The ovarian follicle of the Eurasian ruffe (Gymnocephalus cernua) consists of a single oocyte surrounded by follicular cells, a basal lamina, and thecal cells. The growth of the oocyte during vitellogenesis and the ultrastructure and morphogenesis of its envelope are undescribed in this species. To address these issues, vitellogenic follicles were examined. The oocyte cytoplasm is divided into three compartments: the perinuclear compartment, the endoplasm (which contains yolk spheres and lipid droplets), and the periplasm. The components of the Balbiani body, including mitochondria with well-developed cristae in complexes with spherical, thread-like nuage, are located in the periplasm of early vitellogenic oocytes in the vegetal region. The periplasm also contains annulate lamellae, rough endoplasmic reticulum, Golgi apparatus, endocytotic vesicles containing yolk and oocyte envelope precursors, and mitochondria. Advanced vitellogenic oocytes have a large lipid droplet and a multilamellar body in the perinuclear cytoplasm that may be used during embryo development. The oocyte envelope is primary. It derives from precursor proteins that are secreted by hepatocytes, transported in blood plasma to the ovary, and endocytosed. Nascent envelope proteins are then synthesized in the cytoplasm of oocytes and follicular cells and deposited in the perioocytic space. The envelope of advanced follicles consists of three to seven layers, depending on the oocyte hemisphere. The ultrastructure and sequence of deposition of these layers are described and discussed. The follicular cells diversify into a micropylar cell and mainbody cells. The micropylar cell is shaped like a thumbtack, with a flat head and a pin-like projection. Its cytoplasm is divided into four regions with different sets of organelles. The projection acts as a mechanical barrier to the deposition of the oocyte envelope and forms the micropylar canal. The mainbody cells differentiate into bright, and dark cells, both of which are translationally and secretory active.
The head morphology of an ethanol-preserved specimen of Protopselaphus was examined using synchrotron µCT and SEM. The morphology, including muscles, nervous system, digestive tract and glands, is described in detail for the first time. We interpret the observed external and internal features with respect to their possible phylogenetic implications, mainly focused on the groundplan of the clade Protopselaphinae + Pselaphinae, and on apomorphies of the latter group. Whereas a clade Dasycerinae + (Protopselaphinae + Pselaphinae) is still not strongly supported morphologically, the monophyly of Protopselaphinae + Pselaphinae is robustly established. Adult cephalic synapomorphies are vertical tentorial columns completely detached from the tentorial bridge and dorsally firmly connected with the head capsule, a brain shifted to the narrowed neck region and filling out this space almost completely, and strongly developed labio-hypopharyngeal glands. Predacious habits and correlated falcate mandibles are also likely a groundplan apomorphy of this clade. Enlarged maxillary palps are arguably a typical feature but this condition varies strongly in the subfamily and also within Staphylinidae. Pselaphinae are characterized by several cephalic apomorphies such as a thin (or anteriorly obliterated, or missing) anterior tentorial arm, an antennal insertion covered by a frontal projection, a labral gland, a thin apical sensillum on the terminal maxillary palpomere, a highly reduced labial palpomere 3, and M. frontopharyngalis posterior composed of only one subcomponent.
Morphological discrimination between closely related amphibian species is often complicated by overlapping phenotypic variation, geographic structuring, and hybridization. In this study, supervised machine learning (ML) algorithms were applied to evaluate morphological differentiation between B. bufo and B. verrucosissimus using morphometric data from 285 adult specimens (77 B. verrucosissimus, 208 B. bufo) measured for 28 morphometric variables. Six supervised ML algorithms (k-Nearest Neighbors, Artificial Neural Networks, Support Vector Machines, Naive Bayes, Decision Tree, and Random Forest) were trained using repeated cross-validation on the training dataset and evaluated on an independent test set. Model performance was compared using accuracy, balanced accuracy, sensitivity, specificity, and area under the ROC curve (AUC). Among the evaluated models, Random Forest achieved the highest test-set accuracy (82.46%), specificity (100%), balanced accuracy (75.0%), and AUC (0.871), whereas Support Vector Machines showed the highest sensitivity for detecting B. verrucosissimus (53.3%) among the better-performing models. Variable importance analyses consistently identified parotoid gland morphology, particularly left and right parotoid width (LPW and RPW) and parotoid angle (PA), as the most informative characters for species discrimination. Additional informative variables included metatarsal tubercle measurements, interorbital distance, and radioulnar length. The results support previous morphometric studies while indicating that ML approaches can detect subtle multivariate morphological patterns that are difficult to capture with conventional analyses alone. These findings suggest that ML may serve as a useful complementary tool for morphological assessment within integrative taxonomic frameworks, although broader geographic sampling and external validation will be necessary to evaluate the generality of the observed classification performance.
