The improbability of a muscular crinoid column

Donovan, Stephen K. 1989 07 15: The improbability of a muscular crirroid column. Lethaia , Vol. 22, pp. 307–315. Oslo. ISSN 0024–1164.
It has sometimes been assumed that the stems of ancient crinoids were muscular. However, the only contractile fibres found in the stems of extant crinoids are in the cirri of isocrinids and comatulids. On uniformitarian grounds, it is improbable that any ancient crinoid had tissues in the stem that would have aided active orientation, apart from the non-muscular catch connective tissue. This conclusion is supported by a detailed functional analysis of the various forms of column and cirrus articulation. The axial canal has been seen as the probable site of any column musculature, but this is functionally impossible with symplexial and synostosial articulations, both of which are poorly adapted for muscular flexure. Columns that articulate synarthrially are much more flexible, but modern bourgueticrinids lack any stem musculature, despite having such stalks. The only crinoid columns that were functionally adapted to utilize contractile fibres were those of certain coiled-stemmed taxa, where the axial canal was not in the plane of the synarthrial fulcra. However, it is unlikely that such stems, even if muscular, possessed any advantage over a non-muscular column. The only pelmatozoans with a probable muscular column were not crinoids, but the glyptocystitid rhombiferans. * Crinoids, stem, columnal, cirrus, catch connective tissue, contractile fibres, functional morphology .     

The primate subarcuate fossa and its relationship to the semicircular canals part II: adult interspecific variation

Studies have reported an empirical link between the size of the semicircular canals and locomotor agility across adult primates. In this paper, we investigate the possibility that this relationship does not follow from the function of the semicircular canals to sense head rotations, but rather reflects spatial constraints imposed by the subarcuate fossa. The latter sits among the three canals and contains the petrosal lobule of the cerebellar paraflocculus, a structure involved in neural processing of locomotion-related eye movements. Hence, it is feasible that agility-related variations of lobule and fossa size affect the arc size of the surrounding semicircular canals. The present study tests such hypothetical correlations by evaluating canal size, fossa size, and agility among extant adult primates. Phylogenetically informed multivariate regression analyses show that, after controlling for body mass, the size of the subarcuate fossa has a significant positive effect on the overall size of the anterior canal and the width of the posterior canal. Multivariate regressions involving the height of the posterior canal and overall size of the lateral canal are not significant. Further bivariate analyses confirm that fossa size is unlikely to play a role in the previously reported link between agility and the size of the posterior and lateral canals. However, fossa size, especially its opening though the arc of the anterior canal, cannot be excluded as a factor that influences the size of the anterior canal more than agility. The findings show that the most reliable functional signals pertaining to locomotion in species that possess a patent subarcuate fossa are likely to come from the lateral canal and are least likely to come from the anterior canal.     

Ultrastructure of Axial Vascular and Coelomic Organs in Comasterid Featherstars (Echinodermata: Crinoidea)

Abstract The spongy body of Davidaster rubiginosa, D. discoidea, and Comactinia meridionalis, is an axial haemal plexus consisting of two structurally similar, but positionally distinct, regions: an oral circumesophageal part and an aboral part which lies lateral to the axial organ. The axial organ is a large axial blood vessel which is infiltrated by hollow cellular tubes lined with monociliated epithelial cells. The spongy body plexus is a tangle of small blood vessels overlain by podocytes and myocytes. The spongy body and the axial organ are situated in the axial coelom, which is confluent with the perivisceral coelom, the water vascular system, and the parietal canals. The parietal canals open to the exterior via ciliated tegmenal ducts and surface pores. The crinoid spongy body is morphologically similar to the axial gland of asteroids, ophiuroids, and echinoids (AOE). Although the axial glands of these three classes of echinoderms are mutually homologous structures, the homology of the crinoid spongy body and the AOE axial gland is questionable because of differences in organization and developmental origin. Alternatively, the crinoid spongy body may be homologous to asteroid gastric haemal tufts, which are podocyte-covered blood vessels suspended in the perivisceral coelom. The functional organization of the spongy body suggests a filtration nephridium and predicts an excretory function. An alternative hypothesis is that the spongy body is a site of nutrient transfer from the blood vascular system to the perivisceral coelom.     

