Eye Morphology Research Articles

Use of Visual Information by Ant Species Occurring in Similar Urban Anthropogenic Environments.

Many insects, including ants, are known to respond visually to conspicuous objects. In this study, we compared orientation in an arena containing only a black target beacon as local information in six species of ants of widely varying degree of phylogenic relatedness, foraging strategy, and eye morphology (Aphaenogaster, Brachyponera, Camponotus, Formica, and two Lasius spp.), often found associated in similar urban anthropogenic habitats. Four species of ants displayed orientation toward the beacon, with two orienting toward it directly, while the other two approached it via convoluted paths. The two remaining species did not show any orientation with respect to the beacon. The results did not correlate with morphological parameters of the visual systems and could not be fully interpreted in terms of the species' ecology, although convoluted paths are linked to higher significance of chemical signals. Beacon aiming was shown to be an innate behavior in visually naive Formica workers, which, however, were less strongly attracted to the beacon than older foragers. Thus, despite sharing the same habitats and supposedly having similar neural circuits, even a very simple stimulus-related behavior in the absence of other information can differ widely in ants but is likely an ancestral trait retained especially in species with smaller eyes. The comparative analysis of nervous systems opens the possibility of determining general features of circuits responsible for innate and possibly learned attraction toward particular stimuli.

Morphological, Immunohistochemical, and Ultrastructural Studies of the Donkey's Eye with Special Reference to the AFGF and ACE Expression.

The donkey is mainly used as a working animal for riding and pack transport, as well as for dairy and meat production. Eye afflictions are common in donkeys, thus requiring a detailed study. A few studies had focused on the donkey's eye, and most of them had considered it, merely, a horse's eye. This study aimed to investigate the anatomy, histology, ultrastructure, and immunohistochemical features of the donkey's eye. The results were recorded and compared to those of horses in certain dimensions. Unlike horses, the donkey's eye is more circular in the contour of the cornea, has smaller lenticular thickness, and has longer anterior and vitreous chambers. Positive immunoreactivity to acidic fibroblast growth factor in the basal cell layers of the cornea was observed, indicating their role in cell differentiation and the renewal of the epithelium. Moreover, the corneal keratocytes expressed angiotensin-converting enzyme, which plays a role in corneal homeostasis and wound healing. Additionally, telocytes, hyalocytes, and other immune cells were observed within the iris and ciliary processes. Hence, this work is an updated detailed study of the morphology and ultrastructure of the donkey's eye and reveals some similarities and dissimilarities to the horse's eyes, which should be considered in clinical practice.

Association analyses of rare variants identify two genes associated with refractive error.

PurposeGenetic variants identified through population-based genome-wide studies are generally of high frequency, exerting their action in the central part of the refractive error spectrum. However, the power to identify associations with variants of lower minor allele frequency is greatly reduced, requiring considerable sample sizes. Here we aim to assess the impact of rare variants on genetic variation of refractive errors in a very large general population cohort.MethodsGenetic association analyses of non-cyclopaedic autorefraction calculated as mean spherical equivalent (SPHE) used whole-exome sequence genotypic information from 50,893 unrelated participants in the UK Biobank of European ancestry. Gene-based analyses tested for association with SPHE using an optimised SNP-set kernel association test (SKAT-O) restricted to rare variants (minor allele frequency < 1%) within protein-coding regions of the genome. All models were adjusted for age, sex and common lead variants within the same locus reported by previous genome-wide association studies. Potentially causal markers driving association at significant loci were elucidated using sensitivity analyses by sequentially dropping the most associated variants from gene-based analyses.ResultsWe found strong statistical evidence for association of SPHE with the SIX6 (p-value = 2.15 x 10−10, or Bonferroni-Corrected p = 4.41x10-06) and the CRX gene (p-value = 6.65 x 10−08, or Bonferroni-Corrected p = 0.001). The SIX6 gene codes for a transcription factor believed to be critical to the eye, retina and optic disc development and morphology, while CRX regulates photoreceptor specification and expression of over 700 genes in the retina. These novel associations suggest an important role of genes involved in eye morphogenesis in refractive error.ConclusionThe results of our study support previous research highlighting the importance of rare variants to the genetic risk of refractive error. We explain some of the origins of the genetic signals seen in GWAS but also report for the first time a completely novel association with the CRX gene.

