Dictyonema Hall and its importance for the evolutionary history of the Graptoloidea

Dictyonema retiforme has been regarded as the benthic ancestor to the planktic Graptoloidea, represented by the earliest planktic Rhabdinopora flabelliformis and its descendants. The revision of the type material of Dictyonema retiforme, the type species of the genus Dictyonema, from the Silurian of New York State shows compound stipes formed by the complexly growing and overlapping tubular thecae of acanthograptid type. The connections between adjacent stipes are formed by thecal tubes or thecal bridges and not by dissepiments. Thus, the species has to be transferred to the Acanthograptidae and cannot be regarded as being related to the early planktic Graptoloidea. The tubarium meshwork of Dictyonema is phylogenetically unrelated to the meshwork of the planktic Rhabdinopora, and represents a case of convergent evolution. The origins of the planktic graptoloids lie among members of middle to upper Cambrian Dendrograpidae, as can be seen from the thecal style and the triad budding patterns with regularly developed bithecae in this group.     

Early Tremadocian (Ordovician) graptolite biostratigraphy and correlation

A revision of the early Tremadocian graptolites of the genus Rhabdinopora shows that Rhabdinopora proparabola from the Xiaoyangqiao section, Dayangcha, North China is the oldest species of the genus. Early Tremadocian species of Rhabdinopora can be differentiated easily by the construction of their nemata. The earliest species, Rhabdinopora proparabola, lacks a nema, while a multibranched nema is present in Rhabdinopora campanulatum (= Rhabdinopora parabola). The Rhabdinopora proparabola, Rhabdinopora campanulatum, Rhabdinopora flabelliformis (Anisograptus matanensis Biozone) and Rhabdinopora anglica biozones can be correlated worldwide. A short interval at the base of the Ordovician System does not contain any planktic graptolites.     

PALAEOECOLOGY OF THE GRAPTOLITHINA, AN EXTINCT CLASS OF THE PHYLUM HEMICHORDATA

1. Whatever heirarchical system of classifying graptolites is adopted, perhaps even raising them to the rank of phylum, the hemichordates including Rhabdopleura and Cephalodiscus remain their closest relatives. 2. Benthonic graptolites preceded and outlasted the planktonic graptolites which exhibited spectacular morphological changes related to a change to a holoplanktonic mode of life and a probable hermaphroditism. 3. The resorption of the narrow-end of the larval skeleton (prosicular cauda) enabled the construction by an outer layer of secreting tissue (extrathecal tissue) of a hollow nema, the dark hollow rod which supported gas-filled tissue and which in turn conferred buoyancy on the colony. 4. The nema provided access to the exterior of the colony for extrathecal tissue which began to strengthen the outside of the prosicular and metasicular parts of the larval skeleton with laminated cortical deposits before the first non-sicular individual of the colony was budded. 5. Attachment of the larval stage in those graptolites having a basal disc or ‘roots’ was by the first-formed extrathecal tissue through a resorbed cauda. 6. Initial attachment of the larval stage in certain encrusting graptolites such as Idiotubus may have been by a larval individual lacking any scleroprotein periderm as a skeletal sheath. 7. After initial attachment the extrathecal tissue continued to secrete additional layers of cortical tissue mostly for the purposes of strengthening the colony. 8. Feeding in graptolites was by ciliated lophophore often positioned so as to take maximum advantage of currents flowing from the dorsal to the ventral side of the colony, for example in Dictyonema and Monograptus. 9. The main function of the nema, particularly of those nemata bearing vanes, was as a support for vacuolated tissue which imparted a holoplanktonic mode of life to planktonic (sensu Zato) graptolites. 10. Attachment of colonies (rhabdosomes) as groups of colonies (synrhabdosomes) was by the extrathecal tissue issuing from the tips of the nemata: such associations were probably sexual rather than for reasons of buoyancy. 11. Attachment of planktonic graptolites to floating algal fronds is an unnecessary hypothesis. Although an undoubted occurrence of graptolites in rocks containing large quantities of carbonaceous matter is beyond dispute, the plant or animal nature of this material has never been established. A symbiotic relationship of planktonic graptolites with a marine, formless alga, perhaps involving the extrathecal tissue, remains a possibility. 12. Although different species may have lived at different depths, the full vertical range of the holoplanktonic graptolites was probably small. The evidence advanced for depth zonation is considered inadequate. 13. Planktonic graptolites were essentially tropical to temperate in distribution with the bulk of the species and individuals in the former environment. 14. Automobility of graptolite rhabdosomes was an unlikely mechanism and does not readily account for the morphology and distribution of the graptolites. 15. Most planktonic graptolites were suspended beneath a nema coated in extrathecal, vacuolated (gas-filled) tissue: changes of position in the water were by passive response to ocean currents. 16. The nature of the graptolite zooid is considered unsolved, although it may have been essentially like that of the extant Rhabdopleura in having paired lophophores. 17. It is possible that a modified pre-oral lobe was capable of secreting both fusellar (inner) and cortical (outer) layers of the periderm. 18. The extrathecal tissue itself would in that case have been derived both from the nemal tube and the thecal individuals.     

