Peter A. Siver

Peter A. Siver
Connecticut College · Botany

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177
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Publications

Publications (177)
Article
Full-text available
Mallomonas is the largest and most speciose genus within the Synurales, a monophyletic clade of siliceous scale-bearing organisms within the class Chrysophyceae. The genus consists of unicellular, motile, photosynthetic organisms found in freshwater localities worldwide. Mallomonas diverged from other synurophytes during the lower Cretaceous at app...
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The Gonorynchiformes are a group of mostly marine fishes that are the sister group to the Otophysi (e.g., carps, tetras, catfishes). They include milkfishes (family Chanidae) and beaked sandfishes (family Gonorynchidae) among extant taxa. The only freshwater genus is the strictly fossil †Notogoneus, which until now contained eight species of Late C...
Article
Synedra planktonica was originally described by Hains and Sebring from a freshwater locality in the southeastern USA using light and transmission electron microscopy. The authors placed S. planktonica into the genus Synedra Ehrenberg because of its solitary habit and lack of marginal linking spines. Since the original description of S. planktonica,...
Article
A new diatom genus, Brevilinea gen. nov., is described from an acidic freshwater lake situated on the Atlantic Coastal Plain of North Carolina, USA. The type for the genus, Brevilinea pocosinensis sp. nov., differs from other diatoms by the presence of a unique and reduced raphe that is restricted to the central portion of the valve. The new taxon...
Article
Rotosphaerids are unicellular, heterotrophic, eukayotic protists that have filopodia, an exterior covering consisting of highly ornamented siliceous scales, and are classified in the Rotosphaerida within the opistokont lineage. Given their appearance as relatively large spherical cells with protruding filopodia and a silica scale covering, they are...
Article
Aulacoseira is a freshwater diatom genus found today in numerous lakes, ponds and rivers worldwide, and inhabiting a wide range of environmental conditions. The genus is one of the oldest diatom lineages known to colonize freshwater environments, dating to the late Cretaceous and radiating over much of the Cenozoic. The purpose of this paper is to...
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When diatoms undergo vegetative cell division the new siliceous wall components are slightly smaller than those of the parent because they are produced within the confines of the parent wall. Thus, with continued growth the mean size of cells in a population declines. Given this unique feature of diatom cell division, if the growth of a species in...
Article
A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus, Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extant Synura speci...
Article
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Chrysophyte algae produce a siliceous stage in their life cycle, through either asexual or sexual reproduction, known as a cyst. Cysts form in response to shifts in environmental conditions, population density, or predation pressure, and upon germination provide a seed source for future populations. Cysts are morphologically distinct for each speci...
Article
We performed a comparison of molecular and morphological diversity in a freshwater colonial genus Synura (Chrysophyceae, Stramenopiles), using the island of Newfoundland (Canada) as a case study. We examined the morphological species diversity in collections from 79 localities, and compared these findings to diversity based on molecular characters...
Article
In 1968, Lohman and Andrews described the freshwater araphid diatom genus Ambistria from the Wagon Bed Formation, a Late Eocene deposit in Wyoming, U.S.A. The genus was distinguished from other genera on the basis of the distinctive shape of the valve coupled with short striae restricted to the valve margins, the latter resulting in a wide hyaline...
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Background and aims – Diatoms began to inhabit freshwater by at least the Late Cretaceous, becoming well established by the early to middle Eocene. Aulacoseira, an important diatom in numerous ponds, lakes and rivers today, was one of the earliest known genera to colonize freshwater ecosystems. Members of this genus with characteristics familiar to...
Article
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The Langhian (middle Miocene) marls of lacustrine succession cropping out in the open cast coal mine Gračanica (Bugojno basin, central Bosnia and Herzegovina) yielded a rich siliceous microfauna. The most common are sponge spicules (megascleres), less common are diatoms and chrysophyte cysts. Cell wall remains of a green alga Botryococcus sp. were...
Article
The genus Mallomonas consists of single-celled flagellates covered with siliceous scales and bristles and is well known in freshwater environments. Two new marine Mallomonas species were collected from Dongho Beach, Jeollabukdo, Korea. To fully understand the taxonomy of the new species, we performed molecular phylogenetic analysis based on a conca...
