Cingular Plates Research Articles

Are Protoperidinium knipowitschii from the Sea of Azov and the Western Mediterranean P. paulseni (Dinoflagellata: Peridiniales) Synonymous?

Thecal morphology and morphometry of the planktonic dinoflagellate Protoperidinium paulseni (Pavill.) Balech were studied in samples taken in the northwestern Black Sea (Odessa Bay). Using epifluorescence microscopy and SEM, data on the apical pore complex, apical intercalary, sulcal and cingular plates were obtained for the first time; the presence of the hypothecal pore in the 1”’ plate is also reported for the first time. The epitheca morphology was clarified (para 1’ and hexa 2a plates). Cells are 50.3-65.4 μm long and 38.5-52.4 μm wide (n=15). Light and scanning electron micrographs of the examined cells are presented. A comparison between the original descriptions and illustrations of P. paulseni, P. knipowitschii, our cells from Odessa Bay, as well as P. fatulipes and P. saltans (the species mentioned in the literature as morphologically similar to the former two), was made. The results showed that Protoperidinium knipowitschii (Usachev) Balech 1974 (basionym: Peridinium Knipowitschii Usachev 1927) described from the Sea of Azov can be considered synonymous to Protoperidinium Paulseni (Pavill.) Balech 1974 (basionym: Peridinium paulseni Pavill. 1909). Data on the geographical distribution of P. paulseni are provided.

New morphological data for two rare species of sand-dwelling marine dinoflagellates, Amphidiniella sedentaria and Pachena cf. leibnizii

Abstract Benthic dinoflagellates have been the subject of extensive taxonomic research in recent decades. Studies of morphologies of already known species of benthic dinoflagellates from various geographical populations remain relevant, as these allow elucidation of some details that were overlooked in the original species descriptions or assessment of their morphological variability. In the present study, two rare species of dinoflagellates, Amphidiniella sedentaria and Pachena cf. leibnizii, have been studied, for the first time, from coastal sands of the northwestern Sea of Japan. In the cells of A. sedentaria from the Sea of Japan, we have found two anterior intercalar plates instead of one. Therefore, the original formula has been changed to APC 4′ 2a 7″ 5c 4s 6‴ 2⁗. As a result of the examination of P. cf. leibnizii from the Sea of Japan, we have counted seven precingular plates and six cingular plates, instead of six and five, respectively, indicated in the original description. The plate formula of the cells of P. cf. leibnizii from the Sea of Japan is APC 4′ 3a 7″ 6c 5s 5‴ 2⁗. It is currently difficult to judge whether these differences are morphological variations. Therefore, we have identified these cells as P. cf. leibnizii.

Taxonomy and Molecular Phylogenetics of Ensiculiferaceae, fam. nov. (Peridiniales, Dinophyceae), with Consideration of their Life-history

In the current circumscription, the Thoracosphaeraceae comprise all dinophytes exhibiting calcified coccoid cells produced during their life-history. Species hitherto assigned to Ensiculifera and Pentapharsodinium are mostly based on the monadoid stage of life-history, while the link to the coccoid stage (occasionally treated taxonomically distinct) is not always resolved. We investigated the different life-history stages and DNA sequence data of Ensiculifera mexicana and other species occurring in samples collected from all over the world. Based on concatenated ribosomal RNA gene sequences Ensiculiferaceae represented a distinct peridinalean branch, which showed a distant relationship to other calcareous dinophytes. Both molecular and morphological data (particularly of the coccoid stage) revealed the presence of three distinct clades within Ensiculiferaceae, which may include other dinophytes exhibiting a parasitic life-history stage. At a higher taxonomic level, Ensiculiferaceae showed relationships to parasites and endosymbionts (i.e., Blastodinium and Zooxanthella) as well as to dinophytes harbouring diatoms instead of chloroplasts. These unexpected phylogenetic relationships are corroborated by the presence of five cingular plates in all such taxa, which differs from the six cingular plates of most other Thoracosphaeraceae. We herein describe Ensiculiferaceae, emend the descriptions of Ensiculifera and Pentapharsodinium, erect Matsuokaea and provide several new combinations at the species level.