Untested Assumptions: The Role of Canals in the Dispersal of Sea Lamprey, Alewife, and other Fishes in the Eastern United States

Canals provide aquatic organisms with an excellent thoroughfare to disperse, expand their range, and gain access to new drainages. The evidence used to support this contention is vast and dates to at least the early nineteenth century. In most cases however, the evidence used to defend the contention is not a direct observation of fish dispersing through a canal. Instead, the transfer is generally inferred after the new species is observed in a new watershed, one connected by a canal to the watershed in which the fish was already established. Often, these inferences are developed without considering aspects of the life history and behavior of the fishes involved, or the structure of the canal. I explore the historic transfer of sea lamprey, alewife and other fishes from one watershed to another in the inland waters of eastern North America, primarily New York. New York is an ideal area for examining this phenomenon as a canal has connected each of the five major drainages in the state during part of the previous 200 years. These twelve major canals, and the Welland Canal that connects lakes Ontario and Erie, bypassed major obstructions and created a continuous water route among drainages. Also, many of the 167 freshwater and diadromous fishes of New York exhibited distribution patterns historically limited to a watershed or set of neighboring watersheds. When several important cases are re-examined, dispersal through a canal is not the most parsimonious explanation for the presence of the species in a new drainage. To argue fish dispersal through navigation canals, researchers must consider the natural history and ecological requirements of the species, the characteristics and environmental conditions of the canal, and alternative explanations. The mere presence of a canal does not demonstrate that fish used the canal for dispersal.     

The Sensory Canal Systems of the Living Coelacanth, Latimeria Chalumnae: A New Instalment

Entire sensory canal systems of the coelacanth, Latimeria chalumnae, are described: not only the course of principal canals with their primary and secondary collaterals, but also the course and branches of the pit-line and reticular canals. The number of pores on the left side of the head were found to be 296 in an early (yolksac) embryo, 321 in a late term fetus, 485 in a juvenile, and 2974 in adults. This means that in latimeria most of the lateral-line canal system develop after parturition. Pit lines of the living coelacanth are not rows of superficial neuromasts but canals covered by a thin epidermis like in other sensory canals of the lateral line. These pit-line canals, however, have a very specific structure and branching pattern: the medial dorsal pit-line canal is connected by fine branches on top of the head. The infra-dentary pit-line canal connects via these branches with canals deep inside the bones. Several fine and richly branched canaliculi of unknown function radiate from each quadratojugal pit-line canal. The gular plate pit-line canal has superficially branching arms as well as connections to numerous deeper canals inside the bone. These canals consist of fine branches that in turn lead to and open on the ventral surface of the gular plates as small pores. The system is reminiscent of the reticular (pore) canal system known only from some fossil agnathans and fishes. Thus latimeria combines the reticular system of ancient vertebrates with the lateral-line system of modern fishes. The significance of this gular (possibly electro-sensory) system for feeding by the coelacanth will be discussed.     

Development of the lateral line canal system through a bone remodeling process in zebrafish

The lateral line system of teleost fish is composed of mechanosensory receptors (neuromasts), comprising superficial receptors and others embedded in canals running under the skin. Canal diameter and size of the canal neuromasts are correlated with increasing body size, thus providing a very simple system to investigate mechanisms underlying the coordination between organ growth and body size. Here, we examine the development of the trunk lateral line canal system in zebrafish. We demonstrated that trunk canals originate from scales through a bone remodeling process, which we suggest is essential for the normal growth of canals and canal neuromasts. Moreover, we found that lateral line cells are required for the formation of canals, suggesting the existence of mutual interactions between the sensory system and surrounding connective tissues.     

