The genus Armadillo Latreille, 1802 (Oniscidea, Armadillidae) from Cyprus, with descriptions of two new species.

The present work aims to morphologically characterize the species of Armadillo from Cyprus. Moreover, two new species of the genus are described, A. konstantinoui sp. nov. from several places along the island, and A. karametae sp. nov. from Pafos region. The circum-Mediterranean species A. officinalis is also redescribed.

More than one way to smell ashore - Evolution of the olfactory pathway in terrestrial malacostracan crustaceans.

Crustaceans provide a fascinating opportunity for studying adaptations to a terrestrial lifestyle because within this group, the conquest of land has occurred at least ten times convergently. The evolutionary transition from water to land demands various morphological and physiological adaptations of tissues and organs including the sensory and nervous system. In this review, we aim to compare the brain architecture between selected terrestrial and closely related marine representatives of the crustacean taxa Amphipoda, Isopoda, Brachyura, and Anomala with an emphasis on the elements of the olfactory pathway including receptor molecules. Our comparison of neuroanatomical structures between terrestrial members and their close aquatic relatives suggests that during the convergent evolution of terrestrial life-styles, the elements of the olfactory pathway were subject to different morphological transformations. In terrestrial anomalans (Coenobitidae), the elements of the primary olfactory pathway (antennules and olfactory lobes) are in general considerably enlarged whereas they are smaller in terrestrial brachyurans compared to their aquatic relatives. Studies on the repertoire of receptor molecules in Coenobitidae do not point to specific terrestrial adaptations but suggest that perireceptor events - processes in the receptor environment before the stimuli bind - may play an important role for aerial olfaction in this group. In terrestrial members of amphipods (Amphipoda: Talitridae) as well as of isopods (Isopoda: Oniscidea), however, the antennules and olfactory sensilla (aesthetascs) are largely reduced and miniaturized. Consequently, their primary olfactory processing centers are suggested to have been lost during the evolution of a life on land. Nevertheless, in terrestrial Peracarida, the (second) antennae as well as their associated tritocerebral processing structures are presumed to compensate for this loss or rather considerable reduction of the (deutocerebral) primary olfactory pathway. We conclude that after the evolutionary transition from water to land, it is not trivial for arthropods to establish aerial olfaction. If we consider insects as an ingroup of Crustacea, then the Coenobitidae and Insecta may be seen as the most successful crustacean representatives in this respect.

The origin of microscopic spheres on the exoskeleton of the woodlouse Porcellionides pruinosus (Crustacea: Isopoda) and their effect on its hydrophobicity.

The dorsal surface of the woodlouse Porcellionides pruinosus is covered with minute spheres, providing its characteristic powdered appearance. Little has been known about their composition and formation. A previously suggested function of these structures was to increase the hydrophobicity of the cuticular surface. We studied the ultrastructure, composition and formation of the spheres as well as tested whether they affect the hydrophobicity of the cuticle. We determined the composition of the spheres with histochemistry and scanning electron microscopy after applying various chemicals. We studied the process of their formation with transmission electron microscopy and assessed the hydrophobicity of the cuticle by measuring contact angles of water droplets with its surface. Our results show that the spheres are largely organic. They contain proteins and glycoproteins or possibly polysaccharides without detectable amounts of lipids. By studying the formation of the spheres we established that they are epicuticular structures. They are deposited early in the premolt stage of the molt cycle around branching extensions of epidermal cells. The sphere-covered cuticle of P. pruinosus is more hydrophobic than the cuticle with experimentally removed spheres as well as the scale-covered cuticle in a related species.

Evaluation of trace element contamination using Armadillo officinalis Duméril, 1816 (Crustacea, Isopoda) as a tool: An ultrastructural study.

To estimate trace element bioaccumulation in Armadillo officinalis, specimens were collected from Ghar El Melh lagoon then exposed for 3 weeks in contaminated sediments with copper, zinc, and cadmium. From the first week until the end of the experiment, a decrease in A. officinalis growth related to the increase of Cd concentration in the sediment was recorded. However, a mass gain was highlighted under Cu and Zn exposures. At the end of experiment, body metal concentrations were measured using flame atomic emission spectrometry. Results of the bioaccumulation factor showed that the species could be considered as a macroconcentrator of copper (BAF > 2) and a deconcentrator of zinc (BAF < 2). Microscopy observations of hepatopancreas cells showed morphological and histological changes even at the lowest concentration. They consisted in the microvillus border destruction, lipid droplets modifications, trace element accumulation, and the condensation of the majority of cellular organelles. The degree of these alterations was found to be dose-dependent. Through these results, the isopod A. officinalis could be used as relevant monitor organisms for soil metal contamination.

