Transapical Axis Research Articles

Pseudogomphonema lukinicum sp. nov. (Bacillariophyceae), a new endophytic diatom found inside multicellular red algae from the Northwest Pacific

Abstract In our collections from the Northwest Pacific waters, we found several specimens of the red algae Lukinia dissecta and Callophyllis perestenkoae with darker spots on their thalli, which contained an unusual pennate diatom. A detailed morphological analysis based on light and scanning electron microscopy observations made it possible to describe a new species of endophytic diatom, Pseudogomphonema lukinicum sp. nov. Stonik et Skriptsova. The new species has some morphological features typical of the genus, such as the heteropolarity of the valves, the presence of pseudosepta and small apical chambers at both poles of the valves, and nonporous girdle bands. Pseudogomphonema lukinicum has been described and distinguished from the other species in the genus on the basis of a combination of morphological traits, including relatively small cell dimensions, a slightly asymmetrical valve to the transapical axis, with obtusely rounded headpole and narrower footpole, the large asymmetrical central area, and the presence of apical chambers at both poles. Pseudogomphonema lukinicum is the second representative of Pseudogomphonema known to be living endophytically. The data on the species composition of endophytic diatoms in marine macroalgae, their habitats, and host organisms reported in the literature to date are summarized.

A new species of genus Crenotia (Bacillariophyta) from Tibet, China.

During the investigation of the freshwater diatoms from Tibet, a monoraphid species was observed from a hot spring near Anduo County, located on a plateau in the central portion of Tibet. This species shares the diagnostic features of Crenotia, such as the valve bent along the transapical axis, striae uniseriate to biseriate from centre to the apices and areolae with special structures located at the end of each stria. We compared the morphological characters of this new species with the others in this genus and show it to be new; it is named Crenotiatibetiasp. nov. This species has small valves with slightly protracted ends with nearly capitate apices, lanceolate axial area, central area unilaterally expanded to the margin, striae uniseriate to biseriate, but, in some valves, the striae are only uniseriate. Areolae are round small to irregular in shape and, at the end of each stria, there is a horseshoe-shaped areola present. Observations of developing valves show all the striae begin biseriate, then they become covered by silica to form uniseriate striae. Comparisons are made amongst the species in this genus and with genera assigned to the Achnanthidiaceae.

Gomphocymbellopsis guijiangensis sp. nov. (Cymbellaceae; Bacillariophyta), a new species from Guangxi Province with comments on associated specimens from Hubei Province, China

Gomphocymbellopsis guijiangensis sp. nov. and G. sp. were collected from the Guijiang River and from fossil deposits of the Jianghan Plain, respectively. The morphology of this new species is described by both light and scanning electron microscopy and compared with G. ancyli, the only other species of the genus Gomphocymbellopsis. G. guijiangensis sp. nov. is characterized by valves that are asymmetrical to the transapical axis and weakly asymmetrical to the apical axis, by the presence of pore fields at the apices, by three differently shaped stigmata, by externally and dorsally deflected distal raphe ends, and by often ventrally deflected proximal raphe ends. Therefore, we describe here G. guijiangensis sp. nov. as species new for science. Concise notes on the associated diatom flora and its ecological preferences are provided.

Descriptions of three new diatom species in the genus Eunotia (Eunotiaceae, Bacillariophyta) from the Eocene Arctic

Eunotia is the largest and most diverse genus within the family Eunotiaceae, a primarily freshwater group of diatoms often found in dilute, acidic and humic-stained environments. Species in this genus are characterized by being asymmetric along their apical axis, symmetric about the transapical axis, and with a simple and reduced raphe system situated largely on the mantle and restricted to the apical ends of the valve. In addition, Eunotia taxa have one or more rimoportula per valve, usually close to the apex. Because of their reduced raphe system, coupled with the presence of rimoportulae, Eunotia and its relatives are often viewed as the oldest lineage of raphe-bearing diatoms. To date, the oldest remains of Eunotia species have been reported from the early to middle Eocene, including from the Giraffe Pipe locality, an ancient Eocene fossil site located in northern Canada near the Arctic Circle. Rocks from this site contain a large and diverse assemblage of Eunotia taxa. The purpose of this study is to begin to characterize this assemblage with descriptions of three new species, Eunotia giraffensis sp. nov., E. petasum sp. nov. and E. pseudonaegelii sp. nov. The new species, representing the longest specimens found at the Giraffe Pipe locality, each possess characteristics common to Eunotia making them easily assigned to this genus. Because the Eunotia lineage was well established by the early part of the Eocene, it is likely to be significantly older.