The architecture of the canal systems of Petrosia ficiformis and Chondrosia reniformis studied by corrosion casts (Porifera,Demospongiae)

Summary The three-dimensional organization of the canal system in two sponge species, Petrosia ficiformis and Chondrosia reniformis, was studied using corrosion casts. Casts were made of live animals, in situ, and canal replicas were analzyed by scanning electron microscopy (SEM). In P. ficiformis the incurrent system consists of a superficial canal network giving rise to large radial canals, which ramify and anastomosize forming an internal web. Excurrent canals are arranged into modular ramified systems radiating from atrial cavities opening to the exterior. Main excurrent canals run at various depths within the sponge, even through the superficial incurrent network. Both incurrent and excurrent canal replicas show smooth, blind-ending capillaries. Some large incurrent canals merge with excurrent ones, thus bypassing choanocyte chambers. In C. reniformis there is a cortical collagen layer crossed by three-like incurrent canals, the twigs of which communicate with groups of inhalant pores. The stems of tree-like canals penetrate into the sponge medulla where they ramify and anastomosize to form a web. Main excurrent canals arise from large cloacal ducts leading to the oscular openings. They give rise to a sequence of branches intersecting the incurrent web. Both incurrent and excurrent canals have sharp, blind-ending capillaries. Morphometric data functions show that diameter scaling in canal branches is exponential in Petrosia and linear in Chondrosia. Structural differences and homologies between the two species are discussed.     

Interrelationships of petiolar air canal architecture,water depth,and convective air flow in Nymphaea odorata (Nymphaeaceae)

• Premise of the study: Nymphaea odorata grows in water up to 2 m deep, producing fewer larger leaves in deeper water. This species has a convective flow system that moves gases from younger leaves through submerged parts to older leaves, aerating submerged parts. Petiolar air canals are the convective flow pathways. This study describes the structure of these canals, how this structure varies with water depth, and models how convective flow varies with depth. • Methods: Nymphaea odorata plants were grown at water depths from 30 to 90 cm. Lamina area, petiolar cross-sectional area, and number and area of air canals were measured. Field-collected leaves and leaves from juvenile plants were analyzed similarly. Using these data and data from the literature, we modeled how convective flow changes with water depth. • Key results: Petioles of N. odorata produce two central pairs of air canals; additional pairs are added peripherally, and succeeding pairs are smaller. The first three pairs account for 96% of air canal area. Air canals form 24% of petiolar cross-sectional area. Petiolar and air canal cross-sectional areas increase with water depth. Petiolar area scales with lamina area, but the slope of this relationship is lower in 90 cm water than at shallower depths. In our model, the rate of convective flow varied with depth and with the balance of influx to efflux leaves. • Conclusions: Air canals in N. odorata petioles increase in size and number in deeper water but at a decreasing amount in relation to lamina area. Convective flow also depends on the number of influx to efflux laminae.     

Ultrastructural shape and three-dimensional organization of the intracuticular canal systems in the mineralized cuticle of the green crab Carcinus maenas

Two main self-contained canal systems are present in the crab mineralized cuticle. The first, or fibre canal system, is constituted by simple, unbranched vertical canals containing axially running fibres in close association with myoepidermal junctions. The second, or pore canal system, is composed of procuticular pore canals and epicuticular channels that prolong the procuticular canals. In opposition to widespread opinion, pore canals make up a three-dimensional branched system extending from the apical plasma membrane of the epidermis up to the epicuticle. Branching occurs by projections of lateral horizontal from the vertical canals at the lower level of the pigmented layer and by innumerable ramifications of epicuticular canals. In agreement with Neville's model for insects, vertical procuticular pore canals of crustacean mineralized cuticle, and also fibre canals, exhibit a twisted ribbon structure reflecting the helicoidal arrangement of the horizontal chitin-protein microfibrils.     

