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Taxonomy and morphology of Calciopappus curvus sp. nov. (Syracosphaeraceae, Prymnesiophyceae), a novel appendage-bearing coccolithophore
Abstract
Based on scanning electron microscopy observations, a new species of the coccolithophore genus Calciopappus (Syracosphaeraceae, Prymnesiophyceae) is described from the surface waters off Bergen and from the lower photic zone of sub-tropical and tropical waters. Morphological, coccolith rim structure and biometric analyses strongly support separation of this morphotype from the two described Calciopappus species, but inclusion of it within the genus. The new form differs from the other species in being noticeably smaller and in morpho-structural details of each of the three coccolith types that form the coccosphere: (1) the body coccoliths have an open central area; (2) the whorl coccoliths have a wide central opening and two thumb-like protrusions; and (3) the appendage coccoliths are curved. On this basis, the species is formally described as Calciopappus curvus sp. nov., its systematic affinity is discussed and compared with other extant coccolithophores.
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Marine phytoplankton play important roles in the global ecosystem, with a limited number of cosmopolitan keystone species driving their biomass. Recent studies have revealed that many of these phytoplankton are complexes composed of sibling species, but little is known about the evolutionary processes underlying their formation. Gephyrocapsa huxleyi, a widely distributed and abundant unicellular marine planktonic algae, produces calcified scales (coccoliths), thereby significantly affects global biogeochemical cycles via sequestration of inorganic carbon. This species is composed of morphotypes defined by differing degrees of coccolith calcification, the evolutionary ecology of which remains unclear. Here, we report an integrated morphological, ecological and genomic survey across globally distributed G. huxleyi strains to reconstruct evolutionary relationships between morphotypes in relation to their habitats. While G. huxleyi has been considered a single cosmopolitan species, our analyses demonstrate that it has evolved to comprise at least three distinct species, which led us to formally revise the taxonomy of the G. huxleyi complex. Moreover, the first speciation event occurred before the onset of the last interglacial period (~140 ka), while the second followed during this interglacial. Then, further rapid diversifications occurred during the most recent ice-sheet expansion of the last glacial period and established morphotypes as dominant populations across environmental clines. These results suggest that glacial-cycle dynamics contributed to the isolation of ocean basins and the segregations of oceans fronts as extrinsic drivers of micro-evolutionary radiations in extant marine phytoplankton.
Coccolithophores are a diverse group of calcifying phytoplankton, which are responsible for a large part of the modern oceanic carbonate production. Here, we describe novel or poorly known coccolithophores and novel life cycle combination coccospheres detected in samples collected either in the Gulf of Aqaba in the northern Red Sea or in the Gulf of Naples in the western Mediterranean. These include Syracosphaera winteri, for which detached coccoliths have previously been recorded but both a formal description and taxonomic affiliation were lacking, and five undescribed sets of combination cells linking HET and HOL forms for S. pulchra, S. mediterranea, S. azureaplaneta, S. lamina and S. orbicula. We also propose the replacement name S. kareniae for the fossil species Deutschlandia gaarderae. We describe a new species of the genus Ophiaster, O. macrospinus, displaying a unique morphological and ecological distribution as well as putative combination cells of two variants of the deep-dwelling Florisphaera profunda, which provide new insights on the affiliation of this genus within the Calcihaptophycideae. Additionally, in the family Papposphaeraceae we detected a new species, Pappomonas vexillata, and combination cells of Picarola margalefi and of a species resembling Papposphaera arctica. Finally, we detected three novel, unpaired holococcolithophore forms (Calyptrosphaera lluisae, Calicasphaera bipora and one form designated as Holococcolithophore A). Overall, this set of novel observations and ensuing discussions provide further insights into the diversity, evolution and life cycle complexity of coccolithophores in the oceans.
General discussion of calcreous nannofossils, techniques for study, stratigraphic distribution, systematics.
New scanning electron microscope observations of unadulterated calcareous nannofossil assemblages on lamina surfaces of Cretaceous Tanzania Drilling Project sediments reveal high diversity in the <3 µm size-range and high abundances of small and frangible morphologies. These assemblages prompt comparison to modern assemblages, which show similar high diversity and abundance of very small and fragile taxa, although these assemblages are generally not preserved in the fossil record due to taphonomic filtering. Not only are there broad similarities between the general composition of modern assemblages and those of the Tanzanian lagerstätte, but also our discovery of several new Cretaceous taxa provides evidence for greatly extended fossil lineages of extant orders, with implications for both deep-time biodiversity divergence and survival through the end-Cretaceous mass extinction. Our findings include: new species that are the first-recorded Mesozoic representatives of the extant Syracosphaeraceae and Papposphaeraceae; potentially previously unrecorded diversity in the Mesozoic Calciosoleniaceae, another extant order, represented by extant species that have been described already; and new species and unusually high abundances of the Mesozoic Stephanolithiaceae. We also highlight the extended range of an incertae sedis Cenozoic genus, Ellipsolithus, into at least the Turonian.
Here, we describe seven new miniscule to very small Cretaceous species: Syracosphaera antiqua, S. repagula, Pocillithus macleodii, P. crucifer, Stradnerlithus wendleri, S.? haynesiae and Tortolithus foramen.
