Biology of the Hyolitha

Hyoliths are Paleozoic fossils that have a calcareous exoskeleton consisting of an elongate, usually bilaterally symmetrical cone, a close fitting operculum, and a pair of curved appendages. Their skeletal ultrastructure resembles the crossed-lamellar shell layers of some molluscs. Several specimens from the Ordovician of France and the Cambrian of Antarctica have parts of the gut preserved by infilling matrix, showing that both mouth ad anus were located near the cone aperture. Muscle scars in other hyolith shells indicate that the animal had a series of dorsoventral and longitudinal, or longitudinal and circular muscles, which operated through a hydrostatic skeleton to protract and retract the head, to open and close the operculum, and to move the appendages. Although the shell form and skeletal ultra-structure of hyoliths are of a molluscan type, the muscle insertions suggest that the hyolith cone is not homologous with the dorsal exoskeleton of primitive molluscs. Hyoliths probably constitute a small extinct branch of phylum size, related to the Mollusca and the Sipunculoidea. All three groups may have had common ancestors in the late Precambrian.     

SKELETAL MICROSTRUCTURE OF HELENS, LATERAL SPINES OF HYOLITHIDS

Abstract:  In hyolithids the skeleton consists of four elements: a conch, an operculum and a pair of long, logarithmically curved 'spines' called helens. These last elements are rarely preserved, and have therefore remained poorly known and enigmatic. We have studied three-dimensionally preserved helens of the species ' Hyolithes ' lanceolatus , from the Permian of New South Wales, Australia, and ' Hyolithes ' groenwalli , from the Cambrian of Bornholm, Denmark. Helens were massive calcareous elements. Their original microstructure, herein reported for the first time, consisted of concentric lamellae surrounding a narrow elongated core, which may have been rich in organic matter. This concentric pattern resulted from the successive accretion of shell material at the proximal, internal portion of helens. This growth model is in accordance with helen morphology and with the presence of a characteristic surface sculpture of overlapping lamellae.     

THE MORPHOLOGY OF HYOLITHIDS AND ITS FUNCTIONAL IMPLICATIONS

Abstract:  The exceptionally preserved hyolithids Gompholites striatulus , Maxilites robustus , Maxilites snajdri and Maxilites sp. are described with particular emphasis on helen and muscle scar morphology. These two aspects of hyolithid morphology have remained controversial. In life position, each helen curved ventrally. When the operculum closed the aperture of the conch, each helen was locked at the commissure slit with its dorsal edge tilted forward. Inside the conch, it was held in the dorsal apertural plane and clear of the inner surface of the operculum. Previously unidentified muscle scars are described from both the operculum and the conch. Dorsal scars on the conch aperture held muscles directed to the operculum. Comparative study of the muscle insertion pattern indicates that hyolithids did not have serially arranged muscles and that all hyolithids may have had a common skeleto-muscular system. The arrangement of the muscle scars with respect to the helens suggests that the latter were capable of relatively complex movements and could have been used to propel the organism over the substrate. The general morphology and orientation of the helens suggests that in addition they functioned to stabilize the organism on the sea-floor.     

Permian Toxeumorphorida from Greenland: an appraisal of the molluscan class Xenoconchia

Macrotheca Waagen 1880, previously known only from the Salt Range of Pakistan and from Timor, and Toxeumorphora Shimanskiy, previously known only from the Ural Mountains, have been identified in the Permian of northern East Greenland. The new specimens are assigned to the order Toxeumorphorida which is transferred to the class Hyolitha. The class Xenoconchia tentatively proposed by Shimanskiy two decades ago to include the toxeumorphorids is abandoned. Macrotheca almgreeni n. sp. is described. Mollusca, Hyolitha, Toxeumorphorida, Xenoconchia, Permian, Greenland.     

Aspects of the biology of Hyolitha (Mollusca)

Hyolitha constitute an extinct group of class rank assigned to Molhsca. Two orders, Ortho-thecida and Hyolithida, are well established and most knowledge of morphologic detail is derived from the latter. Both orders had an operculum not hinged to the conch. Hyolithida also had paired, curved, whiskerlike appendages, requiring complex musculature to move them and the operculum. The Hyolithida were probably deposit feeders living in shallow water, and accordingly were tentaculate. A reconstruction of the soft parts of this sedentary organism is given — a shallow mantle cavity on the dorsal side, anterior tentacles, a long intestine, and a reduced ventral foot. Except for the more complex musculature associated with an elaborate operculum, Orthothecida are judged to have had a similar anatomy.     

