The ultrastructure of the midgut epithelium in millipedes (Myriapoda, Diplopoda)

The venom and telopodal defence systems of the centipede Lithobius forficatus are functionally convergent serial homologues

BACKGROUND

Evolution of novelty is a central theme in evolutionary biology, yet studying the origins of traits with an apparently discontinuous origin remains a major challenge. Venom systems are a well-suited model for the study of this phenomenon because they capture several aspects of novelty across multiple levels of biological complexity. However, while there is some knowledge on the evolution of individual toxins, not much is known about the evolution of venom systems as a whole. One way of shedding light on the evolution of new traits is to investigate less specialised serial homologues, i.e. repeated traits in an organism that share a developmental origin. This approach can be particularly informative in animals with repetitive body segments, such as centipedes.

RESULTS

Here, we investigate morphological and biochemical aspects of the defensive telopodal glandular organs borne on the posterior legs of venomous stone centipedes (Lithobiomorpha), using a multimethod approach, including behavioural observations, comparative morphology, proteomics, comparative transcriptomics and molecular phylogenetics. We show that the anterior venom system and posterior telopodal defence system are functionally convergent serial homologues, where one (telopodal defence) represents a model for the putative early evolutionary state of the other (venom). Venom glands and telopodal glandular organs appear to have evolved from the same type of epidermal gland (four-cell recto-canal type) and while the telopodal defensive secretion shares a great degree of compositional overlap with centipede venoms in general, these similarities arose predominantly through convergent recruitment of distantly related toxin-like components. Both systems are composed of elements predisposed to functional innovation across levels of biological complexity that range from proteins to glands, demonstrating clear parallels between molecular and morphological traits in the properties that facilitate the evolution of novelty.

CONCLUSIONS

The evolution of the lithobiomorph telopodal defence system provides indirect empirical support for the plausibility of the hypothesised evolutionary origin of the centipede venom system, which occurred through functional innovation and gradual specialisation of existing epidermal glands. Our results thus exemplify how continuous transformation and functional innovation can drive the apparent discontinuous emergence of novelties on higher levels of biological complexity.

Effect of gluten on the digestive tract and fat body of Telodeinopus aoutii (Diplopoda)

Adult specimens or larvae of invertebrates used as food for vertebrates are often maintained close to gluten so they might become vectors for cereal proteins. However, the tissues and internal organs can respond differently in animals with different feeding habits. The midgut epithelium might be a first and sufficient barrier preventing uptake and effects of gluten on the whole body, while the fat body is the main organ that accumulates different xenobiotics. Good models for such research are animals that do not feed on gluten-rich products in their natural environment. The project's goal was to investigate alterations in the midgut epithelium and fat body of the herbivorous millipede Telodeinopus aoutii (Diplopoda) and analyze cell death processes activated by gluten. It enabled us to determine whether changes were intensified or reversed by adaptive mechanisms. Adult specimens were divided into control and experimental animals fed with mushrooms supplemented with gluten and analyzed using transmission electron microscopy, flow cytometry, and confocal microscopy. Two organs were isolated for the qualitative and quantitative analysis: the midgut and the fat body. Our study of the herbivorous T. aoutii which does not naturally feed on gluten containing diet showed that continuous and prolonged gluten feeding activates repair processes that inhibit the processes of cell death (apoptosis and necrosis) and induce an increase in cell viability.

Methanogenesis in the Digestive Tracts of the Tropical Millipedes Archispirostreptus gigas (Diplopoda, Spirostreptidae) and Epibolus pulchripes (Diplopoda, Pachybolidae)

