The origin of the spiriferidine brachiopods

Wright, Anthony D. 197901 15: The origin of the spiriferidine brachiopods. Lethaia . Vol. 12. pp. 29–33. Oslo. ISSN 0024–1164.
In recent years doubts have been expressed as to whether the strophic spiriferidines should continue to be grouped with the non-strophic spiriferids in the order Spiriferida or not. The solution to this problem will only be found by establishing the origin of the spiriferidines. A characteristic feature of the spiriferidines is their well developed micro-ornament; this is shared also by the orthid Platystrophiinae, and together with the striking similarity in overall morphology (well recognized in the early nineteenth century) it suggests that here, in the Platystrophia plexus, is the ancestral stock of the strophic spirebearers.
The Platystrophünae share with the non-strophic Rhynchonellida the potential to develop a spire. It is here considered that the former gave rise to the spiriferidines and the latter to the non-strophic spire-bearers. These quite separate developments justify the separation of the spire-bearers into the two orders Spiriferida and Atrypida.     

Influence of valve geometry, ornamentation, and microstructure on fractures in Late Ordovician brachiopods

Among Late Ordovician brachiopods from southeastern Indiana. strophomenids display a ratio of 4:1 parabolic to linear repaired fractures in contrast to the 1:2 ratio found for orthids and rhynchonellids. Additionally, only strophomenids display repaired elliptical fractures. The weakest parts of strophomenid and orthid-rhynchonellid shells are the regions of the adductor muscle scars and the sulcus, respectively. Fractured biplanate shells of strophomenids are commonly cleaved anteriorly to posteriorly, whereas fractures are localized on the anterior of strongly curved to geniculate conspecific specimens. Rugae on leptaenids, thickened anterior margins of the brachial valve of rafinesquinids, and the dense distribution of pseudopunctate in all strophomenids, functioned to localize anteriorly the (un)repaired linear and parabolic fractures. No sublethal fracture occurs on any biconvex shell where the height is greater than 14 mm, despite the fact that numerous specimens of certain species attained shell heights of 20 mm or more, an observation suggesting the upper limit in the gape of the crushing elements of the predator. Crushing experiments on valve 'models' reveal that the inflated equibiconvex, plicate shape of the shells of Plarysfrophia is the strongest. However, the architecture of the concave strophomenid valves is relatively stronger than the corresponding valves of many orthids and rhynchonellids when normalized for valve thickness.     

Model for origin,function and fabrication of fluted cephalopod septa

The model supposes that sub-hemispheric septa of deep-water cephalopods evolved transverse pillars by meridional fluting in order to support flat and therefore weak areas of the shell wall. Several trends toward reduction of sutural spacing for improved wall support resulted in rise of fluting and finally, marginal crenulation. During ontogeny, the function of the ammonite septum as complex vault system against ”normal“ pressure from the body was succeeded by compound-pillar function for wall support. Fabrication of ammonitic septa probably involved positive pressure differential of new ”cameral“ liquid, orientation of mantle fibers along stress lines, and successively affixed tie-points which lay on an aponeurosislike mantle structure.     

Commissural asymmetry in brachiopods

Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against.     

'Flapping valves' in brachiopods

M. J. S. Rudwick and others postulate 'rhythmic-flow' feeding for the Permian richtho-feniacean bi-achiopods, whereas R. E. Grant claims that they fed by normal ciliary action. Suspension-feeding has two components, current generation and food capture; normal brachiopod lophophores do both, but this is neither universal nor compulsory among animals. Opening and closing the richthofeniid shell generated a 'tidal-flow' current precisely analogous to respiratory currents in mammals; this is neither inefficient nor 'self-defeating', as Grant claims. Grant's analysis fails because he chose the wrong mechanical analogy (a pump). Morphological features of richthofeniids are better explained on a tidal-flow hypothesis than on a ciliary-flow model, and all the data adduced by Grant in rejecting the former is compatible with it or favorable to it. It explains morphological features that are bizarre mysteries on the ciliaiy-current model, and is therefore superior even though it implies that these Permian brachiopods were radically innovative.     