Rodents can be divided into three major morphological groups (myomorphy, sciuromorphy, and hystricomorphy; additionally, protogomorphy can be found in only one recent species) based on the configuration of the skull and jaw muscles. These three morphotypes have been suggested to be adapted to different food types and allow for different chewing movements. Previous authors have postulated that the masticatory grinding movements should occur mostly in the antero-posterior direction, but other studies have suggested that different degrees of antero-posterior movement may occur across the rodent tree of life and in response to differences in food properties. Here, we use 3D reconstructed movements from X-Ray videos to show that both morphology and food type influence masticatory movements in two myomorphous and two hystricomorphous rodents. Yet, while hystricomorphs do not change the frequency of their masticatory movements in response to different food items, myomorphs do so. Additionally, myomorphs and hystricomorphs that exhibit propalinal chewing movements tend to possess a relatively lower mandibular condyle. Overall, our data suggest that molar morphology, in connection with dietary habits, directly influences masticatory movements. These results show that relatively small differences in a relatively conserved bauplan can have a large impact on jaw movements.
Calcareous corpuscles are present in the myocytes of eucestodes, yet little is known about their formation, and amphilinidean cestodes have not been investigated in this respect. Here, we present an ultrastructural study of the calcareous corpuscles and their formation in adult Amphilina foliacea, a parasite of the body cavity of the sterlet sturgeon Acipenser ruthenus and several eucestode species. Ultrastructural differences are shown to occur between the morphogenesis of calcareous corpuscles in this amphilinidean and adult bothriocephalideans, Triaenophorus nodulosus, Eubothrium rugosum and Paraechinophallus japonicus, an adult cyclophyllidean, Shipleya inermis, and plerocercoids of the phyllobothriidean Clistobothrium sp. In all of the cestode species studied, the formation of calcareous corpuscles takes place in myocytes. Unlike eucestodes, in which corpuscle formation occurs within a sarcoplasmic vacuole with the displacement of the nucleus to the cell periphery, in amphilinideans their formation is intranuclear and occurs in two sites. Firstly, within the myocytes of parenchymal muscle fibers, with the autophagic disruption of both nucleus and sarcoplasm, and a subsequent karyoplasmic and sarcoplasmic formation of one corpuscle per myocyte. Secondly, corpuscle formation occurs in storage myocytes, beginning within the nucleus. The possible functions of calcareous corpuscles are discussed in relation to the environmental needs of the parasite. Atypical ultrastructural characteristics of amphilinideans support current opinions concerning the long evolutionary history of these enigmatic cestodes.
Eye closure is a fundamental protective mechanism for the vertebrate visual system, yet it is rare among fully aquatic vertebrates. Pufferfishes (Order Tetraodontiformes: Family Tetraodontidae) exhibit a unique form of eye closure, termed "iris-like eye closure," in which the cornea is covered by radially-directed movements of the surrounding skin rather than by eyelids. A previous study has documented this behavior and its associated musculature in a single species, but its phylogenetic distribution and evolutionary origin are unresolved. Dissection for comparison of 51 specimens representing all tetraodontiform families revealed that the cutaneous muscle (CT), a sheet-like subcutaneous muscle, is present only in Tetraodontidae and Diodontidae, whereas a specialized concentric subdivision, the cutaneous muscle orbicularis (CTO), is restricted to Tetraodontidae. Mapping the presence or absence of CT and CTO onto different previously published phylogenetic trees, followed by ancestral state reconstruction, indicates that CT occurred only once, in the common ancestor of Tetraodontidae and Diodontidae, presumably in association with the evolution of body inflation. CTO subsequently evolved only within Tetraodontidae through differentiation of the orbital portion of CT, enabling iris-like eye closure. These results suggest a stepwise evolutionary scenario in which a preexisting muscular system was co-opted for a novel protective function. Iris-like eye closure in tetraodontids therefore represents an independent evolutionary solution to corneal protection, functionally convergent with eye-closing mechanisms in other vertebrate lineages. This study highlights the diversity of morphological strategies for eye protection in aquatic vertebrates and underscores the role of muscle repurposing in the evolution of novel functional traits.