Methanogens represent the final decomposition step in anaerobic degradation of organic matter, occurring in the digestive tracts of various invertebrates. However, factors determining their community structure and activity in distinct gut sections are still debated. In this study, we focused on the tropical millipede species Archispirostreptus gigas (Diplopoda, Spirostreptidae) and Epibolus pulchripes (Diplopoda, Pachybolidae), which release considerable amounts of methane. We aimed to characterize relationships between physicochemical parameters, methane production rates, and methanogen community structure in the two major gut sections, midgut and hindgut. Microsensor measurements revealed that both sections were strictly anoxic, with reducing conditions prevailing in both millipedes. Hydrogen concentration peaked in the anterior hindgut of E. pulchripes. In both species, the intestinal pH was significantly higher in the hindgut than in the midgut. An accumulation of acetate and formate in the gut indicated bacterial fermentation activities in the digestive tracts of both species. Phylogenetic analysis of 16S rRNA genes showed a prevalence of Methanobrevibacter spp. (Methanobacteriales), accompanied by a small fraction of so-far-unclassified "Methanomethylophilaceae" (Methanomassiliicoccales), in both species, which suggests that methanogenesis is mostly hydrogenotrophic. We conclude that anoxic conditions, negative redox potential, and bacterial production of hydrogen and formate promote gut colonization by methanogens. The higher activities of methanogens in the hindgut are explained by the higher pH of this compartment and their association with ciliates, which are restricted to this compartment and present an additional source of methanogenic substrates. IMPORTANCE Methane (CH₄) is the second most important atmospheric greenhouse gas after CO₂ and is believed to account for 17% of global warming. Methanogens are a diverse group of archaea and can be found in various anoxic habitats, including digestive tracts of plant-feeding animals. Termites, cockroaches, the larvae of scarab beetles, and millipedes are the only arthropods known to host methanogens and emit large amounts of methane. Millipedes are ranked as the third most important detritivores after termites and earthworms, and they are considered keystone species in many terrestrial ecosystems. Both methane-producing and non-methane-emitting species of millipedes have been observed, but what limits their methanogenic potential is not known. In the present study, we show that physicochemical gut conditions and the distribution of symbiotic ciliates are important factors determining CH₄ emission in millipedes. We also found close similarities to other methane-emitting arthropods, which might be associated with their similar plant-feeding habits.

Bioinspired energy absorbing material designs using additive manufacturing

Nature provides many biological materials and structures with exceptional energy absorption capabilities. Few, relatively simple molecular building blocks (e.g., calcium carbonate), which have unremarkable intrinsic mechanical properties individually, are used to produce biopolymer-bioceramic composites with unique hierarchical architectures, thus producing biomaterial-architectures with extraordinary mechanical properties. Several biomaterials have inspired the design and manufacture of novel material architectures to address various engineering problems requiring high energy absorption capabilities. For example, the microarchitecture of seashell nacre has inspired multi-material 3D printed architectures that outperform the energy absorption capabilities of monolithic materials. Using the hierarchical architectural features of biological materials, iterative design approaches using simulation and experimentation are advancing the field of bioinspired material design. However, bioinspired architectures are still challenging to manufacture because of the size scale and architectural hierarchical complexity. Notwithstanding, additive manufacturing technologies are advancing rapidly, continually providing researchers improved abilities to fabricate sophisticated bioinspired, hierarchical designs using multiple materials. This review describes the use of additive manufacturing for producing innovative synthetic materials specifically for energy absorption applications inspired by nacre, conch shell, shrimp shell, horns, hooves, and beetle wings. Potential applications include athletic prosthetics, protective head gear, and automobile crush zones.

Postembryonic development and differentiation of the midgut in the freshwater shrimp Neocaridina davidi (Crustacea, Malacostraca, Decapoda) larvae

Neocaridina davidi is a freshwater shrimp that originates from Taiwan and is commonly bred all over the word. Like all decapods, which develop indirectly, this species has pelagic larvae that may differ entirely in their morphology and habits from adult specimens. To fill a gap of knowledge about the developmental biology of freshwater shrimps we decided to document the 3D-localization of the midgut inside the body cavity of larval stages of N. davidi using X-ray microtomography, and to describe all structural and ultrastructural changes of the midgut epithelium (intestine and hepatopancreas) which occur during postembryonic development of N. davidi using light and transmission electron microscopy. We laid emphasis on stem cell functioning and cell death processes connected with differentiation. Our study revealed that while the intestine in both larval stages of N. davidi has the form of a fully developed organ, which resembles that of adult specimens, the hepatopancreas undergoes elongation and differentiation. E-cells, which are midgut stem cells, due to their proliferation and differentiation are responsible for the above-mentioned processes. Our study revealed that apoptosis is a common process in both larval stages of N. davidi in the intestine and proximal region of the hepatopancreas. In zoea III, autophagy as a survival factor is activated in order to protect cells against their death. However, when there are too many autophagic structures in epithelial cells, necrosis as passive cell death is activated. The presence of all types of cell death in the midgut in the zoea III stage confirms that this part of the digestive tract is fully developed and functional. Here, we present the first description of apoptosis, autophagy and necrosis in the digestive system of larval stages of Malacostraca and present the first description of their hepatopancreas elongation and differentiation due to midgut stem cell functioning.

