VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS I. FRAGILARIA CAPUCINA VAR. MESOLEPTA1,2

Acid cleaned cells from clonal cultures of Fragilaria capucina var. mesolepta Rabh. were examined with light and scanning electron microscopy. Recently isolated cells are linear-lanceolate in shape with a median constriction. After several transfers over 25 mo, cells exhibit size diminution resulting in small elliptically shaped valves. Adjacent valves are united to one another by interlocking marginal spines. Every valve has an apical pore field at each apex. A single labiate process is present infrequtently, appearing underdeveloped most often in size-reduced cells. The girdle region consists of two cingula, each composed of a series of underlapping bands. Each pleura in the series is a discontinuous ring with a central ligula. A survey of past ultrastructure studies on the freshwater Fragilariaceae reveals that the occurrence of the apical pore field and labiate process are likely key characteristics for the family. The apical pore field of Diatoma, Asterionella and Tabellaria is positioned on the valve face, whereas the apical pore field of F. capucina var. mesolepta is located on the valve mantle, the girdle region of F. capucina var. mesolepta is basically similar to that of Gomphonema parvulum (Kütz.) Grun.     

STUDIES ON MARINE PLANKTON DIATOMS. III. STRUCTURE AND CLASSIFICATION OF GOSSLERIELLA TROPICA1

The structure of the tropical oceanic diatom Gossleriella tropica Schütt was examined in the light and electron microscopes. The species is characterized by a primarily poroid valve, surface, it single central labiate process and a unique ring of spines attached to the cingulum. Placement of the genus in the family Rhizosoleniaceae is suggested. Although G. tropica is widely distributed in the world's oceans, it is usually confined to the lower photic zone, salinities of 34.5–35.5% and temperatures of 15–30 C.     

FURTHER OBSERVATIONS AND SOME COMMENTS ON THE FINE STRUCTURE OF THE CENTRIC DIATOM AULACOSEIRA ISLANDICA (BACILLARIOPHYCEAE)1

Using light and electron microscopy, the diatom species Aulacoseira islandica (O. Müll.) Sim. was examined with special emphasis on the following characteristics: structure of the valve areolae, heterovalvy, and distribution of the rimoportulae. The mantle and valve face areolae were pores containing volate occlusions. However, observations only using transmission electron microscopy may result in an incomplete interpretation because of the fragility of the dissected system of volae. Relief valves with a stepped mantle and intaglio valves with a plain mantle occurred. Another form of heterovalvy resulted from the formation of separation valves. Linking valves had spatulate spines while separation valves bore tapering spines. In Aulacoseira, the rimoportulae usually occurred near the “Ringleiste.” The presence of several rimoportulae on the mantle was one of the most striking features in Aulacoseira islandica.     

TAXONOMY AND FRUSTULAR STRUCTURE OF THE MARINE CENTRIC DIATOM PARALIA SULCATA1

Light and electron microscopy were used to investigate the complex structure of the frustule of Paralia sulcata (Ehrenb.) Cleve. Rimoportulae are reported for the first time in this diatom and two types of linking processes are described. The ease with which the cingulum is lost is explained with regard to its attachment to the valve. Two kinds of heterovalvy were observed and the taxonomic significance of one of these is discussed. The validity of Heiberg's genus Paralia is confirmed and a type slide of the species is designated.     

VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS. IV. OUTER SURFACE MUCILAGE OF NAVICULA CONFERVACEA VAR. CONFERVACEA1

The development of the mucilage on the outer surface of Navicula confervacea (Kütz.) Grun., a raphed, filamentous diatom, was studied with scanning electron microscopy. This nonstructural cell wall material, present on the surface after critical-point drying and absent after acid cleaning, was of two types: strands and papillae. Strands were associated with the raphe system, areolae, elongated pores of the mantle, and all girdle sutures. Organic papillae were a common feature of valves, valvo-copulae and pleurae, but their origin and distribution could not be explained since they often occurred between the obvious openings in the frustule. Strands from the raphe and areolae may function in attaching terminal cells to a substrate and adjacent cells to each other. Other strands of the girdle arise from sutures during cell enlargement and continue to lengthen and intertwine until the individual frustules within a filament are obscured. Strands from sutures might originate from the advalvar row of pores of the girdle bands since these pores lie along the suture, but direct observation of this was not made. Secretion between, the bands also cannot be ruled out. Although mucilaginous papillae may sometimes occur at random on the entire surface of frustules, there is also a distinct, narrow multiseriate row of them around the edge of valves without marginal spines.     