Calcifying marine phytoplankton—coccolithophores— are some of the most successful yet enigmatic organisms in the ocean and are at risk from global change. To better understand how they will be affected, we need to know “why” coccolithophores calcify. We review coccolithophorid evolutionary history and cell biology as well as insights from recent experiments to provide a critical assessment of the costs and benefits of calcification. We conclude that calcification has high energy demands and that coccolithophores might have calcified initially to reduce grazing pressure but that additional benefits such as protection from photodamage and viral/bacterial attack further explain their high diversity and broad spectrum ecology. The cost-benefit aspect of these traits is illustrated by novel ecosystem modeling, although conclusive observations remain limited. In the future ocean, the trade-off between changing ecological and physiological costs of calcification and their benefits will ultimately decide how this important group is affected by ocean acidification and global warming.
A contingent of weakly calcified coccolithophorid genera and species were described from polar regions almost 40 years ago. In the interim period a few additional findings have been reported enlarging the realm of some of the species. The genus Wigwamma is revisited here with the purpose of providing, based on additional sampling from both polar regions, an update on species morphology, life history events and biogeography that can serve as a reference for the future. A new genus, Pseudowigwamma gen. nov. is described to accommodate Wigwamma scenozonion, a species which critically deviates from a core group of five Wigwamma species in terms of coccolith morphology and life history events. Wigwamma armatura sp. nov. is described on the basis of material from the Weddell Sea, Antarctica. While fitting nicely into the Wigwamma generic concept, the species adds new dimensions to the overall appearance of the coccolith armour of the cell.
Genetic approaches to exploring in situ marine phytoplankton assemblages have revealed previously unsuspected diversity at different taxonomic levels. However, the phylogenetic species concept has rarely been compared to classical morphologically based taxonomy, which forms the basis of most current ecological, physiological, and paleontological knowledge of phytoplankton. Here we use the coccolithophores as a case study to test the relationship between these two taxonomic approaches. Analysis of 217 coccolithophore LSU rDNA sequences and 729 specimens observed by light and electron microscopy obtained from three water samples (Atlantic Ocean, Pacific Ocean and Mediterranean Sea) demonstrated that parallel analysis of morphological and genetic data highlights limitations inherent to each approach. Combined morpho-genetic analyses increase the scope of description of the composition, richness and structure of natural coccolithophore communities. Overall, genetic determined diversity exceeded morphological determined diversity, which may partly reflect methodological biases, but also probably reflects cryptic speciation and/or the presence of lightly- or non-calcifying species (or life cycle stages) within the coccolithophore clade. Focusing on six coccolithophore family or order level subgroups, we show that the genetic diversity within established morphospecies varied significantly in different environments. Critically, we find that the divergence threshold at which phylospecies corresponded to morphospecies varied between different natural communities, a factor that may have important implications with respect to evaluation of diversity by metagenomics approaches.
Jomonlithus littoralis is a coccolithophore exhibiting unusual coccolith morphology that has previously only been reported from Japanese coastal waters. Jomonlithus is a mono-specific genus that has remained incertae sedis within the Prymnesiophyceae since its original description. We isolated a culture of the calcifying (diploid) stage of this species from Mediterranean coastal waters that subsequently produced a non-calcifying life cycle stage in culture. The non-calcifying (haploid) stage of J. littoralis is described for the first time through light and electron microscope observations of cytology, scale ornamentation and ultrastructure. A 28s rDNA molecular phylogeny is presented and the systematic affinities of Jomonlithus are discussed. This genus is placed in the Hymenomonadaceae and the diagnosis of this family is emended.
Syracosphaera pulchra, the type species of the genus was isolated into unialgal culture and studied with both the light and electron microscope. A conspicuous coiling haptonema is present containing seven microtubules in the shaft and eight in the basal region; features shared with many taxa in the order Prymnesiales. The proximal and distal coccoliths differ in shape but resemble each other structurally: the outer elements alternate to make the rim. The proximal coccoliths possess an organic base-plate scale which is absent in the distal coccoliths. The uncalcified organic scales are ornamented by a radial, more or less concentric, fibrillar pattern and are arranged in several layers between the proximal coccoliths and the plasmalemma. The ultrastructure of the cell is typical of prymnesiophycean algae. The flagellar apparatus is characterized by the absence of secondary microtubular bundles which are usually well developed in other coccolithophorids with two microtubular roots. This feature is also rather similar to that found in members of the Prymnesiales.This investigation has indicated that S. pulchra has, in some respects, a closer affinity with members of the Prymnesiales than with the coccolithophorids.
Wigwamma scenozonion sp. nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadowcast whole mounts prepared from water samples collected in the vicinity of Godhavn (West Greenland) in July and August 1977. This nanoplanktonic coccolithophorid possesses two smooth flagella and a shorter coiling haptonema. Coccoliths of one type cover the whole cell. Each coccolith is composed of a ring of rod-like crystallites joined end to end and arranged parallel to the edge of the oval coccolith base-plates. A single enlarged crystallite is found on most coccoliths. W. scenozonion is distinguished from the two previously described Wigwamma species by the lack of coccolith superstructures and by having one, rather than two rings of crystallites along the base-plate edge. In addition to the West Greenland specimens a single W. scenozonion cell has been encountered in a water sample from Denmark.