The phylum Brachiopoda, which originated in the Cambrian, includes the most diverse subphylum Rhynchonelliformea, comprising the three extant orders: Thecideida, Terebratulida, and Rhynchonellida. These animals possess a calcitic bivalve shell secreted by the mantle. Despite the long evolutionary history of brachiopods, the biomineralization processes in rhynchonelliforms remain poorly characterized. In this paper, we review published data on shell properties (morphology, microstructure, and chemistry) and mantle biology (ultrastructure, ontogeny, and molecular mechanisms) to propose a comprehensive hypothesis for their biomineralization process. We propose that shell secretion in rhynchonelliforms involves a conserved molecular mechanism shared with other carbonate-skeleton-producing animals. Furthermore, we suggest an ontogenetic model based on a cellular "conveyor belt" mechanism of shell secretion. The extremely narrow privileged space, together with the tight spatial association between secondary-layer fibers and the cells of the outer mantle epithelium, indicates an exceptionally high degree of cellular control over shell growth. This precise control likely underpinned the evolution of the remarkably complex skeletal support of the lophophore in rhynchonelliform brachiopods. This apomorphic trait probably played a key role in the evolutionary success of these animals, enabling them to achieve the highest diversity and ecological dominance within the phylum.
A comparative morphological investigation of the hyoid apparatus of atherinomorph fishes supports a new interpretation of homology of the branchiostegal rays. In the atherinomorph orders Atheriniformes and Cyprinodontiformes, and outgroups, the branchiostegal rays are arranged in a posterior group I that forms first in ontogeny and attaches to the lateral surface of the hyoid bar, and an anterior group II which develops later and attaches medially to the anterior portion of the hyoid bar. In contrast, the atherinomorph order Beloniformes is diagnosed by derived skeletal characters of the hyoid apparatus including the branchiostegal rays arranged in a uniform row exclusively along the lateral face of the hyoid bar. This arrangement suggests that the rays are homologous with those of group I and that there are no group II rays. We test this hypothesis with characters from muscle anatomy. In the Atheriniformes, Cyprinodontiformes, and outgroups, the branchiostegal rays of the posterior group I attach to the lateral surface of the hyoid bar with the most anterior rays of this group at the insertion of the interhyoideus. The two thinner, anterior branchiostegal rays (group II), attach medial to the interhyoideus. In beloniforms, the single group of branchiostegal rays on the lateral surface of the hyoid bar has its most anterior rays at the insertion of the interhyoideus. No rays attach medial to the interhyoideus. This evidence supports the hypothesis that beloniforms have solely group I branchiostegal rays. Group II rays never develop. Further modifications of the hyoid apparatus are phylogenetically informative within the adrianichthyoid beloniforms. A unique pair of muscle sheets-the ventroposterior section of the hyohyoideus superior-along the ventroposterior-most portion of the hyoid bar and separated from the more anterior section of the hyohyoideus superior by a distinct gap diagnoses adrianichthyids, which also have a unique ligament that anterolaterally connects the ventral hypohyal and the basihyal cartilage. The ricefish genus Oryzias is diagnosed by modifications of the hyoid-bar skeleton including an enlarged hypohyal cartilage.
