Development of the dorsal and anal fin in Kneria stappersii (Otomorpha: Gonorynchiformes)

The order Gonorynchiformes was repeatedly studied to gain new insights into the evolution of its sister-taxon, the Otophysi, the most successful freshwater fish taxon worldwide. Previous ontogenetic studies of gonorynchiforms mainly focused on the anterior vertebral column to investigate the evolutionary origin of the Weberian apparatus. Herein, we highlight the ontogeny of a different skeletal complex, the dorsal and anal fins. We studied the development of the skeletal elements of both fins in the gonorynchiform Kneria stappersii. We gained new insights into the developmental and formation patterns of K. stappersii. We discuss these patterns as well as the development of certain elements like the fin stay in comparison to other gonorynchiforms and available otomorph data. In general, the fin development in K. stappersii is very similar to that of other gonorynchiforms and even otomorphs. Specific differences, however, reveal that much remains unknown about the evolution of median fin elements such as the fin stay.     

Ontogeny of feeding and respiration in larval Atlantic cod Gadus morhua (Teleostei,Gadiformes): I. Morphology

Cranial development in larval Atlantic cod Gadus morhua was studied throughout ontogeny using specimens treated by staining and clearing, scanning electron microscopy and histology. Newly hatched cod larvae have closed mouths, no operculii, five well-developed branchial arches, and transversii ventralis muscles. During the endogenous feeding (yolk-sac) stage, viscerocranial structures remain simple and nonarticulated. Six days after hatching at 5°C, articulation occurs between the quadrate/Meckel's cartilage and the hyomandibula/cranium. Integration of skeletal elements results in a functional jaw that facilitates the transition from endogenous to exogenous feeding. During later ontogenetic stages, the opercular apparatus and levator-operculi coupling develops, facilitating the transition of cutaneous to branchial respiration. Overall, feeding and respiratory needs are met by changes in form (including composition) and function during larval fish growth and are correlated with demands of energy acquisition essential to survival. © 1996 Wiley-Liss, Inc.     

Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts

Ozarkodinid conodonts were one of the most successful groups of agnathan vertebrates. Only the oropharyngeal feeding apparatus of conodonts was mineralized, and the skeletal elements were generally disarticulated on the death and decay of the body. Occasionally, however, they were preserved in association as ''natural assemblages'', fossilized in situ after post-mortem collapse of the apparatus. From analysis of element arrangement in natural assemblages of Idiognathodus from the Pennsylvanian of Illinois we have produced a precise scale model of the feeding apparatus of ozarkodinid conodonts. At the front lay an axial Sa element, flanked by two groups of four close-set elongate Sb and Sc elements which were inclined obliquely inwards and forwards; above these elements lay a pair of arched and inward pointing M elements. Behind the S-M array lay transversely oriented and bilaterally opposed Pb and Pa elements. Our model sheds new light on food acquisition in conodonts. We propose that the anterior S and M elements of ozarkodinid conodonts were attached to cartilaginous plates. In order for the animal to feed, these plates were first everted, and then drawn back and upward over the anterior edge of an underlying cartilage. These movements produced a highly effective grasping action, the cusps and denticles of the elements converging to grab and impale any food item that lay anterior to the open array. According to this hypothesis, the anterior part of the conodont apparatus is comparable to, and possibly homologous with, the lingual apparatus of extant agnathans; the elements themselves, however, have no direct homologues. <br>     

Histology of melanic flank and opercular color pattern elements in the firemouth cichlid,Thorichthys meeki

Dark melanic color pattern elements, such as bars, stripes, and spots, are common in the skin of fishes, and result from the differential distribution and activity of melanin‐containing chromatophores (melanophores). We determined the histological basis of two melanic color pattern elements in the integument of the Firemouth Cichlid, Thorichthys meeki. Vertical bars on the flanks were formed by three layers of dermal melanophores, whereas opercular spots were formed by four layers (two lateral and two medial) in the integument surrounding the opercular bones. Pretreatment of opercular tissue with potassium and sodium salts effectively concentrated or dispersed intracellular melanosomes. Regional differences in epidermal structure, scale distribution, and connective tissues were also identified. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

On the mechanisms of cytokinesis in animal cells

We present a model that attempts to explain some aspects of cytokinesis in animal cells. We propose two separate phases of cytokinesis. The first is not dependent on the presence of the mitotic apparatus and involves a general activation of cortical contractile elements resulting in the development of a surface tension. In the second phase the asters of the mitotic apparatus interact and modulate the activities of the tension generating elements in the cortex to produce gradients of surface tension with the highest values being at the equator. Tension generating elements are assumed to be free to move in the plane of the cortex so that they will consequently move up the gradient of tension and accumulate as an equatorial belt of oriented elements i.e. the contractile ring. The model was simulated on a computer and is capable of reproducing some of the wide variety of cleavage configurations that are observed.     

