A NEW EARLY CARBONIFEROUS MICRO-PRODUCTID BRACHIOPOD FROM SOUTH CHINA

Abstract:  We describe Muhuarina haeretica gen. et sp. nov. from a recently discovered silicified brachiopod fauna from the Lower Carboniferous of South China. This new microproductid appears to be the oldest representative of the highly differentiated, mainly Permian, aulostegoid family Cooperinidae. The internal structure of the dorsal valve of M. haeretica is dominated by strongly developed, pronounced subperipheral ridges, which suggest support for a simple schizolophe type of lophophore. Brachial ridges, as in other productides, most probably represent an attachment area of the lophophore to the dorsal epithelium. An attempt to homologize subperipheral and brachial ridges among Cooperinidae is presented.     

Structure of the brachiopod lophophore

Data on the development, structure, and functional morphology of the brachiopod lophophore are analyzed. The common origin of the tentacle apparatus in Lophophorata from the postoral ciliary band of the larva is shown. The brachiopod lophophore is based on the brachial axis consisting of the brachial fold running along the row of tentacles. The brachial axis may be attached to the brachial (dorsal) mantle lobe (trocholophe, schizolophe, and ptycholophe lophophores) or extend freely into the mantle cavity to form coiling brachia (spirolophe, zygolophe, and plectolophe lophophores). The circulation of water flows through the mantle cavity in the brachiopods with attached and free lophophores is described. A new hypothesis on the sorting of particles suspended in water during filtration is proposed.     

A biogeographically mixed, Middle Permian brachiopod fauna from the Baoshan Block, western Yunnan, China

A small brachiopod fauna is described from the carbonate rocks of the basal Shazipo Formation of the Baoshan Block, western Yunnan, south-west China, including significant new ventral and dorsal internal morphological features of Cryptospirifer omeishanensis Huang. This fauna is regarded as Wordian (Middle Guadalupian, Middle Permian) because of the presence of Cryptospirifer omeishanensis Huang and associated fusulinids ( Neoschwagerina craticulifera Zone). Palaeobiogeographically, the brachiopod fauna is of considerable interest because of its admixed nature characterized by typical warm-water Cathaysian elements intermingled with temperate Peri-Gondwanan taxa. This in turn is interpreted to indicate that the Baoshan Block may have been situated in an intermediate palaeogeographical position between Gondwanaland to the south and Cathaysia to the north during the Mid Permian and, as such, it probably furnished an important 'stepping stone' for the dispersal of Mid Permian eastern Tethyan marine invertebrate taxa (e.g. Cryptospirifer ) to the western Tethys.     

Architecture and function of the lophophore in the problematic brachiopod Heliomedusa orienta (Early Cambrian, South China)

The detailed structure of the lophophore is a key diagnostic character in the definition of higher brachiopod taxa. The problematic Heliomedusa orienta Sun and Hou, from the Lower Cambrian Chengjiang Lagerstätte of Yunnan, southwestern China, has a well-preserved lophophore, which is unlike that of any known extant or extinct brachiopods. Based on a comparative study of lophophore disposition in H. orienta and the extant discinid Pelagodiscus atlanticus, the in- and excurrent pattern and shell orientation of H. orienta are described and discussed. Reconstructions of lophophore shape and function are based on numerous specimens and comparison with P. atlanticus. The lophophore is composed of a pair of lophophoral arms that freely arch posteriorly rather than coiling anteriorly as commonly seen in fossil and recent lingulids. The lophophore is attached to the dorsal lobe of the mantle; it has neither calcareous nor chitinous supporting structures, and is disposed symmetrically on either side of the valve midline. The mouth can be inferred to be located at the base of the two brachial tubes, slightly posterior to the anterodorsal projection of the body wall. The lophophoral arms bear laterofrontal tentacles with a double row of cilia along their lateral edge, as in extant lingulid brachiopods. The main brachial axes are also ciliated, which presumably facilitated transport of mucous-bound nutrient particles to the mouth. The unique organization of the lophophore in Heliomedusa is not like any known fossil and living brachiopods. This clearly demonstrates that H. orienta is not a member of any crown group. It is here considered as a member of the brachiopod stem group, which challenges recent interpretations of a close discinid affinity.     