Redefinition of the genus Thecadinium (Dinophyceae) using morphological and molecular data, and description of Thecadinium pseudokofoidii sp. nov.

ABSTRACTThe type of the polyphyletic genus Thecadinium, T. kofoidii, differs from other species of the genus in the position and number of thecal plates. We sequenced partial nuclear small subunit (SSU) and large subunit (LSU) rDNA and ITS-5.8S of two T. kofoidii ecotypes collected in winter and summer and compared molecular phylogenetic inferences with morphological observations. Molecular phylogenies based on SSU, LSU, and ITS-5.8S sequences, including sequences of summer and winter strains and those from GenBank, revealed two distinct Thecadinium lineages. The first contained two phylogroups: (1) winter strains together with Atlantic T. kofoidii from GenBank that showed obvious differentiation from (2) summer strains. The second lineage contained sequences of T. yashimaense and showed that species of the second lineage should be placed in a separate genus. Genetic differences between the winter and summer strains suggested that they are two different species: T. kofoidii and T. pseudokofoidii sp. nov. Morphologically, T. pseudokofoidii differed from T. kofoidii in number, size, and position of pores on the large lateral hypothecal plates. Thecadinium pseudokofoidii had about 28 to 48 (37 ± 4.2) pores (diameter: 0.31–0.76, 0.51 ± 0.08 µm) located mainly along the margins of large lateral plates; whereas T. kofoidii had about 24 to 72 (48 ± 11) pores (diameter: 0.22–0.49, 0.36 ± 0.06 µm) scattered over the entire surface of these plates. Moreover, cells of T. pseudokofoidii were 23–37 µm (31.2 ± 2.2) long and 19–32 µm (26.2 ± 2.3) deep and had a stronger ornamented theca, in particular cingular and third postcingular plates, compared to T. kofoidii cells that were 27–34 µm (30.7 ± 1.7) long and 21–27 µm (24.0 ± 1.5) deep and less ornamented. Both species had a unique feature: the right anterior sulcal plate contacted the Po plate. According to morphological and molecular data, Thecadinium was separated into two groups: Thecadinium sensu stricto including T. kofoidii and T. pseudokofoidii sp. nov., and Thecadinium sensu lato including the rest of the genus.

Transferring the freshwater dinoflagellate Peridinium wisconsinense (Dinophyceae) to the family Thoracosphaeraceae, with the description of Fusiperidinium gen. nov.

SUMMARYDistinctive spindle‐shaped thecae first described by Samuel Eddy in 1930 and assigned to the genus Peridinium Ehrenberg are commonly reported from freshwater environments in eastern North America. We demonstrate that thecae incubated from cysts of Peridinium wisconsinense Eddy have six cingular plates and a protuberant apical pore complex characteristic of the family Thoracosphaeraceae Schiller 1930 emend. Tangen in Tangen et al. 1982. Small subunit ribosomal DNA (SSU rDNA) and internal transcribed spacer (ITS) sequences confirm the close genetic similarity with Chimonodinium lomnickii (Wołoszyńska) Craveiro, Calado, Daugbjerg, Gert Hansen & Moestrup and with species recently reassigned to the genus Apocalathium Craveiro, Daugbjerg, Moestrup & Calado that was inferred from previously published LSU rDNA analysis of cysts of P. wisconsinense. Despite sharing identical tabulation with the thoracosphaeracean genera Chimonodinium Craveiro, Calado, Daugbjerg, Gert Hansen & Moestrup and Apocalathium, substantial morphological differences in the morphology of both the thecate and cyst stages of P. wisconsinense led us to reassign this species to the genus Fusiperidinium gen. nov. The phylogenetic position of Fusiperidinium wisconsinense comb. nov., inferred from concatenated data of SSU and LSU sequences, suggests that it evolved from the brackish Scrippsiella lineage, independently of the transition that produced the family Peridiniaceae. Cysts described as Geiselodinium tyonekensis Engelhardt from nonmarine strata from Alaska are apparently identical to the resistant cysts produced by F. wisconsinense. The palynologically‐constrained late Middle Miocene age for the Tyonek Formation provides a minimum age of 11.6 Ma for the evolution of this lineage, coinciding with a rapid glacioeustatic decline in sea level. Our findings also call into question the inclusion of the family Thoracosphaeraceae within the order Peridiniales Haeckel.