In vivo depth-resolved morphological analysis of compound eye dioptric system using full-field optical coherence tomography

Presence of a range of insects with different shape, size, and structural morphology of compound eye reveals the diverse pathways adopted by the nature striving to develop a flawless vision under given set of constraints. Exploration of various compound eyes allows researchers to understand better the various stages of visual system development in insects. By far, the most frequently used techniques for the investigation of structural morphology of a compound eye are scanning electron microscopy, transmission electron microscopy, microcomputed tomography, and histology. The nature of implementation of these techniques restricts in vivo studies, and also the requirements for a complicated and costly setup put limitations on its availability at small research facilities. Despite the widespread acceptance of the optical coherence tomography (OCT) as a standard tool for the various ophthalmological investigations, reports on compound eye study using OCT are uncommon. We demonstrate the application of a full-field OCT (FF-OCT) system for depth-resolved structural imaging and morphological analysis of the compound eye dioptric system. We report the application of a time-domain FF-OCT system for depth-resolved en face and three dimensional in vivo imaging of dragonfly’s prominent compound eye with resolutions of 2.8 and 7.2 μm in lateral and axial directions, respectively. The study shows the effectiveness of the FF-OCT approach for label-free and rapid structural morphology analysis of compound eyes. The results have been compared with the histology results reported in literature.

A freeze-substitution approach with solvent-based glyoxal fixative to prevent distortion of ocular structures

ABSTRACT Investigating the function of delicate mammalian eyes often requires chemical fixation, histological sectioning, immunohistochemistry (IHC) and in situ hybridization (ISH). One of the long-standing challenges in the ocular histology field is the limited success of maintaining intact morphology via cryo- or paraffin procedures. Although our latest protocol significantly improved the morphology of mouse eyeball sections, the window technique is time-consuming and requires extensive practice to avoid damage while making windows. In this study, we present a novel glyoxal fixative that is suitable for a freeze-substitution approach to improve both morphology and molecular target preservation of mouse eyes. The method prevents morphology distortion in all tested eyeballs. Therefore, it suits a variety of research needs from morphological examination to investigation of single-molecule RNA expression, using hematoxylin and eosin (H&E) stain, IHC, and ISH assays on either frozen (cryo) or paraffin-infiltrated tissue sections. In addition, this method can be easily performed in many histology laboratories.

Drosophila transcription factor NF-Y suppresses transcription of the lipase 4 gene, a key gene for lipid storage

The CCAAT motif-binding factor NF-Y consists of three different subunits, NF-YA, NF-YB, and NF-YC. Although it is suggested that NF-Y activity is essential for normal tissue homeostasis, survival, and metabolic function, its precise role in lipid metabolism is not clarified yet. In Drosophila, eye disc specific knockdown of Drosophila NF-YA (dNF-YA) induced aberrant morphology of the compound eye, the rough eye phenotype in adults and mutation of the lipase 4 (lip4) gene suppressed the rough eye phenotype. RNA-seq analyses with dNF-YA knockdown third instar larvae identified the lip4 gene as one of the genes that are up-regulated by the dNF-YA knockdown. We identified three dNF-Y-binding consensuses in the 5′flanking region of the lip4 gene, and a chromatin immunoprecipitation assay with the specific anti-dNF-YA IgG demonstrated dNF-Y binding to this genomic region. The luciferase transient expression assay with cultured Drosophila S2 cells and the lip4 promoter-luciferase fusion genes with and without mutations in the dNF-Y-binding consensuses showed that each of the three dNF-Y consensus sequences negatively regulated lip4 gene promoter activity. Consistent with these results, qRT-PCR analysis with the dNF-YA knockdown third instar larvae revealed that endogenous lip4 mRNA levels were increased by the knockdown of dNF-YA in vivo. The specific knockdown of dNF-YA in the fat body with the collagen-GAL4 driver resulted in smaller oil droplets in the fat body cells. Collectively, these results suggest that dNF-Y is involved in lipid storage through its negative regulation of lip4 gene transcription.

