snorkelers are fortunate when they come across the beautiful stingray. This creature is easily identifiable as it glides through the water while gently moving its dorsoventrally flattened body to feed on shrimp and small fish. Well adapted to its habitat, the stingray can blend easily into the sand. When the stingray is stepped on or encounters danger, it raises its tail, and “strikes” with its sharp pointed spine. This spine is composed of a bonelike cartilaginous material with unique histologic architecture and a venom-delivery system that can be seen on X-ray (Figure 1). On the underside of the spine are venom-secreting glandular cells. The stingray’s sheath covering breaks apart as it enters the

Consuming viscous prey: a novel protein-secreting delivery system in neotropical snail-eating snakes.

BackgroundEfficient venom delivery systems are known to occur only in varanoid lizards and advanced colubroidean snakes among squamate reptiles. Although components of these venomous systems might have been present in a common ancestor, the two lineages independently evolved strikingly different venom gland systems. In snakes, venom is produced exclusively by serous glands in the upper jaw. Within the colubroidean radiation, lower jaw seromucous infralabial glands are known only in two distinct lineages–the basal pareatids and the more advanced Neotropical dipsadines known as “goo-eating snakes”. Goo-eaters are a highly diversified, ecologically specialized clade that feeds exclusively on invertebrates (e.g., gastropod molluscs and annelids). Their evolutionary success has been attributed to their peculiar feeding strategies, which remain surprisingly poorly understood. More specifically, it has long been thought that the more derived Dipsadini genera Dipsas and Sibynomorphus use glandular toxins secreted by their infralabial glands to extract snails from their shells.ResultsHere, we report the presence in the tribe Dipsadini of a novel lower jaw protein-secreting delivery system effected by a gland that is not functionally related to adjacent teeth, but rather opens loosely on the oral epithelium near the tip of the mandible, suggesting that its secretion is not injected into the prey as a form of envenomation but rather helps control the mucus and assists in the ingestion of their highly viscous preys. A similar protein-secreting system is also present in the goo-eating genus Geophis and may share the same adaptive purpose as that hypothesized for Dipsadini. Our phylogenetic hypothesis suggests that the acquisition of a seromucous infralabial gland represents a uniquely derived trait of the goo-eating clade that evolved independently twice within the group as a functionally complex protein-secreting delivery system.ConclusionsThe acquisition by snail-eating snakes of such a complex protein-secreting system suggests that the secretion from the hypertrophied infralabial glands of goo-eating snakes may have a fundamental role in mucus control and prey transport rather than envenomation of prey. Evolution of a functional secretory system that combines a solution for mucus control and transport of viscous preys is here thought to underlie the successful radiation of goo-eating snakes.