Article
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The Synurophyceae is a well-supported clade of ecologically important heterokont algae found largely in freshwater planktonic habitats worldwide, whose members have cell coverings consisting of species-specific siliceous scales overlapped in a highly organized manner. Many synurophytes have been described as endemic and are found only in specific r...
Article
Despite the rise of marine diatoms in the world's oceans throughout the Cretaceous, only a handful of fossil localities worldwide detail invasion of freshwater habitats by diatoms commencing in the Late Cretaceous. We report on the occurrence of numerous freshwater diatom specimens and species from the Battle Formation, an extensive freshwater loca...
Article
Two new fossil species of the synurophyte genus Mallomonas, M. skogstadii and M. bakeri, are described from Giraffe Pipe, an Eocene locality situated near the Arctic Circle in northern Canada. Scales of both new species share a suite of characters, including an oval-shaped rib encircling approximately half of the base plate and most of the dome, a...
Article
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Climate change has affected freshwater lakes in many ways, including shifts in thermal structure, stability, ice cover, annual mixing regimes and length of the growing season, all of which impact ecosystem structure and function. We examine the impacts climate variables, especially wind speed, had on water temperature and thermal stratification at...
Article
The two-celled colonial synurophyte genus Chrysodidymus was originally distinguished from its close relative Synura on the basis of the colonies always being of two cells, the shape of the cells and the odd swimming nature of the colony. Recently, based on gene sequence data, Chrysodidymus was found to be deeply nested within the Synura clade. As a...
Article
Mallomonas, the largest genus within the class Synurophyceae, consists of unicellular, flagellated, heterokont organisms each with an external cell covering comprised of species-specific overlapping siliceous scales. Most species also possess bristles, which are elongated needle-like siliceous structures that radiate out from the scale coat. A new...
Article
The distributions of scaled chrysophytes in 22 waterbodies from the eastern portion of Newfoundland, Canada, are described relative to environmental gradients. A rich and diverse flora of scaled chrysophytes was recorded that included 47 species from six genera, Mallomonas (n = 29), Synura (n = 7), Neotessella (n = 1), Chrysosphaerella (n = 2), Spi...
Article
Kohli P, Siver PA, Marsicano LJ, Hamer JS, Coffin AM. 2017. Assessment of long-term trends for management of Candlewood Lake, Connecticut, USA. Lake Reserve Manage. 00:00–00. Candlewood Lake, the largest lake in Connecticut, is a pumped-storage reservoir formed in the 1920s for hydropower generation. Since its inception, the lake has experienced sh...
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Eocene paleoclimate reconstructions are rarely accompanied by parallel estimates of CO2 from the same locality, complicating assessment of the equilibrium climate response to elevated CO2. We reconstruct temperature, precipitation, and CO2 from latest middle Eocene (ca. 38 Ma) terrestrial sediments in the posteruptive sediment fill of the Giraffe k...
Article
Species from the Mallomonas bronchartiana complex were examined using material from Vietnam, the U.S.A. and South Korea. The original description of Mallomonas bronchartiana is expanded and descriptions of two new taxa, M. pseudobronchartiana and M. velari, are given. All taxa possess body scales that are large, broad, with an asymmetrically-placed...
Article
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Marine diatoms began colonizing freshwater habitats in the early Cenozoic, or possibly earlier, becoming well established by the Eocene. However, because of a sparse fossil record, little is known about the earliest diatom representatives that signalled this important ecological and evolutionary event. We describe a new centric diatom genus, Fideli...
Article
Mallomonas neoampla is described from the Dzua River, located in Khanh Hoa Province, Central Vietnam, and represents the third taxon now known from the section Multisetigerae. Mallomonas neoampla shares some features of the scale morphology with the fossil species M. ampla, and others with the modern and widely distributed M. multisetigera. Mallomo...
Article
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The freshwater sponge species Ephydatia cf. facunda Weltner, 1895 (Spongillida, Spongillidae) is reported for the first time as a fossil from middle Eocene lake sediments of the Giraffe kimberlite maar in northern Canada. The sponge is represented by birotule gemmuloscleres as well as oxea megascleres. Today E. facunda inhabits warm water bodies, t...