Correlated expression of phenotypic and extended phenotypic traits across stingless bee species: worker eye morphology, foraging behaviour, and nest entrance architecture

Stingless bees are the most species-rich group of eusocial bees and show great diversity in behaviour, ecology, nest architecture, colony size, and worker morphology. How this variation relates to varying selection pressures and constraints is not well understood. Variation can be caused by selection acting on behavioural or morphological traits, both alone and in correlation across traits. Here we tested whether behavioural and morphological traits important for foraging and defence are linked to nest-entrance architecture, an extended phenotype relevant to both foraging and nest defence. Using 23 species we investigated whether eye size, nest entrance size, landing behaviour and foraging method show cross-species correlations. A phylogenetically-controlled comparative analysis revealed that species with relatively smaller eyes build relatively larger entrances, which in turn are associated with faster landing approaches and fewer landing errors by foragers, both of which could reduce predation risk. Concerning foraging, mass-recruiting species have c. 10-times larger entrance holes than species with a solitary foraging strategy. Larger entrances could help species with mass recruitment to rapidly increase forager traffic or mount a strong defensive response when under attack. Our results show that studying correlations among different traits helps understand phenotypic diversity in species rich groups.

Five-year-old children show cooperative preferences for faces with white sclera

The cooperative eye hypothesis posits that human eye morphology evolved to facilitate cooperation. Although it is known that young children prefer stimuli with eyes that contain white sclera, it is unknown whether white sclera influences children’s perception of a partner’s cooperativeness specifically. In the current studies, we used an online methodology to present 5-year-old children with moving three-dimensional face models in which facial morphology was manipulated. Children found “alien” faces with human eyes more cooperative than faces with dark sclera (Study 2) but not faces with enlarged irises (Study 1). For more human-like faces (Study 3), children found human eyes more cooperative than either enlarged irises or dark sclera and found faces with enlarged irises cuter (but not more cooperative) than eyes with dark sclera. Together, these results provide strong support for the cooperative eye hypothesis.

Recent speciation and phenotypic plasticity within a parthenogenetic lineage of levantine whip spiders (Chelicerata: Amblypygi: Charinidae)

Caves constitute ideal study systems for investigating adaptation and speciation, as the abiotic conditions shared by aphotic habitats exert a set of environmental filters on their communities. Arachnids constitute an important component of many cave ecosystems worldwide. We investigated the population genomics of two whip spider species: Sarax ioanniticus, a widely distributed parthenogenetic species found across the eastern Mediterranean; and S. israelensis, a recently described troglomorphic species that is endemic to caves in Israel. Here, we show that S. israelensis is completely genetically distinct from S. ioanniticus and most likely also a parthenogen. Counterintuitively, despite the lack of genetic variability within S. ioanniticus and S. israelensis, we discovered considerable variation in the degree of median eye reduction, particularly in the latter species. Natural history data from captive-bred specimens of S. israelensis validated the interpretation of parthenogenesis. Our results are most consistent with a scenario of a sexual ancestral species that underwent speciation, followed by independent transitions to apomictic parthenogenesis in each of the two daughter species. Moreover, the lack of genetic variability suggests that variation in eye morphology in S. israelensis is driven exclusively by epigenetic mechanisms.

Investment in visual system predicted by floral associations in sap beetles (Coleoptera: Nitidulidae)

AbstractPatterns in morphological variation are a central theme of evolution. Uncovering links between morphological character evolution and natural history, specifically feeding behaviour, is important to understanding biological diversity. Species within the sap beetles (Nitidulidae) exhibit a tremendous diversity of feeding behaviours. This immense diversity of feeding can be seen both between major lineages and very closely related taxa. Feeding behaviour diversity may drive morphological variation in several character systems (e.g., eyes). For example, in a shift from feeding on rotting fruit to flower‐visiting (anthophily), selective pressures on the visual system may vary and ultimately lead to differences in eye morphology. We tested for potential morphological shifts in relative eye size among adult beetles. We specifically tested for significant relationships between relative eye size and the following factors flower‐visiting and sex. We also tested for the influence of phylogeny on the evolution of relative eye size, implementing tests of trait correlation across a topology. We found greater relative eye size in taxa exhibiting anthophilous behaviour, regardless of phylogenetic relatedness or feeding behaviour of sister taxa. We were unable to recover a relationship between relative eye size and sex. Thus, feeding behaviour is currently the strongest predictor of eye size in sap beetles.