Differences between inter- and intraspecific architectonic adaptations to pharyngeal mollusc crushing in cichlid fishes

Because fish heads are densely packed with muscles, ligaments, skeletal elements and other structures, transformations in one structure may influence surrounding structures. Transformations occur during phylogeny, ontogeny and as environmentally induced alterations, i.e. phenotypic plasticity. We describe differences in intra- and interspecific transformations of the pharyngeal jaw apparatus of haplochromine cichlids. Using multivariate clustering techniques we trace possible correlations in transformations of anatomical characters of the pharyngeal jaws and surrounding structures. The intraspecific transformation analysis is based on two environmentally induced morphs of Astatoreochromis alluaudi : a molluscivorous morph with a hypertrophied pharyngeal jaw apparatus and an insectivorous one with a non-hypertrophied apparatus. For the interspecific analysis five other haplochromine species from Lake Victoria with diets ranging from insects to molluscs were investigated. Although ranges in diet are the same, the anatomical ranges differ between A. alluaudi and the species cline. Besides similarities in anatomical changes of the pharyngeal jaw apparatus in the intra- and interspecific cline, differences were also observed. Apparently there are among haplochromines multiple pathways to achieve similar performance. In A. alluaudi architectonic and intrinsic plasticity constraints limit the adaptability of the pharyngeal jaw apparatus. In the species cline, these constraints have been overcome by genetical adaptation.     

Skeletal ontogeny and feeding mechanisms in conodonts

The growth and function of the conodont skeletal apparatus have important implications for early vertebrate relationships and the evolution of vertebrate hard tissues, yet they are poorly understood. Analysis of element length, platform linear dimensions, and platform area in discrete Pa elements of Carboniferous Idiognathodus and Gnathodus bilineatus reveals that the platform increased in size at a rate significantly above that required to maintain geometric similarity. Measurements of P, M and S elements in bedding-plane assemblages of Idiognathodus and G. bilineatus indicate that relative to Pa element length, Pb and S element growth was isometric, whereas M elements grew with negative allometry. There is no evidence to support loss or resorption of S and M elements in later growth stages, or to indicate periodic shedding and replacement of elements. These results are important for understanding apparatus and element Function. The positive allometry of the Pa element platform supports interpretations of a mashing or grinding tooth-like Function for platformed Pa elements. If conodonts were active suspension-feeders, the increasing food requirements of a growing conodont would require the filter array formed by the S and M elements to have grown at a rate significantly above isometry. The lack of positive allometry of S and M elements indicates that conodonts were not suspension-feeders and supports hypotheses that conodonts fed with a raptorial apparatus and teeth. □ Conodonts, vertebrates, skeletal apparatus, ontogeny, allometry, function, suspension-feeding, teeth.     

Opercular regeneration in Pomatoceros lamarckii Quatrefages (Polychaeta: Serpulidae). Differentiation of the operculum and deposition of the calcareous opercular plate

Following opercular amputation, stages in opercular regeneration in Pomatoceros lamarckii have been described by light, transmission and scanning electron microscopy. Two to three days after amputation, the rudimentary opercular filament is invested with a delicate cuticle composed of an outer filamentous layer and an inner thicker component composed of orthogonally-arranged layers of small fibril bundles. The opercular plate is uncalcified and composed of two major components, an outer, thin, electron-dense layer and an inner, thicker component which structurally resembles that of the opercular filament cuticle. Between five and eight days, opercular plate calcification is initiated as needle-like crystallites. The structural organization of the organic components of the opercular plate show changes which are related to the onset of calcification. From 13–17 days, the opercular plate becomes heavily calcified and is composed of highly-ordered, prism-like crystals. X-ray diffraction shows these crystals to be aragonite. The structure of the cuticle remains unchanged except that the orthogonally-arranged fibril bundles aggregate into thicker fibres. Amino acid analysis of the regenerated cuticle and organic components of the opercular plate show that they differ from one another and from the normal cuticle and opercular plate. During opercular regeneration, the differentiation of the cuticle and opercular plate-secreting cells are described and the mechanisms of cuticle and calcareous opercular plate secretion are discussed.     

