Observations on the life-history and ultrastructure of the marine choanoflagellate Choanoeca perplexa Ellis

1977 ◽  
Vol 57 (2) ◽  
pp. 285-301 ◽  
Author(s):  
Barry S. C. Leadbeater
Keyword(s):  
Life History ◽  
Electron Microscope ◽  
Marine Species ◽  
Freshwater Species ◽  
Relative Ease ◽  
Ultrastructural Studies ◽  
Modern Methods ◽  
The Subject ◽  
Stephanoeca Diplocostata ◽  
Whole Mounts

In recent years the external morphology of marine choanoflagellates has been the subject of close scrutiny. This is a result of the attention given to marine nanoplankton, of which choanoflagellates are a part, and the relative ease with which choanoflagellates with loricae of costal construction can be observed in shadowcast whole mounts with an electron microscope. However, detailed ultrastructural studies of choanoflagellate protoplasts have been limited to one freshwater species Codosiga botrytis (Ehr.) Saville-Kent (Petersen & Hansen, 1954; Fjerdingstad, 1961; Hibberd, 1975) and four marine species Salpingoeca pelagica Laval (Laval, 1971), Stephanoeca diplocostata Ellis (Leadbeater & Manton, 1974), Savillea micropora (Norris) Leadbeater (Leadbeater, 1974) and Codosiga gracilis James-Clark (Leadbeater & Morton, 1974b). Of these only the recent studies by Hibberd (1975), Laval (1971), Leadbeater & Manton (1974), Leadbeater (1974) and Leadbeater & Morton (1974b) contain micrographs of material processed by modern methods.

scholarly journals V. On the early development of cirripedia

1894 ◽  
Vol 185 ◽  
pp. 119-232 ◽  
Keyword(s):  
Life History ◽  
Early Development ◽  
Developmental Stages ◽  
Short Stay ◽  
Complete Understanding ◽  
Cambridge University ◽  
Modern Methods ◽  
History Of ◽  
Complete Series ◽  
The Subject

During a short stay at Plymouth, in 1889, I was engaged in studying certain points in the anatomy of Cirripedia; finding, however, that a knowledge of the embryology was necessary in order to arrive at a complete understanding of the adult structure, I became wishful to investigate the life-history of some one member of the group. This I had an opportunity of doing at Naples, where I was appointed to occupy the Cambridge University Table at the Zoological Station for a period of six months, subsequently increased to nine. I here succeeded in obtaining a practically complete series of stages of Balanus perforatus , Bruguiere, as well as many stages in other members of the group. Though a number of able observers have occupied themselves with the embryology of Cirripedes, yet, owing to lack of opportunity, and to the difficulty of obtaining complete series of developmental stages, as well' as to the inherent difficulties in the subject, much remained to be done in this line. Willemoes-Suhm alone, with the advantages afforded by his position during the Challenger Expedition, has hitherto obtained a complete series of stages of any one form, but he failed to trace the history of the earlier stages, and in the later, limited himself to the appearance of fresh and spirit specimens, as seen without cutting sections. In fact the method of sections has been little applied to the development of Cirripedes, and not at all to the earlier stages. There is, therefore, little apology needed for an account embracing the results obtained by the employment of some of the more modern methods of embryological study.

Life-history and ultrastructure of a new marine species of Proterospongia (Choanoflagellida)

1983 ◽  
Vol 63 (1) ◽  
pp. 135-160 ◽  
Author(s):  
Barry S. C. Leadbeater
Keyword(s):  
Electron Microscopy ◽  
Life History ◽  
Life Cycle ◽  
Single Cells ◽  
Marine Species ◽  
The Other ◽  
Developmental Problems ◽  
Starting Point ◽  
History Of ◽  
Whole Mounts

The morphology and microanatomy of two different phases in the life history of a single new marine choanoflagellate (Proterospongia choanojuncta sp.nov.) have been documented and described with the aid of light microscopy and from electron microscopy of whole mounts and sections of material in clonal culture. Completion of the life-cycle has been repeatedly achieved in cultures established from single cells, regardless of which phase is used as a starting point. One phase is colonial and motile (the Proterospongia phase) and the other unicellular and sedentary (the Choanoeca phase). Taxonomic, nomenclatural and developmental problems are summarized and discussed.