To help understand potential biases in coccolithophore paleo-biodiversity estimates various aspects of their biology are reviewed based on the recent monographic guide to extant coccolithophore taxonomy and research developed within the CODENET project. The evidence for life-cycles in coccolithophores involving two biomineralized phases is reviewed in detail, and it is shown that these are likely to have been pervasive through the fossil record of coccolithophores. The extent of polymorphism in extant cocco- lithophores is reviewed and a surprisingly strong correlation with phylogeny is documented, in particular it is shown that there is a very strong correlation between polymorphism in heterococcolith and holococcolith-bearing phases. Recent documentation of (pseudo)cryp- tic speciation in coccolithophores is discussed and it is argued that this provides considerable support for the rather fine morphological taxonomy adopted by nannofossil paleontologists, but also means that accurate recognition of species in the fossil record is an almost im- possible goal. Finally the diversity of extant coccolithophores is compared with that recorded in Holocene sediments and it is shown that the majority of extant diversity is represented by small rare species with very low preservation potential. It is argued that this is the most serious potential biasing mechanism for study of paleobiodiversity changes since estimates of diversity at any time will be strongly influ- enced by the availability of well-preserved shelf sediments and of the intensity of their study by electron microscopy. Moreover, secular changes in coccolith size in relation to environmental change could significantly affect the preserved diversity of coccolithophores.
Most haptophytes are unicellular, photosynthetic flagellates, although some have coccoid, colonial, amoeboid, or filamentous stages. Nearly all have a characteristic filamentous appendage, the haptonema, arising between the two flagella. The small subunit ribosomal RNA gene (l8S ribosomal DNA) from 18 haptophyte species has been sequenced, and the sequences aligned with those of more than 300 published and unpublished chlorophyll a + c algae. Phylogenies were constructed using maximum likelihood, neighbor-joining, and weighted maximum parsimony analyses. The high divergence (6%) be tween members of Pavlova and the remaining haptophytes supports the division of Haptophyta into two classes: Prymne siophyceae and Pavlovophyceae. Three major clades that correspond to known taxa within the Prymnesiophyceae were identified: one clade embraces Phaeocystis spp.; the second includes members of the genera Chrysochromulina, Prymnesium, and Imantonia; and the third includes coccolithophorid genera and the genus Isochrysis. Two other clades contain taxa whose sequences were derived from a gene clone library. These taxa are not strongly related to any of the cultured taxa included in this study. Based on 18S ribosomal DNA sequence data and available information on morphological structure and ultrastructure, we propose that the class Prymnesiophyceae be divided into four orders: Phaeocystales ord. nov., Prym nesiales, Isochrysidales, and Coccolithales. A total of 1-2% divergence at this level in the 18S ribosomal RNA gene analysis warrants a separation above the level of family. Within the Pavlovophyceae, a new genus is established, Rebecca J.e. Green gen. nov., into which Pavlova salina and Pavlova helicata are moved.
The morphology of three remarkable genera of coccolithophores, Ophiaster, Michaelsarsia, and Calciopappus, is reviewed based on new images using field emission scanning electron microscopy. Each of these genera characteristically forms coccospheres with long appendages formed of highly modified coccoliths, which radiate from either the circum-flagellar pole of the coccosphere (Calciopappus and Michaelsarsia) or the antapical pole (Ophiaster). For each genus, it is shown that the appendage coccoliths can also occur in an alternative orientation appressed to the main coccosphere. It is hypothesized that the appendage coccoliths are initially deployed in the appressed orientation and that extension of the appendages is a dynamic response to environmental stress. The observations suggest that coccoliths are more sophisticatedly adapted to specific functions than has been assumed and that the cytoskeleton plays more active roles in coccolith morphogenesis and deployment than has previously been inferred.
For the past 25 years NIH Image and ImageJ software have been pioneers as open tools for the
analysis of scientific images. We discuss the origins, challenges and solutions of these two programs,
and how their history can serve to advise and inform other software projects.
