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The midgut of insects as the function core of the alimentary canal usually exhibits diverse morphology depending on their different food types. Mecoptera is an ideal model for comparative studies of the midgut because this small primitive holometabolous group possesses diverse feeding habits. In this study, the midgut of Panorpodes kuandianensis adult was investigated using light and transmission electron microscopy. The result shows that the midgut of P. kuandianensis is a simple straight tube. The single-layered epithelium is composed of regenerative cells and digestive cells. The regenerative cells are grouped in nidi along the epithelium base with high electron-dense cytoplasm and limited organelles. The regenerative cells undergoing differentiation elongate toward the lumen and accumulate numerous mitochondria in the apical region, gradually forming new digestive cells. The columnar digestive cells are the predominant cell type, with distinct regionalization in organelles distribution. Based on the ultrastructural characteristics of the different cells, the functions of the midgut epithelium of P. kuandianensis and the possible feeding habit are discussed. The results could provide a foundation for further understanding the digestive physiology and phylogeny of Panorpodes.

The present study was conducted to investigate the distribution of pit organ in the critically endangered Chinese sturgeon (Acipenser sinensis), the similarities and differences in the microstructure of pit organ between Hybrid sturgeon and Chinese sturgeon, and to provide a histological basis for studying the pit organ in sturgeon species. We used hematoxylin-eosin (HE) staining, nissl staining, multi-layer fine scanning, and scanning electron microscopy to compare and analyse the microstructure of pit organ between Hybrid sturgeon and Chinese sturgeon. The results showed that the structure of pit organ of Hybrid sturgeon and Chinese sturgeon are similar. The distribution density of pit organ in different parts of Chinese sturgeon was different, and the density of pit organ on the ventral surface of the snout was the highest. Scanning electron microscopy revealed that the pit organ of Hybrid sturgeon and Chinese sturgeon were densely packed and about 500–1000 μm wide. Nissl staining revealed that more peripheral nerves are distributed under the sensory and support cells of the pit organ. Based on previous research and our results, the increase in electrical receptivity of sturgeons with individual development is not only due to the increase in the number of inductive receptors, but may also be related to the increase in the width of the pit organ.

As a reference mitogenome, the complete mitochondrial genome of the white-breasted hedgehog, Erinaceus concolor, was firstly presented in this study by employing Long-Range PCR and Next-Generation Sequencing. The total lengths of the mitogenomes were 17.451 bp and 17.455 bp. A total of 37 genes, namely two ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), 13 protein-coding genes (PCGs), and a non-coding D-loop were encoded in the mitogenome, compatible with the previously reported mitogenomes belonging to representatives of the family Erinaceidae (Mammalia: Eulipotyphla). Maximum Likelihood and Bayesian Inference phylogenetic analyses of Eulipotyphla and Erinaceidae based on the complete mitogenomes revealed a conventional relationship for the relevant organism's groups. Divergence time analyses based on complete mitogenome data revealed that evolutionary divergence events within Erinaceidae began about 58.87 Myr ago corresponding to the early Eocene, and the basal split of Erinaceus dates back to approximately 11.01 Myr ago in the late Miocene. Single cytochrome b-based analyses can be considered weaker, as they produce phylogenies that are relatively inconsistent with the natural classification of Eulipotyphla and put the onset of evolutionary divergence events earlier. The genetic information obtained as a result of this study can be used as a genetic resource for conservation biology studies; it will also undoubtedly contribute to the understanding of molecular evolution of E. concolor and closely related taxa.

Myotis nigricans was previously considered the most widely distributed Neotropical Myotis species, occurring from Mexico to northern Argentina, and several allopatric subspecies have been recognized, including M. n. extremus, from Mexico and Guatemala. However, recent studies have shown that M. nigricans is a species complex—many cryptic. Using molecular and morphological data, we assessed the taxonomic status of M. nigricans populations from Mexico, Guatemala, Paraguayan Chaco, and Brazilian Atlantic Forest. Our phylogenetic analysis indicated that M. nigricans is polyphyletic, and the populations classified as M. n. extremus were recovered in a clade composed of species from the ruber group. Populations from Paraguay and Brazil were recovered in distinct clades within the albescens group. Our morphological and morphometric analyzes corroborate the molecular findings, supporting the recognition of M. extremus as a full species. Furthermore, we propose that M. nigricans is a monotypic species occurring exclusively in the South American Atlantic Forest. Populations from other ecoregions should have their taxonomic status redefined in future studies.

We announce complete mitogenomes of four smelts (Osmeridae) of the San Francisco Estuary (SFE): endemic Hypomesus transpacificus, native H. pretiosus and Spirinchus thaleichthys, and non-native H. nipponensis. The genomes each contained 13 protein coding, 2 ribosomal RNA and 22 transfer RNA genes, a control region (D-loop), and a putative origin of replication of the light strand (O_L); gene order followed other osmerids. Total genomes were 16,767 base-pairs (bp) for H. transpacificus; 16,672bp for H. pretiosus; 16,811bp for S. thaleichthys; and 16,779bp for H. nipponensis. GC content was from 47.8% (S. thaleichthys) to 49.4% (H. pretiosus). Phylogenetic analyses of mitogenomes placed H. transpacificus sequences within the H. pretiosus [Oregon + SFE] clade and most closely related to H. pretiosus [SFE], whereas affinities of derivative cytochrome b sequences supported a Lake Suwa origin for SFE H. nipponensis.