华北寒武系第二统辛集组软舌螺动物化石群*

软舌螺动物是华北板块寒武系小壳化石基本组成之一,也是寒武纪生命大爆发在华北地区的重要见证者。本文系统描述了华北板块南缘-西南缘(河南-陕西地区)寒武系第二统辛集组软舌螺化石9属14种及1未定种。包括直管螺类6属9种:Conotheca australiensis、Cupitheca holocyclata、Cupitheca costellata、Cupitheca? decollata、Tegminites hymenodes、Triplicatella disdoma、Triplicatella xinjia、Protomicrocornus triplicensis和Longxiantheca mira;软舌螺类3属5种及1未定种:Microcornus eximius、Microcornus petilus、Parkula cf. esmeraldina、Parkula bounites、Parakorilithes mammillatus和Parakorilithes sp.。基于大量保存的精美聚合标本,本文准确重建了锥壳和口盖在软舌螺不同属种中的配置。此外,新材料显示华北辛...     

贵州剑河寒武系凯里组脊状单臂螺(Haplophrentis carinatus)埋藏特征及与始海百合共生关系探讨

贵州剑河寒武系凯里组软舌螺化石丰富、埋藏形式多样,其中以脊状单臂螺Haplophrentis carinatus化石数量最多、保存最为完整。过去有关学者对凯里组单臂螺化石的研究主要集中在化石分类学方面,对脊状单臂螺埋藏特征及与其他生物共生关系缺乏深入探讨。本文对324块脊状单臂螺化石标本进行系统研究对比后发现,凯里组脊状单臂螺口盖化石埋藏形式有四类:口盖单独保存、口盖以内模或外模化石形式保存、口盖与锥壳完全绞合保存、口盖与锥壳不完全绞合保存;附肢保存较少;锥壳多以内模化石形式保存;脊状单臂螺内模化石与印痕化石上普遍出现类似软体保存形成的三分叉结构,这类三分叉结构属于后期埋藏因素造成的次生结构。文中还对脊状单臂螺与始海百合共生关系进行探讨,并将二者共生关系归为偏害共生。     

扬子地台早古生代软舌螺化石记述

该文的标本采自云南昆明、晋宁下寒武统筇竹寺组,龙陵上寒武统核桃坪组、柳水组和江苏江宁上奥陶统顶部“新开岭层”。文中描述了软舌螺化石4属5种,1未定种。其中3新属3新种,再次丰富了早古生代碎屑岩地层中的软舌螺化石,对探讨软舌螺类演化进程,确定时代,进行地层对比均有重要价值。     

The bearing of the new Late Cambrian monoplacophoran genus Knightoconus upon the origin of the Cephalopoda

Yochelson, E. L., Flower, R. H. & Webers, G. F.: The hearing of the new Late Cambrian monoplacophoran genus Knightoconus upon the origin of the Cephalopoda.
Knightoconus , a new genus of the Hypseloconidae (Mollusca: Monoplacophora) from rocks of early Franconian age in Antarctica, is multiseptate. The multiple septa are a criticàl feature to be expected in a form ancestral to cephalopods. Fossil cephalopods, however, invariably have a siphuncle as well as septa; some gastropods, some hyolithids, and some monoplacophorans also have septa but lack a siphuncle. Therefore, only the siphuncle can be considered a unique and particularly significant feature of the cephalopod shell. Hypothetical reconstructions of molluscan anatomy support the notion that cephalopods may have been derived directly from a hypseloconid having a high, slightly curved, multiseptate, bilaterally symmetrical shell, by the subsequent development of a siphuncle.     

陕南地区下寒武统筇竹寺阶软舌螺化石

描述陕南地区下寒武统筇竹寺阶软舌螺化石６属８种,其中有５新属（Ningqiangethus gen.nov.,Bilgulitheca gen.nov.,Xixiangethes gen.nov.,Paranicrocornus gen.no.,Inflatatheca gen.nov.),新种,１相似种,１未定种。从组织结构和面貌上论述筇竹寺阶软舌螺和梅树村阶软舌螺匠区别,筇笔直寺阶的软舌螺不仅个体增大、背腹分异、口唇发育、壳体与口盖常共存,而且属种分异度大,为进一步研究软舌螺动物的早期演化和解决下寒武统生物地层划分为对比提供重要的实证材料。     

Quantitative studies of modern wet-ground molluscan faunas from Bossington, Hampshire

