Journal of Morphology最新文献

Protodrilidae is a small family of almost exclusively interstitial annelids that lack parapodia and chaetae and possess a basiepithelial nervous system. This study presents a histological description of Lindrilus flavocapitatus (Uljanin, 1877), a protodrilid species last examined morphologically in the early 20th century, and provides detailed information on the organization of its nervous and sensory systems using histochemical detection of catecholamines (CAs), scanning electron microscopy (SEM), and alpha-tubulin immunolabelling. The epidermal ciliary structures on the head show a species-specific distribution pattern, and SEM reveals three types of ciliary sensory structures, similar to those previously described in other protodrilids. Numerous CA-containing (CAc) cells are found in both central (CNS) and peripheral nervous systems. A spatial correlation between epidermal ciliary structures and CAc cells offers the first direct evidence supporting the sensory function of some known ciliary types and allows hypotheses regarding their sensory modalities. The widespread, mostly diffuse distribution of epidermal CAc cells throughout the trunk, pygidium, and palps suggests a mechanosensory function, although some presumed mechanosensory cells are not catecholaminergic or lack CAs. The presence of CAs in putative phaosomes on the palps also points to a possible role for these neurotransmitters in photoreception. In addition to typical annelid sensory organs such as palpal receptors, nuchal organs, and possible phaosomes, L. flavocapitatus possesses a unique bud-shaped sensory organ and a dorsal ridge-like array of receptor cells, both containing CAs. A prominent CAc gastroesophageal ganglion innervating the complex pharyngeal apparatus of L. flavocapitatus is described for the first time in protodrilids. The results reveal a more differentiated neural and sensory organization in protodrilids than previously recognized. Despite its small body size and a relatively low neuron count, L. flavocapitatus possesses additional CNS regions beyond those common to most annelids and a uniquely organized apical sensory organ.

The cownose ray (Rhinoptera bonasus) and spotted eagle ray (Aetobatus narinari) are benthopelagic myliobatids that forage on the ocean bottom. To sense prey under the bottom substrate, cownose rays deploy two depressible cephalic lobes, which are anterior modifications of the pectoral fins. Spotted eagle rays have a delta-shaped flattened rostrum from two fused cephalic lobes that is angled down in contact with the substrate when foraging. Geometry and orientation of the cephalic lobes of both rays, when in contact with the bottom, potentially indicate a passive hydrodynamic function. CT scans of the heads of the rays were used to construct physical models for water tunnel testing. Without cephalic lobes of the cownose ray deployed, a positive lift was generated when situated in the water column, but a negative lift was observed for a model with the cephalic lobes extended when in near contact with a solid surface. Flow visualization indicated that cephalic lobes deflected the water flow downward due to a Venturi effect from the pressure difference between fluids located externally and internally of the lobes. Likewise when angled downward and situated near a solid surface, cephalic lobes of the spotted eagle ray generated a negative lift. For both species, increased negative lift near a bottom substrate would aid in keeping the sensory surfaces of the cephalic lobes in contact with the substrate and counter any pitching motions induced by propulsive oscillations of the pectoral fins.

The pineal gland is a photoneuroendocrine organ that regulates circadian rhythms, primarily through rhythmic melatonin secretion. In nonmammalian vertebrates such as birds, pinealocytes retain photosensory and endocrine functions. α-Internexin, a neuronal intermediate filament protein, has been implicated in neurodevelopment and cytoskeletal stability. Its expression in the retinal photoreceptors and pinealocytes has been reported in several vertebrate models; however, its expression pattern in the chicken pineal gland remains unclear. In this study, we used immunohistochemistry and western blot analyses to investigate the developmental expression pattern of α-internexin in the chicken (chkINA) pineal gland from embryonic Day 15 (E15) to post-hatching Day 90 (P90). We also compared its expression with that of two functional markers, visinin and tryptophan hydroxylase 1 (TPH1), to clarify the potential role of chkINA during pinealocyte differentiation. Our findings revealed that chkINA was abundantly expressed in the pineal gland as early as E15, and remained stably expressed throughout development and maturation. Despite the dynamic changes in the expression of visinin and TPH1, chkINA levels remained consistent. These results suggest that chkINA may serve as a critical structural factor that supports pinealocyte maturation during functional transition from photoreceptive to endocrine states.

Craniiformea is a clade of brachiopods, insufficiently studied in terms of functional morphology. While the valve-opening mechanism in Linguliformea and Rhynchonelliformea has been reconstructed, the data on the same mechanism in Craniiformea are incomplete, although several hypotheses concerning this issue have been provided since the end of the 19th century. To review these hypotheses, we have studied the ultrastructure of the main visceral coelomic compartments and the muscles involved in shell movements in Novocrania anomala. Our data document that the lateral oblique muscles, together with a well-developed longitudinal musculature of the body wall (described in craniiforms for the first time) compress the perivisceral coelom along the antero-posterior axis. As a result, the perivisceral coelom expands dorso-ventrally, pushing the dorsal valve up. Thus, that the valve-opening mechanism in Craniiformea is, in principle, similar to that in Linguliformea. We also describe the smooth and cross-striated parts of the anterior adductors, and demonstrate that all muscles of N. anomala are formed by myoepithelial cells.

