The present study investigates the gross morphological and surface ultrastructural characteristics of the gills in five Schizothorax species (S. plagiostomus, S. niger, S. esocinus, S. labiatus, and S. curvifrons) inhabiting the Kashmir Himalayan region. Schizothorax plagiostomus, S. niger, S. esocinus, S. labiatus and S. curvifrons. In all species, the gill system was housed within paired, medially communicating gill chambers and consisted of four pairs of crescent-shaped gill arches arranged from lateral to medial positions. Each gill arch bore two rows of gill filaments on the convex border and two rows of gill rakers on the concave border, with filament length being greater in the middle region of the arch than at the extremities. The gill arches showed a consistent decrease in length from the first to the fourth arch. Scanning electron microscopy revealed clear regional differentiation of the gill arch into rostral, middle and caudal regions corresponding to the distribution of gill rakers and filaments. Gill rakers were short, stout and blunt, arranged in medial and lateral rows, and exhibited interspecific variation in length, spacing and surface ornamentation. SEM examination revealed spine-like gill rakers and well-organised primary gill filaments bearing numerous transversely arranged secondary lamellae, forming an extensive respiratory surface. Distinct interspecific variations were observed in the morphology, spacing, and structural organization of the gill rakers and filaments. These qualitative ultrastructural differences complement the morphometric findings and suggest functional adaptations associated with feeding ecology and respiratory requirements in the cold, fast-flowing Himalayan waters inhabited by the examined Schizothorax species. The present study provides baseline gross and ultrastructural data on gill morphology in Schizothorax species and highlights the value of gill architecture in understanding ecological adaptation and species differentiation among closely related cold-water fishes.
Although caudal spines are present in most Myliobatiformes species, their biology and ecological function, beyond self-defense, are still poorly understood. Novel information on the development and replacement of the species’ caudal spines was obtained herein by examining the caudal spines of 63 Gymnura altavela specimens. Our data suggest that G. altavela in the southwestern Atlantic undergoes an annual caudal spine replacement cycle, with new spines forming in spring and summer. This replacement may be anticipated by spine breakage, as double-spined stingrays with broken lower spines were observed in winter. Unlike previously studied stingrays, new spines in G. altavela developed on the dorsal region of old spines. Furthermore, this study is the first to investigate the possible use of caudal spines for assessing stingray age. Although spine width growth follows body morphometry, growth bands were not observed along the length of the caudal spines or in their interior. Therefore, these calcified structures do not appear to be suitable for age assessment, at least when considering the classical approach of counting annuli composed of growth bands.
Tamandua mexicana is a mammal belonging to Xenarthrans, with high interest in medicine, conservation, and evolutionary studies. It has semiarboreal locomotion with specific adaptations to allow its movement on different substrates. To carry out this type of locomotion, the extrinsic muscles that allow scapular stabilization as well as retraction and protraction movements are essential. Despite their importance, no studies have analyzed the anatomy and muscle architecture of this species. Therefore, the objective of this study was to analyze the macroscopic anatomy and muscle architecture of the extrinsic thoracic limb muscles in T. mexicana. Four specimens were dissected and fixed in 10
The teaching and learning of zoology and comparative anatomy face several challenges, including the identification of anatomical structures across different species, understanding evolutionary relationships, and promoting science communication and public engagement. In addition, the fragility of formalin-fixed specimens subjected to repeated handling limits their long-term use in practical classes. Plastination has emerged as an effective alternative for preserving biological specimens while maintaining their anatomical characteristics. In this experience report, we describe the preparation and preservation of amphibian and reptile specimens from the Brazilian herpetofauna using plastination and evaluate their preservation quality and practical applicability for educational purposes. Six vertebrate specimens — five Squamata reptiles and one Anura amphibian — were plastinated using the standard S10B silicone technique. Following curing, all specimens exhibited good preservation of their external morphology and anatomical structures, enabling visualization of superficial musculature in Rhinella diptycha and Iguana iguana, the topographic organization of internal organs in Ameiva ameiva, and the external morphology of Coleodactylus natalensis, Epicrates assisi, and Bothrops erythromelas. A semiquantitative assessment indicated high preservation quality, with only minor changes in color, anatomical definition, and structural integrity. Furthermore, all specimens showed high educational usefulness and museum display suitability, as well as good handling suitability and ease of observation. These findings demonstrate that plastination is an effective and feasible preservation method, providing durable, anatomically informative specimens with considerable potential for teaching vertebrate anatomy and zoology, scientific outreach, and museum exhibition.