Publicación online disponible en: http://www.icm.csic.es/scimar/index.php The present Atlas contains a detailed study, based in scanning electron microscopy (SEM) observations, of living coccolithophores from NW Mediterranean waters. The study contains 103 figures with 411 micrographs, which correspond to 168 coccolithophores (including different taxonomic and morphotypic entities). The figured specimens were collected during different cruises carried out from 1995 to 1999. Classification of the organisms follows modern taxonomy of living calcareous nannoplankton. Measures of the specimens and notes on their taxonomy are given in addition to abridged descriptions of the studied taxa. The atlas contains a large number of previously undescribed forms, specially in the genera Syracosphaera, Papposphaera, Polycrater, Anthosphaera, Corisphaera and Sphaerocalyptra. Several species never illustrated in the literature are presented here for the first time. Coccospheres having coccoliths of different recognized species are presented. These combination coccospheres are nowadays considered as transitional steps between different phases in the cellular life-cycle. An introduction with a brief overview of the actual coccolithophore knowledge and an abridged glossary with figures of the basic terminology are included. This research was supported by the C.S.I.C. and projects MAR91-0359, GRQ93-8041, AMB94- 0853; MAS2-CT93-0063, MAS3-CT96-0051 and MAR98-0932. Samples were provided by, projects MAS2-CT930063, MAS3-CT95-0037, MAS3- CT95-0016 and programe MEC-HF98-207. The EC TMR project CODENET, Coccolithophorid Evolutionary Biodiversity and Ecology Network (FRMXET97- 0113), financed part of this research and the present volume. Peer reviewed
The genera Ericiolus and Mercedesia are distinctive extant coccolithophores that are characterized by monothecate, monomorphic coccospheres with one type of triradiate star-shaped nannoliths. The two genera were described from the Danish coastal waters, the surface waters of the Arctic, and the Southern Oceans. During a study of samples from the low photic zone of the Mediterranean and Sargasso Seas, and from the subtropical gyres of the South-eastern Pacific and the South Atlantic Oceans, 44 collapsed coccospheres with triradiate star-like nannoliths were observed via scanning electron microscopy. Observations on the morphologies and biometric assessments of these specimens revealed that three distinct sets of nannoliths can be distinguished and that these were morphologically differentiated from all currently known species of Ericiolus and Mercedesia. The new forms and the previously described species of Ericiolus and Mercedesia were, however, similar, as they all demonstrated a distinctive set of collectively shared morphological characters and almost identical size ranges. On the basis of this, and instead of describing a third genus for the same group of nannoliths, we preferred to taxonomically synonymize Mercedesia with Ericiolus and revise the definition of Ericiolus. Therefore, we describe three new species, Ericiolus bendifii sp. nov., Ericiolus sheldoniae sp. nov. and Ericiolus mattioliae sp. nov., and an incompletely defined taxon, as Ericiolus cf. bendifii, and establish the new combinations E. aspiphorus comb. nov., E. multistellatus comb. nov. and E. pusillus comb. nov.
The genus Anthosphaera Kamptner emend. Kleijne is one of the most taxonomically confusing modern coccolithophores and its species level taxonomy has long been in a state of flux. Based on the review of imaged specimens from our collections, we attempt to rectify the nomenclatural problems and elucidate the obfuscated taxonomy of the genus. Review of included formally and informally described species shows that they are a distinctive group with shared characters, including ten different morphotypes of probable species level. Two of these, including the type species A. fragaria, have been shown to form life-cycle associations with heterococcoliths of the Syracosphaera molischii type. Hence, all species are transferred to Syracosphaera and the new combinations S. periperforata, S. lafourcadii, and S. origami are proposed. In addition, various informally described morphotypes are now formally described as Syracosphaera molischii var. pertusa, S. periperforata var. cylindrata, S. periperforata var. tridentata, S. rotaconica, and S. elevata. urn:lsid:zoobank.org:pub:0E5D4BD7-BC3B-4D30-B319-964AC887DDDE
It is an established fact that coccolithophores are of little importance with respect to biomass and diversity in the Baltic proper. The likely biogeochemical and environmental reasons for this have recently been critically analyzed and reviewed. The main conclusion is that the calcium carbonate saturation of the Baltic Sea is the main controlling feature, and that in particular an undersaturation during wintertime remains the critical bottleneck for coccolithophores to prevail in the Baltic proper. While there is no reason to question these observations, it is still relevant to put on record the actual findings of coccolithophores from the Baltic proper. Examinations of Baltic Sea material from the Bothnian Sea, the Bothnian Bay and the Gulf of Finland prepared for transmission electron microscopy has thus revealed a consistent presence of a low diversity community of lightly calcified coccolithophores (i.e. Balaniger virgulosa HOL and HET, Papposphaera arctica HOL cfr. and Papposphaera iugifera). When including here also material examined from the Danish transitional waters connecting the North Sea and the Baltic proper, it is possible to generally support the presence in the western Baltic, the Sounds and the Kattegat of a contingent of coccolithophores that appear to be either persistently present within the area or episodically occurring as determined by larger scale hydrographical events within the North Sea/Baltic Sea confluence area.
Coccolithophores are a group of microscopic marine phytoplankton that obtain their energy from sunlight. They are distinguished from other phytoplankton by their construction of calcium carbonate plates, called coccoliths, with which they surround their cells. They are one of the most abundant phytoplankton groups, making up about 10% of total global phytoplankton biomass. They are short-lived and can switch between diploid and haploid life stages, with each stage sometimes possessing a different type of coccolith, or the haploid stage sometimes none at all. Some species, in particular the intensively studied species Emiliania huxleyi, under certain conditions undergo unrestrained proliferation to form massive blooms. Because E. huxleyi cells also produce unusually large numbers of coccoliths, which scatter light, their blooms form bright waters which are conspicuous in satellite images. Coccoliths make up about half of the open ocean vertical flux of inorganic carbon (calcium carbonate), and are therefore important in the marine carbon cycle. Research is presently being undertaken to ascertain whether, and if so to what degree, they will be affected by ocean acidification.