Dental development of the Taï Forest chimpanzees revisited

Developmental studies consistently suggest that teeth are more buffered from the environment than other skeletal elements. The surprising finding of late tooth eruption in wild chimpanzees (Zihlman et al., 2004) warrants reassessment in a broader study of crown and root formation. Here we re-examine the skeletal collection of Taï Forest juvenile chimpanzees using radiography and physical examination. Several new individuals are included, along with genetic and histological assessments of questionable identities. Only half of the Taï juveniles employed by Zihlman et al. (2004) have age of death known with accuracy sufficient for precise comparisons with captive chimpanzees. One key individual in the former study, misidentified during field recovery as Xindra (age 8.3), is re-identified as Goshu (age 6.4). For crown formation we find that onset and duration greatly overlap captive chimpanzees, whereas root development may be more susceptible to acceleration in captive individuals. Kuykendall's (1996) equation relating captive tooth formation stage to age gives reasonable estimates of young wild subjects' true ages. Direct comparisons of tooth eruption ages are limited. A key 3.76 year-old individual likely possessed an emerging mandibular M1 at death (previously estimated from the maxillary molar as occurring at 4.1 years). Wild individuals appear to fall near the middle or latter half of captive eruption ranges. While minor developmental differences are apparent in some comparisons, our reanalysis does not show an “unambiguous pattern” of slower tooth formation in this wild environment. These data do not undermine recent developmental studies of the comparative life histories of fossil hominins.     

Finite element,occlusal, microwear and microstructural analyses indicate that conodont microstructure is adapted to dental function

Conodonts constitute the earliest evidence of skeletal biomineralization in the vertebrate evolutionary lineage, manifest as a feeding apparatus of tooth‐like elements comprised of enamel‐ and dentine‐like tissues that evolved in parallel with these canonical tissues in other total‐group gnathostomes. As such, this remarkable example of evolutionary parallelism affords a natural experiment in which to explore the constraints on vertebrate skeletal evolution. Using finite element analysis, informed by occlusal and microwear analyses, we tested the hypothesis that coincidence of complex dental function and microstructural differentiation in the enamel‐like tissues of conodonts and other vertebrates is a consequence of functional adaptation. Our results show topological co‐variation in the patterns of stress distribution and crystallite orientation. In regions of high stress, such as the apex of the basal cavity and inner parts of the platform, the crown tissue comprises interwoven prisms, discontinuities between which would have acted to decussate cracks, preventing propagation. These results inform a general occlusal model for platform conodont elements and demonstrate that the complex microstructure of conodont crown tissue is an adaptation to the dental functions that the elements performed.     

Differentiation of the Opercular Integument in Rana pipiens

The opercular skin develops in its own specific fashion differing from other areas of the integument previously studied. It remains typically larval until it is sloughed off.
The opercular integument first deviates from the common skin development pathway at stage XV [1] when the rough endoplasmic reticulum. proliferates to form a large part of the cytoplasm and is accompanied by numerous large mitochondria. The Golgi apparatus becomes very large and many vesicles are found in the cytoplasm.
The mitochondria become large and swollen with atypical structure. The cytoplasm becomes highly vesiculated. Degeneration begins at the dermal edge of the basement lamella and proceeds toward the epidermis, being marked by the disorientation of collagen fibrils.
Epidermal cells become progressively more necrotic having cytoplasm consisting mainly of residual bodies and vesicles: the nucleus is the last cellular structure to undergo autolysis.
The dermal cells are the first to be lost (stages XVIII–XIX). The opercular integument is shed as a sheet of cells at stage XX when the forelimbs emerge. The necrotic zone of the opercular integument appears to stop at the junction of the body skin and the skin of the forelimb.     

Ontogeny of the suspensorial and opercular musculature in the suckermouth armoured catfish <Emphasis Type="Italic">Ancistrus</Emphasis> cf. <Emphasis Type="Italic">triradiatus</Emphasis> (Loricariidae,Siluriformes)

Several morphological features characterizing Loricariidae or suckermouth-armoured catfishes (Siluriformes, Teleostei) are related to their ability to attach onto substrates with their sucker mouth, and to scrape algae and other food items from these substrates. Suspensorial and opercular muscles are among those muscles usually involved in respiration (and feeding). In several loricariids including the genus Ancistrus, the opercular musculature is decoupled from the respiratory mechanisms. Results show that the adductor arcus palatini is relatively large throughout the whole ontogeny, while the levator arcus palatini is minute. It develops in association with the dilatator operculi, which exhibits substantial growth only in the juvenile and adult stages. The levator and adductor operculi are connected during early ontogeny, and anterior fibres of the latter muscle differentiate into the adductor hyomandibulae, a muscle previously thought to be absent in loricariids. Relative muscle sizes and orientations, as well as articular transformations and the transition from cartilaginous to bony skeletal elements, indicate ontogenetic transformations in the skeleto-muscular system, affecting and steering functionalities.     