Life history and ecological correlates of extinction risk in European freshwater fishes

2005 ◽  
Vol 62 (4) ◽  
pp. 854-862 ◽  
Author(s):  
John D Reynolds ◽  
Thomas J Webb ◽  
Lorraine A Hawkins
Keyword(s):  
Life History ◽  
Threatened Species ◽  
Native Species ◽  
Life Histories ◽  
Extinction Risk ◽  
Marine Species ◽  
Freshwater Fishes ◽  
Freshwater Species ◽  
Threat Status ◽  
Close Relatives

We used phylogenetically based comparative analyses to test for associations between extinction risk in European freshwater fishes and a variety of life history, ecological, and biogeographical traits. Based on the World Conservation Union classification scheme, a total of 47% of Europe's 287 native species are classified as threatened with extinction. Threatened species are significantly smaller than less-threatened species in the same genera when analyses are restricted to fully freshwater species. This trend is reversed when anadromous genera are included. These comprise many large-bodied species in which fishing has often played a greater role in declines than in other taxa. Threatened species did not differ significantly in their habitats, although they tended to occupy a narrower variety of habitats biased toward streams and rivers. Threatened species occupy much narrower latitudinal ranges than close relatives that are less threatened, and they also have more southerly distributions where pressures on habitats are intense. This study suggests that links between life histories and threat status of freshwater fishes are not as clearcut as for marine species. For fish restricted entirely to freshwater, small-bodied species are most at risk owing to their naturally small ranges, which may put them in a more precarious position when their habitats are impacted by humans.

scholarly journals Ultrastructural Studies and Na+,K+-ATPase Immunolocalization in the Antennal Urinary Glands of the Lobster Homarus gammarus (Crustacea, Decapoda)

2005 ◽  
Vol 53 (10) ◽  
pp. 1203-1214 ◽  
Author(s):  
Saber Khodabandeh ◽  
Guy Charmantier ◽  
Mireille Charmantier-Daures
Keyword(s):  
Basal Membrane ◽  
Marine Species ◽  
Freshwater Species ◽  
Homarus Gammarus ◽  
Ultrastructural Studies ◽  
Antennal Gland ◽  
Cytological Features ◽  
Antennal Glands ◽  
Bladder Cells ◽  
Structure And Ultrastructure

Unlike in crustacean freshwater species, the structure and ultrastructure of the excretory antennal gland is poorly documented in marine species. The general organization and ultrastructure of the cells and the localization of Na+,K+-ATPase were examined in the antennal gland of the adult lobster Homarus gammarus. Each gland is composed of a centrally located coelomosac surrounded ventrally by a labyrinth divided into two parts (I and II) and dorsally by a voluminous bladder. There is no differentiated nephridal tubule between them. The labyrinth and bladder cells have in common a number of ultrastructural cytological features, including basal membrane infoldings associated with mitochondria, apical microvilli, and cytoplasmic extrusions, and a cytoplasm packed with numerous vacuoles, vesicles, lysosome-like bodies, and swollen mitochondria. Each type of cell also presents distinctive characters. Na+,K+-ATPase was detected through immunofluorescence in the basal part of the cells of the labyrinth and in the bladder cells with an increasing immunostaining from labyrinth I to the bladder. No immunoreactivity was detected in the coelomosac. The cells of the labyrinth and of the bladder present morphological and enzymatic features of ionocytes. The antennal glands of the lobster thus possess active ion exchanges capabilities.

Ultrastructural Studies of Bovine Respiratory Disease Complex

1975 ◽  
Vol 33 ◽  
pp. 428-429
Author(s):  
James C.S. Kim
Keyword(s):  
Michigan State University ◽  
State University ◽  
Diagnostic Laboratory ◽  
Ultrastructural Studies ◽  
Bovine Respiratory Diseases ◽  
Etiologic Agents ◽  
Diagnostic Difficulties ◽  
The Subject ◽  
Capillary Walls ◽  
Alveolar Capillary

Bovine respiratory diseases cause serious economic loses and present diagnostic difficulties due to the variety of etiologic agents, predisposing conditions, parasites, viruses, bacteria and mycoplasma, and may be multiple or complicated. Several agents which have been isolated from the abnormal lungs are still the subject of controversy and uncertainty. These include adenoviruses, rhinoviruses, syncytial viruses, herpesviruses, picornaviruses, mycoplasma, chlamydiae and Haemophilus somnus.Previously, we have studied four typical cases of bovine pneumonia obtained from the Michigan State University Veterinary Diagnostic Laboratory to elucidate this complex syndrome by electron microscopy. More recently, additional cases examined reveal electron opaque immune deposits which were demonstrable on the alveolar capillary walls, laminae of alveolar capillaries, subenthothelium and interstitium in four out of 10 cases. In other tissue collected, unlike other previous studies, bacterial organisms have been found in association with acute suppurative bronchopneumonia.