Axial elongation has evolved repeatedly in vertebrates, and previous research has revealed insights into the developmental and evolutionary mechanisms that shape this body plan. Snakes, with their elongated, functionally limbless bodies, offer an exceptional system to investigate how vertebral regions are organised or modified throughout elongation. Recent work suggests that snakes retain ancestral regionalisation and that heart position coincides with the boundary between two regions, but how methodological choices such as vertebral sampling density and landmark dimensionality affect the detectability of these regions remain untested. Here, we used three-dimensional geometric morphometrics (3D GM) and segmented linear regressions on complete vertebral columns from 12 elapid snakes to investigate regionalisation and interspecific differences. We compared multiple subsampling strategies (every vertebra, or sampling every 2%, 2.5%, 4% or 5%) to assess how resolution can influence the detection of regional boundaries. We also tested various landmarking schemes, examining if previously utilised landmarking schemes differ greatly in region detection. Our analyses reveal a 4- or 5-region model to be most suitable among elapids, including a short cervical region spanning 2%-4% of the column, a robust morphological shift at ~20% of the column aligning strongly with heart position and a distinct lumbar boundary in the final 5%. Interspecific shape differences were detected but lacked sufficient distinction to identify reliably. Fine-scale sampling improves the detection of small regions, decaying with coarser subsampling. Our results determined that the coarsest reliable sampling method was found at the 2.5% mark. These findings show that despite axial elongation, snakes retained a short cervical and lumbar region, with most of the elongation happening in the thoracic region. This, in turn, has resulted in the thoracic region undergoing axial repatterning, with three modules detected within the thoracic region. This study refines our understanding of vertebral modularity and highlights how regionalisation evolves in elongated vertebrates.
The evolution of body shape in animals reflects the interplay between functional constraints and habitat structure. While cave environments are well known to promote regressive traits in fish such as eye and pigment loss, their influence on overall body form remains poorly understood. Here, we examine patterns of body shape variation in cave-dwelling and surface-dwelling trichomycterid catfishes from northeastern Colombia to assess whether consistent associations exist between habitat type and morphology. Using geometric morphometric analyses, we quantified differences in body shape among species inhabiting subterranean and surface environments. Our results reveal significant habitat-associated differentiation in body shape along the main axes of morphological variation, despite some overlap indicating that habitat does not fully predict morphological variation. Cave-dwelling species exhibit more elongated and fusiform body shapes, whereas surface-dwelling species tend to have deeper and more robust morphologies. These patterns are consistent with differences in habitat-associated ecological conditions, although no direct functional or performance data were evaluated. The recurrence of similar body shapes among species from different clades occupying comparable habitats is consistent with repeated morphological responses to shared ecological constraints.
In this study, we provide a detailed description of the eggs, larvae, and juveniles of Hoplias intermedius, focusing on their morphological, meristic, and morphometric characteristics. Specimens were obtained through induced spawning using the hypophysation technique. The eggs (n = 82) were large and spherical, with a yellowish yolk, transparent chorion, and a small perivitelline space. During development, 135 larvae and 16 juveniles were examined, with standard lengths ranging from 5.48 to 39.00 mm. Larvae exhibited a terminal mouth, simple nostrils, spherical eyes, a large yolk sac, occupying approximately one-third of the body, and an intestine extending beyond the mid-body region. Pigmentation was initially sparse but became more intense during the preflexion stage. Juveniles already exhibited body morphology similar to that of adults. Fin rays counts varied as follows: pectoral (9-10), pelvic (7-9), dorsal (12-14), anal (10-13), and caudal (18-20). The total number of myomeres ranged from 36 to 44, with a modal distribution of 28 preanal and 16 postanal myomeres. Morphometric analysis revealed variation in body height (from elongated to moderate), head length (from small to large), and eye diameter (from moderate to large). Throughout development, increases were observed in snout length, head height, and distances from the snout to the pectoral, pelvic, dorsal, and anal fins. Growth analyzes indicated that most morphometric variables changed progressively during ontogeny, although some exhibited shifts in growth trajectories (breakpoints), likely associated with major developmental transitions such as yolk absorption and fin differentiation. These findings expand knowledge on Neotropical fish development. Specifically, the convergence of the lower margins of the dentary bones toward the mandibular symphysis provides a reliable diagnostic character to distinguish Hoplias intermedius from its congeners. This study offers essential morphological and meristic criteria for taxonomic identification, with direct implications for aquaculture and biodiversity conservation.
