A new marine diatom, Cocconeis shikinensis sp. nov. (Bacillariophyceae) from Japan

A new species of Cocconeis has been found growing on the green seaweed Caulerpa racemosa (Forsskål) J. Agardh var. laete‐virens (Montagne) Weber van Bosse from Shikine Island in the Izu Islands on the Pacific coast of Japan; we propose the name Cocconeis shiki‐nensis Hid. Suzuki and describe the species by light microscopy (LM) and electron microscopy (EM). This taxon was also collected from the plastic plates used for rearing in seed production systems of the abalone Nordotis discus hannai Ino and the horned turban Turbo cornutus Solander in the Toyama Prefectural Fisheries Research Institute facing the Sea of Japan. The main morphological features of C. shikinensis are as follows. The valves are elliptic. The valve face of the raphid valve (RV) is slightly concave and that of the araphid valve (AV) is complementary to the RV and convex. The single plastid is flat, C‐shaped and elaborately lobed. The raphe on the RV is straight. The each terminal area expands to both sides along the valve margin, forming an arrowhead‐shaped, thickened hyaline area. The striae consist of small, round areolae and are radiate and uniseriate. On the AV, the striae consist of several alveoli. Each alveolus opens internally by means of a circular foramen. The valvocopula of each valve is fimbriate and open. The cingulum attached to the AV consists of three girdle bands; a valvocopula and two bands (copula and pleura), which are open and have ligulae. The relationship between C. shikinensis and similar members of the genus Cocconeis is discussed.     

VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS. V. VARIATIONS IN THE CINGULUM OF PLEUROSIRA LAEVIS (BACILLARIOPHYCEAE)1

Frustule ultrastructure of Pleurosira laevis (Ehr.) Compère from an epilithon sample collected from the Missouri River was examined using scanning electron microscopy. Valve characteristics were similar to those found by other authors, whereas certain features of the cingulum were new. The cingulum consists primarily of three girdle bands (a valvocopula and two pleurae). The valvocopula can be complete but open at one end, below the ocellus. However, it is more commonly bisegmented, with two narrow and severable connecting points located in the pars interior region underlapping the mantle. The first and second pleurae are either biligulate or uniligulate and closed, but the former, when uniligulate, may be an open band as well. The second pleura is narrower and more delicate than the first. When a natural cleavage of a band subtends a ligula, the band is prone to break along the cleavage during specimen preparation, thus making difficult the assessment of band form and cingulum arrangement. Regions of band overlap have smooth poreless edges, whereas those of underlap are rimmed with either fine fimbriae or, occasionally, a coarser comblike fringe. The variability of the bands results in a cingulum that can be assembled in at least four different arrangements.     

Observations on the valve structure of marine species of the diatom genus Cocconeis Ehr.

The valve structure of three marine diatom species, Cocconeis molesta var. crucifera, C. dirupta and C. pellucida was studied by transmission and scanning electron microscopy. In all Cocconeis examined, the areolae are occluded by hymenes located near the internal openings in the raphid valve and near the internal openings in the araphid valves.     

Xenococconeis opunohusiensis gen. et sp. nov. and Xenococconeis neocaledonica comb. nov. (Bacillariophyta) from the tropical South Pacific

During a survey of the coral reef diatoms of Moorea Island (Society Archipelago, South Pacific) a small‐sized member of the order Achnanthales was studied using a light microscope (LM) and a scanning electron microscope (SEM). This marine taxon has: a raphe valve (RV) with a non‐crenulate edge; a high cingulum; a sternum valve (SV) often irregularly striated and areolae with concave hymenate pore occlusion; a thick and plain SV valvocopula (SVVC), ring‐shaped, composed of large fused fimbriae, with a central elliptic foramen bordered by the peg‐like edge of the fimbriae. On abvalvar side, the SVVC bears radiate concave and robust transapical ribs, interlinking with short elevated transverse ribs of the RV valvocopula (RVVC). Large marginal fenestrae of the RVVC give access to pseudoloculi. One oblong, unique and striated papilla is located on each RVVC rib. Given this unique set of features, we describe Xenococconeis opunohusiensis gen. et sp. nov. as a new taxon belonging to the Achnanthales. The characteristics of the new taxon are compared with Campyloneis Grunow and Cocconeis Ehrenberg. From New Caledonia, Cocconeis neocaledonica Maillard ex Lange‐Bertalot et Steindorf, a freshwater diatom, was described with two internal septa with marginal pseudoloculi. Based on subsequent SEM illustrations and remarks, we propose the transfer of C. neocaledonica to the new genus, and compare it to the type species, Xenococconeis opunohusiensis.     