Biogeography of the recent brachiopods

The vertical, latitudinal, and circumcontinental zonality of the distribution of the species, genera, and families of recent brachiopods is considered. The distortions of the latitudinal and meridional symmetry of the biogeographic structure of the ocean are analyzed in view of the patterns of the global circulation of the surface and intermediate waters. Thus ancient faunas may be reconstructed based on data on the structural characteristics of the taxocene of recent brachiopods. The features of the paedomorphic evolution of brachiopods from the different families in extreme habitats (interstitial, underwater caverns, submarine rises, abyssal depths, hydrothermal areas, and margins of habitats) are discussed. The biogeographic structure of bottom dwellers is shown to simplify with depth as well as with simplification of the hydrological structure of the ocean. The important role of the bathyal oceanic zone (slopes of continents, islands, submarine mountains, ridges, and rises) in the preservation of faunal relicts is shown. The historical change from brachiopods to bivalves that occurred from the Paleozoic to the Mesozoic and Cenozoic is shown to have resulted not from competitive exclusion, but from complex and global changes in the plankton composition, which were unfavorable for articulate brachiopods, which had already developed specialized feeding habits, feeding on food that led to the production of almost no metabolic waste products; they had even partly lost their alimentary canal. The development of shelly plankton and, especially, of diatoms hampered the post-Paleozoic revival of large assemblages of articulate brachiopods in shallow-water habitats. The unfilled ecological niches were colonized by bivalves, which were widely adapted to feeding on live phyto-and zooplankton. Recent articulate brachiopods, which are adapted to feeding on the products of decay of dead plankton, form a belt of densely populated settlements of the organic biofilter outside the photic zone on the seaward edge of shelves and on the upper parts of the slopes of continents, islands, and submarine rises throughout the world.     

The structure and development of septa inNeurospora crassa

Summary Electron microscopy of septa ofNeurospora crassa has shown that microfibrillar material is a major structural component. These microfibrils are arranged in a predominantly tangential orientation and in young (24 hours) mycelium can often be seen in unextracted septal preparations. In older (5 days) mycelium they are overlain with amorphous material, which can be removed by treatment with Pronase, or by chemical extractions. The structure of septa is described and compared with that of the lateral hyphal wall.Developing septa are typically surrounded by vesicles, and sometimes by alignments of cytoplasmic tubules. Electron and light microscopic autoradiography have shown that N-acetylglucosamine is quickly and specifically incorporated into developing septa, and there is no evidence for its prior incorporation into any cytoplasmic site. Glucose is also incorporated into septa, but less specifically. From the autoradiographic results and from experiments with chemical and enzymic extractions it is suggested that chitin is a major component of the septum. A model of the septum is constructed from these data.     

The role of the coelom as a hydrostatic skeleton in lingulid brachiopods

Anatomical and experimental studies of the perivisceral coelom and pedicel of Lingula ana lina indicate that the coelomic fluid functions as a hydrostatic skeleton in respect of valve and pedicel movements, valve opening always being associated with positive pressures. The perivisceral coelom is surrounded by a body wall containing circumferential muscle fibres, whilst all muscles passing between the valves (principally adductor and oblique fibres) are located within the body wall. These two sets of muscles function similarly to the circular and longitudinal muscles of a classical hydrostatic skeleton.
Pressure recordings from the lumen of the pedicel and perivisceral coelom, during opening or rotary movements of the valves, were similar and showed pressure pulses of up to 0.8 kPa. During the initial stages of burrowing, pulses of up to 2.5 kPa were observed when the valves were being pressed into the sand. These values are well within the capability of the circumferential muscles of the body wall.     

The central role of septa in the basidiomycete Schizophyllum commune hyphal morphogenesis

The purpose of the present research was to observe in the filamentous basidiomycete Schizophyllum commune, the connection between the nuclear division and polymerization of the contractile actin ring with subsequent formation of septa in living hyphae. The filamentous actin was visualized using Lifeact-mCherry and the nuclei with EGFP tagged histone 2B (H2B). Time-lapse fluorescence microscopy confirmed that in monokaryotic and dikaryotic hyphae, the first signs of the contractile actin ring occur at the site of the nuclear division, in one to two minutes after division. At this stage, the telophase nuclei have moved tens of micrometers from the division site. The actin ring is replaced by the septum in six minutes. The apical cells treated with filamentous actin disrupting drug latrunculin A, had swollen tips but the cells were longer than in control samples due to the absence of the actin rings. The nuclear pairing and association with clamp cell development as well as the clamp cell fusion with the subapical cell was disrupted in latrunculin-treated dikaryotic hyphae, indicating that actin filaments are involved in these processes, also regulated by the A and B mating-type genes. This suggests that the actin cytoskeleton may indirectly be a target for mating-type genes.     

Climatic control of brachiopods in the lower Namurian

The fauna and lithology of a marine band in the lower Edale Shales (Namurian E₂b) at Edale, Derbyshire, England, are described quantitatively. Two brachiopods, Rugosochonetes sp. and Productus hibernicus were the dominant elements of the fauna. The average age at death was about 3 years, although the maximum age of Rugosochonetes (ca. 7 years) was probably a little greater than that of Productus (ca. 5 years). Both sediment deposition and fauna were climatically controlled. The climate was seasonal from wet to dry. Quartz was deposited and Rugosochonetes sp. flourished during the wet periods. Carbonate deposition and Productus hibernicus were dominant during the dry periods.     

Independent similarity in the morphological evolution of brachiopods

The close similarity of the shell exterior of articulate brachiopods from different orders, which must be taken into account in taxonomic identifications and phylogenetic reconstructions, is analyzed. A possible mechanism of the appearance of such brachiopods in connection with the morphogenetic generality of the structurally similar organisms is evaluated.     