Further use of fluorochromes in the cytochemical characterization of phytoplankton

Summary The rapid, specific effects of 25 fluorochromes at low concentration and physiological conditions of pH and temperature were investigated on live cells of five phytoplankton species (Prorocentrum micans, Amphidinium carterae, Dunaliella tertiolecta, Chlamydomonas moewusii andFragilaria crotonensis). They allowed the identification of cellular components such as the plasma membrane, endoplasmic reticulum, Golgi apparatus, thecal plates, nucleus, mitochondria, trichocysts, vacuoles/lysosomes, polyphosphate and starch granules, lipid bodies and hydrolytic enzymes. Morphological alterations of some of these constituents were examined in cells at different metabolic states. It was found that the thickness ofProrocentrum thecal plates increases during cell development while surface pores appear to be formed in the early stages of thecal formation. The number and size of mitochondria varies among cells at different stages of growth. The number of trichocysts, the size of vacuoles and the quantity of polyphosphates, starch or lipid inclusions increases in nitrogen-depleted cells. Photodegradation and photoenhancement phenomena are described. Some important factors helping to avoid quenching and some applications of the fluorochroming technique are presented.     

UPPER ORDOVICIAN BRYOZOANS OF THE PIN FORMATION (SPITI VALLEY, NORTHERN INDIA)

Abstract: Twenty‐nine species of bryozoans from the Upper Ordovician–Lower Silurian Pin Formation (Spiti, India) have been identified. Eight of these are new: Trematopora minima, Ulrichostylus bhargavai, Ptilodictya exiliformis, Phaenopora ordinarius, Oanduellina himalayaica, Pesnastylus? vesiculosum, Ralfina? originalis and Pinocladia triangulata. The fossil record and facies analyses of the area investigated indicate shallow‐water conditions within the subtropical–tropical realm. The distribution pattern of fossils among the Ordovician/Silurian succession on the Northern Gondwana shelf and the influence of the Late Ordovician cooling phases on marine organisms are distinctive owing to a dramatic reduction in diversity globally. As far as the bryozoan taxa of Spiti are concerned, only one (Helopora fragilis) of the 29 species was recorded above the Ordovician/Silurian boundary. Observed bryozoan communities are very similar to faunas of Laurentia, the Baltic, Siberia and southern China of early–late Ordovician age.     

Roscoffia minor sp. nov. (Peridiniales, Dinophyceae): A new, sand-dwelling, armored dinoflagellate from Hokkaido, Japan

A new, sand-dwelling, armored dinoflagellate, Roscoffia minor sp. nov., is described from Ishikari beach, Hokkaido, Japan. The dinoflagellate has been collected from sand samples taken both near the water's edge and further upshore (25 m from the water's edge at a depth of 1 m), indicating that it is a true sand-dwelling species. Roscoffia minor is heterotrophic and lacks both a chloroplast and an eye-spot. The cell consists of a flattened cap-shaped epitheca and a large hemispheroidal hypotheca, and it is quite different from cells of the typical armored dinoflagellates. The thecal plate formula is: Po, 3′, la, 5″, 3c, 3s, 5″, 1″″. Its distinct cell shape and the thecal plate arrangement indicate affinity to the monotypic genus Roscoffia. Roscoffia minor is distinguished from Roscoffia capitata, the type species, by its smaller size and the possession of a finger-like apical projection. The thecal arrangement of the epitheca is similar to those of the members of the family Podolampaceae, while the hypothecal arrangement is the same as that of members of the subfamily Diplopsalioideae (family Congruentidiaceae). The organism seems to be positioned somewhere intermediate between these two families, but the family to which this dinoflagellate should be affiliated could not be determined.     

