The genus Alpheus Fabricius, 1798 is the second most speciose among caridean shrimps; however, its larval development remains poorly understood, with only about 10% of species having their first larval stages described. Within the Alpheus armillatus H. Milne Edwards, 1837 species complex, recent taxonomic rearrangements have emphasized the need for integrative studies to differentiate cryptic species. Following this direction, this study described and illustrated the first two larval stages (zoea I and zoea II) of A. angulosus McClure, 2002, based on specimens collected in two distinct localities in the state of Alagoas, Northeastern Brazil. Morphological descriptions were conducted using light microscopy and camera lucida, following standard setal classification systems. Partial sequence of the 16S rRNA gene of one parental female was analysed, providing molecular support for species identification. Our results showed that zoea I of A. angulosus can be distinguished from other members of the A. armillatus complex which have larval morphology described (A. brasileiro Anker 2012 and A. carlae Anker 2012) by specific setal counts on the maxillule, maxilla and maxillipeds. This study highlights the relevance of larval morphology as complementary information for decapod taxonomy and suggests that the differences observed in A. angulosus warrant further integrative taxonomic revision.
Despite the tail of the red swamp freshwater crayfish playing an important role in locomotion and environmental interactions, comprehensive studies integrating gross anatomy, ultrastructural features and elemental composition remain scarce. Therefore, the current study aimed to characterize its morphology and sensory structures using scanning electron microscopy (SEM) and SEM-Energy Dispersive X-ray (SEM-EDX) analysis. The tail segment, situated at the end of the abdomen, comprises the telson and biramous uropods, responsible for locomotion and escape reflexes. The telson, a quadrilateral structure with an anal opening, is surrounded by uropods, which are exopod and endopod appendages articulated to the last abdominal segment. Telson and uropods display feather-like setae that enhance swimming efficiency, with distinct specializations on their dorsal and ventral surfaces revealed by SEM observations. The ventral surface showed a smooth cranial region and a caudal folded area with longitudinal grooves and a thick transverse basal ridge bearing basket-like projections anchoring setae. Papillae of varied shapes, each exhibiting central bulbs and sensory openings, were abundant, suggesting potential sensory specializations that may be associated with mechanosensory and chemosensory roles. The dorsal surface featured a spinated region and a papillary crest with 55-65 triangular papillae interspersed with feather-like setae, contributing to tactile and hydrodynamic functions. SEM-EDX elemental analysis indicated a composition dominated by carbon (37.57%) and oxygen (29.96%), followed by calcium (16.67%) and nitrogen (12.54%), with trace silicon (0.21%), reflecting the chitinous and calcified nature of the exoskeleton. These findings provide detailed insights into the structural adaptations of the crayfish tail segment, revealing its intricate functionality in locomotion, sensory perception and environmental interaction.
Research into the electric eel (Electrophorus) has focused on its production of high-voltage electrical discharges for predation and defence, and its divergence from other fish species in terms of molecular activities. However, the knowledge of its digestive biology remains limited. Here, using conventional histological and histochemical methods, we elucidate the structure of the digestive tract, including accessory digestive organs, and the localization of protein fibres in Electrophorus sp. Our observations of the morphological organization of the digestive tract in the coelomic cavity revealed that all regions presented a typical four-layer organization (mucosa, submucosa, muscularis, and serosa). Both the stomach and intestine had well-developed histological layers. The anterior intestine exhibited well-developed longitudinal folds while the posterior intestine exhibited a slight longitudinal fold. Specialized mucus-secreting cells were widely distributed throughout the digestive epithelial tract, particularly the submucosa in the stomach. Histochemical analyses demonstrated a wide distribution of collagen and elastic fibres throughout the digestive tract, with prominence in the muscularis layer. These findings provide updated foundational anatomical information on the digestive system of the electric eel, supporting future studies on its digestive physiology and feeding evolution.
Oestrus ovis (sheep nasal botfly) is a cosmopolitan myiasis-causing parasite responsible for substantial health and productivity losses in small ruminants. Despite its veterinary importance, integrated epidemiological and molecular data from endemic regions such as Pakistan remain limited. This study provides a comprehensive investigation of O. ovis in sheep and goats by combining abattoir-based epidemiology, detailed larval morphology and mitochondrial cox1-based genetic analysis. A total of 311 small-ruminant heads (176 goats, 135 sheep) were examined, revealing an overall prevalence of 37.6%, with slightly higher infestation in sheep. In goats, infestation was significantly associated with host sex and nasal pigmentation (p < 0.05), whereas in sheep only nasal pigmentation showed a significant effect. Morphological and morphometric analyses identified second- (L-2) and third-instar (L-3) larvae, with L-3 exhibiting greater body dimensions and more developed cephalopharyngeal structures, including robust mouth hooks and dense ventral supination. Molecular characterization based on a 392 bp fragment of the mitochondrial cox1 gene revealed moderate haplotypic diversity, with a dominant haplotype shared among multiple samples. Comparative analysis demonstrated high nucleotide similarity (97%-99%) and low genetic divergence (0.00-0.02) with global reference sequences. Phylogenetic and haplotype network analyses placed Pakistani isolates within a well-supported, globally distributed O. ovis lineage lacking clear geographic structuring. These findings highlight a high burden of O. ovis infestation in Pakistani small ruminants, confirm distinct larval stage differentiation and demonstrate limited mitochondrial variability consistent with recent common ancestry and host-mediated dispersal. This integrative approach provides essential baseline data for surveillance and control strategies in endemic regions.
ABSTRACT The study of genes involved in sexual differentiation, as Vasa and Sox9 , is of great importance, as they serve as specific markers for the germline and the male differentiation pathway, respectively. This study characterized using immunofluorescence the expression of the Vasa and Sox9 genes and laminin during gonadal differentiation in larvae at stages (S) 50, 53, 55, 57 and in 3 months‐old urodele amphibian Ambystoma mexicanum . At S50 and S53, laminin delineated the gonad‐mesonephros complex and the medullary and cortical regions of the differentiating gonad; Sox9 was detected in somatic cell nuclei and Vasa was expressed in the cytoplasm of germ cells. During gonadal differentiation at S55 and S57, laminin delimited the ovarian cavity and, in the testes, surrounded the testicular cords; Sox9 and Vasa maintained the expression patterns observed at earlier stages. In 3 months‐old ovaries, laminin was detected surrounding the follicles, Sox9 expression was absent and Vasa was expressed in the peripheral cytoplasm of oocytes; in the testes, laminin surrounded the testicular cords, Sox9 was expressed in Sertoli cell nuclei and Vasa was detected in spermatogonia. These results suggest that, in A. mexicanum , Sox9 and Vasa are conserved genes that likely perform functions analogous to those observed in other vertebrates.