Quantitative analysis strengthens qualitative assessment: a case study of Devonian brachiopod species

Species recognition attributed to the brachiopod family Atrypidae is evaluated based on qualitative and quantified morphological characters. I identified two brachiopod species—Pseudoatrypa lineata and Pseudoatrypa devoniana—from a rich assemblage of brachiopods recovered from the middle Devonian Genshaw Formation of the Traverse Group. Qualitative examination suggested that the former had fine-medium-sized ribbing, a narrow hinge line, widened anterior, moderately steep mid-anterior fold, domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched-shape dorsal valve, and flat ventral valve of the latter. The shell outline appears rounded for P. lineata and elongated for P. devoniana. Quantitative assessment of the morphological characters on the dorsal, ventral, anterior, and posterior regions of the valves of the two species using geometric morphometric and statistical analyses suggests that the morphologies of the two species are considerably different (P  $ \ll $  0.01). Thus, qualitative differences between the two atrypid species were further corroborated by quantitative results. This emphasizes the fact that these two species of Pseudoatrypa were indeed different from each other. This study highlights the necessity of incorporating quantified morphological characters to successfully investigate the taxonomic distinctness of fossil invertebrates to the species level.     

Shell Structure And Inferred Growth, Functions And Affinities Of The Sclerites Of The Problematic Micrina

The stratiform laminae of Micrina sclerites originally consisted of rheomorphic successions of monolayers of micrometric–sized, apatitic tablets, presumably interleaved with chitin and glycosaminoglycans (GAGs). Paired laminae enclose slot–like chambers swelling into lobes distally that originally contained GAGs and deposits of spherulitic and prismatic apatite. The laminae are pervaded by apatitic tubes, apparently secreted by microvillous setoblasts and containing, at the surface, chitinous setae. Internal markings suggest that the triangular (sellate) sclerite supported a pair of muscles and the planospiral (mitral) sclerite, a medial muscle and gonadal sacs flanked by a pair of crescentic muscle bases. Both sclerites were secreted by a mantle with a circumferential fold. The sellate and mitral sclerites are homologized with the anterior and posterior shells of Halkieria and could have become the dorsal and ventral valves of the ancestral brachiopod by a sequence of transformations. These include: the folding of the halkieriid body axis; accelerated mixoperipheral growth of the anterior (dorsal) shell to enclose, with the posterior (ventral) shell, a mantle cavity lined with modified ciliated epithelium of the foot; reduction of sclerite–secreting epithelium to the locus of the brachiopod pedicle epithelium; and the anterior (dorsal) spread of gonadal lamellae.     

On the origin systematic position of the calcareous-shelled inarticulate brachiopods

Available data on the anatomy, ontogeny embryology of Brachiopoda ( sensu lato ) suggest that this Phylum in the traditional view is in fact a clade of organization includes two stocks of lophophorate organisms of quite different origins. Their rank does not correspond to existing Class divisions. The phosphatic-shelled in articulates are regarded as a separate Class Lingulata. The Phylum Brachiopoda ( sensu stricto ) is restricted to the calcareous-shelled inarticulate articulate lineages. Ancestors of the calcareous-shelled brachiopods probably differentiated from the protolophophorates before the radiation of the other lophophorate stocks took place. The articulation of the valves appeared independently in several lineages during the early stages of brachiopod evolution.     

Neuromuscular development in Novocrania anomala: evidence for the presence of serotonin and a spiralian-like apical organ in lecithotrophic brachiopod larvae