The development of growth lines on articulate brachiopods

Three types of growth lines are recognised on articulate brachiopod shells: (1) very fine diurnal growth lines formed by calcite increments at the shell margin, (2) seasonal growth lines, formed by inward reflection (doubling back) of the mantle edge, seen as concentric steps on the shell surface and marked by re-orientation of growth vectors evidenced by secondary shell fibres, (3) disturbance lines, formed by abrupt regression of the mantle edge, also seen as concentric steps on the shell surface, but indicated by a dislocation in the shell fabric. Lamellose and spinose ornaments of the sort seen in Tegulorhynchia are essentially genetically controlled. Periodic outgrowths from the outer mantle lobe secrete frills of primary shell that project from the shell surface and form short hollow spines where they cross the radial ornament. In longitudinal section spine formation is seen to involve gradual increase in the rate of secretion of primary shell followed by retraction, and often collapse, of the mantle outgrowth, accompanied by regression. Reflection of the mantle edge usually follows spine formation.     

Ultrastructure of the loop of terebratulide brachiopods

The folded and twisted calcareous ribbon, forming both the ascending and descending lamellae of the loop of Waltonia inconspicua (Sowerby), is a two-layered structure consisting of a wedge of regularly stacked secondary layer fibres that overlie a thin layer of non-fibrous calcite (herein termed brachiotest). On one surface, that facing into the mantle cavity, secondary fibrous mosaic predominates, but smooth, finely banded brachiotest occurs as a narrow marginal lip upon which secondary layer fibres proliferate and progressively overlap. This growing edge of the ribbon is secreted by long, folded epithelial cells with digitate extensions to their apical plasmalemmas, which are distinguishable from the cuboidal epithelium-secreting fibres and their membranous sheaths. The other surface, facing the body cavity and the brachial coelom, consists entirely of roughened brachiotest exhibiting prominent banding that is aligned parallel to the growing loop edge. This surface is overlain by microfilamentar epithelium acting as a holdfast for the connective tissue frame of the lophophore. The other edge of the ribbon consists of truncated sections of both secondary-layer fibres and brachiotest which bear signs of resorption consistent with the degenerated state of the associated epithelium. Growth of the Waltonia loop is controlled by these localized processes of secretion and resorption of the fibrous and brachiotest layers and is typical of all terebratulides so far studied. The brachiotest is not homologous with the non-fibrous primary shell secreted at the valve margin. □ Brachiopoda, Articulata, Terebratulida, ultrastructure, lophophore, loop.     

Microborings in Recent brachiopods and the functions of caeca

Microborings in the primary shell layer of Recent brachiopods are clearly seen to avoid endopunctamicroscopic canals pervading the shell fabric and housing papillose extcnlions of the mantle (the caeca). This avoidance confirms the suggestion that the caecal contents inhibit boring organisms (Owen & Williams 1969; Proc. R. Soc. Loud. B, 172 ), and as such the caecum can be considered as an important instrument in protecting the brachiopod shell. A comparison of the relative fecundity of co-habitating impunctate and cndopunctate New Zealand brachiopods provides indirect evidence that the caecum may indeed also function in a nutrient storage capacity. Brachiopods, microborings, primary shell layer, endopuncta, defence, storage.     

The reconstructive strategy for improving elbow function in late obstetric brachial plexus palsy.

Children with previously untreated obstetric brachial plexus palsy frequently have abnormal elbow function because of motor recovery with aberrant reinnervation, or because of paresis or paralysis. From 1988 to 1997 (9-year period), 62 children with obstetric brachial plexus palsy with resulting elbow deformity underwent various methods of palliative reconstruction to improve elbow function. For motor recovery with aberrant reinnervation, release of aberrantly reinnervated antagonistic muscles and augmentation of paretic muscles form the basis of surgical intervention. The surgical procedures included triceps-to-biceps transfer, biceps-to-triceps transfer, brachialis-to-triceps transfer, or combined biceps- and brachialis-to-triceps transfer. Choice of procedures was individualized and randomly determined on the basis of the degree and pattern of aberrant reinnervation between elbow flexors and extensors. In patients' motor recovery with paresis or paralysis, persistently weak elbow flexion was salvaged with a functioning free muscle transplantation or Steindler's flexorplasty, or regional shoulder muscle transfer. In addition, patients with aberrant reinnervation between shoulder abductors and elbow flexors underwent anterior deltoid-to-biceps transfer with a fascia lata graft. All patients had a minimum follow-up of 2 years. Results are assessed and discussed and a reconstructive algorithm is recommended. In general, reconstruction of elbow extension should precede that of elbow flexion. Biceps-to-triceps transfer with preservation of an intact brachialis muscle, or brachialis-to-triceps transfer with preservation of an intact biceps, allows 50 percent of these patients to achieve acceptable elbow flexion and extension in a single-stage procedure.