ULTRASTRUCTURE OF THE FILAMENTOUS HABIT IN THE DIATOM NAVICULA CONFERVACEA (KÜTZ.) GRUN.1

Frustules of the filamentous diatom Navicula confervacea (Kütz.) Grun. are united by the overlapping of marginal teeth located alongside the junction of valve face and mantle. Scanning and transmission electron microscopy show this connecting mechanism to differ from the previously reported inter-digitating spines or teeth in the genera Melosira, Stephanodisus, and Fragilaria.     

Aberrant valve formation in a centric diatom,Ditylum brightwellii

Summary Interphase cells of the centric diatom,Ditylum brightwellii (West) Grunow, were treated with a microtubule-inhibitor (amiprophosmethyl, 6×10^–7 M); the cells could proceed to divide, but the spindle apparatus in about 25% of the cells was displaced and their two sibling cells has either two nuclei or none. The cells with two nuclei formed a new valve with two labiate processes, instead of one as in normal cells. Most of the cells lacking a nucleus were unable to form a new valve, and of the 2% that did form new valves, all did so without dividing. The valves with two labiate processes were originally formed in two separate silica deposition vesicles (SDVs) and the two embryonic siliceous valves fused when these two expanding SDVs met. Accordingly, both the pattern of perforations and the shape of the marginal ridges on the new valve vary with the distance between the two initiation sites of the two SDVs. Implications of these observations in the evolution of valves in diatoms are discussed and a hypothesis on multiple origins of the valves is proposed.     

Minidiscus,a New Recorded Nanodiatom Genus for China

Minidiscus trioculatus, M. comicus and M. chilensis are new records for China, and M. subtilis, is a new species. They differ from Thalassiosira species by their strutted processes and one single labiate process being distant from valve margin and they differ from each other by their areola patterns on valves and distribution patterns of strutted processes and the labiate process. A key to the species of Minidiscus is given. Minidiscus subtilis Gao, Cheng et Chin sp. nov., figs 7-8 Valves disc-shaped, slightly concave in center, weakly silicified, 3.5-5.5μm in diameter. Areola unequally radiate-striate, striae 8.5 / lμm. A narrow valve mantle without striae. Three strutted processes and a single labiate process located in the central area of the valve. Among them, one strutted process in the very center with the other two adjacent to it, forming an isometric triangle with the labiate process between the two subcentral strutted processes. Two small satellite pores in each base of the strutted processes. M. subtilis differs from M. chilensis mainly by their radiate striae continuously distributed from the valve center tothe margin.     

THE MORPHOLOGY AND INTEGRATION OF VALVES AND BANDS IN NAVICULA MUTICA VAR. MUTICA (BACILLARIOPHYCEAE)1

Navicula mutica (Kütz.) var. mutica was isolated from the air, cloned on agar, cultured in soil-water bottle, and studied with transmission and scanning electron micros-ropy. The frustules were lanceolate to ovoid with rounded apices, with the apical axis 8.5 ± 3.2 μ and the trans-apical and the transapical axis 3.6 ± 0.6 μm. Striae were composed of two or three puncta, and the mantle bore a single row of puncta aligned with the striae. The ends of the raphe turned away from an isolated punctual in the central area of the valve. The mantle puncta and one or two of the valve-face puncta in each stria opened into a series of transapical grooves in the interior of the valve, the grooves contributing to the appearance of striae in the light microscope. The interior of the mantle also possessed a pair of longitudinal grooves, discontinuous at the apices of the valves. An undulate advalvar margin of the valvocopula likely articulates along the interior longitudinal groove of the mantle. The projections of the undulate margin are perhaps positioned between the transapical grooves and along the longitudinal groove between the dentiform structures formed by the intersection of the double-grooved system. The girdle bands each had two (occasionally three) rows of pores. The pleurae margins were straight and not undulate.     