Bite force is a key component of feeding performance and is closely linked to cranio-mandibular morphology in rodents. However, the relationship between bite force and cranio-mandibular shape remains poorly understood in arvicoline rodents, including the bank vole, Clethrionomys glareolus. This study examined the relationships among body mass, estimated incisor bite force, and cranio-mandibular shape in the bank vole, C. glareolus, from Slovakia. Body mass, incisor measurements, and estimated bite force were analysed across age classes and sexes, and shape variation was quantified using geometric morphometrics. Associations between bite force and shape were tested using Procrustes regression. Body mass increased across age classes, from 13.3 ± 1.64 g in juveniles to 22.65 ± 3.73 g in adults, and estimated incisor bite force followed the same trend, increasing from 6.57 ± 0.56 N to 7.44 ± 0.85 N. Log-transformed body mass and estimated bite force were positively associated in both sexes, with a stronger relationship in females (R² = 0.579) than in males (R² = 0.197). Estimated incisor bite force was significantly associated with both cranial (R² = 0.074, F = 5.30, p = 0.001) and mandibular shape (R² = 0.056, F = 4.004, p = 0.003), independently of sex and age class. These results demonstrate a significant association between estimated bite force and cranio-mandibular shape in C. glareolus, indicating that even subtle intraspecific shape variation is associated with variation in feeding-related functional proxies.
The sand-swimming skink, Scincus scincus, exhibits pronounced cranial adaptations for its fossorial lifestyle, yet the interplay between sexual selection and allometry in shaping its skull remains unquantified. This study utilizes a structure-from-motion photogrammetry workflow and three-dimensional geometric morphometrics (3D GMM) to analyze cranial variation in 48 adult skulls (22 males, 26 females) from southeastern Algeria. We investigated sexual dimorphism in skull size (centroid size) and shape, while rigorously quantifying the role of static allometry using the symmetric component of landmark configurations. Results, validated by high-repeatability landmarking (R > 0.95), confirm significant male-biased size dimorphism. A multivariate regression identified a significant pattern of static allometry (P = 0.007), indicating that size-related shape changes are a consistent factor in adult morphology. Crucially, the sexes exhibit divergent allometric trajectories, as demonstrated by a significant size × sex interaction term (P = 0.015). This indicates that males and females follow different shape trajectories as they increase in size. While mean shape differences were not significant after controlling for this divergence (P = 0.096), males exhibited significantly higher morphological disparity than females (P = 0.023), suggesting relaxed stabilizing selection on male cranial geometry compared to the tightly canalized female phenotype. We propose that the intense biomechanical constraints of “sand-swimming” impose a stabilizing pressure that limits extreme morphological divergence between the sexes. This study provides the first 3D morphometric quantification of the S. scincus skull, elucidating how static allometry and ecological constraints interact to produce a functionally conserved morphology in a highly specialized desert reptile.
Terrestrialization is one of the major transitions in animal evolution, and adaptation to intertidal habitats is considered an intermediate stage in this process. Gastropods have repeatedly colonized land, typically by achieving resistance to desiccation through a shell and aerial respiration via a lung. Notably, shell-less air-breathing slugs of the genus Peronia (Onchidiidae) inhabit rocky intertidal shores and actively move across exposed substrates during low tide, suggesting adaptations that support terrestrial activity. Here, we examined the post-embryonic development of two traits potentially involved in intertidal adaptation in Peronia sp.: the lung for air breathing and mucous glands associated with desiccation tolerance. We first identified the study species as P. setoensis, using molecular and morphological data and documented its embryogenesis. From histological observations conducted across developmental stages from hatchlings to adults, it was revealed that hatchlings lacked differentiated mucous glands, although an immature lung-like structure extended from the posterior visceral region toward the body surface, suggesting an early pneumostome formation. Subsequently, mucous gland abundance and internal lung ridge complexity increased progressively during growth. Finally, adults possessed both mucous glands densely distributed along the mantle margin and dorsal surface, as well as a well-developed posterior lung with numerous internal ridges. These results indicate that post-embryonic development of lung structure and mucous glands is closely linked to increasing terrestrial activity during periodic aerial exposure in P. setoensis. The stepwise development of lung and mucous glands, which may correspond to the gradual acquisition of air-breathing capacity and desiccation tolerance may reflect a developmental pathway underlying intertidal adaptation.