The tubarium construction of Lower Ordovician (Dapingian) Baltograptus species (Graptolithina) from Dalarna,Sweden

Isolated and chemically bleached graptolite specimens of Baltograptus from Skattungbyn, Dalarna (central Sweden), reveal important new information on the internal construction of the tubarium. The specimens show the typical metasicular origin of th1¹ and the presence of numerous longitudinal rods in the prosicula. The investigation provides some insight into intraspecific variation and on the differentiation of individual species. It also provides information on the early evolution of the two‐stiped dichograptids. Three distinct species, identified as Baltograptus minutus (Törnquist) B. kurcki (Törnquist) and B. extremus sp. nov. can be recognized in the collection of hundreds of specimens. The Baltograptus species are associated with a diverse Dapingian graptolite fauna, prepared by Roland Skoglund, but never investigated in detail, including specimens of Pseudophyllograptus densus, Acrograptus gracilis and other taxonomically and biostratigraphically important taxa.     

Astogenetic aspects of the dendroid graptolite Airograptus (Late Cambrian-Early Ordovician) and their phylogenetic implications

Based on a Backscatter Electron (BSE) examination of partially 3-dimensional graptolite specimens of Airograptus from the Tremadocian (Early Ordovician) Yehli Formation at Dayangcha, Baishan of Jilin Province, NE China, the thecal structure and astogenetic aspects of this genus (except for the missing proximal part) are described and illustrated in detail. In the present collection, no furcating but only peltate thecal apertural processes are confirmed. A comparison between the presumably benthic dendroid Airograptus and Rhabdinopora, the earliest planktonic graptolite, indicates that there are remarkable similarities in astogenetic aspects between them, although there are also differences in the development of dissepiments and thecal apertural processes. A possible ancestor-descendent relationship between the two genera is herein proposed.     

遗迹化石Trichophycus在贵州仁怀下–中奥陶统湄潭组中的首次报道及意义*

遗迹化石研究对揭示奥陶纪生物大辐射事件期间, 底栖生物在陆棚区定居的具体过程有重要意义。Trichophycus在寒武系–奥陶系有广泛报道, 但是针对其时空分布、演化轨迹、造迹生物属性和生态等的系统总结和讨论较少。本文首次在贵州仁怀地区下–中奥陶统湄潭组内陆棚沉积中报道了遗迹属Trichophycus。该遗迹化石由宽的U型、平直或弯曲的潜穴管以前进式方式构成潜穴系统。底部和侧部以纵向排列的、平行或近似平行的抓痕为特征, 发育后退式蹼状构造, 不发育衬里。上述特征支持将其划归到T. venosus Miller, 1879。湄潭组中Trichophycus可能为一类未知的节肢动物居群所建造的觅食/居住遗迹。地质历史中Trichophycus的造迹生物来自多个类群, 是行为趋同的产物。作为Glossifungites遗迹相的常见分子, 它的出现可能指示沉积物的初始硬结或存在较短的沉积间断。Trichophycus相对狭窄的沉积相分布区间表明它可以作为浅海固底的指相遗迹化石。作为先锋遗迹属, Trichophycus的地史分布表明, 全球各板块底栖造迹生物在陆棚区的定居是不等时的。湄潭组中Trichophycus的出现, 是华南扬子区奥陶纪生物大辐射事件期间, 底栖造迹生物探索陆棚区生态空间的一个缩影。     

THE THECAL STRUCTURE OF MONOCLIMACIS? GALAENSIS

Monoclimacis? galaensis (Lapworth), a biform Llandoverian graptolite, is interpreted as having proximal thecal ‘hooks’ composed of paired lateral lappets, and lacking retroversion of the dorsal thecal wall. A parallel is drawn between M? galaensis and members of the Ludlovian genus Lobograptus Urbanek. The significance of the thecal structure is discussed with reference to the principles involved in the classification of the monograptids.     

The ontogeny of cinctans (stem‐group Echinodermata) as revealed by a new genus,GraciaCystis, from the middle Cambrian of Spain

Abstract:  A new cinctan echinoderm, Graciacystis ambigua gen. et sp. nov. from Cambrian Series 3 rocks of Spain, is described based on more than 100 articulated specimens that range from 6 to 14.5 mm in thecal length. This material shows that Graciacystis ambigua, while plastic in thecal shape, is highly conservative in its thecal construction, with a fixed number of marginal plates and very limited addition of plates in the stele and ventral membrane through ontogeny. Ventral swellings on marginal elements are absent from the smallest specimens and become gradually more marked during growth. A cladistic analysis shows Graciacystis to be a basal cinctan, more derived than Sotocinctus and the Trochocystitidae and as sister group to a large clade formed by Sucocystidae + Gyrocystidae. The determinate growth pattern seen in Graciacystis seems to be the general pattern for all cinctans.     