Ten new species of the coccolithophore genus Syracosphaera are described from temperate and sub-tropical to tropical waters: Syracosphaera andruleitii sp. nov., Syracosphaera castellata sp. nov., Syracosphaera didyma sp. nov., Syracosphaera hastata sp. nov., Syracosphaera hirsuta sp. nov., Syracosphaera leptolepis sp. nov., Syracosphaera operculata sp. nov., Syracosphaera reniformis sp. nov., Syracosphaera serrata sp. nov. and Syracosphaera squamosa sp. nov. An emended description is given for Syracosphaera nanaKamptner. These and other Syracosphaera species are placed in a revised classification scheme for the genus, based on the morphological structure of endothecal and exothecal coccoliths, and coccosphere characteristics. The Syracosphaera noroitica group is introduced for species with exothecal murolithswith a beaded proximal flange and varimorphic endothecal muroliths. The three new subgroups in the Syracosphaera nodosa group are characterised by their exothecal coccolith structure: subcircular and delicate in the leptolepis-subgroup, oval in the nana-subgroup and laminated in the squamosa-subgroup. The corolla-subgroup, with its large funnel- shaped exothecal coccoliths, is new in the Syracosphaera pulchra group.
Detailed descriptions are given of the structure and morphology of the heterococ-coliths of the six CODENET taxa; Gephyrocapsa oceanica, Coccolithus pelagicus, Calcidiscus leptoporus, Umbilicosphaera foliosa, Helicosphaera carteri and Syracosphaera pulchra. These descriptions highlight the quality of phylogenetic data which can be obtained from coccoliths, and the coccoliths of the closely related genera Coccolithus, Calcidiscus and Umbilicosphaera are compared to explore the interplay between evolutionarily conservative and non-conservative aspects of morphology. These case studies emphasize that identifying homologies between coccoliths is most meaningfully done at the crystal unit level rather than the overall morphology level. This way, focus is kept as close as possible to the process of biomineralisation itself, which is essential because a minor shift in process can cause a large morphological change — exemplified here particularly by development of bicyclicity in shield elements. These case studies are also used to develop our understanding of coccolith biomineralisation processes. In particular: (1) The role of crystal growth in controlling aspects of coccolith structure is highlighted. (2) The unique morphology of H. carteri coccoliths is related to a growth model. (3) The lath elements of S. pulchra are shown to have tangential c-axis orientations, resulting in an important modification of the V-/R-model.
COCCOLITHS, the calcite plates formed by unicellular phyto-planktonic
algae (coccolithophores, phylum Prymnesiophyta)1, are
produced in enormous quantities and probably constitute the largest
single carbonate sink in oceanic biogeochemical cycles. They are major
sediment formers, are of great value to geologists as biostratigraphic
indicators and have been extensively studied as models for
biomineralization2,3. We have applied the understanding of
coccolith biomineralization to the fossil record4 and present
evidence from electron and optical microscopy that there has been a
conserved mechanism of crystal nucleation throughout the 230 million
year history of coccolithophores. This fundamental feature of coccolith
growth, which we term the V/R model, involves the assembly of a ring of
single crystals with alternating orientations, radial (R) and vertical
(V), and provides a powerful tool for tracing phylogenies, identifying
homologous structures and rationalizing the higher taxonomy of the
group. The living cocco-lithophorid, Emiliania huxleyi, seemed anomalous
because only R crystals had been observed; transmission electron
microscopy of proto-coccolith rings, however, revealed relict V crystals
which are overgrown by preferential development of R units in complete
coccoliths. A speculative model based on a plicated macromolecular
template is presented as a possible explanation for the conserved
nucleation process.
The descriptive terminology applicable to coccoliths and other calcareous nannofosils is reviewed and revised. A listing of about 400 terms is given with brief explanations and explanatory figures. General terms are given first, followed by terms for specific taxonomic groups. Appendices list terms we have not used and summarize terms, such as caneolith, which have been proposed for particular types of coccoliths.
A comprehensive classification of extant haptophytes is presented, with full citations of all taxa from species to class level
within the division Haptophyta. Almost 100 notes discuss aspects of classification and nomenclature, with particular attention
being paid to problems related to recognition of life-cycle associations. One new genus Holococcolithophora is described and six species are recombined in it. Appendices list conserved and rejected names, the type species of genera,
and basionyms of recombined species.
The examination of whole mounts prepared for transmission electron microscopy has resulted in the finding of thirteen taxa of nanoplanktonic coccolithophorids from the Weddell Sea, Antarctica. The material was collected as part of the AMERIEZ programme, March 1986. Cold-water adapted nanoplanktonic coccolithophorids have previously been shown to constitute a recurrent plankton element at subarctic and arctic localities. Three of the Weddell Sea species, Wigwamma annulifera, W. arctica, and Papposphaera sagittifera, are conspecific with northern hemisphere material, while two species, Calciarcus alaskensis and Turrisphaera arctica, are possibly identical with previously described arctidsubarctic material. Six taxa new to science have been described from the Weddell Sea, Wigwamma antarctica, W. triradiata, Trigonaspis melvillea, Pappomonas weddellensis, Papposphaera obpyramidalis, and P. simplicissima. The cooccurrence of identical forms at the two poles, and the fact that the species described are allocated to “arctic” genera, indicate a geologically relatively recent exchange of biological material between the poles.