Ultrastructural differentiation of plasma membrane and cell junctions in the hindgut cells is synchronized with key developmental transitions in Porcellio scaber.

Differentiation of transporting epithelial cells during development of animal organisms includes remodelling of apical and basal plasma membranes to increase the available surface for transport and formation of occluding junctions, which maintain a paracellular diffusion barrier. This study provides a detailed ultrastructural analysis of apical and basal plasma membrane remodelling and cell junction formation in hindgut cells during late embryonic and early postembryonic development of the crustacean Porcellio scaber. Hindgut cells in late-stage embryos are columnar with flat apical and basal plasma membranes. In early-stage marsupial mancae the hindgut cells begin to acquire their characteristic dome shape, the first apical membrane folding is evident and the septate junctions expand considerably, all changes being probably associated with the onset of active feeding. In postmarsupial mancae the apical labyrinth is further elaborated and the septate junctions are expanded. This coincides with the transition to an external environment and food sources. First basal infoldings appear in the anterior chamber of early-stage marsupial mancae, but in the papillate region they are mostly formed in postmarsupial mancae. In molting late-stage marsupial mancae, the plasma membrane acquires a topology characteristic of cuticle-producing arthropod epithelia and the septate junctions are considerably reduced.

Tailored disorder in calcite organization in tergite cuticle of the supralittoral isopod Tylos europaeus Arcangeli, 1938.

The crustacean cuticle forms skeletal elements consisting of chitin-protein fibrils reinforced by amorphous and crystalline calcium carbonate and phosphate minerals. The edges of skeletal elements are of particular interest. They are subject to repeated strain and stress because they form transitions to the arthrodial membranes connecting them. These allow for relative movements of skeletal elements. In this study, we investigate structure, chemical composition, mineral organization and local mechanical properties of the anterior and posterior edges of the tergite cuticle in the conglobating beach isopod Tylos europaeus and compare these with the protective dorsal region of the tergites. The distribution of mineral phases at the edges resembles that of dorsal regions of the tergites. At the transition with the unmineralized arthrodial membrane the calcite containing distal exocuticle is replaced by epicuticular material and the subjacent cuticular layers containing amorphous calcium carbonate become enriched with amorphous calcium phosphate. At the edges, the local elastic modulus and hardness values are significantly lower compared to dorsal regions of the tergite cuticle, for both, the calcite and the amorphous mineral containing layers. The calcite within the tergite cuticle is assembled in different texture patterns: (i) almost random co-orientation, (ii) almost single crystalline calcite, and (iii) a graded organization. Calcite organization and co-orientation strength is highly variable, not only on very few tens of micrometres, but also between regions with different skeletal functionality. Our results show that besides structure and composition, patterns of calcite organization contribute to the hierarchical architecture and functionality of biological composites.

Development of calcium bodies in Hylonsicus riparius (Crustacea: Isopoda).

Calcium bodies are internal epithelial sacs found in terrestrial isopods of the family Trichoniscidae that contain a mineralized extracellular matrix that is deposited and resorbed in relation to the molt cycle. Calcium bodies in several trichoniscids are filled with bacteria, the function of which is currently unknown. The woodlouse Hyloniscus riparius differs from other trichoniscids in that it possesses two different pairs of calcium bodies, the posterior pair being filled with bacteria and the anterior pair being devoid of bacteria. We explored the development of these organs and bacterial colonization of their lumen during the postmarsupial development with the use of optical clearing and whole-body confocal imaging of larval and juvenile stages. Our results show that calcium bodies are formed as invaginations of the epidermis in the region of intersegmental membranes during the postmarsupial development. The anterior pair of calcium bodies is generated during the first postmarsupial manca stage, whereas the posterior calcium bodies first appear in juveniles and are immediately colonized by bacteria, likely through a connection between the calcium body lumen and the body surface. Mineral is deposited in calcium bodies as soon as they are present.

Exoskeletal cuticle of cavernicolous and epigean terrestrial isopods: A review and perspectives.