Further observations on Archaeosphaerodiniopsis verrucosa Rampi (Dinophyceae)

The recently rediscovered dinoflagellate genus Archaeosphaerodiniopsis Rampi emend. Carbonell-Moore has been found in material from different oceans to that from where it was rediscovered. In all cases the cells were identified as Archaeosphaerodiniopsis verrucosa. Scanning electron microscopy (SEM) observations of these recently identified cells permitted completion of its description. It was confirmed that all large epithecal plates (1''–5'') have one large pore surrounded by a larger ring, except for plate 1'', which has two of these pores. Plates 2''' and 4''' lack the large pores, while the other postcingular plates and the antapical plate display the same large pore and ring. The relative position of this pore and ring on the plate was the same regardless of the geographic location where the cell was found. What was thought to be a growth band between the apical pore area and the first precingular plate was determined to be a very small separate plate, bringing the total number of apical plates to five. The number of cingular plates was confirmed to be six. All the cells of A. verrucosa observed to date, including Rampi’s, display well-developed intercalary bands, similar to those found in peridinioids, though with an overlapping plate pattern more typical of gonyaulacoids, where only the overlapping plate develops the growth band. The number of plates in the epitheca and the tabulation pattern closely resembles that of a typical gonyaulacoid (except the apical pore area), while its hypotheca is more of a peridinioid. The overlapping plate pattern matches that described in the literature for gonyaulacoids and peridinioids. A. verrucosa may be found in the Mediterranean, Central Equatorial Pacific, Coral Sea and Western Indian Ocean, in either surface or deep water. Plate tabulation formula: Po, Pt, X, 5', 6'', 6C, 4S, 5''', 1''''.

Ultrastructure and molecular phylogenetic position of a new marine sand-dwelling dinoflagellate from British Columbia, Canada: Pseudadenoides polypyrenoides sp. nov. (Dinophyceae)

ABSTRACT Two monospecific genera of marine benthic dinoflagellates, Adenoides and Pseudadenoides, have unusual thecal tabulation patterns (lack of cingular plates in the former; and no precingular plates and a complete posterior intercalary plate series in the latter) and are thus difficult to place within a phylogenetic framework. Although both genera share morphological similarities, they have not formed sister taxa in previous molecular phylogenetic analyses. We discovered and characterized a new species of Pseudadenoides, P. polypyrenoides sp. nov., at both the ultrastructural and molecular phylogenetic levels. Molecular phylogenetic analyses of SSU and LSU rDNA sequences demonstrated a close relationship between P. polypyrenoides sp. nov. and Pseudadenoides kofoidii, and Adenoides and Pseudadenoides formed sister taxa in phylogenetic trees inferred from LSU rDNA sequences. Comparisons of morphological traits, such as the apical pore complex (APC), demonstrated similarities between Adenoides, Pseudadenoides and several planktonic genera (e.g. Heterocapsa, Azadinium and Amphidoma). Molecular phylogenetic analyses of SSU and LSU rDNA sequences also demonstrated an undescribed species within Adenoides.