Smaller size is generally seen as a negative response of organisms to stressful environmental conditions, associated with low diversity and species dominance. The mean size of the coccolithophorids decreased through the Neogene, leading to the prediction that their extant representatives are characterized by poor diversification and low specialization. The study of the (exo)coccospheres of selected taxa in the order Syracosphaerales negates this prediction, revealing that on the contrary some living lineages are highly diversified and remarkably specialized. Whereas the general role of coccoliths remains indeterminate, this analysis suggests that some may be modified for the collection of food particles, including picoplankton, thus implying that mixotrophy may characterize these lineages. In the living coccolithophorids, species richness of genera is inversely correlated with the size of cells (2µm to 36µm), definitive evidence that small size is part of a morphologic strategy rather than a sign of evolutionary failure. Because of their extreme minuteness, the living nannoplankton can be well compared to Lilliputians, but the trend toward size decrease in Neogene lineages is not attributable to the Lilliput effect described by Urbanek (1993).
Marine plankton flagellates attributable to Michaelsarsia elegans Gran (type species of its genus) and Halopappus adriaticus Schiller (sensu Gaarder) have been investigated by means of scanning and transmission electron microscopy supplementing light microscopy of dry whole mounts prepared in situ in the Galapagos Islands. Some external features, notably coccolith arrangement, have been re-interpreted, and information on others added or amplified. Some of the new details include the body coccoliths, which have been shown to be more complex than previously supposed, the bar-crystallites in particular being compound in both taxa. In addition, unmineralized components are shown to be present in all types of coccolith. They include patternless membranes spread across the proximal faces of body coccoliths and occupying the apparently vacant centres of ring-shaped coccoliths, while a highly characteristic, fragile, reticulum is limited to the central areas of the elongated appendage links in both taxa. The impact of these findings on general biological concepts is discussed in a preliminary way, drawing on cognate data previously published for Ophiaster and Calciopappus. It is concluded that the presence of apical appendages (anterior or posterior) in each of these genera is an independently acquired adaptation to some as yet unknown environmental factor or factors, whereas coccolith substructure is phyletically more meaningful. This indicates that Michaelsarsia, to which H. adriaticus should be transferred, is more remote from the other two genera than has hitherto been supposed. Finally an attempt has been made, in the light of all the evidence, to assess for the first time the possible functional significance of the unmineralized coccolith components and some constructive suggestions have been tentatively formulated. The paper ends with a factual summary in the form of revised taxonomic diagnoses for M. elegans, M. adriaticus and the genus Michaelsarsia.
On the basis of electron microscopy of dry whole mounts of wild material set up in situ mainly in the Galapagos Islands but with two introductory specimens from South Africa, the presence of unmineralized periplast components has been demonstrated in two genera of fully calcified coccolithophorids (Ophiaster and Calciopappus) and also in a broken cell, otherwise attributable to Chrysochromulina aff. fragilis Leadbeater. The last possesses many small elliptical plate scales with characteristic surface markings, together with fewer but larger sheet scales, each membranous, flexible, and almost without patterning except at the edge which carries a narrow zone of sparse radial striations. Both types of scale recur in the two coccolithophorid genera, the small elliptical plates as an underlayer beneath the coccoliths and the peripherally streaked membranes individually attached to the proximal surfaces of coccoliths as an integral part of their structure. Though present, these are more difficult to detect in Calciopappus than in Ophiaster in which they have been clearly demonstrated in specimens from both South Africa and the Galapagos Islands. In addition, some types of Ophiaster have also been shown to possess completely patternless membranes, detectable only by their indirect effects, occupying the apparently vacant plate centres of coccoliths in special positions. Other aspects of coccolith substructure are discussed with special reference to recurring difficulties regarding speciation in the two genera. Revised generic descriptions are provided but specific descriptions are limited to Ophiaster. These include revision of the two existing taxa (especially necessary for `O. formosus Gran') and the erection of three additional new taxa (O. reductus sp.nov., O. minimus sp.nov. and O. formosus var. inversus var.nov.). The final discussion summarizes and comments on present knowledge of Chrysochromulina fragilis sens. lat. in relation to several genera of coccolithophorids including, but not limited to, Ophiaster and Calciopappus.