Comparative ultrastructural studies of the integument in terrestrial isopod crustaceans show that specific environmental adaptations of different eco-morphotypes are reflected in cuticle structure. The biphasic molting in isopods is a valuable experimental model for studies of cuticular matrix secretion and degradation in the same animal. The aim of this review is to show structural and functional adaptations of the tergal cuticle in terrestrial isopods inhabiting cave habitats. Exoskeletal cuticle thickness, the number of cuticular layers, epicuticle structure, mineralization, pigmentation and complexity of sensory structures are compared, with greater focus on the well-studied cave trichoniscid Titanethes albus. A large number of thinner cuticular layers in cave isopods compared to fewer thicker cuticular layers in related epigean species of similar body-sizes is explained as a specific adaptation to the cavernicolous life style. The epicuticle structure and composition are compared in relation to their potential waterproofing capacity in different environments. Cuticle mineralization is described from the functional point of view as well as from the aspect of different calcium storage sites and calcium dynamics during the molt cycle. We also discuss the nature and reduction of pigmentation in the cave environment and outline perspectives for future research.

Egg envelopes of Armadillidium vulgare (Latreille, 1804) (Crustacea, Isopoda Oniscidea): Ultrastructure and lectins binding.

The ultrastructural study carried out on (a) oocytes of Armadillidium vulgare during vitellogenesis, (b) mature eggs taken from the ovaries during the parturial moult of the posterior half of the body, and (c) fertilized eggs collected within a few hours of their release into the brood pouch, has clearly demonstrated that before the fertilization the chorion is the only envelope present in the egg of oniscidean isopods. In the mature eggs, the chorion appears as a uniformly electron-dense lamina, about 0.4-0.5 µm thick, which does not show any specialized area. A second envelope, described by other authors as vitelline envelope, is formed above the oolemma only right after fertilization and appears separated from the chorion by a space full of liquid. The ways in which the genesis of this envelope is realized are not yet clear; it could be interpreted rather as a fertilization membrane. The investigations carried out with the aid of a battery of FITC-lectins have highlighted the presence at the chorion surface of unfertilized eggs of various saccharide residues distributed in uniform way. No significant change was observed in the pattern of lectins binding to the chorion of eggs taken from the brood pouch, thus demonstrating how, after the fertilization, no significant rearrangement in the distribution of saccharide residues present on the egg surface occurs in A. vulgare. The ways in which, therefore, the recognition, the binding and the entry of the peculiar sperm of oniscidean isopods into the egg occur, still remain all to be deciphered. Microsc. Res. Tech. 79:792-798, 2016. © 2016 Wiley Periodicals, Inc.

'Venus trapped, Mars transits': Cu and Fe redox chemistry, cellular topography and in situ ligand binding in terrestrial isopod hepatopancreas.

Woodlice efficiently sequester copper (Cu) in 'cuprosomes' within hepatopancreatic 'S' cells. Binuclear 'B' cells in the hepatopancreas form iron (Fe) deposits; these cells apparently undergo an apocrine secretory diurnal cycle linked to nocturnal feeding. Synchrotron-based µ-focus X-ray spectroscopy undertaken on thin sections was used to characterize the ligands binding Cu and Fe in S and B cells of Oniscus asellus (Isopoda). Main findings were: (i) morphometry confirmed a diurnal B-cell apocrine cycle; (ii) X-ray fluorescence (XRF) mapping indicated that Cu was co-distributed with sulfur (mainly in S cells), and Fe was co-distributed with phosphate (mainly in B cells); (iii) XRF mapping revealed an intimate morphological relationship between the basal regions of adjacent S and B cells; (iv) molecular modelling and Fourier transform analyses indicated that Cu in the reduced Cu(+) state is mainly coordinated to thiol-rich ligands (Cu-S bond length 2.3 Å) in both cell types, while Fe in the oxidized Fe(3+) state is predominantly oxygen coordinated (estimated Fe-O bond length of approx. 2 Å), with an outer shell of Fe scatterers at approximately 3.05 Å; and (v) no significant differences occur in Cu or Fe speciation at key nodes in the apocrine cycle. Findings imply that S and B cells form integrated unit-pairs; a functional role for secretions from these cellular units in the digestion of recalcitrant dietary components is hypothesized.

Influence of season and site location on European cultured sea bass parasites in Corsican fish farms using indicator species analysis (IndVal).