This study presents the first comprehensive account of comparative sagittal otolith morphology across ontogenetic changes in 17 deep-sea demersal scorpaenoid fish species, encompassing 14 genera and four families from the northern Indian Ocean. Two techniques were used; stereomicroscopy to illustrate general patterns, and scanning electron microscopy to reveal fine-scale otolith surface microstructures. A high morphological variability was observed between families and to a lesser degree within families, although the elliptic shape was more common. The sulcus acusticus is of the heterosulcoid-type, but the position of the sulcus varies from inframedian to median or supramedian. Only Ectreposebastes imus displays a particular half-moon shape with a pseudo-archaesulcoid sulcus. However, the inter-specific otolith morphological variations are less for species of Minous, whereas those of Pterygotrigla exhibit distinct dissimilarities. A morphometric analysis shows that the sulcus area-to-otolith area ratio varies widely among species ranging from 18.02 in Pterygotrigla macrorhynchus to 41.17 in Setarches guentheri. Otolith relative length was high across the studied species except in members of Triglidae. In contrast, a high otolith relative size was observed in Scorpaenidae, highlighting family-level differences in otolith morphology. However, high regional variations in the otolith morphology are evident for all the species studied which underscore their utility in delineating population boundaries. Furthermore, the morphological descriptions of otoliths provided in the present study serve as a valuable tool for taxonomy, systematics and feeding ecology of deep-sea demersal scorpaenoid fishes.
A recent revision resulted in the description or resurrection from synonymy of 19 species of Astyanax from Panama to Texas, most of them formerly identified as A. aeneus. The review was based mostly on osteology, informed by previous genetic studies. Although traditional morphometrics and meristics were included in the diagnoses, extensive overlap among species in most traits makes identification very difficult without dissection. This study applies geometric morphometrics to discriminate similarly-shaped sympatric or neighboring species of Astyanax in seven geographical areas: (1) Northern Mexico and Texas; (2) West-Central Mexico; (3) Southern Mexico to El Salvador; (4) Yucatan Peninsula; (5) Mexican Caribbean versant to Honduras; (6) the Verapaces of Guatemala; (7) Nicaragua to Panama. The results show that most species that occur within a given region or in adjacent regions are indeed discernible morphologically without need for dissection or molecular analysis. This finding supports the new taxonomy of the genus in Mesoamerica.
The brown marmorated stink bug Halyomorpha halys (Hemiptera: Pentatomidae) is a globally invasive pest, but detailed information on the ultrastructure and sensory organization of its mouthparts remains incomplete. Using scanning electron microscopy, we examined the piercing-sucking apparatus of H. halys adults, focusing on sensilla morphology, number, and distribution. The mouthparts consist of the labrum, four-segmented labium, and paired mandibular and maxillary stylets. Twelve types of sensilla were identified and classified into six categories: basiconica, campaniformia, chaetica, coeloconica, styloconica, and trichodea. The labrum and labium emerged as primary sensory regions, integrating mechanical, chemical, and physical inputs. Sensilla campaniformia, chaetica, and trichodea are mainly interpreted as mechanoreceptors. Sensilla coeloconica have been associated with thermo- and hygroreception, contributing to the detection of physical parameters. The apical sensory fields host basiconica, styloconica, and specialized chaetica, likely mediating gustatory, olfactory, and thermo-hygroreceptive functions during host evaluation. Based on the characteristics observed at the II-III and III-IV transition areas, an alternative labial position was hypothesized, potentially facilitating stylet cleaning and allowing modulation of insertion angle into plant tissues. This study provides the first comprehensive account of the mouthpart sensilla of H. halys, emphasizing their functional significance and species-specific traits. The morphological and functional insights gained here contribute to a deeper understanding of feeding biology in Pentatomidae and may support the development of innovative approaches for monitoring and managing this invasive pest.