Two new genera of coccolithophorids, one with two species, have been described and illustrated by means of electron microscopy of wild material from various sources in the northern or southern hemisphere. The main diagnostic features of the new genus Wigwamma (type species W. arctica sp.nov.) include 'ring-shaped' coccoliths, attached to the edges of unmineralized plates with characteristic surface patterning, and with some or all carrying superstructures composed of four (or sometimes two) rod-shaped crystallites, converging to a point distally and attached proximally to the subtending calcified scale-rim in a characteristic manner. After comparisons with the unmineralized scales of Chrysochromulina, these coccoliths are interpreted as equivalent to the bases, including the support struts, of certain spined scales comparable in a general way with those of C. pringsheimii but with the spine itself undeveloped or vestigial. Analogous changes, carried out independently and with many differences of detail implying a different prototype source, are inferred to explain the coccolith morphology of another new genus, Calciarcus, at present only known in a preliminary way in the north Pacific (near Homer, S. Alaska). The coccoliths of this organism have been investigated chemically by means of the electron probe CORA. Further comparisons between Wigwamma, more especially W. annulifera sp.nov., and other coccolithophorids, notably Ceratolithus, Pappomonas and Papposphaera have emphasized the value of crystallographic details as taxonomic and phyletic markers, in situations where coccolith morphology as a whole is equivocal as a result of convergence. The available distributional data for all known arctic coccolithophorids are then summarized and the conclusion is drawn that collectively they may represent a highly selected community adjusted to arctic conditions and perhaps able to perennate locally but ultimately derived by immigration from the north Pacific. Other conclusions to which the arctic coccolithophorids collectively have led are summarized in a final paragraph.
Chromobiote algae are unusual in having an additional smooth periplastid membrane outside their chloroplast envelope and in the location of the chloroplast/periplastid membrane complex within the lumen of their rough endoplasmic reticulum. They are often brown in colour because of the carotenoid fucoxanthin in addition to their usual accessory chlorophylls c 1–3. They are divided into two well-defined phyla: the heterokont Ochrophyta (or Ochrista, e.g. brown algae, diatoms, chrysophytes; sometimes informally known as ‘core chromophytes’) and the Haptophyta. Reticulosphaera is an enigmatic genus of net-like chromobiotes, with only two described species, which morphologically do not fall clearly into either category. We have therefore sequenced the 18S rRNA gene of R. japonensis, together with those of two known species of haptophyte (Pavlova salina and two independent isolates of Prymnesium patelliferum), in order to clarify its evolutionary position. Though it was previously classified with heterokont Ochrophyta, our maximum likelihood, maximum parsimony, and neighbor-joining phylogenetic analyses unambiguously show that Reticulosphaera japonensis was placed in the wrong phylum, and is in fact an aberrant haptophyte without a haptonema. We show that the deepest division within the Haptophyta is that between the two classes Prymnesiophyceae (synonym Patelliferea, including Prymnesium and the coccolithophorids) and Pavlovophyceae (Pavlova and other Pavlovales). R. japonensis branches within Prymnesiophyceae close to Emiliania and Phaeocystis, which have a reduced haptonema. Although Reticulosphaera species differ greatly morphologically from previously known Prymnesiophyceae, in view of their close relationship to Prymnesiophycidae it now seems unnecessary to continue to classify them in a separate class, Flavoretea. We therefore reduce Flavoretea in rank to a subclass, Flavoretophycidae, that is grouped with subclass Prymnesiophycidae in the revised haptophyte class Prymnesiophyceae. A new family Reticulosphaeraceae and order Reticulosphaerales are created for Reticulosphaera. A new family Dicrateriaceae and order Dicrateriales are proposed for Dicrateria, the only prymnesiophyte lacking both scales and a haptonema. Though ribosomal RNA sequences are most informative about the internal phylogeny of Haptophyta, we conclude after extensive analysis that they are unable to refute or confirm the monophyly of the Chromobiota (Haptophyta plus Heterokonta) or the kingdom Chromista (subkingdoms Chromobiota and Cryptista).
Light and electron miscroscope observations show that Ophiaster cells have centrally placed spines on coccoliths surrounding the area where the two flagella emerge. The spectacular starlike appendage is located at the opposite cell pole. Two species are suggested retained: Ophiaster formosus Gran and Ophiaster hydroideus (Lohm.) Lohm., distinguished by differences in the morphology of their appendices. Syracosphaera confusa Halldal & Markali is included in the latter species. A distribution map, based on available published and unpublished data for the two species, is presented.
The Haptophyta comprises a group of microalgae of particular importance in marine habitats, often occurring in ‘bloom’ concentrations, sometimes with devastating effects where the bloom is composed of species toxic to other forms of life. The most familiar species are the coccolithophorids, unicellular organisms encased in calcified scale-like structures, the coccoliths, which are readily preserved in marine sediments and have for a long time been important indicators in micropalaeontological studies. In the middle of this century it was recognized that there was a need to compile and standardize the terminology used in coccolith morphology (Braarud et al., 1955; Halldal & Markali, 1955). This approach was continued by several authors (e.g. Hay et al., 1966; Okada & McIntyre, 1977; Tappan, 1980; Perch-Nielsen, 1985) in published articles, and in the report from a Round Table session at the Rome 1970 Plankton Conference (Farinacci, 1971), which included terms from both fossil and extant taxa. Over the last two decades many new terms have been introduced as observations on coccolith morphology have improved through the use of the electron microscope, and recent glossaries covering various aspects of haptophyte terminology have been published by Heimdal (1993), Kleijne (1993) and Margulis et al. (1993).