Morphology and phylogenetic interpretation of a new Cambrian edrioasteroid (Echinodermata) from Spain

Abstract: The edrioasteroid, Aragocystites belli gen. nov. sp. nov. from the middle Cambrian Murero Formation of Spain, is described based on a small number of very well‐preserved specimens. Important anatomical characteristics include star‐shaped and pseudoclavate theca, rare or absent epispires, well‐developed interradially positioned oral plates and several unorganized cover plates associated with each widely exposed flooring plate. A phylogenetic analysis including several Cambro–Ordovician species shows it is more derived than Stromatocystites and Totiglobus but is a sister group to a clade comprising Cambraster and Edriodiscus. Ontogenetic observations based on juveniles of 5 mm in diameter suggest that this species changed thecal shape markedly during growth. A. belli gen. nov. sp. nov. probably lived in quiet environments where it attached directly to the sea floor on stabilized substrates.     

Structure and Secretion of the Graptolite Prosicula, and its Application for Biostratigraphical and Evolutionary Studies

Studies on graptolite taxonomy and phylogeny in recent years have placed great emphasis on the proximal development of the rhabdosome, particularly the presence or absence of a virgella and early thecal growth patterns. As the prosicula was the earliest part of the graptolite skeleton to be secreted, it may also reveal fundamental information about evolutionary relationships within the Graptoloidea. The prosiculae from a variety of Ordovician taxa ranging in age from Tremadoc to Caradoc have been examined using a combination of light microscopy, SEM and TEM. Parameters investigated include the overall morphology, transition into the nema, pattern of longitudinal ridges and spiral line. Taxa show a change from early Tremadoc graptoloids which have a low diaphragm, prominent spiral line and lack longitudinal ridges, through late Tremadoc and early Arenig taxa which have longitudinal cortical bandages or spiralled, paired longitudinal ridges, into later Arenig and Llanvirn forms which have simple longitudinal ridges and indistinct spiral line and diaphragm. With additional work at higher stratigraphical levels, graptolite prosiculae may prove to be useful biostratigraphically when more complete material is absent, such as in palynomorph preparations from subsurface studies.     

The biosynthesis of estrogens by cow follicles

Separated and recombined granulosa and thecal cells of ripening cow follicles were incubated $\text{in}$$\text{vitro}$ in the presence of different steroid precursors involved in the Δ⁴ and Δ⁵-pathways. The experiments indicate that both in the granulosa and the thecal cells the transformation of pregnenolone to androstenedione occurs predominantly through the Δ⁵-pathway. Although both cell types are able to transform androstenedione to estrogens, this capacity is very small in the thecal tissue as compared to the granulosa cells. Incubations of combined granulosa and thecal cells yielded larger amounts of estrogens than the incubations of each cell type separately, indicating a positive interaction between both cell types in the experimental conditions.     

SEM survey on mediterranean species of Podolampas

Abstract

In this work we have considered the features of thecal plates of some mediterranean species of Podolampas. The thecal plates have pores different in size and distribution according to their position and to the species considered. We have found some constant structures: kind of perforations of the apical, preequatorial and postequatorial thecal plates. The antiapical thecal plates have both constant and distinctive specific features.     

Establishing a new genus,Chiharadinium gen. nov. (Peridiniales,Dinophyceae) for a tidal pool dinoflagellate formerly known as Scrippsiella hexapraecingula

