Journal of Morphology最新文献

Amphibian testes vary in shape, from multilobed in caecilians and salamanders to compact, ovoid organs in anurans. Although these variations have been studied extensively in amphibians, there has been little investigation into the structural, copulatory, and reproductive behavioral consequences of unpaired testes, a character shared among some amphibians, cyclostomates, and some teleosts. We analyzed the morphology and structure of unpaired testes in Pristimantis fetosus and Pristimantis permixtus. We also report a single testis in P. hernandezi. Our results suggest that the testis arrangement in these species results from the hypertrophy and fusion of two testes rather than the loss or reduction of one testis. Furthermore, the occurrence of germ cells at different stages of development suggests that spermatogenesis is similar to that described for vertebrates, with spermatogonia undergoing mitosis to form spermatocytes, which then undergo meiosis to form spermatids. Like other brachycephaloid frogs, Pristimantis with fused testes exhibit direct development and reproduction on land, but they are the only anurans known to undergo testicular fusion. We propose to recognize the occurrence of fused testes as a unique putative synapomorphy for a new species group distributed in the Colombian Andes, which we refer to as the P. hernandezi species group. A comparative survey among vertebrates reveals no apparent variations in testicular organization, sperm development, or copulative and reproductive behavioral characters associated with the fusion of testes, suggesting that its occurrence might not have functional implications for vertebrate testes. The independently evolved occurrence of fused testes in cyclostomates, teleosts, and amphibians raises an exciting perspective on the study of the molecular origin, evolution, and functional significance of testis variation in vertebrate reproduction and biology.

In live specimens of the nemertodermatidan Flagellophora apelti Faubel and Dörjes, 1978, a peculiar organ looking like a fascicle of bristles—and so called a broom organ by its discoverer—occupies the front third or so of the body. The animal can extrude the organ to splay the bristles in a fan-like array, each bristle having an adhesive tip. Described first by light histology as a bundle of flagella, this organ can be seen by transmission electron microscopy to be actually a bundle of exceedingly long necks of glands. Bodies of the glands sat well behind the brain, and the necks reached forward through the brain and folded back to a small bulb where they emerged into a canal. Protrusion of the organ would involve unfolding of the necks, projection of the bulb through a pore at the rostral end of the canal, and eversion of the bulb to form a knob-like point from which the gland necks radiate. Confocal microscopy of specimens stained for F-actin showed the muscles that drive protrusion and retraction and cell junctions that anchor the necks at the bulb, and we propose mechanisms through which these motions can be produced. The animal's rostrum had many other glands besides those of the broom organ, including a set forming a brush-like protruberance immediately ventral to the pore of the broom organ, and it likely plays a role in processing prey captured by the broom. Longitudinal muscles of the ventral body wall were specialized into strong bands that could serve to transfer the prey, then, to a facultative mouth.

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.