Clinical Characteristics of the Eye with Fuch’s Corneal Endothelial Dystrophy after Descemet Stripping Only

Purpose: To report the effect of removal of a central descemet membrane on the endothelial function, morphology, and clinical symptoms of eyes with Fuch’s endothelial dystrophy.Methods: From August 2019 to January 2021, patients with Fuch’s endothelial dystrophy, i.e., with confluent, central corneal guttae and cataracts that required surgery, underwent phacoemulsification, intraocular lens implantation, and central descemet membrane stripping. To evaluate the effect of descemet stripping only (DSO), visual acuity and intraocular pressure were measured, and corneal pachymetry, slit-lamp and specular microscopy, and anterior segment optical coherence tomography performed, before surgery and at 1, 7, and 30 days and 3 and 6 months after surgery.Results: Seven patients (10 eyes) were included. Visual acuity improved from 1.01 ± 0.40 logarithm of the minimum angle of resolution (logMAR) preoperatively to 0.33 ± 0.22 logMAR 6 months after surgery (p = 0.008). The mean central corneal thickness decreased from 578.50 ± 36.88 μm preoperatively to 568.50 ± 48.61 μm 6 months after surgery; the difference was not significant (p = 0.507). The endothelial cell count increased significantly from 663.80 ± 356.40/mm2 preoperatively to 1,082.00 ± 274.46/mm2 6 months after surgery (p = 0.043).Conclusions: DSO can serve as a useful alternative when corneal transplantation is not possible in patients with Fuch’s endothelial dystrophy, but treatment efficacy and safety require further evaluation.

What is unique about the human eye? Comparative image analysis on the external eye morphology of human and nonhuman great apes

The gaze-signaling hypothesis and the related cooperative-eye hypothesis posit that humans have evolved special external eye morphology, including exposed white sclera (the white of the eye), to enhance the visibility of eye-gaze direction and thereby facilitate conspecific communication through joint-attentional interaction and ostensive communication. However, recent quantitative studies questioned these hypotheses based on new findings that certain features of human eyes are not necessarily unique among great ape species. Accordingly, there is currently a heated debate over whether external eye features of humans are distinct from those of other apes and how such distinguishable features contribute to the visibility of eye-gaze direction. The present study leveraged updated image analysis techniques to test the uniqueness of human eye features in facial images of great apes. Although many eye features were similar between humans and other great apes, a key difference was that humans have uniformly white sclera which creates clear visibility of both the eye outline and iris—the two essential features contributing to the visibility of eye-gaze direction. We then tested the robustness of the visibility of these features against visual noise, such as shading and distancing, and found that both eye features remain detectable in the human eye, while eye outline becomes barely detectable in other species under these visually challenging conditions. Overall, we identified that humans have unique external eye morphology among other great apes, which ensures the robustness of eye-gaze signals in various visual conditions. Our results support and also critically update the central premises of the gaze-signaling hypothesis.

De-evolving human eyes: The effect of eye camouflage on human attention

Eyes are communicative. But what happens when eyes are camouflaged? In the present study, while either wearing sunglasses (that camouflaged the eyes) or clear glasses, participants were presented with sexually provocative and neutral images, which they viewed in the presence of another person who they knew was observing their eyes. Unbeknownst to the participants, however, we also surreptitiously monitored and recorded their eye gaze in both conditions. People spontaneously looked more and for longer at the sexually provocative images when their eyes were camouflaged by sunglasses. This finding provides convergent evidence for the proposal that covert attention operates in service of overt social attention, and suggests that decoupling overt and covert attention is much more prevalent than previously assumed. In doing so it also sheds light on the relation between the evolution of human eye morphology and systems of attention.

Immediate and cumulative effects of upper-body isometric exercise on the cornea and anterior segment of the human eye.