Structural and elemental changes in avian eggshells during embryonic development remain poorly characterized, particularly in altricial species. This study describes the morphological and elemental organization of the eggshell of Mimus saturninus (chalk-browed mockingbird) throughout embryogenesis. Eggshell structure and embryonic development were analyzed using optical microscopy and scanning electron microscopy (SEM) on 90 sections (transversal, dorsal, and internal surface) from an ontogenetic series of 30 eggs at different developmental stages, including hatching. SEM analysis identified an external calcareous layer, an internal fibrous organic layer, and an internal limiting layer in contact with the yolk. During embryonic development, localized calcium reabsorption was observed, reflected in a progressive decrease in shell thickness. Increased porosity was detected in the external calcareous layer, suggesting its involvement in calcium mobilization. Embryonic developmental stages were described alongside changes in eggshell structure, including thickness reduction, increased porosity, and compaction of shell layers. These observations suggest a temporal association between eggshell structural modifications and embryonic development. Interpreting these changes contributes to understanding the redistribution of essential elements during embryogenesis.
Studies on the microanatomy of the tadpole oral apparatus are limited, particularly for Amazonian species. Therefore, the present study aimed to describe the ontogenetic development, as well as the buccopharyngeal morphology, of the oral apparatus of Physalaemus ephippifer tadpoles. Egg clutches were transported to the laboratory and maintained in plastic containers filled with water at an average temperature of 24 °C, where embryonic and larval development took place. Periodic sampling was conducted according to developmental stage, and specimens were analyzed using light and scanning electron microscopy. At stage 18, the stomodeum was formed. By stage 21, thickening of the lower and posterior lips was observed, together with the development of the upper and lower horny beaks. At stage 23, five lips with denticles became apparent. By stage 25, the oral apparatus was fully developed, exhibiting a dental formula of 2(2)/3(1). The internal cavity contained several papillae, and both the dorsal and ventral velum were observed at the posterior end of the buccopharyngeal cavity. The development of the oral apparatus in P. ephippifer follows a pattern similar to that observed in other Physalaemus species; however, the main difference lies in the timing of structural development. This study contributes to a better understanding of the taxonomic identification and feeding behavior of this species and provides additional knowledge about the regional amphibian fauna.
The order Carcharhiniformes represents the most diverse group of sharks, encompassing about 300 valid species that occupy a wide range of habitats and exhibit diverse feeding strategies. Despite this ecological diversity, knowledge of the comparative morphology of the gustatory system in this group remains limited. In this study, we describe and illustrate the morphological variation of gustatory papillae in the oropharyngeal cavity of carcharhiniforms, discussing potential relationships between morphology and ecological aspects. Oral papillae occur predominantly in the ventral part of oropharyngeal cavity, whereas they are few or absent along the dorsal and branchial regions. Interspecific variation in papillae density was observed and two main morphotypes are described herein. Our results provide a comparative morphological basis for understanding potential relationships between morphology, evolution and function of the gustatory system of sharks of the order Carcharhiniformes, but examining more taxa is still required to ameliorate our comprehension about the gustatory system.
Sericulture is the practice of rearing silkworms on specific host plants for the production of natural silk. It has been carried out since ancient times. Among the various silkworms, the fully domesticated mulberry (Bombyx mori), the semi-domesticated Eri (Samia ricini) and the wild species or vanya silkworms- Muga (Antheraea assamensis) and Tasar (Antheraea mylitta) represent the major sources of commercial silk in India. Each species has distinct physiological and anatomical features that determine its feeding behaviour, silk production and adaptability to environmental conditions. Although their ecology, host plants, silk characteristics and rearing practices differ among these species, the internal anatomy of these silkworms follows a conserved lepidopteran pattern. In the present study, comparative analysis of internal organs and other external structures of all four different silkworm species were examined using a stereo zoom microscope. The major internal organ includes a digestive tract, tracheal system, circulatory system, nervous system, excretory system, silk gland and reproduction system. Observations revealed species-specific differences in tracheal coloration, silk gland development, fat-body texture and reproductive morphology, influenced by their ecological adaptation and host-plant specialization. External features such as true legs, pseudo-legs, spiracles, eyes and antennal structures of adult moths are also documented to provide integrated anatomical profiles. Such comparative analyses have helped to elucidate functional adaptations concerning feeding habits, cocoon formation, spinning behaviour and environmental tolerance.