Article
We used phylogenetic analyses based on multiple gene sequences (partial nr SSU and LSU rDNA, partial pt LSU rDNA, psaA and rbcL) from 148 strains (including three outgroups) and scale ultrastructure to examine phylogenetic relationships among species of the colonial genera Synura and Tessellaria. The phylogenetic tree based on the combined dataset...
Article
A new fossil species of Mallomonas,M. elephantus sp. nov.,is described from an Eocene maar lake situated near the Arctic Circle in northern Canada. The new species has three distinctly different types of scales,craspedodont bristles,and is believed to represent a stem taxon of the section Planae. Body scales are large,oval to square-shaped,with a s...
Chapter
Members of the class Synurophyceae are unicellular or colonial motile flagellates, with one or two golden-colored plastids and a cell covering of siliceous scales. The scales are highly organized on the cell and form species-specific designs used to identify each taxon. Informally, the organisms are often referred to as scaled chrysophytes. There a...
Article
Two new species belonging to the Synurophyceae are described from Orchid Bog Pond, a highly acidic, humic-stained bog, low in dissolved substances, situated in Newfoundland, Canada. Mallomonas baskettii has three types of scales, including highly asymmetric body and apical scales, and caudal scales with a small base plate and exceptionally long spi...
Article
A new, and presumably extinct, species representing the genus Mallomonas, M. schumachii, is described from an Eocene maar lake situated near the Arctic Circle in northern Canada. The new species bears bristles and possesses three types of scales. Body scales are large, square-shaped, with a posterior rim encircling approximately half of the perimet...
Article
Eunotioid diatoms that express asymmetry in both the apical and transapical axes, forming heteropolar valves, are generally placed in the genus Actinella. The degree of heteropolarity varies between species, ranging from subtle differences between poles to highly differentiated head poles bearing an apical protuberance. Actinella species with less...
Article
Full-text available
• Heterokont algae of the class Synurophyceae, characterized by distinctive siliceous scales that cover the surface of the cell, are ecologically important in inland waters, yet their evolutionary history remains enigmatic. We explore phylogenetic relationships within this group of algae relative to geologic time, with a focus on evolution of silic...
Article
Chrysophyte algae are common in the plankton of oligotrophic lakes and produce a rich microfossil record of siliceous cysts and scales. Paleolimnological investigations and phytoplankton records suggest that chrysophyte populations are increasing in a wide range of boreal and arctic lakes, ultimately representing one component of the limnological r...
Article
A new species representing the genus Synura, S. cronbergiae, is described from two Paleogene maar lakes situated near the Arctic Circle in northern Canada. The new taxon is characterized by long, slender, siliceous scales each bearing a small forward projecting spine, a base plate with evenly spaced pores and a secondary layer consisting of hexagon...
Article
Well-preserved siliceous plates representing multiple species of euglyphids are described from a Middle Eocene maar lake deposit located near the Arctic Circle in northern Canada. Siliceous plate morphotypes including scutiform, rectangular, hexagonal, oval and circular body forms, six apertural plate types containing from five to thirteen teeth an...
Article
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We used a molecular analysis based upon three genes, coupled with the ultrastructure of scales and bristles, to investigate phylogenetic relationships within Mallomonas, with a focus on the section Planae. Fossil taxa discovered in Middle Eocene lacustrine deposits from northwestern Canada were used to calibrate a relaxed molecular clock analysis a...
Article
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We report the oldest fossil occurrence of freshwater potamolepid sponges (Demospongiae, Spongillina, Potamolepidae) to date, originating from middle Eocene lake sediments accumulated in the Giraffe kimberlite maar, northern Canada. Sponges are represented by strongyle spicules that are gemmuloscleres. These are described herein as belonging to a ne...
Article
Synurophytes, also known as scaled chrysophytes, are ecologically important algae that produce an array of siliceous structures upon which their taxonomy is based. Despite occupying a key position within the photosynthetic heterokonts, the evolutionary history of synurophytes remains poorly constrained. Here, modern and Middle Eocene siliceous scal...
Article
Mallomonas insignis, a cosmopolitan freshwater alga belonging to the class Synurophyceae, has a cell covering consisting of three types of siliceous scales, apical spined scales, body scales, and caudal spined scales. Body scales comprise the majority of scales on an individual cell and form the basis of this study. Recently, fossil scales were unc...