Histopatology and HSP70 analysis of the midgut of Rhinocricus padbergi (Diplopoda) in the evaluation of the toxicity of two new metallic-insecticides

Millipedes are organisms of the edaphic fauna and have been used as bioindicators for the evaluation of pollutants in the environment, as they are in constant contact with the soil. This study used the millipede Rhinocricus padbergi as surrogate to evaluate the toxicity of two metallic-insecticides that has been developed for leaf-cutting ants management. Millipedes were exposed in terrariums containing different concentrations of the metallic-insecticides and, after periods of 21 and 90 days, three individuals from each terrarium were dissected in order to remove the midgut, the organ where absorption of nutrients and, consequently, toxic substances occurs. The toxic action of the metallic-insecticides was analyzed through qualitative and semi-quantitative analysis of morphophysiological alterations and by quantitative analysis of the HSP70 stress protein. The results showed that the metallic-insecticides may increase HSP70 labeling, although not at all concentrations and periods of exposure. Histopathological alterations were not significant at any concentration, indicating that the cytoprotective action of HSP70 is able to prevent severe damage to the midgut. It is therefore suggested that the metallic-insecticides are not toxic to the species studied here as no toxicity was observed under the conditions tested. In addition, stress protein localization in midgut helps understand how morphophysiological processes can potentially be affected by pesticide exposure.

Enzymatic activities in the digestive tract of spirostreptid and spirobolid millipedes (Diplopoda: Spirostreptida and Spirobolida)

Millipedes represent a model for the study of organic matter transformation, animal-microbial interactions, and compartmentalisation of digestion. The activity of saccharidases (amylase, laminarinase, cellulase, xylanase, chitinase, maltase, cellobiase, and trehalase) and protease were measured in the midgut and hindgut contents and walls of the millipedes Archispirostreptus gigas and Epibolus pulchripes. Assays done at pH 4 and 7 confirmed activities of all enzymes except xylanase. Hydrolysing of starch and laminarin prevailed. The hindgut of E. pulchripes was shorter, less differentiated. Micro-apocrine secretion was observed only in the midgut of A. gigas. Merocrine secretion was present in midgut and hindgut of E. pulchripes, and in the pyloric valve and anterior hindgut of A. gigas. Alpha-polysaccharidases were mostly active in the midgut content and walls, with higher activity at pH 4. The low activity of amylase (A. gigas) and laminarinase (E. pulchripes) in midgut tissue may indicate their synthesis in salivary glands. Cellulases were found in midgut. Chitinases, found in midgut content and tissue (E. pulchripes) or concentrated in the midgut wall (A. gigas), were more active at an acidic pH. Polysaccharidases were low in hindguts. Protease shows midgut origin and alkaline activity extending to the hindgut in E. pulchripes, whereas in A. gigas it is of salivary gland origin and acid activity restricted to the midgut. Some disaccharidases, with more alkaline activity, showed less apparent midgut-hindgut differences. It may indicate an axial separating of the primary and secondary digestion along the intestinal pH gradient or the presence of enzymes of hindgut parasites.