PERIZONIUM AND INITIAL VALVE FORMATION IN THE DIATOM NAVICULA CUSPIDATA (BACILLARIOPHYCEAE)1

This paper describes the perizonium and initial valve formation in Navicula cuspidata Kütz., based on light microscope (LM) and scanning electron microscope (SEM) observations. The perizonium consists of concentric over-lapping bands, laid down sequentially at the tips of the expanding biconical auxospore during its elongation. The central perizonial band has fimbriate edges and is considerably more rigid than the more distal bands. During auxospore elongation and the band secretion, the chloroplasts continuously oscillate between the two ends of the cell; this oscillation ceases once the elongation is complete. The initial valves, formed within the perizonium, are molded into the basically biconical shape of the perizonium except for a central flattening of each valve face. In contrast to the raphes in gametangial and vegetative valves which are surrounded by a smooth axial area, the raphes in initial valves lie within a raised ridge running along the apical axis of the valve. The regular pattern of apically oriented ridges on the outer surface of vegetative valves is also lacking on initial valves. Comparison of pore–pore spacing within striae of gametangial valves, initial values and post-initial valves (first division and vegetative cells) reveals that the pore–pore distance within striae is conserved at all sexual stages. However, the distance between striae is considerably larger in initial valves than in gametangial and post-initial valves. Vegetative interstriae spacing as well as the planar morphology of the valve face is regained at the first division of the initial cell. This suggests that the spacing between striae is dependent on the sexual stage of the cell during valve formation (i.e. not directly dependent on the cell size) and can be altered independently of the pore–pore spacing.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). V. INITIAL CELL AND SIZE REDUCTION IN RH. CURVATA AND A DESCRIPTION OF THE RHOICOSPHENIACEAE FAM. NOV.1

The initial epivalve of Rhoicosphenia curvata (Kütz.) Grun. differs from vegetative valves in having a strongly arched section, a wide hyaline marginal strip, no pseudosepta, an unthickened margin, and a terminal raphe fissure at the head pole. The initial epivalve is of the D type, with short raphe fissures. The epicingulum consists of three bands as usual, but they are narrower and more delicate than those of vegetative cells. The initial hypovalve and hypocingulum are similar in every way to those of vegetative cells, except for the rounded section of the hypovalve. During size reduction the almost isopolar outline of the initial valves and their immediate descendants gives way to an increasingly strong heteropolarity, and this is accompanied by changes in the relative lengths of the raphe slits and the shape of the central area. Different populations have different gametangium and initial cell sizes, suggesting the presence of races within the species. The structure of the initial cell indicates that Rhoicosphenia is less closely related to the monoraphid genera than to the gomphocymbelloid genera, confirming conclusions reached from studies of the vegetative cell and auxospore formation. Rhoicosphenia should therefore be separated into a new family, the Rhoicospheniaceae, which is described.     

VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS. II. INTEGRATION OF VALVES AND BANDS IN NAVICULA CONFERVACEA VAR. CONFERVACEA12

Chemically cleaned and critical-point dried cells of a clonal culture were examined with scanning electron microscopy. Cells form filaments by valve-to-valve connections maintained by organic material which adheres to the central area of the valve face. Bending of filaments is probably restricted to some extent by the articulation of overlapping spatulate marginal spines with an adjacent underlapping set of much shorter spines (ridges), and with the mantle edge itself. Cell division results in three possible spine patterns for each cell: a set of overlapping and a set of underlapping spines; no overlapping sets of spines (two underlapping); or two sets of overlapping spines (no underlapping). Each filament inherits cells with spine set patterns in the ratio of 2 (with 1 set overlapping): 1 (with no sets overlapping): 1 (with 2 sets overlapping). Valvocopulae are shaped similarly to pleurae except that the partes exteriores of the valvocopulae are wider. The pars interior of both is delimited by an advalvar row of pores continuous around the cell apex. The pars exterior also has a row of pores, but it is median in the valvocopula and first pleura and does not continue around the cell apex. The valvocopulae always underlap the mantle and the pleurae always underlap their preceding band. The ends of both appeared attached, but may become free in acid-cleaned preparations. Bands alternate with each other so that the ends of the valvocopula attach to the first continuous apical portion of the first pleura; the ends of the first pleura attach in that same fashion to the second pleura but at the opposite apex; and all subsequent pleurae alternate in the same fashion with up to at least 13 pleurae/epicingulum. The continuous apical portion of each band is elevated so that a functional (but not structural) ligula is formed, with the continuous apical portion of alternate bands becoming adjacent and underlapping each other only in this region. The valvocopulae in a single cell, or of adjacent cells, may have their continuous apical ends on the same or on opposite apices. It is recommended that N. confervacea var. peregrina (W. Sm.) Grun. be merged with the nominate variety.     