The genus Dendrophryniscus, an early-diverging lineage of Bufonidae endemic to the Brazilian Atlantic Forest, includes 17 species of small toads with reproductive habits mostly linked to phytotelmata. Information about premetamorphic development in these species is very scarce, being restricted to observations on embryos of a single species and tadpoles of three. As part of a long-term project on the study of natural history and reproductive biology in Dendrophryniscus lauroi, this contribution describes premetamorphic morphology and development, and discusses the results in the context of what is known for the genus and other bufonids with similar breeding habits. Embryonic and larval stages of D. lauroi are similar to that of several pond-type bufonids, with common features such as dark pigmentation, Type-B adhesive glands, lack of dorsal curvature, and, in tadpoles, small size, labial tooth row formula 2/3, one pair of infralabial papillae, four lingual papillae, tri/tetrapartite suprarostral, larval otic process absent, and m. subarcualis rectus II-IV inserting posteriorly on ceratobranchial IV. Some heterochronic shifts during embryonic and metamorphic ontogeny concern the accelerated development of hind limbs and the delayed transformation of the larval oral morphology into the adult mouth configuration. While ecomorphological variation among phyotelm-dwelling anuran tadpoles is astonishing, most bufonid species exhibit the general aspect of pond-type larvae, with some modifications likely correlated with the lack of active feeding. These include reduction in mouthparts and a short gut filled with yolk, and are more pronounced in obligate endotrophic forms such as Frostius and Pelophryne, than in D. lauroi, where metamorphosis may occur with or without food supply. Phytotelm ecosystems are of increasing interest for ecological studies at multiple levels, and provide an exceptional setting to investigate community ecology and ecomorphological evolution in confined microhabitats.
The raccoon (Procyon lotor) is an omnivorous carnivoran, with a diet that consists of plant material such as acorns, corn, fruits and berries, as well as animal matter including insects, crustaceans and vertebrates. While the morphology of the teeth of P. lotor is well known, the occlusal functions of crown features of the cheek dentition have not been studied in detail. The aim of this study is to describe the tooth function of the raccoon. Of the 26 raccoon skulls studied, 19 were used in a wear facet analysis and seven were included in a dentine exposure series. Additionally, an Occlusal Fingerprint Analyser (OFA) analysis was performed. The results showed that the power stroke of P. lotor consists of two phases, both with a large horizontal component. This suggests that grinding plays a major role in its tooth function, which is corroborated by the presence of grinding facets on the buccal sides of the P4 hypocone, M1 protocone and metaconule and M2 protocone, as well as on the antagonistic surfaces on the lower molars. Abrasion on multiple cusps of the upper and lower cheek teeth and their antagonistic basins shows that crushing is also an important component of raccoon tooth function, and crushing basins exist on the lower as well as upper teeth. The OFA analysis furthermore revealed an occlusal relationship between the enlarged M1 metaconule and the trigonid basin of the m2, while the hypocone of the M1 is shifted lingually with respect to that of the P4, indicating that the M1 metaconule replaces the function of the hypocone. The observed functional replacement of the hypocone by the metaconule on the M1 has not been recorded previously in Carnivora and opens up new questions about the tooth evolution of P. lotor and other procyonids.