Autophagy and Apoptosis in the Midgut Epithelium of Millipedes

The process of autophagy has been detected in the midgut epithelium of four millipede species: Julus scandinavius, Polyxenus lagurus, Archispirostreptus gigas, and Telodeinopus aoutii. It has been examined using transmission electron microscopy (TEM), which enabled differentiation of cells in the midgut epithelium, and some histochemical methods (light microscope and fluorescence microscope). While autophagy appeared in the cytoplasm of digestive, secretory, and regenerative cells in J. scandinavius and A. gigas, in the two other species, T. aoutii and P. lagurus, it was only detected in the digestive cells. Both types of macroautophagy, the selective and nonselective processes, are described using TEM. Phagophore formation appeared as the first step of autophagy. After its blind ends fusion, the autophagosomes were formed. The autophagosomes fused with lysosomes and were transformed into autolysosomes. As the final step of autophagy, the residual bodies were detected. Autophagic structures can be removed from the midgut epithelium via, e.g., atypical exocytosis. Additionally, in P. lagurus and J. scandinavius, it was observed as the neutralization of pathogens such as Rickettsia-like microorganisms. Autophagy and apoptosis ca be analyzed using TEM, while specific histochemical methods may confirm it.

Fine structure of the midgut epithelium of Thulinius ruffoi (Tardigrada, Eutardigrada, Parachela) in relation to oogenesis and simplex stage

Thulinius ruffoi is a small freshwater tardigrade that lives in both non-polluted and polluted freshwater environments. As a result of tardigradan body miniaturization, the digestive system is reduced and simplified. It consists of a short fore- and hindgut, and the midgut in the shape of a short tube is lined with a simple epithelium. The midgut epithelium is formed by the digestive cells and two rings of crescent-shaped cells were also detected. The anterior ring is located at the border between the fore- and midgut, while the posterior ring is situated between the mid- and hindgut. The precise ultrastructure of the digestive and crescent-shaped cells was examined using transmission electron microscopy, serial block face scanning electron microscopy and histochemical methods. We analyzed the changes that occurred in the midgut epithelial cells according to oogenesis (the species is parthenogenetic and there were only females in the laboratory culture). We focused on the accumulation of reserve material and the relationship between this and the intensity of autophagy. We concluded that autophagy supplies energy during a natural period of starvation (the simplex stage) and delivers the energy and probably the substances that are required during oogenesis. Apoptosis was not detected in the midgut epithelium of T. ruffoi.

The role of autophagy in the midgut epithelium of Parachela (Tardigrada)

The process of cell death has been detected in the midgut epithelium of four tardigrade species which belong to Parachela: Macrobiotus diversus, Macrobiotus polonicus, Hypsibius dujardini and Xerobiotus pseudohufelandi. They originated from different environments so they have been affected by different stressors: M. polonicus was extracted from a moss sample collected from a railway embankment; M. diversus was extracted from a moss sample collected from a petrol station; X. pseudohufelandi originated from sandy and dry soil samples collected from a pine forest; H. dujardini was obtained commercially but it lives in a freshwater or even in wet terrestrial environment. Autophagy is caused in the digestive cells of the midgut epithelium by different factors. However, a distinct crosstalk between autophagy and necrosis in tardigrades' digestive system has been described at the ultrastructural level. Apoptosis has not been detected in the midgut epithelium of analyzed species. We also determined that necrosis is the major process that is responsible for the degeneration of the midgut epithelium of tardigrades, and "apoptosis-necrosis continuum" which is the relationship between these two processes, is disrupted.

Fine structure of the midgut epithelium in the millipede Telodeinopus aoutii (Myriapoda, Diplopoda) with special emphasis on epithelial regeneration

The midgut of millipedes is composed of a simple epithelium that rests on a basal lamina, which is surrounded by visceral muscles and hepatic cells. As the material for our studies, we chose Telodeinopus aoutii (Demange, 1971) (Kenyan millipede) (Diplopoda, Spirostreptida), which lives in the rain forests of Central Africa. This commonly reared species is easy to obtain from local breeders and easy to culture in the laboratory. During our studies, we used transmission and scanning electron microscopes and light and fluorescent microscopes. The midgut epithelium of the species examined here shares similarities to the structure of the millipedes analyzed to date. The midgut epithelium is composed of three types of cells-digestive, secretory, and regenerative cells. Evidence of three types of secretion have been observed in the midgut epithelium: merocrine, apocrine, and microapocrine secretion. The regenerative cells of the midgut epithelium in millipedes fulfill the role of midgut stem cells because of their main functions: self-renewal (the ability to divide mitotically and to maintain in an undifferentiated state) and potency (ability to differentiate into digestive cells). We also confirmed that spot desmosomes are common intercellular junctions between the regenerative and digestive cells in millipedes.