THE GENUS ACTINOCYCLUS (BACILLARIOPHYCEAE): FRUSTULE MORPHOLOGY OF A. SAGITTULUS SP. NOV. AND TWO RELATED SPECIES1

Actinocyclus octonarius var. tenellus (Bréb.) Hendey, A. actinochilus (Ehr.) Simonsen and A. sagittulus sp. nov. were examined by light and scanning electron microscopy from field samples and/or culture material. Consistent cingulum patterns of a wide valvocopula and one narrow pleura were found. In A. actinochilus, a small third band was found filling the opening of the pleura and is probably present in the other two taxa. The observed variability of the pseudonodulus, especially in A. actinochilus but also in other members of the genus, was confirmed and our results support the literature definition of Actinocyclus as having: 1) a marginal ring of large labiate processes, laterally expanded internally, 2) no external tubes, 3) essentially radial areolation arranged in fascicles, 4) external cribrum, internal foramen, and 5) a pseudonodulus usually present, but may be absent or difficult to detect on individual valves. On the basis of the present study another characteristic should be added; 6) hyaline bands with a wide valvocopula and at least one pleura. This characteristic appears to extend throughout the family Hemidiscaceae, suggesting a close relationship to those Coscinodiscus species with a single marginal row of large labiate processes and zero or one central labiate processes. In addition, Actinocyclus has been noted to have a thin valve overhang extending outside the valvocopula for as much as one-third of its width.     

Morphology and molecular phylogeny of Thalassiosira sinica sp. nov. (Bacillariophyta) with delicate areolae and fultoportulae pattern

Thalassiosira Cleve is one of the most species-rich marine diatom genera. Previous studies have mainly focused on polar and temperate areas, but recent studies on material from Asian waters suggested that a high and undescribed species diversity of Thalassiosira occurs in Asia. On the basis of plankton samples collected from the South China Sea, a new species, T. sinica sp. nov. Y. Li & Y. Q. Guo is described. The morphology of the cells was examined by light and scanning electron microscopy. The hypervariable region of the nuclear large-subunit ribosomal DNA and the relatively conserved region of the nuclear small-subunit ribosomal DNA were sequenced for information on phylogenetic relationships. The living cells are usually solitary and drum-shaped. The areolae on the valve are delicate, small and arranged in fascicles. In addition to a regular ring of marginal fultoportulae on the valve edge, T. sinica possesses one central fultoportula and a number of fultoportulae arranged into 2–3 irregular rings on the valve face. A rimoportula located inside the ring of marginal fultoportulae possesses a long and strong external tube. The valvocopula and the copulae have rows of pores, but the pores on the valvocopula are larger than those on the copulae. Thalassiosira sinica appears to be included in subgroup C sensu Gedde because of a rimoportula with a distinct external tube located on the valve face. The molecular phylogeny, inferred from both SSU and LSU sequences, does, however, not support the validity of subgroup C, as the closest allies of T. sinica here turned out to be T. diporocyclus and T. lundiana, species in which the rimoportulae are located on the valve margin.     

OVERLOOKED HETEROPOLARITY IN SURIRELLA CF. FASTUOSA (BACILLARIOPHYTA) AND RELATIONSHIPS BETWEEN VALVE MORPHOGENESIS AND AUXOSPORE DEVELOPMENT

Surirella cf. fastuosa is an apparently isopolar elliptic marine raphid diatom. We observed cells before and after sexual reproduction in monoclonal cultures using light and scanning electron microscopy (LM and SEM). After sexual reproduction cells were approximately twice as large as before, in valve length and width. The stria and infundibula densities were stable during the life cycle. Subtle morphological differences were detectable between the two poles of the frustule. One pole (pole A) was characterized by endings of the external raphe fissure that turned toward the valve face, continuity of the domed wall of the raphe canal externally, an elliptic chamber visible internally, a shallow nick in the interior of the valvocopula. The other pole (pole B) was with the following: straight endings of the external raphe fissures, a dent in the domed wall of the raphe canal externally, a double chamber internally, presence of the open ends of the valvocopula nearby, a deep nick in the valvocopula. Furthermore, at pole A virgae developed at an early stage in morphogenesis, whereas at pole B they were not formed. In the auxospores, pole A was situated beneath the primary transverse perizonial band. Pole A is suggested to be homologous with the head pole in heteropolar Surirella and is the “protopole” likely equivalent to the central nodule in naviculoid taxa. Pole B is homologous with the foot pole in heteropolar Surirella and is the “synaptic pole” formed by fusion of components equivalent to both poles of naviculoid taxa.     