The parasites of 536 European sea bass, Dicentrarchus labrax, were studied between January 2012 and December 2013 in six Corsican fish farms. The indicator value (IndVal) method, which combines measures of fidelity and specificity, has been used in this study. Because of its resilience to changes in abundance, IndVal is a particularly effective tool for ecological bioindicator. The IndVal method showed how season can influence the occurrence of parasite species in cultured sea bass and also identified parasites as bioindicators relative to fish farm location. The combination of specificity and fidelity highlighted several parasite species as significant indicators. A randomization test identified five parasite species as having a significant indicator value for season (the monogenean Diplectanum aequans; the copepods Lernanthropus kroyeri and Caligus minimus; the isopod Ceratothoa oestroides, and the myxosporidian Ceratomyxa labracis). If gills parasites are compared, they can be seen to be indicator species for two different seasons. The only Monogenea species D. aequans had fidelity and specificity more pronounced in winter, whereas both copepod species and the Isopoda revealed highest rates of infestation corresponding with an increase of water temperature. Four species have a significant indicator value for site location (D. aequans, L. kroyeri, C. minimus, and C. oestroides). The fact that the farm 6 was isolated on the east coast of Corsica may not have allowed the parasite to infect other farms. The presence of copepods on a single farm can also be explained according to salinity variations. Data for species composition and infection levels should help to improve the monitoring and management of parasitism in cultured sea bass populations.

Hierarchical organization of the cuticle of the subsocial desert isopod, Hemilepistus reaumurii.

The crustacean cuticle is a hierarchically organised material which provides protection and sites for muscle attachment. The physical properties of this exoskeleton envelope are adapted to the function and the eco-physiological requirements of the species. This paper aimed to study, using the TEM, the structure of the tubercle and the tergite cuticle of the arid species Hemilepistus reaumurii in a comparison with a subhumid isopod in order to relate some peculiar features to an adaptive process to environmental constraints. Results showed that wild H. reaumurii cuticles were twice as thick in comparison with Porcellio variabilis which is a subhumid zone isopod. It is suggested therefore that the thick cuticle of wild H. reaumurii can be an adaptation to terrestrial life and a protection against osmotic stress and water loss in an arid environment. In addition the inside of the tubercle showed a high number of lipid droplets stacked into an adipose tissue which suggest that tubercles were used for storage for nutritive material in wild H. reaumurii.

Sound production in the aquatic isopod Cymodoce japonica (Crustacea: Peracarida).

A vast variety of acoustic behaviors and mechanisms occur in arthropods. Sound production, in particular, in insects and decapod crustaceans has been well documented. However, except for a brief, anecdotal statement, there has been no report on the acoustic behavior of aquatic isopods. We present the first empirical evidence in aquatic Isopoda that males of Cymodoce japonica produce sound by stridulation, or the rubbing together of body parts. Sound production was associated with tail-lifting behavior, suggesting that stridulation occurs on thoracic and/or abdominal somites. Acoustic analysis revealed that syllable length was similar throughout the stridulation, at a mode of 2500-3000 Hz. With a scanning electron microscope, we identified file-like structures on the inner surface of the dorsal exoskeleton. Each file consisted of 188 ± 11.1 ridges at about 0.5 µm intervals; the theoretical frequency (number of ridges per syllable length) was estimated to be 2208-3646 Hz. This finding suggests that the stridulation sounds arose from these structures. Laboratory observations show that stridulation may play a role in the threatening of other males in the context of territorial and/or reproductive competitions.

Testis follicles ultrastructure of three species of terrestrial isopods (Crustacea, Isopoda Oniscidea).

The aim of the research, carried out on three species of terrestrial isopods - Armadillidium granulatum, Halophiloscia hirsuta and Trichoniscus alexandrae - is to bring a first consistent contribution to the knowledge of the ultrastructural organization of the testis follicles. The testis follicles are seat of a remarkable dynamic activity of their cell components (somatic cells and germ cells) that results in a continuous variation, related to the trend of spermatogenesis, of their morphology, organization and of the relationships between the two cell populations. The somatic cells, known in literature as follicular cells, nurse cells or Sertoli cells, are arranged at the periphery of the follicle to form an epithelial layer of variable thickness resting on a thin basal lamina in turn surrounded by a discontinuous network of muscle cells. In A. granulatum and H. hirsuta, two types of Sertoli cells are present: a first type, the nurse cells, envelop the spermatids in cavities within their cytoplasm and through their secretion activity play a fundamental role in the formation of the spermatophores; moreover, they phagocytizes the residual cytoplasm of spermatids. A second type of Sertoli cells shows features that leave clearly identify its supporting role to the spermatophores in formation. In T. alexandrae, instead, only one type of Sertoli cells, the nurse cell, is present, whose features are widely superimposable to those observed in the other two species. Moreover, two septa of Sertoli cells depart from the periphery of the testis follicle to constitute an articulated compartmentalization of the follicle itself, probably targeted to realize at its inside a series of microenvironments functionally diversified in order to meets the needs of the different stages of the spermatogenic cycle.