AN INVESTIGATION OF THE CELL WALL COMPONENTS OF ACTINOCYCLUS SUBTILIS (BACILLARIOPHYCEAE)1

The frustule of Actinocyclus subtilis (Greg.) Ralfs has been examined in detail with light and electron microscopy. The complex valve structure can only he appreciated fully by means of thin-sections. The loculate areola is closed to the inside by a basket of organic material, which is supported by a system of radiating, lightly silicified ribs. The basket is easily destroyed by acid cleaning, thus leaving an open hole (foramen). The loculus is connected to the outside by a system of interconnecting channels, whose external openings are too small to be resolved by the SEM. Between the locules of the valve face is a complex system of bullulae. The labiate processes are slightly tilted from the vertical axis vis à vis the valve mantle. Fibrillar material and mucilage are present within each labiate process, observations not reported previously. Histochemistry indicates that acid mucopolysaccharides are present within the lumen of the labiate process. We propose that the secretion of mucilage is related to the rotational, but directed movement noted in this centric diatom. The pseudonodulus is a solid silica plate subtended on the inside by a disc of organic material external to the cytoplasm. The relationship between Actinocyclus, Hemidiscus, Roperia, Charcotia and Azpeitia is discussed based on these new findings of valve morphology. Also the relationship between the families Hemidiscaceae and Coscinodiscaceae is discussed.     

FILAMENT FORMATION IN THE DIATOM MELOSIRA GRANULATA1

The frequency and position of separation valves in filaments of Melosira granulata were observed both in laboratory cultures and in natural habitats. The numerical relationship between mean filament length in a population and the proportion of separation valves produced (the separation valve index-SVI) has also been determined. The data indicate that filament length is controlled through the production of separation valves and that the SVI gives an indication of the mean filament length. Two series of cell divisions (the first producing the separation valves) are necessary before separation of the filament can occur. Paris of separation valves occur predominantly towards the middle of the filament. We suggest that the SVI may prove to be a useful indicator of mean filament length, and hence of ecological change, even when the filaments are no longer intact, as, for example, in sediment core samples and on permanent slides of acid-cleaned collections.     

PUNCTICULATA VERSIFORMIS SP. NOV. AND CYCLOTELLA KATHMANDUENSIS SP. NOV. (BACILLARIOPHYTA), NEW FOSSIL SPECIES FROM MIDDLE PLEISTOCENE LACUSTRINE SEDIMENTS,KATHMANDU, NEPAL HIMALAYA1

New fossil species, Puncticulata versiformis sp. nov. and Cyclotella kathmanduensis sp. nov., are described from lacustrine sediments in the Kathmandu Basin on the southern slope of the Nepal Himalaya. They were dominant in the Middle Pleistocene. Both LM and SEM observations reveal their unique morphological features. Puncticulata versiformis is characterized by (1) various valve outlines (circular, elliptical, or oval), (2) a tangentially undulate central area, (3) a complex alveolar structure composed of three kinds of costae (thick costae, thin costae, and thin and short costae), (4) well‐developed spines (Y‐shaped and tapering) located on one side of the valve face/mantle area junction, and (5) a valvocopula with an extremely undulate margin. The species‐specific feature of C. kathmanduensis is the presence of two kinds of alveolate zones in a single valve: type‐1 zone composed only of normal costae, and type‐2 zone composed of both normal costae and recessed costae bearing fultoportulae. Changes in valve ornamentation occur in these two species from initial valves to vegetative valves. In P. versiformis, the arrangement of areolae with internal domed cribra and fultoportulae in the central area changes from radial rows in the initial valve to groups in the vegetative valve. In the initial valve of C. kathmanduensis, the type‐1 alveolate zone is generally absent.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). I. THE VEGETATIVE CELL OF RH. CURVATA1

Rhoicosphenia Grun. has been placed by some authors in the monoraphid group with Achnanthes Bory and Cocconeis Ehrenb., and by others near Gomphonema Ehrenb. In order to clarify the systematic position of the genus, the morphology and anatomy of the vegetative cells of Rh. curvata (Kütz.) Grun. were investigated using light and electron microscopy. The structure and formation of the two types of valve are described, and the heterovalvy shown to be of a different type from that of the monoraphids; on the basis of raphe, valve and girdle structure a close relationship between these and Rhoicosphenia is unlikely. Rhoicosphenia shows many resemblances to Gomphonema but the types of pore occlusion present, coupled with apparently slight differences in the mucilage-secreting structures and the girdle, suggest that classification in the same family is unwise. The cryptic asymmetry of the valves, and in particular of the raphe system, is noted and explained with reference to their formation; with respect to this asymmetry two configurations of the valves can occur (named cis and trans types) and the distribution of these in raphid genera is discussed briefly. In view of the lack of evidence in raphid diatoms supporting a classification of bands into copulae and pleurae, it is recommended that this practice be suspended.     