Morphological and molecular characterization of the small armoured dinoflagellate Heterocapsa minima (Peridiniales, Dinophyceae)

The dinophycean genus Heterocapsa is of considerable interest as it contains a number of bloom-forming and/or harmful species. Fine structure of organic body scales is regarded as the most important morphological feature for species determination but currently is unknown for the species H. minima described by Pomroy 25 years ago. Availability of a culture of H. minima collected in the south-west of Ireland allowed us to provide important information for this species, including cell size, cell organelle location, thecal plate pattern, body scale fine structure and molecular phylogeny. Light microscopy revealed the presence of one reticulate chloroplast, an elongated centrally located nucleus, and the presence of one pyrenoid surrounded by a starch sheath. Scanning electron microscopy (SEM) of the thecal plate pattern indicated that Pomroy erroneously designated the narrow first cingular plate as a sulcal plate. In addition, SEM revealed as yet unreported details of the apical pore complex and uncommon ornamentations of hypothecal plates. Organic body scales of H. minima were about 400 nm in size, roundish, with a small central hole and one central, six peripheral and three radiating spines. They differ from other body scales described within this genus allowing for positive identification of H. minima. Heterocapsa minima shares gross cell morphological features (hyposome smaller than episome, elongated nucleus in the middle of the cell, one pyrenoid located in the episome on its left side) with H. arctica (both subspecies H. arctica subsp. arctica and H. arctica subsp. frigida), H. lanceolata and H. rotundata. These relationships are reflected in the phylogenetic trees based on LSU and ITS rDNA sequence data, which identified H. arctica (both subspecies), H. rotundata and H. lanceolata as close relatives of H. minima.

Description of the new heterotrophic dinoflagellate Stoeckeria changwonensis n. sp. from Korean coastal waters and emended description of the genus Stoeckeria and the type species Stoeckeria algicida

The planktonic heterotrophic dinoflagellate Stoeckeria changwonensis n. sp. isolated from the coastal waters off Korea is described from living and fixed cells by light, scanning electron (SEM), and transmission electron microscopy (TEM). For comparison with closely related species, the ultrastructure of Stoeckeria algicida, the only Stoeckeria species previously known, using TEM was also examined. Furthermore, DNA sequence data were collected from the small subunit (SSU), the D1–D3 large subunit (LSU), internal transcribed spacer regions (ITS1 and ITS2), and 5.8S of the ribosomal rDNA of S. changwonensis and compared to S. algicida. The SSU, ITS1-5.8S-ITS2, and the D1–D3 LSU rDNA sequences of the new dinoflagellate were ca. 2.2%, 16.8%, and 5.4% different, respectively, from those of S. algicida, but very similar to those of an unidentified dinoflagellate strain from Florida, USA, known as “Shepherd's Crook”. In the phylogenetic tree based on D1–D3 LSU rDNA sequences, S. changwonensis formed a clade with this unidentified strain, which was clearly divergent from a clade comprising S. algicida and another unidentified “Shepherd's Crook” strain. Morphological analysis showed that S. changwonensis had thin plates with a Kofoidian plate formula of Po, cp, X, 4′, 2a, 7″, PC, 6c, 5+s, 5‴, 0p, and 2″″, which conformed to the genus Stoeckeria. The size and overall shape of this dinoflagellate were similar to those of S. algicida. However, the size and position of each cingular plate relative to the surrounding plates in S. changwonensis were clearly different from those of S. algicida. The length of c2, c3, c4, c5, and c6 of S. changwonensis were similar, unlike in S. algicida, in which the lengths of c3 and c4 greatly exceeded that of c2, c5, and c6. In addition, plate c6 of S. changwonensis was sufficiently long to contact the 6″ plate, again in contrast with what happens in S. algicida. Using TEM, an eyespot in the sulcal areas of both Stoeckeria changwonensis and Stoeckeria algicida, which has not been seen in other species of the family Pfiesteriaceae was herein reported for the first time. On the basis of morphological and phylogenetic criteria, it is proposed that this is a new species of the genus Stoeckeria. In addition, the description of S. algicida has been emended to include previously unreported details regarding the relative size and position of the cingular plates, the presence of eyespots, and the ultrastructure of its cells examined using TEM.