Staurophora ouniangaensis sp. nov. (Bacillariophyceae, Anomoeoneidaceae), a new diatom from the Ounianga Lakes in the Sahara, Chad

Modern diatom assemblages were investigated in the Ounianga Lakes located in the driest part of the Chadian Sahara. These lakes still exist today due to groundwater seepage. They contain a variety of diatom species, one of which could not be identified. Here we describe a new species of Staurophora, S. ouniangaensis sp. nov. based on detailed light and scanning electron microscopy observations. The new taxon presents all morphological characters attributed to this genus and differs from other Staurophora species mainly by its specific valve outline and the slightly twisted frustules along the transapical axis. We compared this new species with the morphologically resembling Cymbella obtusa which was reported from Chad. The latter taxon has a much coarser stria density than our newly described species. Staurophora ouniangaensis sp. nov. supports that Staurophora species prefer inland saline environments. Indeed, in the Ounianga lakes, the new species was mainly observed in mesosaline to hypersaline waters.

Description of Gomphothidium gen. nov., with light and scanning electron microscopy: A New Freshwater Monoraphid Diatom Genus from Asia

We describe a new genus of monoraphid diatom based on Achnanthidium ovatum T.Watanabe et Tuji in Watanabe et al., a species described originally from Japan. We encountered this species from Yunnan Province in the southwestern part to eastern China, as well as in Luding, Sichuan Province and Xianju, Zhejiang Province, in pristine lotic environments. The species differs from the genus Achnanthidium by being asymmetrical to the transapical axis and has a pseudoseptum at the poles of the interior of the raphe valve which is fused with each helictoglossa. Moreover, a distinct group of condensed striae can be found at the narrower pole ('footpole') of the raphe valve. This appears to be the only known genus of freshwater monoraphid diatoms that is restricted to a single continent.

New araphid species of the genus Pseudostaurosira (Bacillariophyceae) from southern Patagonia

ABSTRACT We describe five new araphid diatom species belonging to the genus Pseudostaurosira. These new taxa were found in modern and fossil material collected from five southern Patagonian waterbodies (49–52°S), four from the Santa Cruz province, Argentina and one from the Magallanes Region, Chile. When observed under light and scanning electron microscopy, each species differs by a single or a combination of valve character(s). Pseudostaurosira australopatagonica sp. nov. has unique volae that are profusely, dichotomously branched, internally anastomosed, and affixed to the virgae. Pseudostaurosira hyalopatagonica sp. nov. has fusiform valves with cuneate, elongate ends, narrow valves and round to slightly elliptical areolae. Pseudostaurosira catalinae sp. nov. has broadly fusiform valves with cuneate to subrostrate ends; volae form a circular to elliptical ring at the centre of the areolar opening and, externally covering the mantle areolae, it has a watch glass-like flap. Pseudostaurosira tehuelcheana sp. nov. has lanceolate valves with broadly rounded apices, solid incipient conical spines and marginal, transapically elongate areolae occluded by profusely branched volae. Pseudostaurosira zolitschkae sp. nov. is a relatively large-valve species with subrostrate apices, hollow spines, marginal areolae sometimes separated by a thin vimen. The volae in this latter, new taxon, only originate from a position parallel to the transapical axis of the valve, an origin that is uncommon within the genus. We discuss the validity of describing species based on morphological data and highlight the importance of increasing taxonomic resolution on isolated regions such as Patagonia.

Morphological Variability of Pseudo-nitzschia pungens Clade I (Bacillariophyceae) in the Northwestern Adriatic Sea.

Pseudo-nitzschia pungens is a common component of the phytoplankton community of the northern Adriatic Sea. In this study, an in-depth morphological analysis of P. pungens was carried out in both cultured strains isolated in different periods and field samples, revealing a surprisingly wide variability in a number of details, with both the gross morphology and ultrastructural levels deviating from the nominal P. pungens. Colonies showed an overlap (from one-third to one-sixth) and a transapical axis (rarely reaching 3 µm), strongly differing from the original description of the species. Moreover, valves may be either symmetrical or slightly asymmetrical, with striae almost always biseriate but sometimes uniseriate or triseriate. Poroids’ morphology in cingular bands was characterized by a wide variability (square, circular, or rectangular poroids without or with up to two hymen sectors), with several combination of them, even within the same cingular band. Phylogenetic analyses based on ITS rDNA showed that the P. pungens of the northern Adriatic Sea belonged to clade I. Domoic acid was not detected.