Morphological investigations of the frustule, perizonium and initial valves of the freshwater diatom Achnanthes crenulata Grunow (Bacillariophyceae)

The present study clarifies the fine structure of the vegetative frustules, initial valves and perizonium of Achnanthes crenulata Grunow. The valves of the vegetative cell are distinctly linear‐lanceolate with an undulate margin. The valve face is quite flat and in girdle view is smoothly curved as in species of Gephyria (Bacillariophyceae). However, the valve face of the initial cells is slightly rounded and does not have an undulate margin. Furthermore, the rapheless sternum is centrally positioned along the apical axis of the araphid initial valve. As this taxon develops from auxospore to initial valve, it forms only longitudinal perizonial bands; no transverse bands arise. The perizonium consists of three silicified bands: one large, central longitudinal plate and two bands that underlie this plate; these two bands are either open or closed. This taxon has several conspicuous structures compared to other marine species of Achnanthes, but the structure of the perizonium supports the position of A. crenulata within Achnanthes sensu stricto.     

ULTRASTRUCTURE OF THE FRUSTULE OF TRICERATIUM FAVUS (BACILLARIOPHYCEAE)1,2

New structural details of the frustules of the diatom Triceratium favus Ehrenberg seen in the scanning electron microscope are reported. Significant new observations concern the pores of the hexagonal chambers, accessory structures (spines, dendritic processes) on the outer surfaces of the hexagonal chambers, the value margins and girdle structure.     

Aulacoseira calypsi sp. nov. (Coscinodiscophyceae) from an Amazonian lake,northern Brazil

This paper describes a new diatom species, Aulacoseira calypsi Tremarin, Torgan & Ludwig, from specimens in plankton samples from Água Preta lake. This Amazonian lake is a shallow mesotrophic environment situated in northern Brazil. The species is characterized by long filaments united by spatulate linking spines, obovate to conic separation spines, a valve surface variably ornamented, straight striae on the mantle, a narrow ringleist, and one row of sessile rimoportulae near the ringleist. Aulacoseira calypsi's morphometric features are compared with the following similar species: Aulacoseira nygaardii (Camburn) Camburn & Charles, Aulacoseira lacustris (Grunow) Krammer, Aulacoseira coroniformis Pearce & Cremer, Aulacoseira occulta Siver & Hamilton, Aulacoseira lancea Siver & Hamilton, Aulacoseira gessneri (Hustedt) Simonsen, and Aulacoseira islandica (Müller) Simonsen. The species shares similarities as to frustule size, striation pattern, and narrowness of ringleist; but differs in the morphology of separation and linking spines, and the number and position of the rimoportulae.     

New freshwater diatom genus,Edtheriotia gen. nov. of the Stephanodiscaceae (Bacillariophyta) from south‐central China

We describe a new genus and species of the diatom family Stephanodiscaceae with light and scanning electron microscopy from Libo Small Hole, Libo County, Guizhou Province, China. Edtheriotia guizhoiana gen. & sp. nov. has striae across the valve face of varying lengths, and are composed of fine striae towards the margin and onto the mantle. Many round to stellate siliceous nodules cover the exterior of the valve. External fultoportulae opening are short tubes; the opening of the rimportula lacks a tube. Internally a hyaline rim is positioned near the margin. Marginal fultoportulae possess two arcuate opercles. Areolae have domed cribra on the valve face. Those near the margin do not open to the interior. One to three sessile to slightly‐raised rimportulae are placed on the valve face towards the margin; they do not terminate shortened striae towards the center of the valve. This suite of features distinguishes this group from other known genera in the Stephanodicaeae. Cyclotella shanxiensis is transferred to Edtheriotia, making the new combination E. shanxiensis (Xie & Qi) Kociolek et al. comb. nov. It differs from E. guizhoiana by the presence of open pores near the margin of the valve. Features of the new genus are compared and contrasted with others in the Family Stephanodiscaceae. The two species of the genus, unlike most in the family, are known only from rivers and ponds from China and Japan.