Journal of Morphology最新文献

Echiurids, as nonsegmented annelids, have an excretory system of a special organization. The excretory system of the echiuran worms is known to consist of ultrafiltration zones on blood vessels and anal sacs. Prior to this study, the fine structure of the anal sacs had been described in detail only for Thalassema thalassemum (Thalassematinae). In contrast, the more complex anal sacs of Bonelliinae, which contain additional structural elements such as tubules, remained unexplored. This study describes the anatomy, histology, and ultrastructure of the anal sacs of Bonellia viridis Rolando, 1822 (Bonelliinae) using a set of modern morphological methods: computer microtomography, araldite histology, scanning and transmission electron microscopy. New data suggest functional implications for structural elements of the anal sacs: the conical part and the neck of the funnel, the tubules, and the end sac. The ciliary funnels are responsible for collecting filtrate to their conical parts and can close at their base, thus preventing reverse flow. According to the ultrastructural data, the inner epithelium of the tubules and the end sac modifies the incoming filtrate in two ways. The inner epithelium of the tubules carries out pinocytosis and accumulates electron-dense granules. The inner epithelium of the end sac has a basal labyrinth consisting of basal processes with numerous mitochondria extending deep into the extracellular matrix and indicates active ion transport. Additional zones responsible for ultrafiltration were identified in the outer epithelium of the anal sac—specifically within the tubule and at the base of the funnel. The origin of the echiurid anal sacs as a result of fusion and multiplication of the metanephridia at the posterior growth zone of metameric annelid-like ancestor is suggested.

Micromorphism represents a distinctive evolutionary adaptation in certain extinct and extant brachiopods. Previous anatomical studies of micromorphic brachiopods have primarily focused on the reproductive system structure or provided only general descriptions of the skeleton and the morphology of the lophophore. Here, we present a detailed morphological analysis of the micromorphic brachiopod Phaneropora galatheae Zezina, 1981, in the context of its miniaturization. Using histological techniques and micro-computed tomography, we describe the structure of the lophophore and its coelomic system, digestive, muscular, reproductive, and excretory systems. The anatomical organization of Ph. galatheae reveals a combination of juvenile features consistent with a possible paedomorphic origin, alongside modifications indicating the compact arrangement of internal organs associated with miniaturization.

Egg cases in oviparous cartilaginous fishes (sharks, rays, and chimaeras) exhibit diverse morphologies that are closely tied to species-specific reproductive adaptations. However, the diversity and formation mechanisms of these structures remain poorly understood. In this study, we performed a quantitative morphological analysis of egg cases from three species: Okamejei kenojei, Cephaloscyllium sarawakense, and Chiloscyllium plagiosum. The results demonstrated that the egg cases of these species could be distinguished using multiple morphological indices (p < 0.05), supporting species-specificity in egg case morphology. In these species, we observed that egg jelly initially envelops the egg case during early embryonic development and later dissolves, allowing seawater entry—suggesting a conserved reproductive strategy within Elasmobranchii. Furthermore, under artificial breeding conditions, observations of female O. kenojei showed that ovulation occurs before egg case secretion. Specifically, eggs reach the oviduct above the oviducal gland when about half of the egg case has formed. Immunohistochemical staining revealed estrogen and progesterone receptors in the oviductal gland cells. Interestingly, O. kenojei can produce malformed eggs with shark egg case-like features under captive breeding conditions. These findings provide new insights into the species-specificity, timing, and hormonal regulation of egg case formation in cartilaginous fishes, and lay a foundation for future research on their reproductive strategies.

The sperm morphology of Malacobdella japonica, a symbiotic nemertean living in the clam Spisula sachalinensis, has been examined using light and electron microscopy. In this species, the structure of the elongated spermatozoon, consisting of a straight head and a posteriorly oriented flagellum, is similar to that of Malacobdella grossa, as previously studied. In both species, the sperm head has an acrosomal complex, an elongated nucleus, and a neck region. The small acrosomal complex, including a thimble-like acrosomal vesicle, a post-acrosomal ring of electron-dense material, and a subacrosomal space, is located asymmetrically at the anterior end of the nucleus. However, there are some differences between the species in the structure and organization of the mitochondrial compartment. In M. grossa, the mitochondria are elongated along the nucleus and remain separate all along their length. In M. japonica, the mitochondria merge at the base of the neck region, forming a ring around the distal centriole. Above this area, they remain separate, similarly to the pattern observed in M. grossa. This finding suggests M. japonica to be an intermediate stage between M. grossa, distinguished by its unique separate mitochondria, and other hoplonemerteans that have a single, ring-like mitochondrion. We assume that the ultrastructure of spermatozoa in symbiotic nemerteans is shaped rather by the mode of fertilization than by their lifestyle. With external fertilization, without forming clutches, the lifestyle does not lead to the development of highly modified spermatozoa.

Distinguishing between sheep (Ovis aries) and goat (Capra hircus) calcanei is challenging due to their close taxonomic relationship and skeletal similarities, which complicates species identification in veterinary, comparative anatomy, and zooarchaeological contexts. The calcaneus is a robust and functionally significant bone in small ruminants, providing valuable insights into their biomechanical adaptations. This study conducted a comprehensive morphometric analysis of the calcaneus in sheep (n = 163, including Akkaraman, Hamdani, Morkaraman, and Dağlıç breeds) and goats (n = 61, Hair Goats), using a digital caliper to measure 10 standardized linear parameters focused on critical calcaneal tuber and articular surface dimensions, capturing functional weight-bearing and joint articulation aspects. Notably, the maximum width of the sustentaculum tali, which supports the talus and enhances tarsal joint stability, consistently showed larger values in sheep than in goats. Overall, sheep exhibited larger measurements, reflecting adaptations to distinct locomotor and ecological roles. A simplified linear discriminant analysis, based on key functional measurements, achieved a classification accuracy of 87.1%, highlighting the utility of these morphological features in species differentiation. Correlation analysis further revealed strong interrelationships among measurements, indicating coordinated growth patterns in the calcaneus. These findings establish a robust reference framework for future comparative anatomy, veterinary science, and zooarchaeology studies, underscoring the diagnostic and functional importance of the calcaneus in small ruminants.