Description and phylogenetic position of Plagiolemma distortum sp. nov., a new raphid diatom (Bacillariophyceae) from French coastal waters

A new marine raphid diatom, Plagiolemma distortum Nézan, sp. nov. is described from plankton samples from the Atlantic Ocean, south Brittany (north-western France), where it was regularly observed, but never in high abundances. Cells have an unusual and complex shape under light microscopy (LM) depending on their position and orientation. The two valves are highly vaulted and narrow in width (transapical axis). Cells contain four complexly lobed plastids and a variable number of refractive granules without particular localization. In addition, capsules containing motile cells were observed. Ultrastructural details of the frustules were investigated using scanning electron microscopy (SEM). The girdle bands are simple. Each valve possesses a sigmoid raphe raised on a ridge and ending in external large openings with elaborate internal helictoglossae. Moreover, each valve displays outer slit-like foramina and inner rounded hymenes, external terminal minute holes (micropyles) arranged in a row at the poles. In addition, on each valve face, one to several short transverse median costae are observed, terminating far away from the valve edges. Morphological comparisons with closely related taxa show that P. distortum is a new species. A video clip of a moving cell is provided for better understanding of the cell shape. The formation and function of capsules are discussed as well as the species habitat. A phylogenetic study, based on nuclear small subunit (SSU) ribosomal DNA (rDNA) sequence data, which includes new sequences relative to Plagiolemma and Plagiotropis, was performed. Furthermore, some morphological details observed with SEM are included in an emended generic diagnosis of Plagiolemma.

New epizoic diatom (Bacillariophyta) species from sea turtles in the Eastern Caribbean and South Pacific

Obligately epizoic diatoms (Bacillariophyta) on vertebrates were first described from cetaceans, but turtles, both freshwater and marine, also host very specific floras. Several scrapings of juvenile Chelonia mydas have allowed the description of two new diatom taxa whose valves are asymmetrical about the transapical axis, Tripterion societatis sp. nov. and Chelonicola caribeana sp. nov. These taxa are very small and show some morphological plasticity. Such plasticity might suggest their inclusion in genera with slightly different characteristics from Tripterion and Chelonicola as originally delimited. Based on our observations, an emended diagnosis is proposed for Chelonicola.

Phylogeny, ecology, morphological evolution, and reclassification of the diatom orders Surirellales and Rhopalodiales

The Surirellales and Rhopalodiales are large, widespread, and morphologically diverse groups of raphid pennate diatoms (Bacillariphyta) whose raphe, a structure that facilitates active motility, opens internally into a siliceous canal. We collected 202 representatives of the lineage and sequenced genes from the nuclear, plastid, and mitochondrial genomes to infer phylogenetic relationships as a basis for comparative study of ecology and morphological evolution as well as reclassification. The lineage was ancestrally marine, and we report the first evidence for a ‘stepping stone’ model of marine–freshwater transitions in which freshwater invasions were preceded by adaptation to intermediate brackish habitats. Phylogenetic comparative analyses also showed that the shift from an apical (e.g., Entomoneis) to transapical major axis of development (e.g., Surirella) did not have to proceed through subcircular intermediate forms (i.e., Campylodiscus). Rather, subcircular forms evolved both within lineages with longer apical axis or longer transapical axis. We also used the inferred phylogeny as a basis for genus-level reclassification of the lineage. Campylodiscus now includes the fastuosoid members of Surirella and Campylodiscus, but excludes other marine Campylodiscus which are now classified as Coronia. Surirella includes the Surirella striatula clade, Surirella Pinnatae group, and species formerly classified as Cymatopleura. We resurrected the genus Iconella to accommodate Stenopterobia and the robustoid members of Surirella and Campylodiscus. We broadened Epithemia to include members of the paraphyletic genus Rhopalodia. Finally, we discuss the challenges of constructing a classification that best leverages available phylogenetic data, while minimizing disruption to the research community and recognizing practical considerations stemming from the slow rate of progress on systematic studies of understudied organisms.

Rhoicosphenia kloseri, a new isopolar Rhoicosphenia (Bacillariophyta) species from the Antarctic with comparison to other isopolar Rhoicosphenia

Rhoicosphenia is a common diatom in both freshwater and marine ecosystems and the genus can be found on nearly every continent. Despite the fact that the genus is common, few new species have been reported from outside of Europe, Asia, and North America, and only one species has been previously described from the Antarctic. Further, most Rhoicosphenia are heteropolar in valve outline, asymmetrical to the transapical axis, while few taxa are isopolar. During investigations into the epiphytes on the red alga Georgiella confluens from the South Shetland Islands, a new marine, isopolar Rhoicosphenia was discovered and is herein described and documented with both light and scanning electron microscopy. Rhoicosphenia kloseri is isopolar, and in that regard similar to other isopolar taxa, such as R. genuflexa and R. pullus, but does not fit the morphological species concept of those taxa and is thus described as new. This new species discovery is following a trend of high rates of discovery of previously ignored morphological diversity within the genus Rhoicosphenia.