New dinoflagellate species Protoperidinium haizhouense sp. nov. (Peridiniales, Dinophyceae), its cyst‐theca relationship and phylogenetic position within the Monovela group

SummaryThe number of cingular plates has been used to differentiate Protoperidinium from Peridinium and related genera. Protoperidinium is characterized by the presence of three cingular plates plus a transitional plate (3C+t). However, many Protoperidinium species have been described that exhibit different cingular plate tabulations. How these species should be classified within the genus remains unclear. To address this question, the phylogenetic relationship of four Protoperidinium species, with three or four cingular plates and lacking a transitional plate, were examined in relationship to other Protoperidinium species. These four species were germinated from cysts deposited in surface sediments collected from the East China Sea, the Bohai Sea and the Yellow Sea. Three of the isolated species, P. tricingulatum, P. americanum and P. parthenopes, were described previously. The fourth is here described as P. haizhouense sp. nov. with the plate formula Po, X, 4′, 3a, 7′′, 3C, 6S, 5′′′, 2′′′′. Differences in the cyst stages of these four species, which can be taxonomically informative, were compared. Partial large subunit ribosomal DNA sequences were obtained by single‐cell polymerase chain reaction. Maximum‐likelihood and Bayesian inference showed that these four species, P. fukuyoi and Islandinium minutum form a monophyletic clade with maximal support. The genus as a whole, however, appeared polyphyletic. Our results suggest that the presence/absence of a transitional plate is significant in the phylogeny of Protoperidinium.

Azadinium dalianense, a new dinoflagellate species from the Yellow Sea, China

Luo Z., Gu H., Krock B. and Tillmann U. 2013. Azadinium dalianense, a new dinoflagellate species from the Yellow Sea, China. Phycologia 52: 625–636. DOI: 10.2216/13-178.1The dinoflagellate genus Azadinium includes species with a plate formula of po, cp, X, 4′, 3a, 6′′, 6C, 5S, 6′′′, 2′′′′ and is part of the family Amphidomataceae with an uncertain order affiliation. Among six species, at least two produce azaspiracids (AZAs), a group of lipophilic toxins that accumulate in shellfish and can cause human health problems. Diversity within the genus might be underestimated at present due to its small size. In the present study, we searched for Azadinium by incubating freshly collected sediments from the Yellow Sea off China and succeeded in detecting a new species, here described as Azadinium dalianense sp. nov. It shared identical hypothecal, cingular and sulcal plates with the other Azadinium species, but it was unique in having only three apical and two anterior intercalary plates. Up to two stalked pyrenoids were present but their location in the cell varied. Phylogenetic analyses based on concatenated small-subunit, partial large-subunit, and internal transcribed spacer sequences revealed that A. dalianense was nested within Azadinium and formed a strongly supported clade with A. poporum. Liquid chromatography–mass spectrometry analyses did not detect any known AZAs.

Blowin' in the wind… 100 Ma old multi-staged dinoflagellate with sexual fusion trapped in amber: Marine–freshwater transition