奥硝唑用于感染根管消毒的细菌学研究

目的　观察和探讨新型抗厌氧菌药物奥硝唑消毒感染根管的抗菌效果。方法　选择感染根管患牙98颗,常规根管预备后,随机分为试验组(奥硝唑组)和对照组(甲醛甲酚组)各4 9颗。分别在根管预备前、预备后及封药后进行根管内细菌标本采样、培养、分离与鉴定,测定根管内细菌变化及检出情况,并观察封药后临床症状和体征的变化。结果　2组封药后,根管内细菌数量及检出率均较封药前明显降低( P<0 .0 5 ) ,根管内细菌数量及检出率比较,差异无显著性( P>0 .0 5 ) ,奥硝唑的近期临床疗效优于甲醛甲酚。结论　奥硝唑是一种较安全、有效的根管消毒药物     

Bone vascular supply in monitor lizards (Squamata: Varanidae): influence of size, growth, and phylogeny

Bone vascular canals occur irregularly in tetrapods; however, the reason why a species has or lacks bone canals remains poorly understood. Basically, this feature could depend on phylogenetic history, or result from diverse causes, especially cortical accretion rate. The Varanidae, a monophyletic clade that includes species with impressive size differences but similar morphologies, is an excellent model for this question. Cortical vascularization was studied in 20 monitor species, on three bones (femur, fibula, and tibia) that differ in their shaft diameters, and in the absolute growth speed of their diaphyseal cortices. In all species smaller than 398 mm SVL (133-397 mm in sample), bone cortices lack vascular canals, whereas all larger species (460-1,170 mm in sample) display canals. The size 398-460 mm SVL is thus a threshold for the appearance of the canals. The distribution of vascular and avascular bone tissues among species does not precisely reflect phylogenetic relationships. When present, vascular canals always occur in the femur and tibia, but are less frequent, sparser, and thinner in the fibula. Vascular density increases linearly with specific size but decreases exponentially during individual growth. In most species, canal orientation varies between individuals and is diverse in a single section. No clear relationship exists between canal orientation and vascular density. These results suggest that: a) the occurrence and density of bone vascular canals are basically dependant on specific size, not phylogenetic relationships; b) vascular density reflects the absolute growth rates of bone cortices; c) the orientation of vascular canals is a variable feature independent of phylogeny or growth rate.     

Morphology of the mammalian vestibulo-ocular reflex: the spatial arrangement of the human fetal semicircular canals and extraocular muscles

The vestibulo-ocular reflex is the system of compensatory ocular movements in response to stimulation of the kinetic labyrinth seen in all vertebrates. It allows maintenance of a stable gaze even when the head is moving. Perhaps the simplest influence on the VOR is the spatial orientation of the planes of the semicircular canals relative to the extraocular muscles. It is hypothesized that the extraocular muscles are in parallel alignment with their corresponding semicircular canals in order to reduce the amount of neural processing needed and hence keep reflex times to a minimum. However, despite its obvious importance, little is known of this spatial arrangement. Moreover, nothing is known about any ontogenetic changes in the relative orientations of the extraocular muscles and semicircular canals. The morphologies of fetal and adult specimens of Homo sapiens were examined using magnetic resonance (MR) images. Three-dimensional co-ordinate data were taken from the images and used to calculate vector equations of the extraocular muscles and planes of best fit for the semicircular canals. The relative orientations of the muscles and canals were then calculated from the vectors and planes. It was shown that there are significant correlations between both the anterior and lateral semicircular canals and their corresponding extraocular muscles during ontogeny. In the case of the lateral canal with the medial rectus, the lateral canal with the lateral rectus, and the anterior canal with the inferior oblique, the trend is towards, though never reaching, alignment, whereas the anterior canal and the superior rectus muscle move out of alignment as age increases. Furthermore, it was noted that none of the six muscle-canal pairs is in perfect alignment, either during ontogeny or in adulthood. It was also shown that the three semicircular canals are not precisely orthogonal, but that the anterior and posterior canals form an angle of about 85 degrees , while the anterior and lateral canals diverge by approximately 100 degrees . Overall, it was shown that there is significant reorientation of the extraocular muscles and semicircular canals during ontogeny, but that, in most cases, there is little realignment beyond the fetal period.     