There have been few quantitative studies of modern Mollusca in Britain, especially from wet-ground areas. This is particularly true of the English chalklands, which is surprising given the focus of sub-fossil molluscan research in that area. Those studies that are available highlight the difficulty of separating molluscan faunas from structurally complex habitats such as fen and carr. Quantitative molluscan data from a variety of wet-ground habitats situated within the chalklands of southern England were analysed using an indirect ordination technique, Principal Components Analysis. This demonstrated that the separation of faunas from structurally complex wet-ground habitats is possible. The numerical separation does not rely on indicator species, but is a function of variation of the predominant species. It is suggested that further studies of this type might aid the interpretation of sub-fossil Mollusca from wet-ground contexts.     

Ultrastructure of the renopericardial complex in Hypselodoris tricolor (Gastropoda, Nudibranchia)

The histology and ultrastructure of the renopericardial complex of Hypselodoris tricolor (Gastropoda, Nudibranchia, Doridoidea) have been investigated by means of semithin serial sections and transmission electron microscopy (TEM). The examinations revealed a functional metanephridial system comprising a monotocardian heart with ventricle and auricle in a spacious pericardium that is linked with the single, large kidney by a renopericardial duct with prominent ciliation towards its opening. Podocytes as the site of ultrafiltration were not only detected in the auricular epicardium, but also line the entire outer pericardial epithelium. The cuboidal, highly vacuolated excretory cells of the kidney epithelium with extensive basal infoldings and an apical microvillous border indicate secretory and reabsorptive activity. Solitary rhogocytes (pore cells) of the connective tissue and haemocoel represent additional loci of ultrafiltration with a fine structure identical to that of the podocytes (slits between cytoplasmic processes, bridged by fine diaphragms and covered by extracellular matrix). The presence of podocytes situated in the epicardial wall of the auricle is regarded as plesiomorphic for the Mollusca and is confirmed for the Nudibranchia. An additional, extensive and separate ultrafiltration site in the outer pericardial wall is not known from any other taxon of the Mollusca and strongly suggests a significantly increased ultrafiltration activity in H. tricolor.     

Quantitative studies on some living British wetland mollusc faunas

The work described here provides a quantitative basis for die interpretation of fossil assemblages of Mollusca from wetland habitats. Wetlands were sampled for living Mollusca in East Anglia (including an intensive study at Wicken Fen) and Scotland. Within the limited geographical area of Wicken Fen, the mollusc fauna may be used to predict the vegetation and hence to reconstruct the environment. Such a relationship did not continue to hold when scattered sites throughout die East Anglian region were studied. However, the relict nature of these fens should be taken into account. In die central Highlands of Scotland, a better correlation was found between mollusc fauna and flora, though this was inadequate for reconstruction of details of the vegetation. Within the context of wetland, the presence of certain rare species of narrow ecological tolerance is considered the best available measure for the reconstruction of die environment from molluscan assemblages, but their absence is meaningless. Quantitative studies of assemblages of the common species may still prove to be of value at the coarser level of discrimination between wetland, grassland and woodland, but the data are not available. Numerous quantitative studies of fossil assemblages of Mollusca from Quaternary sediments have been made and the results have been interpreted to indicate past environmental and climatic conditions. In previous studies, common species have been placed into ecological categories based on qualitative observations of the occurrence of Mollusca in modern environments, and fossil assemblages have then been interpreted as being formed by transport and accumulation from a variety of different habitats. This may be the case, but equally studies of the living assemblages have shown that the structural complexity of a single habitat may lead to species of very different ecological groups living within the same area of ground. It is simpler to interpret certain fossil assemblages as having been formed in situ in structurally diverse environments, rather than invoking mixing from different environments.     

Evidence of predation damage in Pliocene Apletosia maxima (Brachiopoda)

Abstract:  Little is known about predation of Mesozoic and Cenozoic articulated brachiopods, but it is far from clear whether this is because they suffered very little predation pressure or because there have been few attempts to search for evidence of it. A study of 248 museum specimens of the large Pliocene terebratulid Apletosia maxima from the Coralline Crag (UK) has revealed that more than 16 per cent of them show evidence of having been attacked by predators. The styles of damage can be attributed to drilling muricid gastropods (most of which were successful) and failed crushing attacks probably by decapods. Brachiopods are usually thought to offer a poor tissue yield to potential predators, but in this instance it appears that A. maxima was attractive to predators even though they were living with a rich molluscan fauna. It is suggested that the mass of adductor and diductor muscles (likely to be spicule-free) of these particularly large brachiopods may have made them profitable. Further studies of post-Palaeozoic brachiopod faunas are required, particularly those from mixed shallow-water communities, before it can be established whether articulated brachiopods have or have not been driven into refugia by increasing predation pressure.     