Here we report the unexpected discovery of multi-staged dinoflagellates with organic cellular contents from a paralic habitat trapped in 100millionyear (100Ma) old amber. Amber formed from resin, a fluid medium, that trapped, then remarkably embedded and preserved soft parts of organisms usually destroyed by fossilization processes. We assume that the marine-costal dinoflagellates reached the sticky resin carried away by the wind, inside spray droplets. We answer to a fundamental question dealing with the Peridiniaceae: the paratabulation of Cretaceous cysts reflects the tabulation of Cretaceous thecae. We provide the first life cycle of the fossil record with evidence of cellulosic thecae, sexual fusion and zygote. We highlight an ancestral behaviour for the sexual phase: naked gametes complete fusion outside of gametic thecae, a process known in rare extant Peridinium species. The new taxon, Succiniperidinium inopinatum gen. et sp. nov., belongs to the Peridiniaceae and shares characters with extant marine-brackish Scrippsiella and two freshwater Peridinium clades identified by morphological characters (tabulation, cingular plates, ecdysis, plasmogamy) and molecular phylogenies. Understanding the processes of marine–freshwater transition in microbial lineages is a central goal in evolutionary ecology. Marine dinoflagellates passed through the osmotic barrier and the studies of marine-costal Cretaceous species help to understand the adaptation and the diversification of these species. We discuss the migration according to biological, paleontological and molecular phylogenies data and suggest that the freshwater colonization was the result of Cretaceous species adapted to costal habitats; their lineage isolated in ponds following the Cenozoic global sea-level fall passed through the osmotic barrier. A Scrippsiella-like group (i.e. Subtilisphaera terrula, Palaeoperidinium cretaceum and Succiniperidinium inopinatum gen. et sp. nov.) is suggested as intermediate species in the Peridinium freshwater colonization line.

Further investigations on the sand-dwelling genus Cabra (Dinophyceae, Peridiniales) in South Brittany (northwestern France), including the description of C. aremorica sp. nov.

Cabra is a genus of marine thecate sand-dwelling dinoflagellates that is poorly known and of which only two species are described, C. matta and C. reticulata. In one fixed sample collected in 2007 in South Brittany, both of these species were recorded, together with a new third one. Cells of the three taxa were isolated and their morphology was characterized using scanning electron microscopy. New features previously unseen in C. matta were observed including the presence of a dense group of pores on the first antapical plate and the existence of pores of two different size classes on thecal plates. Cabra aremorica sp. nov. is 37–40 µm long and 31–38 µm deep and possesses a thecal pattern very similar to the other species described in the genus. However, C. aremorica differs from them by its overall ornamentation consisting in shallow alveolae, its polyhedral shape, and its very atypical apical pore complex. Observations of the third cingular plate c3 on the three Cabra species revealed the presence of a narrow extension that lays vertically and borders the ‘x’ (5″) plate on the ventral side of cells, which appears to be a constant feature in the genus. This fact not previously reported is crucial for the interpretation of the plate pattern and is very peculiar among dinoflagellates.

Protoperidinium tricingulatum sp. nov. (Dinophyceae), a new motile form of a round, brown, and spiny dinoflagellate cyst

SUMMARYA small, broadly ovoidal and heterotrophic dinoflagellate containing round, brownish, and spiny cyst was found in the water column of Huibertsplaat in the Wadden Sea off the coast of the Netherlands. This dinoflagellate had these conspicuous morphological characters: a five‐sided first apical plate (1′), only three cingular plates, and an extremely small first antapical plate. Based on these morphological features, Protoperidinium tricingulatum Kawami, vanWezel, Koeman et Matsuoka is described as a new species. The flagellar pore of P. tricingulatum is covered with a small fin, which rises from the left side of the right sulcal plate to the large V‐shaped posterior sulcal plate. This feature suggests that P. tricingulatum is assigned to the Abé's Monovela Group. The cyst stage of P. tricingulatum was positively linked to the vegetative stage by comparison of the ribosomal 5.8S rDNA, internal transcribed spacers (ITS1 and ITS2). Living cysts of P. tricingulatum are round, brownish, and covered with many slender spines bearing capitate or cauliforate distal ends. The cyst also possesses a theropylic archeopyle formed by a slit corresponding to parasutures between three apical and two apical intercaraly plates. These morphological characters indicate that this species is morphologically related to two dinoflagellate cyst‐genera Islandinium and Echinidinium.

ULTRASTRUCTURE AND LSU rDNA-BASED REVISION OF PERIDINIUM GROUP PALATINUM (DINOPHYCEAE) WITH THE DESCRIPTION OF PALATINUS GEN. NOV.(1).