中国硅藻1新记录种——喙状比利牛斯山微小曲壳藻

利用光学和扫描电子显微镜对采自武陵山区澧水的1种中国新记录硅藻——喙状比利牛斯山微小曲壳藻进行了形态研究。该种的鉴定特征为壳面线形披针形,具有喙状的末端,有壳缝壳面末端线纹呈略微会聚状或近平行排列,孔纹膜为筛状。该研究结果扩展了对喙状比利牛斯山微小曲壳藻形态结构和地理分布的认识。     

Two new Cocconeis taxa (Bacillariophyceae) from coral sands off the Mascarenes (Western Indian Ocean) and some related unidentified taxa

Coral sands off Réunion Island and Rodrigues (Mascarene archipelago, Western Indian Ocean) support diverse diatom communities, particularly rich in Monoraphidineae. Recent surveys of reef environments (June 2005 and June 2007) permitted the recognition of several taxa belonging to the diatom genus Cocconeis, among which are two new, relatively small taxa, epipsammic on coral sand. Cocconeis coronata Riaux-Gobin et Romero sp. nov. is similar to C. scutellum but has its own distinctive features. In external view, the concave raphe valve possesses uniseriate striae and a subsident hyaline marginal rim, while the strongly convex sternum valve has a submarginal, generally continuous crest, a hexagonal pattern of areolation, short, rounded spines that are often regularly arranged around valve face areolae, a complex areola hymen and small marginal chambers. Some morphometric differences were noted between the populations of C. coronata at Réunion and Rodrigues. Cocconeis margaritata Riaux-Gobin et Al-Handal, sp. nov. is smaller, possesses a sternum valve like that of C. placentula and C. neothumensis, but has denser striation and small pearl-like concretions around the areola aperture on the sternum valve. Several other taxa that resemble, or may be varieties of, C. margaritata require further study before being formally described. Cocconeis margaritata and C. coronata are small and relatively rare, so their study requires scanning electron microscopy.     

硅藻中国一新记录种——泉生平片藻

利用光学显微镜和扫描电子显微镜对采自湖南省绥宁县巫水水域的硅藻标本进行了观察研究,鉴定出其中一种为硅藻中国新记录种——泉生平片藻［Tabularia fonticola (Hustedt) C.E. Wetzel & D.M. Williams］,该种具有以下鉴别特征：(1) 壳面轮廓为线形披针形,中央胸骨宽,线纹短且宽。(2) 横主肋和纵细肋硅质化增厚。(3) 孔纹开口被数条横向硅质条组成的筛板所遮拦。(4) 每个壳面仅在其一端着生一个唇形突。(5) 壳套顶孔区孔纹有序排列。(6) 第一环带开放。该研究首次报道了泉生平片藻的前正常营养期细胞的超微结构特征,研究结果不仅增加了对泉生平片藻的超微结构认识,而且扩展了其地理分布区域。     

Observations on Cymbella mexicana (Ehrenb.) Cleve var. mexicana (Bacillariophyceae) with special reference to the band structure

Cymbella mexicana (Ehrenb.) Cleve var. mexicana was collected from Tama-gawa (Tama River), Tokyo. The fine structure of the species was examined by scanning electron microscopy (SEM), with special reference to colony formation and band morphology. A mature cingulum of this species is usually composed of four open bands. The correlation between the position of the second band (B2) of the cingulum and the attaching pole of the frustule is discussed.     

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.     

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.     

THE MARINE,PLANKTONIC DIATOMS THALASSIOSIRA OCEANICA SP. NOV. AND T. PARTHENEIA1

The diatom clone 13–1 isolated from the Sargasso Sea by Dr. R. R. L. Guillard as Cyclotella nana Hust. or Thalassiosira pseudonana Hasle and Heimdal is described as a separate species, Thalassiosira oceanica sp. nov. An amplified diagnosis of Thalassiosira partheneia Schrader is given, and a comparison of the two species is made based on light and electron microscopy. Similarities are present in the apparent distribution pattern, cell size, and girdle structure. Differences are present in the shape of the areolae of the valvocopula and the copula, in the structure of the vela of these bands, in the texture of the external valve surface, in the morphology of the strutted processes, in the location of the labiate process, in the distance between the marginal strutted processes, and by the presence of a marginal ridge in T. oceanica. Fifteen nanoplanktonic (maximum diameter = 20 UmUm) Thalassiosira species are listed, among them T. oceanica and T. partheneia.     