SUMMARY The phylogenetic position of Brachiopoda remains unsettled, and only few recent data on brachiopod organogenesis are currently available. In order to contribute data to questions concerning brachiopod ontogeny and evolution we investigated nervous and muscle system development in the craniiform (inarticulate) brachiopod Novocrania anomala . Larvae of this species are lecithotrophic and have a bilobed body with three pairs of dorsal setal bundles that emerge from the posterior lobe. Fully developed larvae exhibit a network of setae pouch muscles as well as medioventral longitudinal and transversal muscles. After settlement, the anterior and posterior adductor muscles and delicate mantle retractor muscles begin to form. Comparison of the larval muscular system of Novocrania anomala with that of rhynchonelliform (articulate) brachiopod larvae shows that the former has a much simpler muscular organization. The first signal of serotonin-like immunoreactivity appears in fully developed Novocrania anomala larvae, which have an apical organ that consists of four flask-shaped cells and two ventral neurites. These ventral neurites do not stain positively for the axonal marker α-tubulin in the larval stages. In the juveniles, the nervous system stained by α-tubulin is characterized by two ventral neurite bundles with three commissures. Our data are the first direct proof for the presence of an immunoreactive neurotransmitter in lecithotrophic brachiopod larvae and demonstrate the existence of flask-shaped serotonergic cells in the brachiopod larval apical organ, thus significantly increasing the probability that this cell type was part of the bauplan of the larvae of the last common lophotrochozoan ancestor.     

A ‘Problematic fossil’ revealed:Pycnoporidium ? eomesozoicum Flügel, 1972 (Late Triassic,Tethys)—not an enigmatic alga but a strophomenid brachiopod (Gosaukammerella n.g.)

Summary The microproblematicumPycnoporidium ? eomesozoicum Flügel, 1972, from Upper Triassic reefs of the Alpine-Mediterranean region, Turkey Oman and Iran (originally interpreted as possible alga) represents the type species of a new strophomenid brachiopod genus (Gosaukammerella n.g.). The genus is characterized by a very small, millimeter-sized plano-convex shell, whose ventral valve is attached to the substratum (mainly sponges) by symmetrically arranged outgrowths developing from a pseudopunctate, lamellose foliated shell wall and composed of densely spaced subparallel ‘tubes’ comparable with productide spines secreted by papillose extensions of the mantle.Gosaukammerella seems to be the only reliable candidate for the existence of post-Paleozoic strophomenid (productid ?) brachiopods. Gosaukammerella eomesozoica is restricted to possibly cryptic, shaded reef environments inhabited predominantly by sponges serving as substrates for micromorphic brachiopods.     

Electron microscopic studies of growth margins of articulate brachiopods

Summary The brachiopod shell is secreted by the mantle epithelium lining the internal surfaces of its two valves. Growth lines, seen on their external surfaces, have been interpreted in terms of mantle regression and transgression from the valve margins. This scanning electron microscope study of the shell microstructure in recent brachiopods confirms these views and shows the skeletal evidence upon which such interpretations can be made. Electron micrographs reveal that from a growth line a plane dips posteriorly into the shell substance along which normal skeletal secretion was interrupted. Commonly a mosaic of secondary fibres, similar to that seen on the inside surface of the valve, is preserved upon this regression plane, most of the inside surface of which is covered by primary shell, usually extending posteriorly well into the secondary shell layer. The regression plane marks the area from which the mantle withdrew and the area over which shell secretion was interrupted. During mantle transgression primary shell was deposited over much of this surface, before the redevelopment of secondary fibres, so that the old internal surface of the valve was preserved as a false mosaic within the shell. In this way it is possible to recognise the extent of mantle regression and to note the position of the primary — secondary shell secreting junction of the mantle at the time when shell secretion was resumed.     

贵州安顺募役剖面晚二叠世腕足动物群落及其生态特征*

本文对贵州募役剖面长兴期腕足动物群进行了系统分类鉴定和古生态分析,发现其与前人所报道的华南同时期腕足动物群存在着显著的差别,以Spiriferellina为绝对优势属,包含少量华南长兴期的常见分子,如Fusichonetes、Araxathyris和Peltichia等。募役剖面的腕足类化石主要产自碎屑岩层位,与华南同期碎屑岩相剖面的腕足动物群落相比,该动物群中的优势分子个体较大、壳体较厚且发育较粗大的壳疹,这可能与长兴期募役剖面动物群所处的特殊栖息地环境(浅水碳酸盐岩台地与深水硅质碎屑岩盆地之间的过渡地带)有关。二叠纪末期大规模的火山作用导致水体中碎屑物质含量增加,影响腕足类的滤食效率,而募役剖面清澈、水动力弱的水体环境,为滤食性的腕足动物提供了有利的环境条件。最后,通过与华南长兴期不同沉积相区腕足动物群落(六枝剖面、稻堆山剖面、中寨剖面、新民剖面、马家山剖面和仁村坪剖面群落)的对比分析,发现募役剖面腕足动物群与毗邻的六枝剖面腕足动物群在属级组成上的相似度较高,且过渡岩相栖息地环境下的腕足动物群在生物灭绝事件前也呈现出高优势度、低均匀度的群落结构特征,指示海洋底栖生物群落已经先于二叠纪末期生物集群灭绝事件出现了早期危机信号。     