Functional changes in the anatomy of the pharyngeal jaw apparatus of Astatoreochromis alluaudi (Pisces, Cichlidae), and their effects on adjacent structures

Organisms are tightly packed with structures so architectonic interdependency of structures is an obvious aspect of integration. This aspect of functional morphology, however, has received remarkably little attention. The present paper presents an example of the spatial relations among several apparatuses in the head of the cichlid fish, Astatoreochromis alluaudi. It investigates the transformations of these apparatuses and their functions due to a change in the pharyngeal jaw apparatus resulting from a functional shift (insect eating to snail crushing or vice versa ). The volume of the pharyngeal jaw apparatus differs 55% between the insect eating- and the snail eating morph. The increase in volume of the pharyngeal jaw apparatus has an impressive number of spatial effects, both direct and indirect, on other structures. Reallocation of space within the pharyngeal jaw apparatus occurs. Total head volume increases 31% but a reallocation of space is still necessary as the increase of the opercular compartment where the pharyngeal jaw apparatus is situated compensates for only 59% of the volume increase of that. Not all spatial effects do impose constraints. Spatial constraints are avoided when one of the apparatuses can use a topographically different volume of space. The respiratory apparatus shows internal reallocations of space without loss of total volume. The same solution occurs for elements of the expansion apparatus and the buccal savity. The eyes are not influenced. Finally spatial effects can have positive repercussions. The muscles of the oral jaw apparatus increase in size. This may be an example of an epiphenomenon.     

Gravitropic responses of the Avena coleoptile in space and on clinostats. IV. The clinostat as a substitute for space experiments

Gravitropic responses of dark grown oat coleoptiles were measured in weightlessness and under clinorotation on earth. The tests in microgravity were conducted in Spacelab during the IML-1 mission and those on clinostats were conducted in laboratories on earth. The same apparatus was used for both kinds of tests. In both cases autotropism and gravitropic responsiveness were determined. This allowed a quantitative comparison between the plants' responses after receiving the same tropistic stimulations either in weightlessness or on clinostats.
Autotropism was observed with oat coleoptiles responding in weightlessness but it did not occur on clinostats. Gravitropic responsiveness was measured as the ratio between the incremental bending response (degrees curvature) and the corresponding incremental g-dose (stimulus intensity times duration for which it was applied). Plants were tested at either of two stages of coleoptile development (i.e. different coleoptile lengths). From a total of six different kinds of critical comparisons that could be made from our tests that provided data for clinorotated vs weightless plants, three showed no significant difference between responses in simulated vs authentic weightlessness. Three other comparisons showed highly significant differences. Therefore, the validity of clinorotation as a general substitute for space flight was not supported by these results.     

On the mechanism of air ventilaton in anabantoids (Pisces: Teleostei)

Summary Air ventilation in most Anabantoid species is diphasic, consisting of exhalation and inhalation. Exhalation is the release of air from the accessory breathing organs (suprabranchial chambers) through the mouth either into the water near the surface (e.g.,Ctenopoma) or directly into the atmosphere (e.g.,Osphronemus goramy). Inhalation, i.e., taking in fresh air through the mouth at the surface, immediately follows exhalation. X-ray films show (Figs. 5 and 6) that evacuation of the suprabranchial chambers during exhalation is total or nearly total. This, together with the fact that these chambers can contract at most to a very small extent, led to the conclusion that gas is replaced by water entering the chambers during exhalation and that this water is replaced by fresh air during inhalation. Further analysis of films, including conventional films showing the behavior of the opercular apparatus during air ventilation (Fig. 7), leads to a theory of a double-pumping mechanism responsible for air ventilation. This mechanism consists of the buccal apparatus and the opercular apparatus. It is suggested that both of these structures are able to act as both suction and pressure pumps, and thus air ventilation may be explained as the result of alternating activity of these two pumps.In the monophasic air ventilation characteristic of (adult)Anabas testudineus, there is no exhalation phase comparable to that of other Anabantoids. Therefore, no water enters the suprabranchial chambers, which remain filled with gas during the whole ventilation process (Fig. 10). Ventilation is limited to one phase comparable to inhalation in other Anabantoids.The structure of the accessory breathing organs (Fig. 1) and its progressive complication with growth (Fig. 4) were studied inOsphronemus goramy. The arrangement of the labyrinthine plates is in accordance with the requirements of transport of water and gas through the suprabranchial chambers. One plate (the inner plate, Fig. 1) separates these chambers into atrium, ventro-caudal, and dorso-caudal compartments, each with its own opening (valve). This organization seems essential for the transport of gas and water through the suprabranchial chambers and ensures that during exhalation, water flows into the chambers from above, so that while water is filling these chambers displaced gas can be sucked through the deep-lying pharyngeal openings into the expanding buccal cavity.Supported by the Deutsche Forschungsgemeinschaft