The role of the ELAV homologue EXC-7 in the development of the Caenorhabditis elegans excretory canals

The exc mutations of Caenorhabditis elegans alter the position and shape of the apical cytoskeleton in polarized epithelial cells. Mutants in exc-7 form small cysts throughout the tubular excretory canals that regulate organismal osmolarity. We have cloned the exc-7 gene, the closest nematode homologue to the neural RNA-binding protein ELAV. EXC-7 is expressed in the canal for a short time midway through embryogenesis. Cysts in exc-7 mutants do not develop until several hours later, beginning at the time of hatching. We find that the first larval period is when the canal completes the majority of its outgrowth, and adds new apical cytoskeleton at a rapid rate. Ultrastructural studies show that exc-7 mutant defects resemble loss of beta(H)-spectrin (encoded by sma-1) at the distal ends of the excretory canals. In addition, exc-7 mutants exhibit synergistic excretory canal defects with mutations in sma-1, and EXC-7 binds sma-1 mRNA. These data imply that EXC-7 protein may affect expression of sma-1 and other genes to effect proper development of the excretory canals.     

F-actin rings are associated with the ring canals of the Drosophila egg chamber

Staining of Drosophila egg chambers with rhodaminyl-lysine-phallotoxin (RLP), a specific stain for F-actin, has demonstrated the presence of dense F-actin rings associated with the inner surfaces of the ring canals. They were first observed in the distal part of the germarium where rings of four different size classes were found, differing in diameter by up to twofold. The ring sizes are considered to correspond to the ring canals formed at each of four successive incomplete cleavages. During the growth of the egg chamber the actin rings were found to increase in diameter from less than 1 micron to approx. 10 micron. Concomitantly a secondary outer ring of more diffuse material is built up in association with the cell membranes. A well developed array of microfilament bundles was also associated with the nurse cell plasmalemma. In stages where the transfer of the bulk of the nurse cell cytoplasm into the oocyte was occurring the rings came closer together in a central area. In late stage chambers the F-actin rings and the microfilament bundles appeared to be incorporated into large irregular masses of actin, which subsequently disappeared as the mature oocyte formed. The F-actin rings are suggested to act as mechanical strengthening elements for the canal plasmalemma, whilst cytoplasmic transport occurs through the ring canals.     

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.     

盔甲鱼类的侧线系统

本文对盔甲鱼类的侧线系统作了系统的描述;盔甲鱼类与异甲鱼类、骨甲鱼类和七鳃鳗在侧线系统方面可作相近的对比;盔甲鱼类众多的横行感觉管暗示在原始脊椎动物里,横行感觉管按节排列、由前而后分布整个头区;在盔甲鱼类中侧线系统存在多鳃鱼型和真盔甲鱼型,两者的分化至迟在早志留世已经完成.     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.     

壳菜果植物树脂道的发生、发育及分布的研究

经解剖观察,发现壳菜果（Ｍｙｔｉｌａｒｉａｌａｏｅｎｓｉｓ）植物初生结构能自然形成树脂道,而次生结构不能自然形成。树脂道原始细胞发生位置为离顶端１２０～１４０μｍ的区段上,与初生分生组织同时形成。以后原始细胞经历;（１）原始细胞分裂阶段;（２）树脂道发生阶段;（３）树脂道扩张阶段;（４）树脂道成熟阶段;（５）树脂道破毁阶段而完成其功能周期。壳菜果植物的树脂道以裂溶生方式发生,分布在维管束外侧的皮层中。此为金缕梅科各亚科系统位置研究提供重要证据