Bothrops atrox is an endemic crotaline snake of the Amazon region, and due to its wide distribution and ample abundance it is the most responsible for snakebites that require medical attention in the North region of Brazil, with the state of Pará having the highest rate of incidences. B. atrox is also a key crotaline species in medical research and its venom has been intensively studied during recent years. As intraspecific variation of its venom between populations from floodplains and upland areas were reported and these differences in venom composition were likely related to a variable feeding ecology of the snakes inhabiting the different ecosystems. We confirmed that habitat variation influenced the external head and venom gland morphology of B. atrox i.e., in floodplains snakes had a smaller head size, venom gland size and mass compared to snakes from the other sampled habitats around western Pará.

No studies have yet been conducted on the morphology and characteristics of the oropharyngeal cavity roof in various reptiles, particularly lizards and Gecko. This study aimed to provide a comprehensive analysis of the oropharyngeal cavity roof morphology and characteristics of T. annularis and H. vittatus. Both species have a palate of two parts: the rostral choanal vomeral part and the caudal part. The rostral palatine part is slightly longer due to a diastema. The palate is more triangular in H. vittatus than in T. annularis. The palatine papilla in H. vittatus is slightly elevated and separated from the incisive teeth by a transverse ridge, while in T. annularis; it is caudal to the incisive teeth. Both species have two cleft-like choana between the premaxillary and the maxillary bones. The caudal palatine part of T. annularis has two elevated tubercles, while H. vittatus carries 2–4 longitudinal ridges. T. annularis has three ridges: one median (which extends into the caudal part) and two transverse ridges, while H. vittatus had one transverse dental ridge and two mucosal folds. The rostral palatine part of T. annularis had glandular openings and taste pores with a taste process, while H. vittatus had numerous glandular openings only.

The evolutionary causes behind the development of taste discs (TDs), recognized as the only gustatory organs in metamorphosed Batrachia (Caudata and Anura), have yet to be determined. Taste buds (TBs) serve as the gustatory organs in aquatic batrachian larvae, as well as in both larval and adult caecilians (Gymnophiona) inhabiting either aquatic environments or moist terrestrial habitats. We describe the morphology of gustatory organs of adult crocodile newts (Tylototriton cf. verrucosus, Salamandridae, Caudata). Crocodile newts are semi-aquatic and exhibit increased specialization towards an aquatic feeding, distinguishing it from most members of the subfamily Pleurodelinae. Our findings confirm that TDs serve as the gustatory organs in adult T. cf. verrucosus, similarly to many batrachians. We also determined the density and sizes of TDs’ sensory zones on the tongue and palate of T. cf. verrucosus, which differs from Batrachia. In terms of micro-morphology, two types of gustatory cells (GCs) were identified in the gustatory epithelium of T. cf. verrucosus. Our literature analysis suggests that TDs were larger in anurans compared to caudate amphibians, but were also larger in aquatic/semi-aquatic than in terrestrial anurans.

This study is the first description of the internal anatomy of the scale mites using the example of parasitizing Pterygosoma pseudotrapelus (Bochkov et al., 2009) – a parasite of agamid lizards. Data on histology of the integument, digestive tract, excretory organs, prosomal glands, tracheae, and body-cavity tissues of females, supplemented by the ultrastructure of major organs, are discussed in comparison with information from other groups of the Acari. The female reproductive system was examined only at the light microscopic level. The shape of mite body is adapted to the existence under the scales of the reptile, where the parasite spends its entire life. The width of the adult females is nearly twice their length, resulting in the eccentric position of certain internal organs: the large reproductive system is oriented across the body, so that the ovary with developing oocytes occupies the right side of the idiosoma, while oviduct, seminal receptacle, and vagina are displaced to the left. The structure of the tracheal system and the podocephalic complex of P. pseudotrapelus is similar to that of Tetranychoidea, a group also regarded as one of the lower taxa in the cohort Raphignathina. A number of previously unknown primitive traits identified in the study confirm a relatively basal position of the scale mites within Raphignathina. These include a panoistic ovary, the postcolon instead of an excretory organ of more advanced forms, and 2 pairs of podocephalic acinar glands against the general trend of their reduction in this cohort. An unpaired tracheal gland was found independent from the podocephalic system. The coxal glands lack a filtering sacculus and their epithelium forms mutual interdigitations with the surrounding modified ventricular wall.

The click-beetle genus Elathous Reitter, 1890 (Elateridae: Dendrometrinae) contains almost 50 species distributed in the Palaearctic and Nearctic realms. Specimens of this genus are rare in collections, partly due to their largely unknown biology and ecology. Until now, larvae were known only for three species, all of them described decades ago. Due to the intensive fieldwork research by the first author, who found larvae of Elathous agilis Németh, 2019 in Lebanon and Elathous brucki (Candèze, 1878) in Greece, we have an opportunity to describe their morphology for the first time. We compare them with each other and the remaining known larvae of Elathous and related genera. Although we are able to differentiate larvae of all known Elathous species, our limited knowledge on dendrometrine immature stages as well as the genus-level systematics is insufficient to propose a reliable generic diagnosis for Elathous based on the larval morphology. Additionally, we provide updated information on biology and ecology of Elathous species.