To determine its accurate taxonomic position, a tidal pool bloom-forming dinoflagellate, Scrippsiella hexapraecingula was re-investigated using light, scanning and transmission electron microscopy together with a phylogenetic analysis based on concatenated ribosomal DNA sequences. The culture strains used in this study were established from intertidal rock pool samples taken from Jogashima, Kanagawa prefecture and Heisaura, Chiba prefecture, Japan and were identified as S. hexapraecingula originally described by Horiguchi and Chihara from a tidal pool in Hachijo Island, Tokyo, Japan in 1983. The thecal plate arrangement was determined as Po, X, 4′, 3a, 6″, 6c, 5s, 5″′, 2″″. The internal structure was investigated for the first time. The organism has typical dinoflagellate cellular organelles such as a dinokaryotic nucleus, mitochondria with tubular cristae, trichocysts and pusule. The chloroplast was single and connected to the central pyrenoid (stalked type). The eyespot found in the sulcus is of the B type with two rows of superficial intraplastidal lipid globules directly overlain by an extraplastidal single layer of crystalline bricks enveloped by a common membrane. The apical pore is plugged by a double-layered stub-like structure. Stalk building material for attachment covered the apical pore. Phylogenetic analysis indicated that S. hexapraecingula was most closely related to a freshwater dinoflagellate, Peridiniopsis borgei, the type species of the genus Peridiniopsis. However, clear differences exist between these two organisms, including their thecal plate arrangement, habitat and habit. As a result, a new genus, Chiharadinium Dawut & T. Horiguchi gen. nov. has been proposed rather than attempting to accommodate S. hexapraecingula in the genus Peridiniopsis. The new combination, Chiharadinium hexapraecingulum (T. Horiguchi & Chihara) Dawut & T. Horiguchi comb. nov. has been proposed.     

AMPHIESMAL ULTRASTRUCTURE OF DINOFLAGELLATES: A REEVALUATION OF PELLICLE FORMATION1

The ultrastructure of the amphiesma during pellicle formation was investigated in two species of Dinophyceae, Amphidinium rhynchocephalum Anissimowa and Heterocapsa niei (Loeblich) Morrill & Loeblich using thin sections. In both species the amphiesma consists of an outermost membrane (i.e. the plasma membrane) underlain by amphiesmal vesicles. In A. rhynchocephalum the latter appear empty whereas each amphiesmal vesicle in H. niei contains a thecal plate and a thin, amorphous layer (dark-staining layer) located between, the thecal plate and the inner amphiesmal vesicle membrane. When cells of both taxa are carefully fixed, amphiesmal vesicles are always separate entities (i.e. the sutures are undisrupted). During ecdysis the following amphiesmal components are shed: the plasma membrane, the outer amphiesmal vesicle membrane, and in H. niei the thecal plates. The inner membranes of the amphiesmal vesicles then fuse with each other and form a continuous membrane (termed pellicle membrane) that remains tightly oppressed to an underlying amorphous layer (pellicular layer). In A. rhynchocephalum the pellicular layer is already present in vegetative non-ecdysed cells, whereas in H. niei it forms during ecdysis beneath the pellicle membrane. During ecdysis in H. niei, material from the dark-staining layer precipitates on the outer surface of the pellicle membrane, where it forms a characteristic honeycomb pattern. The new observations are incorporated into a revised model of pellicle formation in dinoflagellates and contrasted with earlier proposals.     

Ordovician Calcified Algae and Cyanobacteria, Northern Tarim Basin Subsurface, China

Boreholes between Kuqa and Korla, in the northern Tarim Basin, Xinjiang, penetrated Ordovician marine limestones at depths of 5–6.2km. From three boreholes 54 out of a total of 170 limestone samples contain calcified algae, cyanobacteria and associated Microproblematica. Calcified cyanobacteria (GirvanellaBotomaella, ?Subtifloria) account for 37 per cent of occurrences; green algae (Dasyporelleae and Vermiporella) 28 per cent; Microproblematica (NuiaBevocastriaRothpletzellaHalysis) 20 per cent; and ‘solenoporaceans’ 15 per cent GirvanellaNuia are common in the Early Ordovician deposits, and ‘solenoporaceans’ are abundant in the Mid‐Ordovician. Dasyporelleae and Vermiporella are most abundant in Mid–Late Ordovician samples. Calcified cyanobacteria are common throughout the limestone succession, but particularly in the Mid Ordovician part. MoniliporellaContextaPlexaTexturata, and Villosoporella, hitherto placed in the supposed red algal family Moniliporellaceae Gnilovskaya, are here regarded as dasycladalean green algae. Despite some omissions, this Tarim flora broadly resembles others from Kazakhstan, Baltica and North America, indicating the generally cosmopolitan nature of Ordovician calcified algae and cyanobacteria.     

Paired pleural disks in Dicaulograptus cumdiscus n. sp.

A diplograptid graptolite with strongly introverted thecae and unusual thecal processes was isolated from limestones of the Ordovician Pratt Ferry Formation of Alabama and is described as a new species Dicaulograptus cumdiscus. The thecal processes are referred to as pleural disks. They occur in pairs above every thecal aperture and are inferred to have functioned as suspension processes receiving uplift from small-scale turbulent water motion. Such a function is compatible with a passively buoyant mode of life and is difficult to reconcile with an automobile mode of life.