Morphological adaptations and plasticity of radular teeth of the Sacoglossa (= Ascoglossa) (Mollusca: Opisthobranchia) in relation to their food plants

The radular teeth of 55 species of Sacoglossa (= Ascoglossa) (Mollusca: Opisthobranchia) with known diets are classified into three basic groups: triangular, blade-shaped and sabot-shaped. Cell wall composition of the food plant is the single most important factor influencing radular morphology. The algae eaten by sacoglossans have either xylan, mannan or cellulose as their structural wall component. Sabot-shaped teeth are associated with diets of Siphonocladales and Cladophorales, which have cellulose cell walls of a 'crossed fibrillar texture'. Triangular teeth with lateral denticles are associated with diets of Caulerpa or with calcified algae. Most of these have xylan as the major structural polysaccharide. Blade-shaped teeth occur in a large number of species representing a wide variety of diets. It is proposed that the three types of teeth function in different manners. Tooth denticulation is correlated with functional group of the food plant. The radular teeth of Elysia viridis feeding on Codium are longer, wider and have more curved tips than teeth of E. viridis feeding on Chaetomorpha. The teeth of E. viridis transferred from Codium to Chaelomorpha in the laboratory change in shape as well as size.     

Rare Mollusca from the Lower Devonian Hunsrück Slate of southern Germany

Only ten gastropods have been recovered and a single hyolith found in the radiographic study of the Hunsrück fauna. Four gastropods are interpreted as retaining soft parts: the radula may be identified in one and perhaps the liver and digestive organs in the others. These gastropods may have moved into the area on floating vegetation. The hyolith probably lived on the bottom. Soft parts are present within its shell, but they are not readily interpreted. A tentacular mass anterior to a possible mantle cavity is present, with the bulk of the shell being filled by enigmatic tissue. ▭ Gastropoda, Hyolitha, soft parts, radula, pyritization.     

Investigation of molluscan phylogeny using large-subunit and small-subunit nuclear rRNA sequences

The Mollusca represent one of the most morphologically diverse animal phyla, prompting a variety of hypotheses on relationships between the major lineages within the phylum based upon morphological, developmental, and paleontological data. Analyses of small-ribosomal RNA (SSU rRNA) gene sequence have provided limited resolution of higher-level relationships within the Mollusca. Recent analyses suggest large-subunit (LSU) rRNA gene sequences are useful in resolving deep-level metazoan relationships, particularly when combined with SSU sequence. To this end, LSU (approximately 3.5 kb in length) and SSU (approximately 2 kb) sequences were collected for 33 taxa representing the major lineages within the Mollusca to improve resolution of intraphyletic relationships. Although the LSU and combined LSU+SSU datasets appear to hold potential for resolving branching order within the recognized molluscan classes, low bootstrap support was found for relationships between the major lineages within the Mollusca. LSU+SSU sequences also showed significant levels of rate heterogeneity between molluscan lineages. The Polyplacophora, Gastropoda, and Cephalopoda were each recovered as monophyletic clades with the LSU+SSU dataset. While the Bivalvia were not recovered as monophyletic clade in analyses of the SSU, LSU, or LSU+SSU, the Shimodaira-Hasegawa test showed that likelihood scores for these results did not differ significantly from topologies where the Bivalvia were monophyletic. Analyses of LSU sequences strongly contradict the widely accepted Diasoma hypotheses that bivalves and scaphopods are closely related to one another. The data are consistent with recent morphological and SSU analyses suggesting scaphopods are more closely related to gastropods and cephalopods than to bivalves. The dataset also presents the first published DNA sequences from a neomeniomorph aplacophoran, a group considered critical to our understanding of the origin and early radiation of the Mollusca.     

