Characterization of the Arion vulgaris pedal gland system

Analysis of the adhesive secreting cells of Arion subfuscus: insights into the role of microgels in a tough, fast-setting hydrogel glue

The slug Arion subfuscus produces a tough, highly adhesive defensive secretion. This secretion is a flexible hydrogel that is toughened by a double network mechanism. While synthetic double network gels typically require extensive time to prepare, this slug creates a tough gel in seconds. To gain insight into how the glue forms a double-network hydrogel so rapidly, the secretory apparatus of this slug was analyzed. The goal was to determine how the major components of the glue were distributed and mixed. Most of the glue comes from two types of large unicellular glands; one secretes polyanionic polysaccharides in small, membrane-bound packets, the other secretes proteins that appear to form a cross-linked network. The latter gland shows distinct regions where cross-linking appears to be occurring. These regions are darker, more homogeneous and appear more solid than the rest of the secretory material. The enzyme catalase is highly abundant in these regions, as are basic proteins. These results suggest that a rapid oxidation event occurs in this protein-containing gland, triggering cross-linking before the glue is released. The cross-linked microgels would then join together after secretion to form a granular hydrogel. The polysaccharide-filled packets would be mixed and interspersed among these microgels and may contribute to joining them together. This is an unexpected and highly effective way to form a tough gel rapidly.

Chemical defence of a centipede (Clinopodes flavidus)

Chemical substances are of utmost importance for the biotic interactions between animals and their predators/parasites; many of these semiochemicals are emitted for defence purposes. One of the most deterrent and toxic biogenic substances we know of is hydrogen cyanide, which can be stored by certain insects, millipedes, centipedes and arachnids in the form of stable and less volatile molecules. The aim of this study was to analyse the biology and chemistry of such a defence mechanism in a geophilomorph centipede (Chilopoda). The cyanogenic secretion of Clinopodes flavidus is discharged from the ventral glands, whose glandular units are located in the space between the cuticle and the trunk muscles and do not extend deep into the segment. In addition to hydrogen cyanide, the ventral secretion contains 2-methylpentanoic acid, benzaldehyde, benzoyl cyanide, 2-methyl branched C-9 carboxylic acid (tentatively identified as 2-methyloctanoic acid), methyl 2-phenylacetate, benzoic acid and mandelonitrile as well as four major proteins with a molecular weight of 150, 66.2, 59 and 55 kDa. The correlation between the presence of ventral glands and guarding with the female's ventral side facing away from the eggs and young indicates a functional link between these two traits. We hope that the specificity of the chemical composition of the ventral secretion could serve as a criterion for chemotaxonomy and that the analysis of more species will help to clarify the phylogenetic relationships within the Geophilomorpha.

Particle binding capacity of snail saliva

Gastropods forage with their radula, a thin chitinous membrane with embedded teeth, which scratch across the substrate to lose food particles. During this interaction, the risk of loosening particles is obvious without having a specialized mechanism holding them on the tooth surface. As mucus secretions are essential in molluscan life cycles and the locomotion and attachment gels are known to have an instant high adhesion, we have hypothesized that the saliva could support particle retention during feeding. As adhesion of snail saliva was not studied before, we present here an experimental setup to test its particle-binding capacity using a large land snail (Lissachatina fulica, Stylommatophora, Heterobranchia). This experiment was also applied to the gels produced by the snail foot for comparison and can be potentially applied to various fluids present at a small volume in the future. We found, that the saliva has high particle retention capacity that is comparable to the foot glue of the snail. To gain some insight into the properties of the saliva, we additionally studied it in the scanning electron microscope, estimated its viscosity in a de-wetting experiment, and investigated its elemental composition using energy dispersive X-ray spectroscopy reveling higher contents of Ca, Zn and other potential cross-linkers similar to those found in the glue.

Gastropod Mucus: Interdisciplinary Perspectives on Biological Activities, Applications, and Strategic Priorities

Terrestrial gastropod mucus exhibits multifunctional attributes, enabling diverse applications. This comprehensive review integrates insights across biomedicine, biotechnology, and intellectual property to elucidate the bioactivities, physicochemical properties, and ecological roles of snail and slug mucus. Following an overview of mucus functional roles in gastropods, promising applications are highlighted in wound healing, antimicrobials, biomaterials, and cosmetics, alongside key challenges. An analysis of global patent trends reveals surging innovation efforts to leverage gastropod mucus. Strategic priorities include bioprospecting natural diversity, optimizing stabilization systems, recombinant biosynthesis, and fostering collaboration to translate promising potentials sustainably into impactful technologies. Ultimately, harnessing the remarkable multifunctionality of gastropod mucus holds immense opportunities for transformative innovations in biomedicine, biotechnology, and beyond.

A histochemical and morphological study of the mucus producing pedal gland system in Latia neritoides (Mollusca; Gastropoda; Hygrophila)

The freshwater gastropod Latia neritoides is endemic to the streams of New Zealand's North Island. This species has evolved a unique defence system: it exudes a luminescent mucus thought to deter predators. While the bioluminescence itself has been investigated before, the underlying gland system has remained unstudied and relevant information to understand the defence system has been missing till now. For the release of the glowing mucus of L. neritoides two places of origin were assumed: the lateral foot area or the mantel cavity. In this study the focus was on the first suggestion. To gain insight into the defence system, morphological as well as histochemical analyses were performed involving all secretory gland types in the sub-epithelial foot layer. The results were compared with the foot gland system of Neritina sp., a snail living in a comparable habitat, but using a different survival strategy. The gland types of the two gastropods were compared and their mucus types were investigated. Seven subepithelial gland cell types can be distinguished in the foot region of L. neritoides. Neritina sp., in contrast, has six gland cell types of which three laterally located ones are epithelial. Both species show a pedal gland in the anterior foot region. A striking difference between the species are two prominent subepithelial gland cell types (L1l/L2l) in the lateral foot area of L. neritoides, which are missing in Neritina sp. These gland cells are distributed throughout the entire lateral foot area of L. neritoides and make up about 85% of the mucus gland cells in this area. Defence mucus and trail mucus of L. neritoides show different specificities in lectin staining, but are not equally represented in the gland cell types. Yet, based on the huge size and high density of L1l and L2L, we envision a role for these gland types in the defence system.

Mucus-derived exosome-like vesicles from the Spanish slug (Arion vulgaris): taking advantage of invasive pest species in biotechnology

The slug Arion vulgaris has attracted major attention as one of the worst invasive herbivore pests in Europe and is renowned for the stiff mucus it secretes for locomotion. In this study we focused on the isolation and characterisation of extracellular vesicles, specifically exosomes and exosome-like vesicles, from Arion secretions. We developed a method for slug mucus collection and subsequent vesicle isolation by ultracentrifugation. The isolated vesicles with an average diameter of ~ 100 nm carry abundant proteins and short RNAs, as well as adhesion molecules similar to mammalian galectins. We demonstrated that the slug extracellular vesicles are internalised by plant cells and human cancer cells in in vitro assays and are loadable by bioactive compounds, which makes them an interesting tool for utilisation in biotechnology.