A new genus for Entophilus mirabiledictu Markham & Dworschak, 2005 (Crustacea: Isopoda: Cryptoniscoidea: Entophilidae) with remarks on morphological support for epicaridean superfamilies based on larval characters.

A detailed reexamination of male and female Entophilus mirabiledictu Markham & Dworschak, 2005 (an endoparasite of callianassid shrimp), resulted in recognition of seven female and five male characters that separate the species from its sole congener, E. omnitectus Richardson, 1903 (an endoparasite of munidid squat lobsters). These characters show that the two species are so different as to warrant E. mirabiledictu being placed in its own genus within the Entophilidae. Additionally, a review of the morphological features of entophilid cryptoniscus larvae led to the finding that the number of flagellar segments on the second antenna offers morphological support for a recent molecular phylogeny of epicaridean taxa that rearranged the component families within the two recognised superfamilies. This work highlights the power of using larval characters in testing hypotheses on the evolutionary relationships of epicaridean taxa.

Pathogenesis, tissue distribution and host response to Rhabdochlamydia porcellionis infection in rough woodlouse Porcellio scaber.

Rhabdochlamydia porcellionis is a known intracellular pathogen in digestive glands of the terrestrial isopod crustacean Porcellio scaber. To describe the pathogenesis, tissue distribution and host response to R. porcellionis, we conducted microscopic observations and localization of infection in tissues by Fluorescent In Situ Hybridization (FISH). Digestive glands were confirmed as the primary site of infection. From there, R. porcellionis disseminates either through the apical membrane of infected cells into the lumen of digestive glands and further throughout the digestive tract or into the surrounding hemocoel by rupture of the basal membrane and lamina of infected digestive gland cells. Once in the hemocoel, R. porcellionis infects hindgut cells, hemocytes and hemopoetic tissues while the ventral nerve cord and gonads seem to be devoid of infection despite the presence of rhabdochlamydia on the surface of these organs. The host response to R. porcellionis includes aggregation of hemocytes around the infected cells and formation of multilayered melanized nodules exhibiting endogenous fluorescence. The structure of nodules is asymmetric when hemocytes are deposited on the basal side of infected gut and digestive glands cells, or symmetric, when nodules entrapping clusters of rhabdochlamydiae are deposited on other organs in the hemocoel. The study also revealed a high prevalence of infection in P. scaber populations (up to 27%) and confirmed its detrimental effect on the host. Although agility, behavior and molting cycle of infected animals appear unaffected, in the later stages R. porcellionis infection manifests as severe damage to the digestive system and decreased feeding, which eventually lead to the death of the host organism.

Function-related adaptations of ultrastructure, mineral phase distribution and mechanical properties in the incisive cuticle of mandibles of Porcellio scaber Latreille, 1804.

In terrestrial isopods the mandibles consist of a corpus carrying strong muscle tissue, and a pars incisiva (PI) that cuts dry leaves into smaller ingestible pieces. We studied the cuticle of the PI of Porcellio scaber in order to understand region-dependent differences in its ultrastructure, composition, and the resulting mechanical properties, employing several microscopic and analytical techniques as well as nanoindentation experiments. The cuticle of the incisive tip is not mineralized and consists of an unusually thick epicuticle containing thin fibrils, two subjacent cuticular layers, and a central core containing fibrils of different orientation, either longitudinal or circumferential. A thick epicuticle of the middle region just behind the tip projects long epicuticular extensions into the subjacent endocuticle, likely to prevent delamination. A distinct exocuticular layer is lacking in the middle region. Most chitin-protein fibrils within the endocuticle are oriented in parallel pointing towards the tip. Surprisingly, the middle region is mineralized by amorphous calcium phosphate (ACP) only. Near the base, ACP is successively replaced by amorphous calcium carbonate and calcite is restricted to a distal layer in the base. At the transition between middle and base, the epicuticle forms a hybrid material containing fibrils of the exocuticle. Nanoindentation experiments reveal an increase of the stiffness and hardness from the tip towards the base and significantly higher values on transversal in comparison to longitudinal planes. The results suggest that ultrastructure and composition are adapted for conveying high forces from a rather thin cutting edge to the stable base of the PI.