Telling Diaspora Stories: theoretical and methodological reflections on narratives of migrancy and belongingness in the second generation

2009 ◽  
Vol 6 (2) ◽  
pp. 143-153 ◽  
Author(s):  
Anastasia Christou
Keyword(s):  
Life History ◽  
Second Generation ◽  
Life Stories ◽  
Narrative Research ◽  
Social Experiences ◽  
Biographical Approach ◽  
The Subject

This article explores the theoretical and methodological implications of the study of second generation migration through the use of life stories, a narrative and biographical approach. It presents a theoretical contextualisation of life history research in addressing the direction it has taken in the study of migration and identity in order to problematise how the subject and subjectivities in narrative research have been framed by social categorisations such as gender, ethnicity, class as well as social experiences such as trauma, exile, memory and imagination. The paper develops the analytical contribution of researching the biographicity of everyday migrant lives. 

scholarly journals <i>Cabochonicus,</i> a new genus for species of gemmate megaspores previously referred to <i>Verrutriletes</i>

1987 ◽  
Vol 6 (1) ◽  
pp. 65-75 ◽  
Author(s):  
D. J. Batten ◽  
D. J. P. Ferguson
Keyword(s):  
Type Species ◽  
New Genus ◽  
Ultrastructural Studies ◽  
Fungal Attack ◽  
The Subject

Abstract. Several species of Mesozoic megaspores that are sculptured with globular, often gemmate elements are sufficiently distinct from most verrucate forms to warrant their inclusion in a genus other than Verrutriletes. Cabochonicus is erected to accommodate them with C. (al. Verrutriletes) carbunculus as the type species. The form of the gemmae, which have a glossy appearance, has been the subject of past debate with one interpretation being that they are the manifestation of fungal attack rather than sculpture. Evidence from ultrastructural studies suggests, however, that they are exinal excrescences. The spores are assumed to be the products of heterosporous lycopods and the structure of the wall layers may indicate selaginellalean affinities. The plants are more likely to have been terrestrial than aquatic or semi-aquatic.

Ultrastructural Studies of Piscine Erythrocytic Necrosis (PEN) in Atlantic Herring (Clupea harengus harengus)

1978 ◽  
Vol 35 (1) ◽  
pp. 148-154 ◽  
Author(s):  
Paul W. Reno ◽  
Marie Philippon-Fried ◽  
Bruce L. Nicholson ◽  
Stuart W. Sherburne
Keyword(s):  
Electron Microscope ◽  
Key Words ◽  
Clupea Harengus ◽  
Type I ◽  
Atlantic Herring ◽  
Type Ii ◽  
Inclusion Type ◽  
Cytoplasmic Inclusions ◽  
Ultrastructural Studies ◽  
Clupea Harengus Harengus

Erythrocytes of PEN-positive Atlantic herring (Clupea harengus harengus) were examined to determine their ultrastructure. Cytoplasmic inclusions were of two types when observed under the electron microscope. The first type (type I) appeared coarsely granular, electron dense, round, and up to 1.5 μm in diameter. Virions were closely associated with this type of inclusion. The second type of inclusion (type II) had approximately the same appearance as the surrounding cytoplasm, from which it was separated by a discrete membrane, and was variable in size. Virions were not intimately associated with type II inclusions. Virions occurred singly or in clusters within the cytoplasm or in association with type I inclusions and were hexagonal and 145 nm in diameter. Virions were composed of a rigid hexagonal capsid 8 nm wide, a lighter 16-nm region, and a core 100 nm in diameter. The virus of PEN is presumptively classified as an Iridovirus. Key words: ultrastructure, erythrocytes, virology

Modern Methods of Costing Insured Pension Schemes

1970 ◽  
Vol 19 (01) ◽  
pp. 1-41
Author(s):  
R. E. Snelson
Keyword(s):  
Basic Function ◽  
Cost Estimates ◽  
Professional Advice ◽  
The Past ◽  
Funding System ◽  
Pension Schemes ◽  
Modern Methods ◽  
The Subject

1. In the past, concepts of funding and methods of costing have frequently been discussed in papers submitted to the Institute and the Students' Society usually with particular emphasis on selfadministered funds. There is still scope for further thought on the subject of funding methods and it is hoped that this paper will provide an opportunity for further discussion with particular reference to insured schemes. Life offices are not in the same position as consulting actuaries since their basic function is to insure the benefits required rather than to give professional advice. At the same time they have a responsibility to ensure that their costing methods are basically sound and that the issues involved are not misrepresented to their prospective and current policyholders. In recent years there has been a tremendous demand for final salary arrangements using the controlled funding system of administration but little attempt has been made to codify the principles which ought to be followed in making cost estimates.

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