Phoronids are marine invertebrates with a global distribution and are often abundant in benthic communities. Their morphology, anatomy, and ultrastructure is rather uniform, including the organization of their musculature. However, Phoronis embryolabi, which is characterized by an unusual body regionalization, exhibits a distinct morphology in its trunk musculature. This study uses histology, electron microscopy, computer microtomography, histochemistry, and confocal laser scanning microscopy to characterize the musculature in various trunk regions of P. embryolabi, a species that resides commensally within the burrows of burrowing shrimps. This phoronid species is considered the closest relative of Phoronis pallida, which has a unique syncytial musculature. The musculature of P. embryolabi comprises transverse and longitudinal muscles, organized in a single layer, with the absence of diagonal musculature. The longitudinal muscles are organized into bundles, each comprising cross-striated cells in the central part and smooth cells in two marginal parts. Phoronis embryolabi features several sphincters located between the head region and the rest of the body. The organism appears to be optimally adapted to life within the burrow of the shrimp. The water current generated by the shrimp compensates the requirement for the phoronid to possess diagonal muscles for specific adjustments of the lophophore. The combination of cross-striated and smooth longitudinal muscles facilitates robust and sustained contractions in response to threats. Additionally, circular sphincters likely function to prevent hemorrhage when the head region is injured due to the shrimp's movements.

Mouthparts exhibit diverse morphological features in scarab beetles, resulting from the adaptation to the various living and feeding habits. Adoretini is a small tribe of Rutelinae, remarkable for bearing a beak-like projection on the labrum. However, the correlation between peculiar structures and feeding habits remain unsatisfactory. In this study, the adult mouthparts of Proagopertha lucidula, Anomala corpulenta, Popillia quadriguttata and Adoretus sinicus were compared using scanning electron microscopy, to investigate the structural basis underlying the distinctive feeding behavior of A. sinicus. Based on our investigation, the adult incisors of A. sinicus could not meet when closed. Instead, a beak-like labral projection fits precisely between the paired incisors, which is a configuration markedly different from the other three species. Our scanning electron micrographs reveal distinct wear marks on lateral sides of the labral projections and the mesal corners of mandibular incisors, supporting the hypothesis that both structures are involved in the chewing process. These findings help explain the characteristic perforated damage observed on leaves attacked by Ad. sinicus and also provide a potential functional basis for the labral projection unique to adult Adoretini.

The allometry of sexually selected traits is highly variable. Some traits scale steeply in relation to body size while other traits scale more shallowly. Still others scale proportionately to body size. One explanation for this variability is trait function. Sexually selected traits should scale differently according to the function that they perform—the functional allometry hypothesis. Here, we investigate the functional allometry hypothesis in red milkweed beetles, Tetraopes tetrophthalmus (Coleoptera: Cerambycidae), a species that possesses multifunctional sexually selected traits. Males use their mandibles to eat and as weapons to fight rivals. Their antennae act as sensory organs and as tactile signals during copulatory courtship. We measured these sexually selected traits along with body size in both males and females. We also measured thorax and leg size, traits presumably not under sexual selection, as control traits. We found that tactile signal traits used in courtship were negatively allometric, while weapons, traits supporting the weapon, and control traits were isometric. Although male mandible weapons were isometric, we found that female mandibles were negatively allometric. Finally, weapon shape was also examined as this trait is important to fighting outcomes. We found that male mandible weapons have a rugose medial curve with a midpoint ledge that female mandibles lack. These results support the functional allometry hypothesis for variation in trait allometry. We discuss how interactions between the functions that these traits perform may influence the evolution of morphology.

We studied the gross gonad morphology, the morphology of genital structures involved in sperm reception and egg release, as well as oocyte development in female Centropages Hamatus and Temora longicornis from the White Sea. Our research employed a comprehensive morphological approach, including light microscopy, transmission electron microscopy, and three-dimensional reconstructions based on series of semithin cross-sections. This integrated methodology enabled detailed visualization of the fine-scale morphological structures and main muscle bundles associated with the genital complex and precise mapping of oocyte distribution at different stages of development within the ovaries and diverticula of mature females. In T. longicornis, we discovered glands in the last thoracic somite that were similar in structure and position to the shell glands of egg-brooding calanoid copepods. Unlike previous studies, our approach documented anatomical details of the reproductive system which are typically not detectable using two-dimensional imaging techniques alone. Our observations indicate also that during the reproductive season females of both species are characterized by continuous oocyte maturation and readiness to lay eggs. However, due to the lack of a spermatheca, these females cannot store sperm and, subsequently, require repeated matings to fertilize each batch of eggs produced during the reproductive cycle. We assume that the sex ratio skewed towards males in adult populations of C. hamatus and the equal sex ratio in adult populations of T. longicornis reflect these morphological limitations—specifically, the lack of sperm storage capacity in females coupled with sustained oocyte production in females.