Article
Five species of fossil Synura are documented from two freshwater Arctic localities, one known as Giraffe that existed during the Eocene, and a second known as Wombat that existed during the Paleocene. The fossils represent the oldest known remains of Synura and in each case the specimens were easily assigned to the genus. Two of the taxa, Synura re...
Article
The genus Mallomonas, the largest within the Class Synurophyceae, consists of motile, unicellular, freshwater heterokonts that are covered with an outer layer of overlapping siliceous scales. The scales are flat, circular to oval structures with taxonomically distinct designs. In addition to scales, the cell coverings of most Mallomonas species con...
Article
Summary1. We assessed the distribution of scaled chrysophytes in fresh waters along 3200 km of the east coast of North America (29° to 48°N) to determine any biogeographic patterns in relation to chemical, physical, climatic and spatial variables.2. Scaled chrysophytes were identified using scanning electron microscopy and counted from 264 waterbod...
Article
Pinnularia is an ecologically important and species-rich genus of freshwater diatoms (Bacillariophyceae) showing considerable variation in frustule morphology. Interspecific evolutionary relationships were inferred for 36 Pinnularia taxa using a five-locus dataset. A range of fossil taxa, including newly discovered Middle Eocene forms of Pinnularia...
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Abundance of living populations of scaled chrysophytes were used to develop multiple regression models for inferring lakewater pH. Until now, all such inference models had been prepared with surface sediment remains and used to reconstruct historical (down-core) changes. We demonstrate that highly significant models can be prepared from living popu...
Article
The genus Mallomonas, a common and often abundant member of the planktic community in many freshwater habitats worldwide, consists of 180 species divided into 19 sections and 23 series. Classification of species is based largely on ultrastructural characteristics of the siliceous scales and bristles that collectively form a highly organized coverin...
Article
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Freshwater diatoms belonging to the genus Eunotia Ehrenberg 1837 are well preserved in Middle Eocene lake sediments from the Northwest Territories, Canada. Although two distinct valve morphologies are recognized, both have features that are entirely compatible with modern congeneric taxa, including dorsiventral valve morphology, striae spanning the...
Article
The freshwater diatom flora of Cape Cod, Massachusetts, USA, was recently described using surface sediments from 56 largely glacial kettle lakes scattered over the narrow peninsula. During our examination we had the opportunity to study seven rare and interesting taxa with light (LM) and scanning electron microscopy (SEM). Two of these organisms, N...
Article
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Thirty-four scaled chrysophyte taxa are described from 17 Adirondack lakes located in either Hamilton or Franklin counties. Ten taxa, Synura sphagnicola, Syn. echinulata, Syn. petersenii, Mallomonas acaroides var. muskokana, M. hamata, M. caudata, M. crassisquama, M. galeiformis, Spiniferomonas trioralis, and Chrysosphaerella longispina, were found...
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Frequency distributions versus pH and weighted mean pH values are reported for 25 and 40 species of scaled chrysophytes, from water bodies in Connecticut and the Adirondacks, respectively, and are compared with those assembled from a survey of the literature. For most species, similar distributions with respect to a pH gradient and weighted mean pH...
Article
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The siliceous cell covering of Mallomonas consists of a series of imbricated scales and bristles arranged in a very precise pattern. Scales on a given cell are aligned in spiral rows with their longitudinal axes parallel, perpendicular, or at an oblique angle to the longitudinal axis of the cell. The scales within each spiral row are overlapped in...
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Background and aims - The majority of freshwater diatom lineages appear to have evolved before or during the Eocene, with rapid radiation occurring in the Miocene. However, only a few accurately dated fossil localities are available to test this assertion, resulting in an overall poor understanding of the biostratigraphy and early evolution of thes...
Article
In modern samples from lakes in Florida's Ocala National Forest, U.S.A., a new species, Neidium palpebrum sp. nov. was described. This diatom possesses lanceolate valves with protracted, broadly rounded apices and a single, large, rugose longitudinal canal along each valve margin. The new species is also characterized by an elliptical central area,...
Article
The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiq...