Studies on woloszynskioid dinoflagellates VI: description of Tovellia aveirensis sp. nov. (Dinophyceae), a new species of Tovelliaceae with spiny cysts

A new species of Tovellia, T. aveirensis, is described on the basis of light (LM) and scanning electron microscopy (SEM) of motile cells and resting cysts, complemented with transmission electron microscopy (TEM) of flagellate cells and phylogenetic analysis of partial sequences of the large subunit ribosomal rRNA gene. Both vegetative cells and several stages of a life cycle involving sexual reproduction and the production of resting cysts were examined in cultures established from a tank in the University of Aveiro campus. Vegetative cells were round and little compressed dorsoventrally; planozygotes were longer and had a proportionally larger epicone. Chloroplast lobes were shown by TEM to radiate from a central, branched pyrenoid, although this was difficult to ascertain in LM. The amphiesma of flagellate cells had mainly 5 or 6-sided vesicles with thin plates, arranged in 5–7 latitudinal series on the epicone, 3–5 on the hypocone. The cingulum had 2 rows of plates, the posterior row extending into the hypocone and crossed by a series of small projecting knobs along the lower edge of the cingulum. A line of narrow amphiesmal plates extended over the cell apex, from near the cingulum on the ventral side to the middle of the dorsal side of the epicone. Eight or 9 narrow amphiesmal plates lined each side of this apical line of plates (ALP). Resting cysts differed from any described before in having numerous long, tapering spines with branched tips distributed over most of the surface. Most mature cysts showed an equatorial constriction. Neither cysts nor motile cells were seen to accumulate red cytoplasmic bodies in any stage of the cultures. The phylogenetic analysis placed, with high statistical support, the new species within the genus Tovellia; it formed a clade, with moderate support, with T. sanguinea, a species notable for its reddening cells.     

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.     

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.     

Comparison of Cocconeis pseudonotata sp. nov. with two closely related species,C. notata and C. diruptoides,from Posidonia oceanica leaves

Three Cocconeis Ehrenberg species, epiphytic on the leaves of Posidonia oceanica (L.) Delile, were studied by light and electron microscopy. A new species, C. pseudonotata, is described which is closely related to C. notata Petit and C. diruptoides Hustedt. Gross morphology and the presence of a sigmoid raphe and sternum are the characters shared by the three species, whereas the central areas of sternum and raphe-sternum valves, and the stria and areola densities are the main distinctive characters for the species when observed by light microscopy. Scanning and transmission electron microscopic observations revealed that the fine structure of areolae must be also considered in order to identify the species. Comparison among the three species has been carried out by observations on material from our samples, as well as on the type material of C. diruptoides and cleaned samples from the Hustedt collection. The study also provides new information on the geographical distribution of these species.     

<Emphasis Type="Italic">Thalassiosira mala</Emphasis> (Bacillariophyta), a potentially harmful,marine diatom from Chilka Lake and other coastal localities of Odisha,India: Nomenclature,frustule morphology and global biogeography

Our examination of net phytoplankton collected from coastal localities in Odisha on the east coast of India, including Chilka Lake, Chandrabhaga Beach and Puri, in December 2015, revealed the overwhelming dominance of Thalassiosira mala, a gelatinous colony-forming, potentially harmful, marine planktonic diatom. The large numbers of cells allowed us to observe details of the cingulum not previously reported. The epicingulum is composed of four open bands including an areolated valvocopula, an areolated copula and two non-areolated pleurae. The immature hypocingulum includes at least two bands. Openings of alternate bands are arranged in a dextral pattern. Based on previous reports from the west coast and our current findings, Thalassiosira mala appears to be a common, widely distributed primary producer in Indian coastal waters. The presence of morphologically similar species, especially those <20 μm in diameter, underscores the importance of reliable species-level taxonomy using appropriate techniques for meaningful ecological and biogeographic considerations and for monitoring potentially harmful algae in India’s economically important coastal waters. Published reports suggest that Thalassiosira mala is widely distributed in temperate and tropical waters, present in 26 of 232 ecoregions and 18 of 62 provinces recognized in a recent classification of coastal marine ecoregions.     

Structure of the Cells, Cell Division and Colony Formation in the Diatoms Isthmia enervis Ehr. and I. nervosa Ktz

The two common species of Isthmia have been studied mainly byscanning electron microscopy. The occurrence of differing cellshape in the same species is an extremely unusual feature amongstdiatoms. This is coupled with heteropolar valves. The formationof colonies and the peculiar attachment of cells to one anotheris recorded. A particularly intricate attachment of the firstgirdle band (valvocopula) to the valve is recorded. Isthmia, diatom, cell division, colony formation