On the geographical distribution and ecology of Pseudostaurosira cataractarum (Bacillariophyceae): new findings in the Palearctic and Neotropic ecozones

The aim of this paper is to expand the current knowledge on the distribution, ecology and morphology of Pseudostaurosira cataractarum (Hustedt) C.E. Wetzel, E. Morales et Ector. We analysed several freshwater diatom assemblages within the Palearctic (Czech Republic, Europe) and Neotropic ecozones (Argentina and Bolivia, South America). In all localities, small araphids were the dominant or co-dominant group. Inside this group, P. cataractarum was only dominant in the samples from Argentina and Czech Republic, while the Bolivian samples had only a few individuals. RDA and PCA analyses show that the relative abundance of P. cataractarum was positively correlated with water conductivity. The following measurements resulted from the morphometric analysis, apical axis: 2.8–8.2 µm, transapical axis: 2.7–7.2 µm and stria density: 15–29 in 10 µm. In conclusion, the present is the first report of P. cataractarum for continental Europe (from fossil material) and the Neotropic ecozone (from extant populations). Besides having a preference for subaerial habitats, this taxon could be locally conditioned by water conductivity, although in each of the analysed samples this species was associated with cosmopolitan diatoms that are tolerant to a wide range of environmental conditions. Based on the morphometric analyses in studied populations, we propose that the size range for the apical and transapical axes of P. cataractarum should be expanded at the lower end of the range. Likewise, the range of stria density should be expanded since it is wider than that presented for the type population from Indonesia (Java). Consequently, an emended description is presented based on our study and on published data on type and fossil populations.

Gyrosigma rostratum sp. nov. (Bacillariophyta) from the low intertidal zone, Xiamen Bay, southern China

Gyrosigma rostratum, sp. nov., a new diatom species from the low intertidal zone, Xiamen Bay, southern China, was studied with light and scanning electron microscopy. The valves are lanceolate with protracted rostrate apices, symmetrical to both apical and transapical axis, not sigmoid. The raphe is straight, with a raphe angle of approximately two degrees. The external central raphe endings turn in the same direction and are isomorphic. The unique characteristic of the valve is that a conopeum (a lunate flap of silica, approximately 0.8–1.1 µm wide by 4.4–4.8 µm long) covers the terminal axial area and two rows of areolae near each apex. Gyrosigma rostratum is epipsammic and lives in marine habitats.

Cocconeis crozetensis, a new monoraphid diatom from subantarctic freshwater and moss habitats

Ultrastructural observations of one previously misidentified freshwater species of a Cocconeis (Bacillariophyceae) from the Crozet Archipelago, Indian Sector of the Southern Ocean, are presented. Cocconeis crozetensis sp. nov. possesses small valves (apical axis: 10–13 μm; transapical axis: 6.7–8.4 μm). The main frustule features that distinguish the proposed new species are: (1) the sternum valve (SV) areolae with an external vola and the internal vela, (2) the submarginal area of the raphe-sternum valve, and (3) the morphology of valvocopula and fimbriae of the SV. Possible morphological relationships with several other small Cocconeis, such as C. neodiminuta, C. neothumensis, C. placentula var. pseudolineata and C. pseudothumensis, as well as its morphological similarities with placentuloid Cocconeis are discussed. Reliable identification of C. crozetensis sp. nov. under light microscopy can prove difficult for less-experienced diatomologists and ecologists, and the use of electron microscopy proves to be unavoidable for its correct identification.

LANCINEIS RECTILATUS SP. NOV., A NEW FOSSIL SPECIES FROM PLEISTOCENE SEDIMENTS IN JAPAN

A fossil diatom species, Lancineis rectilatus sp. nov., is described from Pleistocene marine sediments of the Kanto Plain, central Japan. Lancineis rectilatus is characterized by (1) uniqueness of occurrence in geological time from the Pleistocene, (2) linear outline, (3) angular inflection of the valve outline, (4) a barely distinguishable narrow hyaline axial area and (5) orientation of a slit of rimoportulae orientated nearly parallel to the transapical axis at both apices. The new species is compared with other Lanceineis species, and the need to investigate valve ultrastructure of other Lancineis species is suggested. The stratigraphic occurrence of L. rectilatus indicates it is a possible stratigraphic marker useful for Pleistocene shallow marine sediments.