A relict Ordovician brachiopod fauna from the Parakidograptus acuminatus Biozone (lower Silurian) of the English Lake District

At Yewdale Beck in northern England, a brachiopod fauna dominated by species of Hindella, Kinnella, Mirorthis, Paromalomena and Plectothyrella , occurs interbedded with a graptolite fauna which includes Akidograptus ascensus , Atavograptus ceryx , Persculptograptus parvulus and Normalograptus spp. (including probable examples of N. normalis , N. angustus and N. medius ) within the lower part of the Skelgill Formation. This suggests that taxa of the terminal Ordovician Hirnantia fauna occur within the lower P. acuminatus Biozone, representing the youngest documented occurrence of the Hirnantia brachiopod fauna. Biostratigraphy, brachiopods, graptolites, Ordovician-Silurian boundary.     

Observations on the ciliary feeding mechanism of the brachiopod Crania anomala

In young Crania anomala with a trocholophe or an early schizolophe one inhalant current enters the anterior gape, filters past the single bell-shaped cirrous basket and spills out diffusely as exhalant current both anteriorly and laterally. Late schizolophe or early spirolophe forms two separate cirrous baskets which produce two separate inhalant currents: the exhalant current still diffuses out anteriorly and laterally. In later stages either one single exhalant current comes out at the anteromedial region, or three exhalant currents, including an additional one at each posterolateral region.
The roof of the visceral cavity is attached in five places to the dorsal valve of Crania to form a mantle recess, an anterior passage and two lateral passages. A hole bored through the dorsal valve into the mantle recess or the anterior passage lets out exhalant current. The palaeobiological significance of this lies in the possible use of the hole in the perforate shell valve of the siphonotretid fossil inarticulate Schizambon australis as an exhalant opening. In this species the hole leads into the mantle recess, which also communicates via a lateral passage with each posterolateral part of the mantle space.     

Latest Guadalupian brachiopods from the Guadalupian/Lopingian boundary GSSP section at Penglaitan in Laibin, Guangxi, South China and implications for the timing of the pre-Lopingian crisis

A brachiopod fauna comprising nine species in eight genera from three closely spaced stratigraphic horizons of the same stratigraphic section is described for the first time from the Laibin Limestone in the uppermost part of the Maokou Formation in the Guadalupian/Lopingian (G/L) GSSP section at Penglaitan, Guangxi Autonomous Region, South China. The brachiopod assemblages are bracketed between two conodont zones: Jinogondolella xuanhanensis Zone below and Jinogondolella granti Zone above and, therefore, they can be safely assigned to the latest Capitanian in age. However, all but one of the nine brachiopod species from the Laibin Limestone carry strong early Lopingian (Wuchiapingian) aspect. Thus, the discovery of this brachiopod fauna not only suggests that some Lopingian brachiopod species had already appeared in the late Guadalupian (Capitanian); more importantly, it has also highlighted the fact that both the previously noted pre-Lopingian life crisis (or end-Guadalupian or Middle Permian mass extinction) and Lopingian recovery/radiation actually occurred in late Capitanian times, sometime before the G/L chronostratigraphic boundary. So far, the Penglaitan GSSP section provides the highest-resolution disappearance patterns of different fossil groups around the G/L boundary.     

