Devonian features in Ludlovian graptolites — no guide to ancestry

A diverse group of Ludlovian Monograptus species is characterized by the retarded growth of thecal hoods, either proximally [ M. colonus (Barrande), M. chimaera (Barrande) and M. haupti Kühne] or throughout the rhabdosome [M. micropoma (Jaekel)]. In all these species the hoods are secondary structures, i.e. later growth additions to the thecae. By contrast, in the Devonian Monograptus species the thecal hoods are primary structures, i.e. the outward extension of the dorsal thecal wall. and are formed by undelayed growth that typically is completed before growth of the succeeding theca begins. It is among Ludlovian ( M. uncinatus Tullberg) and Pridolian ( M. simih Přibyl) forms with homologous hoods that the roots of the majority of the Devonian Monograptus species might be found. The Ludlovian M. micropoma and M. haupti should not be affiliated to the group of Monograptus vomerinus (Nicholson), which is highly characteristic of, and restricted to, the late Llandovery and Wenlock graptolite faunas.     

Proximal structure and development in the Ordovician graptolite Parisograptus Chen and Zhang, 1996

The proximal development of Parisograptus Chen and Zhang is described from three–dimensionally preserved specimens. The unique development features an origin of proximal thecae like a string of pearls vertically upon each other on the reverse side of the rhabdosome with the dorsal sides of the initial stipes placed side by side. The development differs strongly from that found in the superficially similar Arienigraptus in which the first thecal pairs grow downwards side by side, even though the rhabdosome shapes are quite similar. It represents a first step towards the development of a completely biserial rhabdosome and eventually leads to the biserial, monopleural glossograptids.     

ISOLATED GRAPTOLITES FROM THE TELYCHIAN (UPPER LLANDOVERY, SILURIAN) OF LATVIA AND ESTONIA

Abstract:  Isolated material of 21 graptolite species from the upper Telychian of Latvia and Estonia is described. New thecal structures are recognized in Streptograptus , for example enrolment of the disto-lateral margin of the flange in distal S. nodifer thecae, possession of proximal lobes in S. wimani and elongated proximal lobes in S. sp. 3. S. spp. 1 and 2 both possess a nozzle, but do not have coiled metathecae. Thecal asymmetry in Oktavites falx is shown to be the reverse of that in O. spiralis . Several new Streptograptus and Monoclimacis species remain to be described. The absence of many of the taxa described herein from Silurian equatorial regions strengthens the case for a distinct equatorial graptolite province.     

西藏南部聂拉木志留纪笔石新材料*

西沙群岛琛航岛琛科二井(CK-2)有878.3 m厚的新生代珊瑚礁灰岩(Cenozoic reef limestone)。新生代珊瑚礁灰岩自上而下包括了第四系的全新统和更新统以及新近系的上新统和中新统。其中, 中新统厚514.3 m, 产19属石珊瑚(Scleractinia corals)。更新统厚215.6 m, 产21属石珊瑚(Scleractinia)和1属八射珊瑚(Octocorallia)。珊瑚是营底栖固着生活的动物, 在地层断代方面它没有能像一些浮游动物(例如浮游有孔虫等)那么“精准”。但也有一些珊瑚的地质历程相对比较短暂的, 它们在地层划分和对比方面还是能起到一定的重要作用。根据本文的研究在琛科二井井深364–878.3 m的这一段中新世地层中就鉴定出有好几个只见于中新世或者常见于中新世的珊瑚, 如: 星日珊瑚(Astrhelia)、安的列斯珊瑚(Antillophyllia)和大安的列斯珊瑚(Antillia)等。另外在井深21.4–237 m的更新世地层中也发现了好几个只限于第四纪的珊瑚, 如: 叶状珊瑚(Lobophyllia)、合叶珊瑚(Symphyllia)、轮沙珊瑚(Trochopsammia)和苍珊瑚(Heliopora)等。上述那些珊瑚的地质分布与有孔虫(Foraminifera)生物地层鉴定的结果以及古地磁(Palaeomagnetism)和同位素(Isotope)年代地层测定的数据完全吻合。此外, 珊瑚除了在地层的划分对比方面(subdivision and correlation of the stratigraphy)能够起到一些关键的作用外, 更重要的是它在恢复和解释古地理(Palaeogeography)、古气候(Palaeoclimatology)和古生态(Palaeoecology)等方面也都能起到非常重要的作用。     