Nupela marvanii sp. nov., and N. lapidosa (KRASSKE) LANGE-BERTALOT in Poland with notes on the distribution and ecology of the genus Nupela (Bacillariophyta).

Two species of Nupela were identified in a spring and in a small spring-fed pool in the Polish Tatra Mts, - these were N. lapidosa and Nupela sp. The second species is described as N. marvanii. The new species is characterized by heteropolar, narrowly elliptic valves with capitate apices. Sternum valve has very short, sometimes rudimental raphe branches. Under a light microscope transapical striae are not discernible. Externally both valves are covered with hymen. The central area of sternum valves has irregular silicate thickenings. Proximal raphe fissures are straight and terminate in small pores. Distal raphe fissures double-deflected into the same side of the valve, form ?-shaped structures that extend onto the mantle. Internally visible linear-lanceolate axial area, which forms unilateral fascia on raphe valve, which reaches valve margin. Proximal raphe fissures are T-shaped. Distal raphe fissures are straight, and terminate in small, linear helictoglossa. Sternum valve has large, clearly visible internally, asymmetrically lanceolate central area and discernible externally reinforced median costa. Raphe fissures are strongly reduced, rudimental. The areole are round to elliptical, expanded along the transapical axis, with the wider opening on the external surface. An irregular row of similar areoles is present along pleural side of valve. Both species are documented with LM and SEM micrographs and briefly discussed. The distribution and autecology of 46 Nupela members are summarized.

Morphology, phylogeny and taxonomy of species within the Pseudo-nitzschia americana complex (Bacillariophyceae) with descriptions of two new species, Pseudo-nitzschia brasiliana and Pseudo-nitzschia linea

Pseudo-nitzschia americana and the two closely related species P. brasiliana Lundholm, Hasle & G.A. Fryxell sp. nov. and P. linea Lundholm, Hasle & G.A. Fryxell sp. nov. are described, based on morphology. The phylogenetic positions of P. americana and P. brasiliana are inferred from partial nuclear-encoded large-subunit ribosomal DNA and their toxin production is assessed. The new species P. brasiliana and P. linea form stepped colonies, whereas P. americana is single celled. Pseudo-nitzschia americana, P. brasiliana and P. linea possess morphological features typical of Pseudo-nitzschia and Fragilariopsis, differentiating them from Nitzschia. All three species possess valve shapes similar to many Fragilariopsis species and they seem to constitute a morphological continuum between Pseudo-nitzschia and Fragilariopsis. Molecular phylogenetic analyses showed P. americana and P. brasiliana to be sister taxa within a strongly supported monophyletic clade comprising Pseudo-nitzschia and Fragilariopsis. On the basis of both the morphological and phylogenetic results, we conclude that P. americana can be assigned to Pseudo-nitzschia, following previous uncertainty as to whether it might belong to Nitzschia. Both P. americana and P. linea have been observed as epiphytes on other diatoms, which might indicate physiological differences from P. brasiliana, which has only been found free-living. In addition, P. americana and P. brasiliana differ with respect to valve width (transapical axis), the density of the transapical ribs (interstriae) and fibulae and the structure of the girdle bands (copulae). The results of the phylogenetic analyses and differences in distribution support these morphological differences. Pseudo-nitzschia linea differs with respect to valve shape, density of interstriae and structure of the girdle bands.

COCCONEIS SEDIMENTARIASP. NOV. (BACILLARIOPHYTA), A MARINE DIATOM FROM THE SOUTHEASTERN COASTAL WATERS OF THE PACIFIC OCEAN

Cocconeis sedimentaria sp. nov. usually occurs associated with SE Pacific bottom sediments but is also epiphytic on green macroalgae. The valves are frequently orbicular, 13-35 μm long and the transapical axis 10-27 μm wide. The sternum valve (or araphid valve) is only submarginally convex, depressed towards the margins and concave towards the sternum. The raphe-stemum valve (or raphid valve) is submarginally concave, elevated towards the sternum and the valvar margin. The raphe is straight and filiform and lies in a narrow sternum. The valvocopula is open at one end and bears fimbriae. Both valves have uniseriate striae. Morphological and structural relationships with similar taxa are discussed.

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

ABSTRACT 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.