Exoskeletal cuticle differentiation during intramarsupial development of Porcellio scaber (Crustacea: Isopoda).

Exoskeletal crustacean cuticle is a calcified apical extracellular matrix of epidermal cells, illustrating the chitin-based organic scaffold for biomineralization. Studies of cuticle formation during molting reveal significant dynamics and complexity of the assembly processes, while cuticle formation during embryogenesis is poorly investigated. This study reveals in the terrestrial isopod Porcellio scaber, the ultrastructural organization of the differentiating precuticular matrices and exoskeletal cuticles during embryonic and larval intramarsupial development. The composition of the epidermal matrices was obtained by WGA lectin labelling and EDXS analysis. At least two precuticular matrices, consisting of loosely arranged material with overlying electron dense lamina, are secreted by the epidermis in the mid-stage embryo. The prehatching embryo is the earliest developmental stage with a cuticular matrix consisting of an epicuticle and a procuticle, displaying WGA binding and forming cuticular scales. In newly hatched marsupial larva manca, a new cuticle is formed and calcium sequestration in the cuticle is evident. Progression of larval development leads to the cuticle thickening, structural differentiation of cuticular layers and prominent cuticle calcification. Morphological characteristics of exoskeleton renewal in marsupial manca are described. Elaborated cuticle in marsupial larvae indicates the importance of the exoskeleton in protection and support of the larval body in the marsupium and during the release of larvae in the external environment.

Olfactory projection neuron pathways in two species of marine Isopoda (Peracarida, Malacostraca, Crustacea).

The neuroanatomy of the olfactory pathway has been intensely studied in many representatives of Malacostraca. Nevertheless, the knowledge about bilateral olfactory integration pathways is mainly based on Decapoda. Here, we investigated the olfactory projection neuron pathway of two marine isopod species, Saduria entomon and Idotea emarginata, by lipophilic dye injections into the olfactory neuropil. We show that both arms of the olfactory globular tract form a chiasm in the center of the brain, as known from several other crustaceans. Furthermore, the olfactory projection neurons innervate both the medulla terminalis and the hemiellipsoid body of the ipsi- and the contralateral hemisphere. Both protocerebral neuropils are innervated to a comparable extent. This is reminiscent of the situation in the basal decapod taxon Dendrobranchiata. Thus, we propose that an innervation by the olfactory globular tract of both the medulla terminalis and the hemiellipsoid body is characteristic of the decapod ground pattern, but also of the ground pattern of Caridoida.

Ultrastructure and mineral composition of the cornea cuticle in the compound eyes of a supralittoral and a marine isopod.

The cuticle of the cornea in Crustacea is an interesting example of a composite material compromising between two distinct functions. As part of the dioptric apparatus of the ommatidia within the complex eye it forms transparent micro-lenses that should as well maintain the mechanical stability of the head capsule. We analyzed the ultrastructure and composition of the isopod cornea cuticle of the terrestrial species Ligia oceanica and the marine Sphaeroma serratum. We used a variety of tissue preparation methods, electron microscopic techniques as well as electron microprobe analysis and Raman spectroscopic imaging. The results reveal various structural adaptations that likely increase light transmission. These are an increase in the thickness of the epicuticle, a reduction of the thickness of the outer layer of calcite, a spatial restriction of pore canals to interommatidial regions, and, for S. serratum only, an increase in calcite crystal size. In both species protein-chitin fibrils within the proximal exocuticle form a peculiar reticular structure that does not occur within the cuticle of the head capsule. In L. oceanica differential mineralization results in a spherically shaped interface between mineralized and unmineralized endocuticle, likely an adaptation to increase the refractive power of the cornea maintaining the mechanical stability of the cuticle between the ommatidia. The results show that the habitat and differences in the general structure of the animal's cuticle affect the way in which the cornea is adapted to its optical function.