Crenulations of the hinge plate of pectinoideans

Checa, A.G., Esteban‐Delgado, F.J. and Salas, C. 2010. Crenulations of the hinge plate of pectinoideans. —Acta Zoologica (Stockholm) 92 : 344–354. Crenulations are a succession of micron‐sized elongated ridges and troughs with a general dorsoventral pseudo‐labyrinthine pattern that are present on the hinge plate of most pectinoideans. The crenulations of opposing valves are complementary and interpenetrate in a hinge‐like fashion. They are also imprinted in the dorsal mantle, although there is evidence that the mantle adheres only at the ridges, but not at the troughs. Those mantle areas that secrete the ridges contain cells that are richer in structures, indicating an active metabolism than those facing the troughs. Crenulations are formed because the dorsal mantle expands allometrically along the anteroposterior direction. The excess length is accommodated by creasing. Crenulations initiate at the anterior and posterior ends of the hinge plate as shallow spheruliths, which increase in height with time until the mantle on both sides detaches from the shell areas forming the neighbouring troughs. A contact differentiation of the mantle into actively and passively secreting bands follows. This genetic model explains the general pattern as well as the changes in the morphology of crenulations that occur during growth. Crenulations are secondary postlarval structures unrelated to the provinculum. Their presence in the earliest pectinoideans makes crenulations a plesiomorphic character of the group.     

The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell

Shiino, Y & Suzuki, Y. 2011: The ideal hydrodynamic form of the concavo‐convex productide brachiopod shell. Lethaia, Vol. 44, pp. 329–343. Water‐flume experiments were performed to determine whether the concavo‐convex Permian brachiopod Waagenoconcha imperfecta was hydrodynamically adapted for feeding. The generation of passive currents inside the valves was observed experimentally. The use of four transparent, hollow polyhedron models, each differing in a single morphological feature, permitted observation of the currents inside the valves and allowed evaluation of the hydrodynamic significance of the ears and the prominent geniculated trail. Regardless of the direction of ambient flow, only the approximate‐imitation model generated a stable flow pattern consisting of inhalation from the ear gapes and exhalation from the anterior trail gape; models lacking or with small changes in these morphological features failed to generate stable flow patterns. The stable flow pattern was probably maintained by a pressure difference between the posterior lower ear gapes (maximum pressure) and the anterior trail gape (minimum pressure). Notably, bilaterally rotating internal currents formed parallel to the brachial ridges; such flow patterns would facilitate the capture of food particles by the animal via tentacles on its lophophore, which is most likely were located on the brachial ridges. Our results demonstrate that the immobile brachiopod W. imperfecta, an animal incapable of widely opening its valves, probably fed on the passive internal currents generated by its shell form. This unique valve morphology appears to be perfectly adapted from a hydrodynamic point of view. □Biomechanics, ecomorphology, evolution, morphological disparity, Productidina, suspension feeder.     

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

Based on embryological and morphological evidence, Lophophorata was long considered to be the sister or paraphyletic stem group of Deuterostomia. By contrast, molecular data have consistently indicated that the three lophophorate lineages, Ectoprocta, Brachiopoda and Phoronida, are more closely related to trochozoans (annelids, molluscs and related groups) than to deuterostomes. For this reason, the lophophorate groups and Trochozoa were united to Lophotrochozoa. However, the relationships of the lophophorate lineages within Lophotrochozoa are still largely unresolved. Maximum-likelihood and Bayesian analyses were performed based on a dataset comprising 11,445 amino acid positions derived from 79 ribosomal proteins of 39 metazoan taxa including new sequences obtained from a brachiopod and a phoronid. These analyses show that the three lophophorate lineages are affiliated with trochozoan rather than deuterostome phyla. All hypotheses claiming that they are more closely related to Deuterostomia than to Protostomia can be rejected by topology testing. Monophyly of lophophorates was not recovered but that of Bryozoa including Ectoprocta and Entoprocta and monophyly of Brachiozoa including Brachiopoda and Phoronida were strongly supported. Alternative hypotheses that are refuted include (i) Brachiozoa as the sister group of Mollusca, (ii) ectoprocts as sister to all other Lophotrochozoa including Platyzoa, and (iii) ectoprocts as sister or to all other protostomes except chaetognaths.