Toxicity evaluation of vinasse and biosolid samples in diplopod midgut: heat shock protein in situ localization

Large amounts of residues generated by agricultural, urban and industrial activities are dumped daily on the soil. This practice deserves special attention because it causes serious environmental problems. This study evaluated the toxic potential of the sugarcane vinasse, a by-product of the sugar-alcohol industry, and the biosolid, a residue produced by wastewater treatment plants, both widely used as fertilizers. The evaluation was performed through bioassays using a typical soil bioindicator, the diplopod Rhinocricus padbergi. The specimens were exposed to soils containing these residues in concentrations that are compatible with the Brazilian regulation for agricultural use. Semi-quantitative immunolabelling analyses of the stress protein HSP70 were performed on the midgut of the studied diplopods. There was a significant increase in the immunolabelling of HSP70 proteins as a response to xenobiotics from both residues, particularly in regions where the function of the cells is the detoxification of the organ (e.g. the hepatic cell layer and specific regions of the epithelium). Higher immunolabelling was observed in the specimens exposed to vinasse in comparison with the biosolid exposure. This demonstrates that the substances in the tested residues had proteotoxic action in the exposed animals and induced a cytoprotective response, which led to higher stress protein immunolabelling. Therefore, caution is needed for the use of such residues in agriculture.

Ultrastructure of the midgut in Heteroptera (Hemiptera) with different feeding habits

Heteroptera have diverse feeding habits with phytophagous, zoophagous, and haematophagous species. This dietary diversity associated with the monophyly of Heteroptera makes these insects a good object for comparative studies of the digestive tract. This work compares the ultrastructure of the middle midgut region in the phytophagous Coptosoma scutellatum (Plataspidae), Graphosoma lineatum (Pentatomidae), Kleidocerys resedae (Lygaeidae), and zoophagous Rhynocoris iracundus (Reduviidae), Nabis rugosus (Nabidae), and Himacerus apterus (Nabidae), to verify if diet affects midgut cells in phylogenetically related insects. The middle region of the midgut was used for comparison because it is the main site for digestion and absorption of the midgut. The digestive cell ultrastructure was similar in the six species, with features of secretory, absorptive, transport, storage, and excretory cells, suggesting a stronger correlation of middle digestive cell ultrastructure with the phylogeny of these species than with the different heteropteran feeding habits.

Midgut of the diplopod Urostreptus atrobrunneus: structure, function, and redefinition of hepatic cells

Abstract Diplopods are considered important macroarthropods the soil as part of its maintenance and balance. These animals usually do not occur in high densities, but population explosions caused by environmental disturbances, climate changes, and use of pesticides that eliminate possible competitors, have been reported. The millipede Urostreptus atrobrunneus Pierozzi and Fontanetti, 2006 have become a nuisance to humans in infestation sites in urban centers of the state of Sao Paulo, Brazil. As a contribution to the understanding of this potential pest, this study describes the histology, histochemistry, and ultrastructure of the U. atrobrunneus midgut, and presents the redefinition of hepatic cells somewhat controversial in the literature. The region of the midgut is characterized by the absence of a cuticular intima, and composed of a pseudostratified epithelium on a thick basal membrane, followed by a muscle layer, a layer of hepatic cells, lined by an external membrane. The morphology observed in U. atrobrunneus is similar to that reported for other species of diplopods. The hepatic cells have been previously described as randomly without forming a layer, however, the present results clearly demonstrate that these cells form a continuous layer over the whole midgut.