The insect pretarsi are the sites of direct contact with the proximal environment. Aspects of pretarsal structures have been described in the literature. Comprehensive and detailed histological analyses of the pretarsal composition depicting the interaction of the different types of outside and inside tissues in insects are, however, anecdotal. Here, we present a tri-dimensional image of the tarsal ends of the housefly Musca domestica at the ultrastructural level using focussed-ion beam combined with scanning electron microscopy. In particular, we find that the different functional elements of the pretarsus have distinct cuticle thicknesses. In detail, the cuticle is thin at the joint to the fifth tarsomere, thickens in the dorsal claws and the ventral unguitractor plate; the ventral pulvilli, again, have a rather thin cuticle with the basis of their tenent acanthae (adhesive cuticle protrusions) arranged like roof tiles before the shafts protrude forming the adhesive acanthal cushion. Inside the cuticular tube, we discerned a composite filament with the distal end of a large gland, paired bundles of axons projecting into the claws but not the pulvilli and a tracheal tube. These elements are associated with the cuticular unguitractor tendon in the fifth tarsal subsegment that bridges to the external cuticle via a possibly flexible membranous cuticle. These data will serve in studying the pretarsal function regarding its interaction with the environment associated with its different structures in molecular and reverse genetic experiments.
Aedes albopictus serves as a vector for multiple viruses in tropical and subtropical regions worldwide, including those that cause encephalitis, Zika and dengue fever. Although species identification traditionally relies on characteristics of the fourth larval instar, SEM based studies on Ae. albopictus remains limited. In this study, SEM was used to document key morphological features, including the antennae, feeding mouth brushes, mandibles, maxillae, labia, comb scales, siphon, respiratory spiracle, and row of pecten teeth. The eighth abdominal segment of the fourth-instar larva is small, bearing nine comb scales. The siphon is itself equipped with two rows of pecten teeth, each row containing 11 individual teeth. While the larval and adult stages of Ae. albopictus have been described previously, the pupal stage has not been examined yet using SEM. Therefore, this study investigates the external morphology of Ae. albopictus pupae for the first time to identify additional diagnostic characters. The pupal body is enclosed by a translucent cuticle, comprising a cephalothorax and a slender, articulated abdomen. Respiration occurs through paired respiratory horns on the cephalothorax. On anterior region the cephalothorax bears mouthparts, flattened head, developing compound eyes, and posteriorly curved antennae. On posterior region ninth abdominal segment is comparatively small and bears paired paddles supported by a midrib, which are essential for pupal movement. SEM of adult mosquitoes enables precise characterization of diagnostic structures such as sensilla, setae, scales, spiracle, haltere, mouthparts and cuticular pattern. SEM based morphological data of larva, pupa and adult stages enhance our understanding of mosquito biology, development, and functional adaptation, which is essential for designing effective vector surveillance, control strategies, and integrated mosquito management programs.
The present study provides a comprehensive analysis of the gut of the teleost fish Trichopodus trichopterus, with a focus on morphology, histology, histochemistry, and the localization of neuropeptides. Gross morphology revealed a well-delineated foregut, midgut, and hindgut. Histologically, HE staining confirmed the canonical arrangement of mucosa, submucosa, muscularis, and serosa. Histochemical assays such as periodic acid Schiff’s (PAS), Alcian blue (AB), and combined AB + PAS demonstrated region-specific distributions of neutral and acidic mucopolysaccharides within goblet cells. Immunohistochemical localization of neuropeptide Y (NPY) and secretagogin (SCGN) revealed a rich diversity of enteroendocrine cells (EECs) within the gut epithelium. NPY-immunoreactive EECs exhibited a wide variety of shapes and positions, including both open- and closed-type cells, with at least 16 distinct morphological variants. For the first time in lower vertebrates, we identified the presence of SCGN-immunoreactive cells, exhibiting notable diversity with approximately ten distinct cell types in gut. These findings suggest a complex and heterogeneous population of EECs involved in gut endocrine signaling and homeostasis in T. trichopterus. This study provides key insights into gut architecture and neuropeptide-secreting cell distribution in a teleost model, laying the groundwork for future research on EECs’ roles in nutrient absorption and intestinal homeostasis.