Information on the internal structure of the Chrysophyceae is reviewed and some new data are presented. From these a model has been constructed which represents the combination of features constructed to be the basic pattern of cell structure in this group. A brief review is given of modern research, which demonstrates that the choanoflagellates should be removed not only from the Chrysophyccae but also from the plant kingdom. The organization of the Prymnesiophyceae classis nova (= Haptophyceae) is compared with that of the Chrysophyceae, and the relationship of both groups to the Xanthophyccae, Phaeophyceac anti Bacillariophyceae is considered. This leads to the conclusion that the Prymnesiophyceae must be considered as a class separate from the Chrysophyceae. Removal of the Prymnesiophyceae and choanoflagellates from the Chrysophyceae leaves a largely homogeneous and monophyletic group, though the family Pedinellaceae appears to have a unique organization and may be found to be separated from the Chrysophyccae by a phyletic distance at least as great as that between the remaining classes of heterokont algae. It is suggested that this family should occupy a more isolated position in the Chrysophyceae than at present, possibly in a separate order Pedinellales.
A new coccolithophorid genusJomonlithus withJ. littoralis as the type species, is described based on specimens isolated from a sand sample collected at the mouth of Nakagawa river,
Ibaraki, Japan. This genus is characterized by the coccolith which is composed of an organic base-plate scale and calcified
rim elements made up of two different subelements.J. littoralis has been found in several localities along the coast of Japan. Culture and ultrastructure studies gave special attention
to the cell cycle, coccolith and scale morphology and the ultrastructure of the cellular organelles. It was confirmed thatJomonlithus is similar toWigwamma Mantonet al., Papposphaera Tangen andPappomonas Manton et Oates on the basis of coccolith morphology and toCricosphaera Braarud andHymenomonas Stein in cellular structure.
A molecular clock has been constructed for the haptophyte algae using the 18S rDNA gene and calibrated using the fossil record of the coccolithophorid algae, which have the best fossil record of any microalgal group. There is high consistency between the molecular genetic estimates of relative timing of divergence and palaeontological estimates of divergence times, so ages can be inferred for undated nodes in the tree with a reasonable degree of confidence. The placement of the K/T boundary across the tree strongly supports the palaeontological model that extant coccolithophorid algae diversified after this event and are the survivors of a few lineages that survived this major extinction. In contrast, the non-calcifying haptophytes are diverse before and after the extinction, with no evidence of bottlenecking associated with the event. This result is surprising, because it has been assumed that ability to produce resting stages was a key determinant of phytoplankton survival across the K/T boundary, but in this regard the coccolithophores and non-calcifying haptophytes are similar. The adaptation of non-calcifying haptophytes to eutrophic coastal environments and their ability to switch modes of nutrition from autotrophy to mixotrophy are discussed as possible explanations for their survival during this abrupt global change event.
Recent measurements of surface coccolithophore calcification from the Atlantic Ocean (50°N–50°S) are compared to similar measurements from other oceanic settings. By combining the different data sets of surface measurements, we examine general and regional patterns of calcification relative to organic carbon production (photosynthesis) and other characteristics of the phytoplankton community. Generally, surface calcification and photosynthesis are positively correlated, although the strength of the relationship differs between biogeochemical provinces. Relationships between surface calcification, chlorophyll-a and calcite concentrations are also statistically significant, although again there is considerable regional variability. Such variability appears unrelated to phytoplankton community composition or hydrographic conditions, and may instead reflect variations in coccolithophore physiology. The contribution of inorganic carbon fixation (calcification) to total carbon fixation (calcification plus photosynthesis) is ∼1–10%, and we estimate a similar contribution from coccolithophores to total organic carbon fixation. However, these contributions vary between biogeochemical provinces, and occasionally coccolithophores may account for >20% of total carbon fixation in unproductive central subtropical gyres. Combining surface calcification and photosynthetic rates with standing stocks of calcite, particulate organic carbon, and estimated phytoplankton carbon allows us to examine the fates of these three carbon pools. The relative turnover times vary between different biogeochemical provinces, with no clear relationship to the overall productivity or phytoplankton community structure found in each province. Rather, interaction between coccolithophore physiology (coccolith production and detachment rates), species diversity (cell size), and food web dynamics (grazer ecology) may control the composition and turnover times of calcite particles in the upper ocean.
The relationship between calcite biomineralisation and coccolith ultrastructure is analysed across the diversity of calcifying haptophytes. The emphasis is on integration of evidence from crystallographic and ultrastructural studies but additional relevant information from biochemical and phylogenetic work is reviewed. We attempt to identify aspects of ultrastructure which are most likely to be the product of self-organising processes. The principal topics reviewed are heterococcolith rim nucleation, including reassessment of the V/R model; crystal growth regulation in heterococcoliths; holococcolith biomineralisation; and the diversity of other biomineralisation modes in haptophytes. It is concluded that the diverse range of calcareous structures produced by haptophytes probably has a common phylogenetic origin and is produced via operation of a limited set of mainly shared genetic and biochemical pathways. Copyright 1999 Academic Press.
BIO Hesperides: MATER-2 (leg 3): HE059: Informe de Campaña
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A new coccolithophorid from northern waters, Calciopappus caudatus. n. gen., n. sp
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Cruise Report: PABESIA, RV Sonne Cruise SO-184
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