Investigation of the midgut structure and ultrastructure in Cimex lectularius and Cimex pipistrelli (Hemiptera: Cimicidae)

Cimicidae are temporary ectoparasites, which means that they cannot obtain food continuously. Both Cimex species examined here, Cimex lectularius (Linnaeus 1758) and Cimex pipistrelli (Jenyns 1839), can feed on a non-natal host, C. lectularius from humans on bats, C. pipistrelli on humans, but never naturally. The midgut of C. lectularius and C. pipistrelli is composed of three distinct regions-the anterior midgut (AMG), which has a sack-like shape, the long tube-shaped middle midgut (MMG), and the posterior midgut (PMG). The different ultrastructures of the AMG, MMG, and PMG in both of the species examined suggest that these regions must fulfill different functions in the digestive system. Ultrastructural analysis showed that the AMG fulfills the role of storing food and synthesizing and secreting enzymes, while the MMG is the main organ for the synthesis of enzymes, secretion, and the storage of the reserve material. Additionally, both regions, the AMG and MMG, are involved in water absorption in the digestive system of both Cimex species. The PMG is the part of the midgut in which spherites accumulate. The results of our studies confirm the suggestion of former authors that the structure of the digestive tract of insects is not attributed solely to diet but to the basic adaptation of an ancestor.

Gelsolin role in microapocrine secretion

A role of gelsolin in opening the way along the microvilli for secretory vesicles during microapocrine secretion is proposed here. Data obtained with different techniques showed that many digestive enzymes are released by microapocrine secretion in insects. Proteins that might be involved in the machinery of microapocrine secretion were selected from our transcriptomes and literature searches. The proteins were annexin, Complex actin-related proteins 2 and 3 (ARP 2/3) cofilin, fimbrin, gelsolin 1, gelsolin 2, moesin, myosin 1, myosin 6, protein disulphide isomerase 1 (PDI 1), PDI 2 and profilin. The cDNAs coding for annexin, fimbrin, gelsolin 1, myosin 1, PDI 1 and PDI 2 were cloned and their sequences deposited in GenBank. Only gelsolin 1 and myosin 1 are expressed exclusively in the midgut (semiquantitative reverse transcriptase PCR). As myosin 1 may have a structural role in microvilli, gelsolin 1 is the best guess to be involved in the secretory machinery. A truncated recombinant gelsolin 1 was used to generate antibodies with which it was shown labelling inside and around midgut cell microvilli shown in an electron microscope, reinforcing a microvillar role for gelsolin 1. Suppression of gelsolin 1 synthesis by RNA interference prevents secretory vesicles from advancing inside the microvilli, in agreement with its putative role in severing the actin filaments to free the way for the vesicles.

Ultrastructure of the salivary glands in Lithobius forficatus (Myriapoda, Chilopoda, Lithobiidae) according to seasonal and circadian rhythms

The salivary glands (mandibular epidermal glands) of adult males and females of Lithobius forficatus (Myriapoda, Chilopoda) were isolated during spring, summer and autumn. In addition, the organs were isolated at different times of the day - at about 12:00 (noon) and about 00:00 (midnight). The ultrastructure of these organs depending on seasonal and circadian rhythms was analyzed using transmission and scanning electron microscopy and histochemical methods. The paired salivary glands of L. forficatus are situated in the vicinity of the foregut and they are formed by numerous acini that are surrounded by the fat body, hemocytes and tracheolae. The salivary glands are composed of a terminal acinar component and a system of tubular ducts that are lined with a cuticle. The glandular part is composed of secretory epithelial cells that are at various stages of their secretory activity. The saliva that is produced by the secretory cells of the acini is secreted into the salivary ducts, which are lined with a simple epithelium that is based on the non-cellular basal lamina. The ultrastructural variations suggest that salivary glands function differently depending on seasonal rhythms and prepare the animal for overwintering. Therefore, the salivary glands of the centipedes that were analyzed participate in the accumulation of proteins, lipids and polysaccharides during the spring, summer and autumn. Subtle differences in the ultrastructure of the secretory cells of the salivary glands during the circadian cycle must be related to the physiological reactions of the organism. The salivary ducts showed no differences in the specimens that were analyzed during the day/night cycle or during the seasonal cycle.

