Brachiopod tentacles: Ultrastructure and functional significance of the connective tissue and myoepithelial cells in Terebratalia

Summary The fine structure of the tentacles of the articulate brachiopod Terebratalia transversa has been studied by light and electron microscopy. The epidermis consists of a simple epithelium that is ciliated in frontal and paired latero-frontal or latero-abfrontal longitudinal tracts. Bundles of unsheathed nerve fibers extend longitudinally between the bases of the frontal epidermal cells and appear to end on the connective tissue cylinder; no myoneural junctions were found. The acellular connective tissue cylinder in each tentacle is composed of orthogonal arrays of collagen fibrils embedded in an amorphous matrix. Baffles of parallel crimped collagen fibrils traverse the connective tissue cylinder in regions where it buckles during flexion of the tentacle.The tentacular peritoneum consists of four cell types: 1) common peritoneal cells that line the lateral walls of the coelomic canal, 2) striated and 3) smooth myoepithelial cells that extend along the frontal and abfrontal sides of the coelomic canal, and 4) squamous smooth myoepithelial cells that comprise the tentacular blood channel.Experimental manipulations of a tentacle indicate that its movements are effected by the interaction of the tentacular contractile apparatus and the resilience of the supportive connective tissue cylinder. The frontal contractile bundle is composed of a central group of striated fibers and two lateral groups of smooth fibers which function to flex the tentacle and to hold it down, respectively. The small abfrontal group of smooth myoepithelial cells effects the re-extension of the tentacle, in conjunction with the passive resiliency of the connective tissue cylinder and the concomitant relaxation of the frontal contractile bundle.The authors wish to express their appreciation to Professor Robert L. Fernald for his advice and encouragement throughout the course of this study. Some of the work was conducted at the Friday Harbor Laboratories of the University of Washington. The authors are indebted to the Director, Professor A.O.D. Willows, for use of the facilities. Part of this study was supported by NIH Developmental Biology Training Grant No. 5-T01-HD00266 and NSF grant BMS 7507689     

Early Cambrian organophosphatic brachiopods from the Xinji Formation,at Shuiyu section,Shanxi Province,North China

Abundant and diverse small shelly fossils have been reported from Cambrian Series 2 in North China, but the co-occurring brachiopods are still poorly known. Herein, we describe seven genera, five species and two undetermined species of organophosphatic brachiopods including one new genus and new species from the lower Cambrian Xinji Formation at Shuiyu section, located on the southern margin of North China Platform. The brachiopod assemblage comprises one mickwitziid (stem group brachiopoda), Paramickwitzia boreussinaensis n. gen. n. sp., a paterinide, Askepasma toddense Laurie, 1986, an acrotretoid, Eohadrotreta cf. zhenbaensis Li and Holmer, 2004, a botsfordiid, Schizopholis yorkensis (Holmer and Ushatinskaya in Gravestock et al., 2001) and three linguloids, Spinobolus sp., Eodicellomus cf. elkaniiformis Holmer and Ushatinskaya in Gravestock et al., 2001 and Eoobolus sp. This brachiopod assemblage suggests a late Age 3 to early Age 4 for the Xinji Formation and reveals a remarkably strong connection with coeval faunas from East Gondwana, particularly the Hawker Group in South Australia. The high degree of similarity (even at species level) further supports a close palaeogeographic position between the North China Platform and Australian East Gondwana during the early Cambrian as indicated by small shelly fossil data.     

Sero‐taxonomy of skeletal macromolecules in living Terebratulid brachiopods

Antibodies prepared against macromolecules isolated from the shells of three living brachiopod genera have proved to be of considerable taxonomic significance, in that the pattern of cross‐reactivity of all three antisera consistently points to a new interpretation for the evolution of the largest extant brachiopod order, the Terebratulida. This new molecular evidence actually complements rather than contradicts the existing morphology‐based taxonomy, since detailed systematic investigation of the taxa in question has already demonstrated subtle but significant morphological differences in the major taxonomic characters which appear to reflect this new interpretation.

As fragments of skeletal macromolecules, including antigenic determinants, are known to survive for many millions of years within the protected micro‐environments provided by enclosing biominerals, these results suggest that such molecular fossils could well provide important insights on at least the high‐level taxonomic relationships of fossil organisms.     