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Mallomonas porifera was originally described from Middle Eocene lake sediments based on isolated siliceous microfossils and named for the single large pore found centrally on the base plate. Both domeless body and domed scales were described, however it was not known how the scales were positioned on the cell covering nor if the organism possessed...
Article
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Complex bristle types formed by species in the genus Mallomonas include those with helmet or lance-shaped apices. The ornamentation on each side of the helmet has been thought to be equivalent or symmetrical, whereas on a lance-shaped bristle an expanded portion folds over one side of the shaft to form an asymmetrical structure. We describe, for th...
Article
During our investigations of freshwater sites along the Atlantic Coastal Plain of North America we had the opportunity to critically study five interesting diatoms with light (LM) and scanning electron microscopy (SEM), each of which is described here as a new species.Two of the organisms are in the genus Eunotia, Eunotia lewisii Siver & Hamilton s...
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We report on exquisitely preserved specimens of freshwater siliceous algae belonging to the classes Synurophyceae (scaled chrysophytes) and Bacillariophyceae (diatoms) from middle Eocene lake sediments in Northern Canada. When considered in the context of closest extant relatives, these microfossils present unequivocal biogeographic and ecological...
Article
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The evolutionary history of diatoms is only constrained partially by the fossil record. The timing of several key events, such as initial colonization of freshwater habitats by marine taxa, remains poorly resolved. Numerous specimens of the genera Cyclotella, Discostella, and Puncticulata (Ochrophyta: Thalassiosirales) have been recovered in Middle...
Article
Identification of diatom frustules, a vital step during ecological analyses, is greatly influenced by the magnification at which samples are examined. The striking differences between Light Microscopy (LM) and Scanning Electron Microscopy (SEM) reveal inconsistencies in the identification of diatoms at low magnifications. These inconsistencies hind...
Article
Fragilaria lancettula was described in 1867 by Julius Schumann from freshwater material collected near Königsberg, Prussia. The limited description and presentation of two slightly different original illustrations of the valve form, has created confusion in the literature with published recombinations as varieties under Fragilaria pinnata, Fragilar...
Article
SUMMARYA new diatom genus, Brevilinea gen. nov., is described from an acidic freshwater lake situated on the Atlantic Coastal Plain of North Carolina, USA. The type for the genus, Brevilinea pocosinensis sp. nov., differs from other diatoms by the presence of a unique and reduced raphe that is restricted to the central portion of the valve. The new...
Article
ABSTRACTA study of attached diatom communities on artificial and natural substrates was conducted in Wheelwright Pond, New Hampshire, during 1975. There were differences in the species composition growing on artificial glass slides and natural substrates. The slides favored the accumulation of Achnanthes minutissima Kütz. and decreased the relative...
Article
Although Chrysosphaerella longispina and C. brevispina are common species reported from freshwater localities, only scattered ecological records exist. In addition. most identifications and descriptions are based on features of their siliceous components as viewed with transmission electron microscopy. In this study details of scales and spines are...
Article
Morphological observations of the siliceous cell coverings of five taxa of Synurophyceae are made based on specimens collected from acidic, seepage lakes situated in either the Ocala National Forest, Florida, U.S.A. or the Cape Cod National Seashore, Massachusetts, U.S.A. All but one of the lakes, Lake Dorr, were clearwater in nature. A new taxon,...
Article
Siver, P. A. & Skogstad, A. 1988. Morphological variation and ecology of Mallomonas crassisquama (Chrysophyceae). - Nord. J. Bot. 7: 99–107. Copenhagen. ISSN 0107–055X. Mallomonas crassisquama is one of the most common and widely distributed species of Mallomonas. In this study we compare the morphology and ecology of the species based on 309 colle...
Article
A new species, Mallomonas retrorsa, with a unique siliceous armour, is described from four slightly humic and acidic localities in Connecticut, U.S.A., each low in specific conductance. Cells of the new species have three types of siliceous scales each of which is asymmetric, domeless and arranged with their longitudinal axis parallel to the longit...
Article
During an investigation of freshwater diatoms from highly acidic ponds scattered along the Atlantic Coastal Plain of North Carolina we encountered a large number of specimens from the genus Stenopterobia. All of the specimens were representative of straight, not sigmoidal-shaped, taxa and collectively ranged in length from ca. 10 mu m to over 200 m...