Craniofacial growth determines the proper functional coordination of skeletal and soft tissue structures. Alterations related to size, volume, and other parameters may impair expected growth and function. Thus, this study aimed to analyze the effects of volume-reduced and volume-enlarged tongue base on craniofacial skeletal growth. Three groups of Yucatan minipigs included control, 7-8-month-old (n = 8), half each sex; experimental volume-reduction group treated by coblation (n = 6), with concurrent left masseter volume-reduction as well for later myoregeneration analysis; and experimental volume-enlargement group (n = 6), via diet-induced obesity. Both experimental groups were 7-9-month-old same-sex sibling pairs, half each sex. After cardiac perfusion fixation, the tongue and masseter were dissected, followed by soft tissue removal from each skull. Over 90 anatomic landmarks yielded 51 linear distances, and weights/sizes/volumes of the tongues and masseters were measured. All measured variables in controls were normalized for age prior to statistical analysis. One-way ANOVA with Bonferroni post hoc and Pearson's correlations were used. The reduction group showed significantly smaller craniofacial skeletal and dental arch than controls. For instance, the midfacial width (p = 0.042), maxillary inter-canine width (p = 0.001), and mandibular ramus height (p = 0.035) were significantly reduced. The enlargement group also showed significantly decreased distances between sides compared to controls (i.e., inter-canine width p = 0.001, inter-premolar width p = 0.005, and inter-molar width p = 0.007). Strongest associations were found between the whole tongue and structures in the base of the skull of the reduction group, and between the tongue base volume and mandibular structures such as the mandibular ramus height (r = -0.804, p = 0.016). In conclusion, volumetric alterations of the tongue base either enlargement or reduction significantly increase and decrease craniofacial growth. These findings may help clinicians to understand the potential mechanisms of disease in respiration and swallowing disorders induced by changes in soft tissue affecting the craniofacial skeleton.
The lappet moth, Gastropacha quercifolia Felder et Felder, 1862, is a highly polyphagous species in the family Lasiocampidae that poses a significant threat to forestry and crops across multiple ecosystems. This study investigated the external morphology and ultrastructure of the adult antennae of G. quercifolia using scanning electron microscope (SEM). The antennae of both male and female individuals are bipectinate in shape and comprise three segments: scape, pedicel, and flagellum. Nine distinct types of antennal sensilla were identified: sensilla chaetica (I and II), sensilla coeloconica (I and II), sensilla trichodea, sensilla basiconica (I and II), sensilla styloconica, sensilla squamiformia (I and II), sensilla gemmiformia, sensilla campaniformia, and Böhm bristles (I and II). These findings provide morphological foundation for functional analyses of sensilla in G. quercifolia, with implications for behavioral and taxonomic studies.
The ovarian follicles of Gymnocephalus cernua consist of a single oocyte surrounded by follicular cells (FCs), a basal lamina and thecal cells. To address the lack of knowledge regarding the early development of oocytes, the early, mid-, and late previtellogenic follicles were examined. The oocytes are polarized. In early previtellogenic oocytes the nuclei are eccentrically located and emit nuage to the cytoplasm (ooplasm), in close proximity to the follicular epithelium in the animal region. There, a micropylar cell responsible for the formation of the micropylar canal in the egg envelopes is determined. The mitochondria in the Balbiani body (Bb) form complexes with the perinuclear nuage on the opposite side of the nucleus, forming germline precursors (complexes of mitochondria and nuage-like material). In midprevitellogenic oocytes, the nucleus moves to a central position, continues to emit nuage, and the Bb forms a perinuclear ring. The mitochondria multiply and accumulate. Nuage, composed of threads appears and forms a spherical accumulation in close contact with the mitochondria. In late previtellogenic oocytes, the Bb enlarges and becomes fragmented. Fragments containing mitochondria, nuage, and complexes of mitochondria and nuage-like material, as well as Golgi complexes move to the ooplasm near the plasma membrane. The spherical accumulation of thread-like nuage is located at the vegetal pole. Various stages of autophagic degradation of mitochondria are present within autolysosomes (multilamellar bodies) in the Bb. These results support the hypothesis that the primary evolutionary role of the Bb is to select healthy mitochondria and transfer them to the next generation. The function of autolysosomes in the circulation and storage of membranes, and in the deposition of egg envelopes, is also discussed. Oocytes are covered by three primary egg envelopes, and their ultrastructure and deposition are described. Both the oocytes and the FCs are involved in this process.