ObjectivesThe execution of isometric resistance training has demonstrated to cause changes in the ocular physiology. The morphology of the cornea and anterior chamber is of paramount importance in the prevention and management of several ocular diseases, and thus, understating the impact of performing isometric exercise on the eye physiology may allow a better management of these ocular conditions. We aimed to determine the short-term effects of 2-minutes upper-body isometric effort at two different intensities on corneal and anterior eye morphology.MethodsEighteen healthy young adults performed a 2-minutes isometric biceps-curl exercise against two loads relative to their maximum strength capacity (high-intensity and low-intensity) in a randomized manner. An Oculus Pentacam was used to measure the corneal morphology and anterior chamber parameters in both experimental conditions at baseline, during the isometric effort (after 30, 60, 90 and 120 seconds), and after 30 and 120 seconds of passive recovery.ResultsWe found that isometric effort causes an increase in pupil size (P < 0.001), and a decrease in the iridocorneal angle (P = 0.005), anterior chamber volume (P < 0.001) and K-flat (P < 0.001) during isometric effort, with these effects being more accentuated in high-intensity condition (P < 0.005 in all cases).Performing 2-minutes upper-body isometric effort did not alter anterior chamber depth, central corneal thickness, corneal volume, and K-steep (P > 0.05 in all cases).ConclusionsOur data exhibit that performing 2-minutes of upper-body isometric exercise modifies several parameters of the corneal morphology and anterior eye biometrics, with these changes being greater for the high-intensity exercise condition. The findings of this study may be of relevance for the prevention and management of corneal ectasias and glaucoma.

Foveal Morphology of Normal Fellow Eyes of Patients with Unilateral Macular Hole

To determine the morphology of the fovea in the ophthalmoscopically and tomographically normal fellow eyes of patients with a unilateral idiopathic macular hole (MH) and determine the association between foveal morphological parameters and foveal outer nuclear layer (ONL) thickness. Retrospective observational study. Two hundred three normal fellow eyes of patients with a unilateral MH and 216 normal eyes of 216 healthy subjects. All the eyes were examined using swept-source OCT. A built-in software was used to measure the average retinal and choroidal thickness in the center and in the inner 4 subfields defined in ETDRS. The total retinal thickness, thickness of 3 retinal layers at the fovea and parafovea (0.25 and 0.5 mm nasal and temporal from the fovea), and foveal floor width (FFW) were measured on a scan image of a horizontal line passing through the center of the fovea. We defined the thickness between the internal limiting membrane and outer plexiform layer as inner retinal thickness and the thickness between the external limiting membrane and retinal pigment epithelium as outer retinal thickness. Multiple regression analyses were performed with age, sex, axial length, and the presence of a posterior vitreous detachment as the dependent variables. OCT measurements and correlations between foveal parameters and foveal ONL thickness. The fellow eyes had a thinner central retinal subfield, thinner fovea, thinner ONL at all points except at 0.5 mm nasal, significantly thicker outer retina at all points, and a wider FFW (P= 0.040 to P < 0.0001). The foveal ONL thickness was significantly and positively correlated with the central subfield retinal thickness and foveal thickness and negatively correlated with the FFW (all P < 0.0001). The thinner and deeper fovea and the thinner ONL of the fellow eyes of patients with a unilateral MH make these eyes more susceptible to the formation of an MH.

Eye morphology of Guiana dolphins (Sotalia guianensis) and Clymene dolphins (Stenella clymene)

Recent studies showed that vision and hearing in dolphins are mechanisms for perception of the environment, and transmission of information among individuals. Considering that Guiana dolphins (Sotalia guianensis) are distributed in costal regions, and Clymene dolphins (Stenella clymene) are found in oceanic environments, the objective of this study was to compare the morphology of the eyes of these two species, assessing the differences in eye structures in both environments. Five specimens of Sotalia guianensis and four specimens of Stenella clymene were analyzed. All the specimens were found stranded in the northeastern coast of Brazil. Samples were fixated in 10% formaldehyde, dissected, photographed, processed, and analyzed by optical microscopy. The inferior palpebral region of the two species showed a granular layer, subcutaneous lymphoid tissue, and innervation. Morphometric values of the eyelid structures and eye bulb were greater in S. clymene. The cornea showed four layers in S. clymene: anterior epithelium, anterior lamina, stroma, and posterior lamina. The sclera of S. guianensis showed more melanocytes and presence of mechanoreceptors next to the Harderian gland. It is possible to suggest that the geographical distribution of these cetaceans determine their eye morphology, which is an adaptation to the intrinsic characteristics of the aquatic environment.