Attachment positions of long digital extensor and popliteus tendons and the shape of lateral condyle are important for functional aspects and help explain the adaptation mechanism of weight in dogs with different weights. The aims of the present osteological study were twofold: First, to determine whether or not there exists any difference concerning the lateral condyle shape of the femur, and second, to record the attachment positions of the long digital extensor and popliteus tendons according to the lateral collateral ligament in mid-, large, and giant dogs. Measurements of the lateral femoral condyle and distance between epicondyle, popliteal and extensor fossa centres were obtained in dogs with three weight groups—variables subjected to one-way analysis of variance among the weight groups of dogs. The level of significance was set at P < 0.05 for all analyses. Lateral condyle shape was more vertically oval in medium dogs than in large and giant dogs. The condyle diameter and bowl length were shorter in giant dogs than in medium and large dogs. Distances between the popliteal fossa centre and epicondyle, extensor fossa centre and epicondyle, and popliteal and extensor fossa centres were shorter in giant dogs than in medium and large dogs. In conclusion, increasing weight in normal dogs causes changes in lateral condyle shape and muscular positions attached to it. These changes reflect the adaptation mechanism for mechanical environments.
The study of the composition, size, and distribution of cnidae is fundamental for the identification and description of sea anemone species. However, intraspecific variability in cnidae length and types has already been documented for the group, leading some authors to question their usefulness as a taxonomic tool. Moreover, few studies have examined the intra-structural qualitative and quantitative variation of the cnidom within the tissues of individuals. In this study, we investigate patterns of variation in the composition and biometry of the cnidom in the tentacle crown of Actinostola crassicornis. To this end, 2014 cnidae were measured from three tentacle cycles—internal, middle, and external—and from three positions along each tentacle—apical, middle, and basal. Our results reveal a clear pattern in the cnidae of the tentacle crown of A. crassicornis: lengths tend to increase from the base toward the tip of the tentacle in all types analyzed, a pattern particularly pronounced in basitrichs and b-mastigophores, where differences are statistically significant. No consistent trend was observed among tentacle cycles. The random variable “individual”, included in the models, had a significant effect in all cases, indicating the commonly observed intraspecific variability. These findings underscore the importance of considering intra-structural variation within the group when the cnidom is used in descriptive studies, given its direct impact on the taxonomic and ecological interpretation of sea anemones.
This study provides a comprehensive anatomical and histological description of the eyelids of the Egyptian agama, Trapelus mutabilis. Both the movable upper and lower eyelids, as well as the thin and reduced third eyelid, represent distinctive features of the Egyptian agama's eye. The upper eyelid appears shorter than the lower one; furthermore, the cranial skin above the upper eyelid extends laterally to form a superior projection. Micro-ornamentations and sensory organs are located at the tips of the eyelid scales, which are arranged in an imbricated pattern. The histological structure of the upper eyelid closely resembles that of the lower eyelid. The external surface of both eyelids consists of keratinized stratified squamous epithelium composed of two to four cell layers, while the internal surface is lined with stratified cuboidal epithelium. Melanophores and iridophores constitute the principal pigment cells in both eyelids. The third eyelid is a reduced fold with a concave surface that connects posteriorly with the lacrimal gland at the medial canthus of the eye. Its external surface is covered by stratified squamous epithelium, whereas the internal surface is lined with one or two layers of cuboidal cells with rounded nuclei that are continuous with the conjunctival epithelium. Video recordings of the species under laboratory conditions demonstrated synchronization between eyelid and eyeball movements. Based on these observations, the present authors propose that this species possesses multiple structural and functional adaptations that enhance ocular protection. Protection against ultraviolet radiation is reinforced by two types of pigment cells, while the hard eyelid scales, superior extensions of wide scales, and the presence of sensory organs at the scale tips collectively enhance the protective reflex against external stimuli. These features represent morphological adaptations to the harsh environmental conditions in which this species lives.