The Boring Cunctichnus probans Fürsich,Palmer and Goodyear, 1994, from the Type Maastrichtian (Upper Cretaceous,Northeast Belgium)

The ichnogenus Cunctichnus Fürsich, Palmer and Goodyear, 1994 is monotypic, its type ichnospecies, C. probans Fürsich, Palmer and Goodyear, 1994, having hitherto been described solely from the Upper Jurassic (Tithonian) of southern England and the Paris Basin. Cunctichnus probans is recorded herein from the type Maastrichtian (Upper Cretaceous) of the province of Liège, northeast Belgium, that is, about 75 million years younger than previous published records. This specimen differs from the holotype in having a Y-shaped branch.     

论二叠贝类(Permianellids)

本文研究了二叠纪一类形态很特殊的腕足动物——二叠贝类。在仔细观察了迄今所有的有关材料和采用系统切面法和电镜扫描技术分析部分标本后,认为二叠贝类代表着欧姆贝目的1个新支系,即二叠贝科,包括3属,其中1新属(Laterispina gen. nov. )和1新种(Laterispina liaoi gen. et sp. nov. )。根据二叠贝类在地层分布上所显示的形态变化,将二叠贝类的形态演化分成3个阶段:早二叠世、晚二叠世早期和晚二叠世晚期。本文还探讨了二叠贝类的生态特点,认为它属近礁相生物群落中或浅海近浪基面泥质基底上生物群落中的高层附生悬食类,是二叠纪特提斯生物群的特有类群。     

Biogeochemistry of Late Paleozoic North American brachiopods and secular variation of seawater composition

Sr/Ca ratios in modern brachiopod shells reflect variations in ambient seawater, whereas their Na contents show no relationship with water depth or habitat. Their Mn and Fe contents are controlled, in part, by leaching of these elements from oxide coatings or the low input/sedimentation rate of detrital material into depositional areas such as Quatsino Sound. For most Carboniferous brachiopods from North America, the Mn and Fe contents are similar to those recorded by their Recent counterparts. The high Mn and Fe contents in the brachiopods from shales suggest several possibilities for these levels. One possibility is the leaching of Mn and Fe from oxide coatings/matrix which was not completely removed in the cleaning process, or the high levels in part reflect unusual depositional conditions (some degree of anoxia) for the local shaly environments. The Sr/Ca ratio of brachiopods and, by inference, complementary seawater, did not vary significantly during the Carboniferous. The Sr/Ca minimum observed in brachiopods of Mississippian age coincides with a dip in the ⁸⁷Sr/⁸⁶Sr curve and correlates with the Hercynian orogeny. This is attributed to the cycling of seawater through mid-ocean ridge basalts, and postulated exchange reactions account for variation in the composition of seawater-Ca. The unidirectional trend of heavier δ¹³C values from the Devonian to the Permian is intricately coupled with the evolution of the terrestrial biomass. In addition to expansion of terrestrial plants, burial of reduced carbon in the form of coal (organic matter) contributed to the observed shift. The start of the Permo-Pennsylvanian glaciation is marked by a negative excursion of the secular carbon trend, which is linked to weathering of reduced carbon and its return to the oceanic reservoir with its oxidized carbon. The oxygen isotope values reflect the unidirectional trend towards higher values of the carbon data with decreasing geologic age. Negative excursions of the trend may be related to extensive weathering of terrestrial and submarine rocks, whereas positive excursions may be related to hydrothermal alteration of submarine rocks and dehydration of oceanic crust during times of active sea-floor spreading. Oxygen-calculated water temperatures of unaltered brachiopod material are unrealistically high for all of the Devonian, and the Chesterian-Meramecian, Desmoinesian-Missourian, and Artinskian Epochs. During these times maximum water temperatures of 42° to 56°C are well above the thermal threshold of protein denaturation. This process, which is lethal to most higher organisms, demands an adjustment in oxygen of -2.5%. for samples older than Missourian, and of -1.250%. for samples spanning the Missourian-Artinskian interval. With these adjustments and salinity considerations made prior to calculations, water temperatures become reasonable for the Late Paleozoic epeiric, tropical seas of North America.     