Maeandrograptus schmalenseei and its bearing on the origin of the diplograptids

The earliest diplograptids were apparently monophyletic and are characterized by a streptoblastic development and strongly overlapping, markedly sigmoidal thecae. They may be grouped as the genus Undulograptus Bou¯ek 1973. The biramous, reclined Maeandrograprus schmalenseei Moberg 1892 of the upper Arenig Didymograptus hirundo Zone has a striking and detailed resemblance to these early diplograptids in the form of its proximal thecae, the style and degree of prothecal folding, and in the symmetry, form and orientation of the sicula and early thecae. Its appearance coincides with or slightly predates the appearance of diplograptids in the D. hirundo Zone. It is proposed as a representative of the group of biramous graptolites which were directly ancestral to the diplograptids. Derivation of the diplograptids from such a source would have involved some changes in the proximal thecal development, in the attitude of stipes and also in the form of the distal thecae - evolutionary changes which are known to have occurred in other graptolite groups.     

Preservation of soft tissues in Silurian graptolites from Latvia

The contractile stalks of graptoloid zooids are preserved as organic carbon residues in thecae of the middle Llandovery graptoloid graptolites Rastrites geinitzii and Neolagarograptus? sp. from the Aizpute‐41 core, Latvia. The contractile stalks are surrounded by equant pyrite crystals, resulting in three‐dimensional preservation of the graptolite rhabdosomes, and are associated with sediment of similar composition to, and derived from, the adjacent matrix. Matrix entered the thecae after pyrite crystal growth and filled some of the space left by collapse of the contractile stalks and some intercrystalline cavities; other space is partially infilled by diagenetic minerals. The contractile stalks are parallel‐sided and occupy up to one‐half the metathecal width, which is not inconsistent, assuming post‐mortem shrinkage, with the suggestion that graptoloid zooids filled their thecal tubes in life. The location of the preserved soft tissues, towards the distal ends of the metathecae, is very different from that predicted by decay experiments on the extant pterobranch hemichordate Rhabdopleura; the latter's soft tissues may thus not be a reliable analogue for those of these Silurian graptoloids.     

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.     

ULTRASTRUCTURAL ASPECTS OF SEXUAL REPRODUCTION IN THE RED TIDE DINOFLAGELLATE GONYAULAX TAMARENSIS1

The marine dinoflagellate Gonyaulax tamarensis Lebour is best known for its propensity to form blooms known as red tides in coastal waters worldwide. This paper examines the sexual cycle of this organism using light and electron microscopy. Sexual reproduction begins with contact between thecate gametes which subsequently shed their thecae to fuse along their pellicular layers. Nuclear fusion occurs well after cytoplasmic fusion and is characterized by several distinctive features: a highly vesiculate nucleoplasm without microtubules; nucleoli and V-shaped chromosomes abut the nuclear envelope distal to the region of nuclear contact; and each chromosome possesses a longitudinal line, the central chromosomal axis. Fusion results in a planozygote with numerous cytoplasmic storage products and a slightly thickened layer beneath the pellicle. Subsequent loss of thecal plates and a thickening of the sub-pellicular layer results in a non-motile hypnozygote. A newly-formed hypnozygote possesses numerous minute papillae along its outer surface, formed by the up-folding of the accumulating wall layer. Maturation of the hypnozygote wall results in a smooth three-layered wall, the outermost layer of which is the pellicular layer. Hypnozygote germination produces a large quadriflagellate plan-omeiocyte with a single nucleus and thecal plates identical to vegetative cells. Two subsequent divisions, presumably meiotic, result in Jour cells morphologically identical to vegetative cells.     

Origin of the Retiolitidae: insights from a new graptolite genus from the early Silurian of Arctic Canada

Isolated specimens of Hercograptus introversus n. gen., n. sp. show features characteristic of the Retiolitidae, such as partial periderm reduction, and extended ancora lists and a reticulum that are attached to the thecal margins, on a rhabdosome that, in most other respects, resembles Pseudorthograptus. This newly discovered graptolite provides support for the hypothesis that Pseudoretiolites is the first-evolved retiolitid, since they share a similar ancora type and unique thecal style. It is also clear that the suite of features that normally distinguish the Retiolitidae did not all evolve simultaneously. It is proposed that development of a complete thecal framework of lists, permitting complete periderm reduction, should be the character used to distinguish the Retiolidae from the Petalolithidae. Unusual apertural modifications, such as strong introversion, lateral lappets, and a short, free dorsal wall suggest that Hercograptus may be an offshoot of the lineage leading from Pseudorthograptus to Pseudoretiolites.     