Acuity and summation strategies differ in vinegar and desert fruit flies

SummaryAn animal's vision depends on terrain features that limit the amount and distribution of available light. Approximately 10,000 years ago, vinegar flies (Drosophila melanogaster) transitioned from a single plant specialist into a cosmopolitan generalist. Much earlier, desert flies (D. mojavensis) colonized the New World, specializing on rotting cactuses in southwest North America. Their desert habitats are characteristically flat, bright, and barren, implying environmental differences in light availability. Here, we demonstrate differences in eye morphology and visual motion perception under three ambient light levels. Reducing ambient light from 35 to 18 cd/m2 causes sensitivity loss in desert but not vinegar flies. However, at 3 cd/m2, desert flies sacrifice spatial and temporal acuity more severely than vinegar flies to maintain contrast sensitivity. These visual differences help vinegar flies navigate under variably lit habitats around the world and desert flies brave the harsh desert while accommodating their crepuscular lifestyle.

The finely defined shift work schedule of dung beetles and their eye morphology.

In nature, nothing is wasted, not even waste. Dung, composed of metabolic trash and leftovers of food, is a high‐quality resource and the object of fierce competition. Over 800 dung beetle species (Scarabaeinae) compete in the South African dung habitat and more than 100 species can colonize a single dung pat. To coexist in the same space, using the same food, beetles divide the day between them. However, detailed diel activity periods and associated morphological adaptations have been largely overlooked in these dung‐loving insects. To address this, we used a high‐frequency trapping design to establish the diel activity period of 44 dung beetle species in their South Africa communities. This allowed us to conclude that the dung beetles show a highly refined temporal partitioning strategy, with differences in peak of activity even within the diurnal, crepuscular, and nocturnal guilds, independent of nesting behavior and taxonomic classification. We further analyzed differences in eye and body size of our 44 model species and describe their variability in external eye morphology. In general, nocturnal species are bigger than crepuscular and diurnal species, and as expected, the absolute and relative eye size is greatest in nocturnal species, followed by crepuscular and then diurnal species. A more surprising finding was that corneal structure (smooth or facetted) is influenced by the activity period of the species, appearing flat in the nocturnal species and highly curved in the diurnal species. The role of the canthus—a cuticular structure that partially or completely divides the dung beetle eye into dorsal and ventral parts—remains a mystery, but the large number of species investigated in this study nevertheless allowed us to reject any correlation between its presence and the nesting behavior or time of activity of the beetles.

Microstructure characteristics of cornea of some birds: a comparative study

BackgroundLight is the critical factor that affects the eye's morphology and auxiliary plans. The ecomorphological engineering of the cornea aids the physiological activities of the cornea during connections between photoreceptor neurons and light photons. Cornea was dissected free from the orbit from three avian species as ibis (Eudocium albus), duck (Anas platyrhynchus domesticus) and hawk (Buteo Buteo) and prepared for light and scanning electron microscopy and special stain for structural comparison related to function.ResultsThe three investigated avian species are composed of three identical layers; epithelium, stroma, and endothelium, and two basement membranes; bowman's and Descemet’s membrane, separating two cellular layers, except for B. buteo which only has a Descemet’s membrane. The corneal layers in the investigated species display different affinity to stain with Periodic Acid Schiff stain. The external corneal surface secured by different normal epithelial cells ran from hexagonal to regular polygonal cells. Those epithelial cells are punctured by different diameter microholes and microplicae and microvilli of various length. Blebs are scarcely distributed over their surface. The present investigation utilized histological, histochemical and SEM examination.ConclusionsThe study presents a brief image/account of certain structures of cornea for three of Avian’s species. Data distinguish the anatomic structures of the owl's eye. The discussion explains the role of some functional anatomical structures all through the vision.

On the morphospace of eurypterine sea scorpions

ABSTRACTEurypterids (sea scorpions) are a group of extinct, marine euchelicerates that have an extensive Palaeozoic record. Despite lacking a biomineralised exoskeleton, eurypterids are abundantly preserved within select deposits. These collections make statistical analyses comparing the morphology of different genera possible. However, eurypterid shape has not yet been documented with modern geometric morphometric tools. Here, we summarise the previous statistical assessments of eurypterid morphology and expand this research by presenting landmark and semi-landmark analyses of 115 eurypterid specimens within the suborder Eurypterina. We illustrate that lateral compound eye morphology and position drives specimen placement in morphospace and separates proposed apex predators from more generalist forms. Additionally, evidence for size clusters inEurypterusthat may reflect ontogeny is uncovered. We highlight the use of geometric morphometric analyses in supporting the naming of new taxa and demonstrate that these shape data represent a novel means of understanding inter-generic ontogenetic trajectories and uncovering developmental changes within the diverse euarthropod group.