凯里生物群腕足动物与游泳动物共存现象研究

腕足动物是贵州凯里生物群中重要的化石门类,不仅化石数量丰富,分异度高,还具有丰富的生态现象。在寒武系的化石记录上,腕足动物常与海绵、藻类、棘皮动物、水母状生物、软舌螺、威瓦西亚虫、其他腕足动物等保存在一起,凯里生物群中的腕足动物也有类似的共存现象。本文就凯里生物群中腕足动物与游泳动物的共存现象进行了初步研究,认为腕足动物与贵州拟轮盘水母Pararotadiscus guizhouensis存在共栖、共埋两种关系,讨论了这两种关系的不同之处;分析了腕足动物与大型双瓣壳节肢动物加拿大虫Canadaspis的共存现象,推测一只腕足动物与Canadaspis共同保存的化石记录表明这两种生物存在共栖关系。本文的研究丰富了凯里生物群物种之间的生态关系,为凯里生物群的生态多样性提供了更多的证据。     

Intense drilling in the Carboniferous brachiopod Cardiarina cordata Cooper, 1956

The brachiopod Cardiarina cordata, collected from a Late Pennsylvanian (Virgilian) limestone unit in Grapevine Canyon (Sacramento Mts., New Mexico), reveals frequent drillings: 32.7% (n = 400) of these small, invariably articulated specimens (<2 mm size) display small (<0.2 mm), round often beveled holes that are typically single and penetrate one valve of an articulated shell. The observed drilling frequency is comparable with frequencies observed in the Late Mesozoic and Cenozoic. The drilling organism displayed high valve and site selectivity, although the exact nature of the biotic interaction recorded by drill holes (parasitism vs. predation) cannot be established. In addition, prey/host size may have been an important factor in the selection of prey/host taxa by the predator/parasite. These results suggest that drilling interactions occasionally occurred at high (Cenozoic-like) frequencies in the Paleozoic. However, such anomalously high frequencies may have been restricted to small prey/host with small drill holes. Small drillings in C. cordata, and other Paleozoic brachiopods, may record a different guild of predators/parasites than the larger, but less common, drill holes previously documented for Paleozoic brachiopods, echinoderms, and mollusks.     

Ciliary sieving and active ciliary response in capture of particles by suspension-feeding brachiopod larvae

Larvae of a brachiopod, Glottidia pyramidata, used at least two ciliary mechanisms to capture algal cells upstream from the lateral band of cilia that produces a feeding/swimming current. (1) Filtration: the larvae retained algal cells on the upstream (frontal) side of a sieve composed of a row of stationary laterofrontal cilia. Movement of the laterofrontal cilia could not be observed during capture or rejection of particles, but the laterofrontal cilia can bend toward the beating lateral cilia, a possible mechanism for releasing rejected particles from the ciliary sieve. (2) Localized changes of ciliary beat: the larvae may also concentrate particles by a local change in beat of lateral cilia in response to particles. The evidence is that the beat of lateral cilia changed coincident with captures of algal cells and that captured particles moved on paths consistent with a current redirected toward the frontal side of the tentacle by an induced local reversal of the lateral cilia. The change of beat of lateral cilia could have been an arrest rather than a reversal of ciliary beat, however. The similar ciliary bands in adult and larval lophophorates (brachiopods, phoronids, and bryozoans) suggest that these animals share a range of ciliary behaviours. The divergent accounts of ciliary feeding of lophophorates could be mostly the result of different authors observing different aspects of ciliary feeding.     

Common crystal nucleation mechanism in shell formation of two morphologically distinct calcite brachiopods

Closely related mineral-producing organisms share common biomineralisation processes. We demonstrate that, in cases of disparate mineral structures where crystal growth mechanisms are necessarily diverse, nucleation processes are the common underlying mechanism during shell formation. Detailed crystallography in the context of shell microstructure in two morphologically distinct calcite brachiopods indicates that, despite differences in shell growth and fabric, at the centre of growth, calcite crystals nucleate with the c-axis 0001 parallel to the shell surface. Such detailed contextual crystallography of biomineralisation using electron backscatter diffraction (EBSD) will have significant applications for future research in biological and medical sciences.