Echinorhiniformes and Echinorhinidae are a distinct order and family of sharks comprising two species showing several outstanding morphological characteristics, such as their tooth morphologies. Their teeth display unique shapes among sharks with main and secondary cusps which also allow tracking the fossil record of Echinorhinidae. In this study, we review the dental morphological characters of Echinorhinus spp. and further analyse intraspecific morphological variation in a population tentatively identified as E. cf. brucus from the Indian Ocean. Previously suggested hypotheses of intra- and interspecific morphological variations are critically tested, i.e., we examine ontogenetic changes in dental morphologies in E. cf. brucus and test for species-specific differences of dental morphologies between E. brucus, E. cf. brucus, and E. cookei. Results show that within and between species dental variation is limited. Neither tooth size nor cusp angle are jaw position specific. An ontogenetic change in cusplet numbers is detected. Species-specific dental morphological differences within the examined specimens of Echinorhinus were not found; however, the overall tooth formula may be a useful character for species identification. Further, our tooth measurements are useful for estimating the average total length of specimens, which, in combination with the detected ontogenetic change in cusplet numbers, we suggest using for the characterization of the fossil record of Echinorhinus.
The growth of birds is a subject of constant interest to researchers, and somewhat contradictory data on this issue have accumulated. It is known that the growth patterns of fore- and hind limbs differ during the embryonic and postnatal periods, whereas their increments change rather similarly. The question arises: how are these contradictory trends reconciled, and what role do they play in shaping body proportions? Our study was carried out on Rook embryos and nestlings. We studied the dynamics of changes in head, forelimb, and hind limb length in relation to body mass using regression analysis. Then, the dynamics of relative sizes were compared with the dynamics of relative increments of these traits that we studied earlier. We distinguished four periods in the dynamics of relative sizes, just as we identified earlier in the dynamics of relative increments, when the growth trajectories of traits undergo significant changes. The studied traits scaled mainly with positive allometry in the first period (from the 10th to 13th days of embryogenesis) and third period (from the 5th to 23rd days of the postnatal period), negative allometry in the second period (from the 14th day of embryonic to the 3rd day of postnatal development) and isometrical in the fourth period (from 25th to 30th days of the postnatal period). Despite the roughly consistent changes in an organism within the designated periods, variations in the regression exponents led to changes in proportions. The hind limb had the highest growth rate during embryogenesis, while the forelimb grew faster across most of the nesting period. We assume that changes in the dynamics of body parts' growth are associated with the preparation of organs for function and with the influence of factors that limit the growth of an entire organism.
Spinal cord supports (medially projecting bony protuberances within the neural canal) are found in several lineages of fossil and extant salamanders and have been interpreted as a synapomorphy of Caudata. Previous studies that have reported the absence of spinal cord supports in caecilian amphibians were based on an incomplete survey. Here, we re-examine the condition in caecilians using micro-CT scans and histological sections of vertebrae. We find that spinal cord supports are widespread among caecilians, occurring at least in the atlas of most examined species. In caecilians, the supports are most prominent in the atlas and appear to form through the expansion of the perichondral ossification of the septal bundles, consistent with the condition observed in salamanders. The presence of spinal cord supports in caecilians requires a reassessment of current hypotheses regarding the evolution of this character in tetrapods and may help clarify the phylogeny of Lissamphibia. Variation within Gymnophiona may provide novel characters of use in caecilian systematics.
The pharyngeal muscular system of polychaetes is highly complex and shows remarkable variation in structure and function among taxa. In this study, the functional anatomy of the pharynx of G. tridactyla was investigated using micro-computed tomography (micro-CT). Sixteen Glycera specimens were imaged in different pharyngeal positions to examine the roles of key muscular structures in pharyngeal movement. The high-resolution imaging provided by micro-CT allowed visualisation of the pharyngeal muscles in their original topography, revealing essential components for pharyngeal function, including the ring muscle, retensor muscles, intestinal retractor muscles, and longitudinal muscles of the buccal tube and oesophagus. Comparison with previous studies addressed gaps in our knowledge of Glyceridae functional anatomy. Specifically, detailed analysis of the muscular system in different pharyngeal positions clarified the mechanisms of proboscis movement, which indicate the rapid and effective responses of these worms during burrowing and feeding behaviour.