PREPARATION AND CHARACTERIZATION OF PROTOPLASTS OBTAINED FROM THE PRASINOPHYTE SCHERFFELIA DUBIA (CHLOROPHYTA)1

The prasinophyte genera Scherffelia and Tetraselmis are the only genera that form a cell wall by an extracellular fusion of scales called a theca. We established a protocol for the production of protoplasts from Scherffelia dubia Pascher emend. Melkonian et Preisig using 3 mM Ellman's reagent (5,5′‐dithio‐bis‐2‐nitrobenozoic acid [DTNB]). Protoplasts analyzed by EM lacked flagella and thecae but were otherwise similar to control cells. In response to treatment with DTNB, many protoplasts synthesized new thecal scales in the Golgi apparatus, indicating that cells attempted to regenerate new cell walls. However, complete regeneration of the thecae only occurred once DTNB was washed out from the medium. At higher DTNB concentrations (5 mM), two protoplasts were found within the parental cell wall and scales accumulated between the plasma membrane of the protoplasts and the original theca but failed to form a new theca.     

志留纪笔石Oktavitesexcentricus(Bjerreskov,1975)的古生物学特征及地层意义*

陕西紫阳地区在古地理上位于扬子台地西北缘,区域内志留纪地层发育,其中志留系兰多维列统(Llandovery)特列奇阶(Telychian)笔石相地层出露较为完整,笔石带较为连续。Oktavites excentricus(Bjerreskov,1975)是特列奇阶Oktavites spiralis笔石带重要的伴生分子,在世界范围内广泛分布。文中通过对紫阳地区一系列特列奇阶剖面研究后认为,Oktavites excentricus较短的化石延限和广泛的古地理分布使其具备地层对比潜力,这将为Oktavites spiralis笔石带的进一步细分提供依据。同时,Oktavites excentricus胞管为典型的奥氏笔石式,其笔石体的盘旋方式又与稍晚的Cyrtograptus lapworthi(Tullberg,1883)(笔石带化石,弓笔石类的早期代表)十分接近,因此,对该种的演化过程的研究也为讨论弓笔石的起源过程提供了更多参考。     

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.     

Bohemograptus papilio sp. nov. three-dimensionally preserved monograptid (Graptolithina) with an adaptation to retard sinking,from the Upper Silurian Poland

An unexpected new form of Bohemograptus with unusual morphological structure has been found in the upper part of the Bohemograptus praecornutus Biozone, Upper Ludlow of the Mielnik borehole, Poland. Bohemograptus papilio sp. nov. has the characteristic rhabdosome for Bohemograptus, in addition to extraordinary paired latero-dorsal additions, not comparable to any processes typical for Bohemograptus thecal openings. The new structure, a patagium, is located in the proximal part of the rhabdosome, and is built from main rods dividing repeatedly into thinner lists with significant remnants of membranes spread between them. Another new structure is the virgellarium, a membranous addition to the virgella. Membranes of the patagium and virgellarium are not built from microfusellar tissue as additions in other bohemograptids. It is suggested that the membranous additions were orientation devices, constructed to retard the sinking of the colony in the water column.     

Further Observations on the Chemical Composition of Thecae of Platymonas tetrathele West (Prasinophyceae) by Means of the X-ray Microanalyser Electron Microscope (EMMA)

Preliminary observations on the elemental contents of driedthecae of the marine green flagellate Platymonas tetratheleshow that calcium, silicon, phosphorus, chlorine, and sulphurare present in quantities sufficient to give significant readingswith the electron probe EMMA although the silicon content isso low that this element could be a contaminant from glasswareused when harvesting the thecae. Changes induced by washing,and by washing followed by boiling, have been traced and arediscussed. The most important result, namely the behaviour ofcalcium, is interpreted in terms of previous information onthe thecal chemistry (Gooday, 1971). It is concluded that calciumis present in native thecae mainly as the calcium salt of galacturonicacid, a major structural component.     