Identification of Several Cytoplasmic HSP70 Genes from the Mediterranean Mussel (Mytilus galloprovincialis) and Their Long-Term Evolution in Mollusca and Metazoa

The HSP70 protein family consists one of the most conserved and important systems for cellular homeostasis under both stress and physiological conditions. The genes of this family are poorly studied in Mollusca, which is the second largest metazoan phylum. To study these genes in Mollusca, we have isolated and identified five HSP70 genes from Mytilus galloprovincialis (Mediterranean mussel) and investigated their short-term evolution within Mollusca and their long-term evolution within Metazoa. Both sequence and phylogenetic analyses suggested that the isolated genes belong to the cytoplasmic (CYT) group of the HSP70 genes. Two of these genes probably represent cognates, whereas the remaining probably represent heat-inducible genes. Phylogenetic analysis including several molluscan CYT HSP70s reveals that the cognate genes in two species have very similar sequences and form intraspecies phylogenetic clades, differently from most metazoan cognate genes studied thus far, implying either recent gene duplications or concerted evolution. The M. galloprovincialis heat-inducible genes show intraspecies phylogenetic clustering, which in combination with the higher amino acid than nucleotide identity suggests that both gene conversion and purifying selection should be responsible for their sequence homogenization. Phylogenetic analysis including several metazoan HSP70s suggests that at least two types of CYT genes were present in the common ancestor of vertebrates and invertebrates, the first giving birth to the heat-inducible genes of invertebrates, whereas the other to both the heat-inducible genes of vertebrates and the cognate genes of all metazoans. These analyses also suggest that inducible and cognate genes seem to undergo divergent evolution. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Yves Van de Peer] Elena Drosopoulou and Nikolas Nikolaidis contributed equally to the present report.     

典型养殖湖泊大通湖软体动物的时空分布格局

研究于 2008 年 12 月至 2009 年 10 月按季度对大通湖水质及软体动物资源监测, 并通过纵向比较, 探讨了集约化养殖对大通湖水域环境及软体动物群落的影响, 以期为其渔业可持续发展提供理论依据。结果显示, 大通湖水质全年呈碱性 (8.62 0.07), 具有较高的还原性 (-88.40 9.10) mv, 属富营养水体。软体动物共计 5 科 15 种, 梨形环棱螺(Bellamya purificata)、河蚬(Corbicula fluminea)和圆顶珠蚌(Unio doug lasiae)是主要优势种。软体动物平均密度和生物量具有明显的时空差异, 时间上呈现由春夏季到秋冬季逐渐升高的趋势, 空间上整体呈现由东北向西南逐渐递减的趋势。典范对应分析表明氧化还原电位、pH、溶氧、水深、电导率和水温与大通湖软体动物时空变化的关系最显著。与 1960 年相比, 大通湖水体碱性显著增强 (7.0-7.5 vs 8.4-8.8), 电导率增加了 9 倍 (0.25-0.27 vs 2.17-2.56 mS/cm), 环境类型由氧化型转变为还原型。湖区喜好水草 (白旋螺、光亮隔扁螺、萝卜螺) 与流水生境 (德氏狭口螺、湖沼股蛤、橄榄蛏蚌) 的物种消失, 软体动物优势种群呈现由双壳类向腹足类演替的特征。生境破坏和过度捕捞是大通湖软体动物资源面临的最大威胁, 也是湖区渔业可持续发展所面临的核心问题。       

Plywood‐like shell microstructures in hyoliths from the middle Cambrian (Drumian) Gowers Formation,Georgina Basin,Australia

Hyoliths are a group of Palaeozoic fossils with calcareous shells whose affinities remain controversial. As their shells were originally aragonitic, their fossils are usually coarsely recrystallized, and few data on their microstructure are available. We report hyoliths from the middle Cambrian (Drumian, Floran) Gowers Formation of the eastern Georgina Basin, Queensland. These are preserved as phosphatic internal moulds, often with the inner layers of the shell also partly replaced by phosphate. Microstructural details preserved by this early diagenetic phosphatization show that these hyolith conchs were originally composed of fibrous crystallites, c. 0.5 μm wide, parallel to one another and to the inner surface of the shell. In several species, the fibres are arranged in a plywood‐like structure composed of multiple lamellae with a different fibre orientation in each lamella: often they are transversely oriented (relative to the long axis of the conch) in the inner part of the wall and longitudinally oriented in the outer part. Opercula also show a microstructure of parallel fibres. The lamello‐fibrillar microstructure we report from hyoliths is reminiscent of microstructures of many Cambrian molluscs; that this microstructure is found in both conchs and opercula suggests that these structures are serial homologues of one another, and in this respect they resemble brachiopod valves. As with many other biological plywoods, the hyolith shell probably records self‐organization in a liquid‐crystal‐like organic matrix. This provided a straightforward way to construct a material that could resist stresses from different directions, offering an effective defence against predators.