Compartmentalization of microbial communities that inhabit the hindguts of millipedes

The gut lumen of the arthropod detritivore provides hospitable and multifaceted environments for diverse assemblages of microbes. Many microbes, including trichomycetes fungi, bacteria, and archaea establish stable, adherent communities on the cuticular surface secreted by the hindgut epithelium. Regional differences in the surface topography within the hindgut of a given millipede are reflected in differing and diverse microbial assemblages. The spirostreptid millipede Cambala speobia is a detritivore found on the floors of Texas caves. This millipede species has a very circumscribed distribution in North America and a diet confined to the limited litter that accumulates on floors of these caves while the common julid millipede Cylindroiulus caeruleocinctus, an introduced European species, feeds on the diverse litter found in organic soils throughout North America. In both millipedes, the gut lumina are inhabited along their entire lengths by microbes, with the highest microbial densities in the hindguts. The anterior third of the hindgut with its distinctive six-fold symmetry is lined by cuticle having fine polarized scales, and the posterior-most third is lined by smooth cuticle. Trichomycetes only inhabit the anterior third of the hindgut, and scattered patches of filamentous bacteria along with their smaller adherent microbes occupy the posterior third. The densest populations of microbes inhabit the central region of the hindgut. Over the cuticular surface of this hindgut region, uniformly distributed indentations mark possible channels for nutrient and water exchange between the hindgut lumen and host hemolymph. Films of microbes are adherent to the cuticle that lines the hindgut while those microbes in the remainder of the gut (i.e., foregut + midgut) represent mostly unattached inhabitants.

A novel arrangement of midgut epithelium and hepatic cells implies a novel regulation of the insulin signaling pathway in long-lived millipedes

Nutrients absorbed by the epithelial cells of the millipede midgut are channeled to a contiguous population of hepatic cells where sugars are stored as glycogen. In insects and other arthropods, however, nutrients absorbed by midgut epithelia are first passed across the epithelial basal surface to the hemolymph before storage in fat body. The inter-digitation of cellular processes at the interface of hepatic and midgut epithelial cells offers a vast surface area for exchange of nutrients. At this interface, numerous small vesicles with the dimensions of exosomes (∼30nm) may represent the mediators of nutrient exchange. Longevity and the developmental arrest of diapause are associated with reduced insulin signaling. The long lifespans for which millipedes are known may be attributable to a novel pathway with reduced insulin signaling represented by the novel arrangement of hepatic storage cells and midgut epithelial absorbing cells.

Structural Design Elements in Biological Materials: Application to Bioinspiration

Eight structural elements in biological materials are identified as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the field of biological materials science as they can serve as a toolbox for rationalizing the complex mechanical behavior of structural biological materials and for systematizing the development of bioinspired designs for structural applications. They are employed to improve the mechanical properties, namely strength, wear resistance, stiffness, flexibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, weight reduction). The structural elements identified are: fibrous, helical, gradient, layered, tubular, cellular, suture, and overlapping. For each of the structural design elements, critical design parameters are presented along with constitutive equations with a focus on mechanical properties. Additionally, example organisms from varying biological classes are presented for each case to display the wide variety of environments where each of these elements is present. Examples of current bioinspired materials are also introduced for each element.

Structure and Ultrastructure of the Endodermal Region of the Alimentary Tract in the Freshwater Shrimp Neocaridina heteropoda (Crustacea, Malacostraca)

The freshwater shrimp Neocaridina heteropoda (Crustacea, Malacostraca, Decapoda) originates from Asia and is one of the species that is widely available all over the world because it is the most popular shrimp that is bred in aquaria. The structure and the ultrastructure of the midgut have been described using X-ray microtomography, transmission electron microscopy, light and fluorescence microscopes. The endodermal region of the alimentary system in N. heteropoda consists of an intestine and a hepatopancreas. No differences were observed in the structure and ultrastructure of males and females of the shrimp that were examined. The intestine is a tube-shaped organ and the hepatopancreas is composed of two large diverticles that are divided into the blind-end tubules. Hepatopancreatic tubules have three distinct zones - proximal, medial and distal. Among the epithelial cells of the intestine, two types of cells were distinguished - D and E-cells, while three types of cells were observed in the epithelium of the hepatopancreas - F, B and E-cells. Our studies showed that the regionalization in the activity of cells occurs along the length of the hepatopancreatic tubules. The role and ultrastructure of all types of epithelial cells are discussed, with the special emphasis on the function of the E-cells, which are the midgut regenerative cells. Additionally, we present the first report on the existence of an intercellular junction that is connected with the E-cells of Crustacea.