Five new species of Trichostomatida (ciliated protozoa) from the colon of wild African rhinoceroses

Five new species of Charonina Strand, 1928 were revealed, in addition to 41 species of 20 other apparent genera, in a survey of ciliated intestinal protozoan endocommensals of both black and white wild African rhinoceroses. Charonina species infected the ventral and dorsal region of the ascending colon, where the average total protozoan populations (× 10³/ml digesta fluid) were 100 and 80, respectively, in the white and 270 and 260, respectively, in the black rhinoceroses. Charonina species constituted up to 50% in the ventral and 25% in the dorsal populations. Measurements in micrometres and specific characteristics of the five species are: C. odontophora n. sp. length 70±5.7, width 32±7.2, dorso-ventral thickness 7±1.1, slender ovate-lanceolate-shaped body with frontal lobe and prong-like protrusion in oral-opening; C. tortuosa n. sp. length 87±9.3, width 42±5.3, dorso-ventral thickness 15±2.7, body-shape ovate-lanceolate without frontal lobe, oral-opening with longitudinal ridge, cytopharyngeal canal with sharp bend after emerging from oral-opening; C. dicerotis n. sp. length 67±8.6, width 37±4.0, dorso-ventral thickness 12±2.2, body-shape ovate-lanceolate without frontal lobe, oral-opening without ridge, cytopharyngeal canal curved without sharp bend; C. tenuis n. sp. length 56±10.0, width 16±4.1 at anterior end and 10±2.7 at posterior end, dorso-ventral thickness 7±1.2 at anterior end and 5±1.1 at posterior end, body-shape cone-like with longitudinal striations and frontal lobe; C. tetragona n. sp. length 58±4.7, width 26±3.2, dorso-ventral thickness 12±1.8, body-shape rectangular with frontal lobe and caudal flaps. The length, width and dorso-ventral thickness of the five species are on average in the approximate ratio of 6:3:1, thus showing them to be dorso-ventrally compressed. The body conformation of C. tetragona n. sp. closely resembles that of Didesmis quadrata Fiorentini, 1980, but is distinguished from the latter by the absence of a concrement vacuole and the presence of an elongate cytopharyngeal canal.     

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.     

Stamen development in the Ericaceae. I. Anther wall, microsporogenesis, inversion, and appendages

Development of the introrse, tetrasporangiate, and normally dorsifixed and poricidal stamens has been studied at the gross morphological and cellular level in ten species of Ericaceae. Microsporogenesis, followed in four species, is normal, with cytokinesis simultaneous, forming tetrahedral tetrads. The tricolp(or)ate pollen is shed as permanent tetrads with each segment two-celled except in Enkianthus in which pollen grains are three-celled monads. Anther-wall development is similar in all four species initially, but no regular pattern of wall development could be recognized thereafter. The tapetum, of parietal origin, is binucleate, glandular, and mainly uniseriate. Viscin threads occur with the tetrads in the three rhododendroid species. A well-developed endothecium appears only in Enkianthus.Soon after stamen initiation, anthers of nine species invert at the eventual filament-anther junction to become introrse; in Enkianthus inversion occurs close to anthesis. Microsporogenesis starts during early inversion; greater cell elongation on the abaxial side of the young anther completes inversion by the late sporogenous-tissue stage. In Erica and, to a lesser extent Calluna, inversion results from greater abaxial than adaxial increase in cell number and length just above the filament-anther junction. The single vascular strand reflects the degree of inversion. Stamens of six species are appendaged; three have only awns, two only spurs, while one has both. Appendages arise from residual meristems after inversion is completed (or almost so) in all except Enkianthus. Awns develop at what will be the apex at maturity of each anther half. Their length and orientation vary among species. Only in Vaccinium do the awns become hollow (tubules). Spurs, varying in length, shape, and size, arise on the abaxial side from the filament, connective, or thecae.     

The rhabdosome structure of aSaetograptus species (Graptoloidea, Monograptacea) from a North German glacial boulder

Saetograptus sp. cf.Saetograptus leintwardinensis from the late Ludlow is described from material isolated from a glacial boulder. The species shows several unexpected rhabdosome structures, especially a considerably widening trumpetshaped sicular aperture with a forked dorsal tongue. The high infraspecific variation of the species is documented.     

Undulograptus dicellograptoides n. sp., an abnormal diplograptid from the Late Arenig of western Newfoundland, Canada

The unusual diplograptidUndulograptus dicellograptoides n. sp. from the late ArenigUndulograptus dentatus Zone of western Newfoundland is described from isolated material. The species bears two reclined stipes and resembles a species of the stratigraphically younger genusDicellograptus. The dicellograptid to dicranograptid rhabdosome form appeared several times independently in the Diplograptina.