The name Peridinium palatinum Lauterborn currently designates a freshwater peridinioid with 13 epithecal and six cingular plates, and no apical pore complex. Freshwater dinoflagellate floras classify it in Peridinium group palatinum together with P.pseudolaeve M. Lefèvre. General ultrastructure, flagellar apparatus, and pusular components of P.palatinum were examined by serial section TEM and compared to P.cinctum (O. F. Müll.) Ehrenb. and Peridiniopsis borgei Lemmerm., respectively, types of Peridinium and Peridiniopsis. Partial LSU rDNA sequences from P.palatinum, P.pseudolaeve and several peridinioids, woloszynskioids, gymnodinioids, and other dinoflagellates were used for a phylogenetic analysis. General morphology and tabulation of taxa in group palatinum were characterized by SEM. Differences in plate numbers, affecting both the epitheca and the cingulum, combine with differences in plate ornamentation and a suite of internal cell features to suggest a generic-level distinction between Peridinium group palatinum and typical Peridinium. The branching pattern of the phylogenetic tree is compatible with this conclusion, although with low support from bootstrap values and posterior probabilities, as are sequence divergences estimated between species in group palatinum, and typical Peridinium and Peridiniopsis. Palatinus nov. gen. is proposed with the new combinations Palatinus apiculatus nov. comb. (type species; syn. Peridinium palatinum), P.apiculatus var. laevis nov. comb., and P.pseudolaevis nov. comb. Distinctive characters for Palatinus include a smooth or slightly granulate, but not areolate, plate surface, a large central pyrenoid penetrated by cytoplasmic channels and radiating into chloroplast lobes, and the presence of a peduncle-homologous microtubular strand. Palatinus cells exit the theca through the antapical-postcingular area.

Neoceratium gen. nov., a New Genus for All Marine Species Currently Assigned to Ceratium (Dinophyceae)

The dinoflagellate genus Ceratium contains marine and freshwater species. Freshwater species possess six cingular plates, thick plates in the concave ventral area and usually develop a third hypothecal horn. The marine Ceratium species (>62 species) possess five cingular plates and thin plates in the concave ventral area; a third hypothecal horn is atypical. Resting cysts, a common feature in the freshwater species, are unreported in marine species. We illustrate for the first time resting cysts in marine Ceratium species (C. furca and C. candelabrum). We obtained small subunit ribosomal RNA gene (SSU rDNA) sequences of 23 Ceratium species (more than one third of the total marine species described so far), with representatives of the four acknowledged subgenera. Phylogenetic analyses including the type species, the freshwater C. hirundinella, showed that the four available sequences of freshwater species formed a strongly supported subclade, very distant from the marine cluster. Our data support the splitting of Ceratium sensu lato into two genera. Ceratium sensu stricto should be reserved for freshwater species possessing six cingular plates (three cingular plates in dorsal view). The new genus name, Neoceratium gen. nov. should be applied to the marine species of Ceratium sensu lato that possess five cingular plates (two cingular plates in dorsal view).

Protoperidinium bolmonense sp. nov. (Peridiniales, Dinophyceae), a small dinoflagellate from a brackish hypereutrophic lagoon (South of France)

N. Chomérat and A. Couté. 2008. Protoperidinium bolmonense sp. nov. (Peridiniales, Dinophyceae), a small dinoflagellate from a brackish hypereutrophic lagoon (South of France). Phycologia 47: 392–403. DOI: 10.2216/07-82.1Described is a new Protoperidinium species from a brackish and hypereutrophic lagoon in the South of France, the Bolmon lagoon (‘Étang de Bolmon’). Protoperidinium bolmonense sp. nov. is a small dinoflagellate with a plate formula of Po, X, 4′, 3a, 7″, 3c, 4(?)s, 5‴ and 2″″. Its peculiar features are the presence of only three cingular plates, the marked extension of the second intercalary plate (2a) which abuts the second precingular plate (2″), the marked dorsoventral flattening and the shape of characteristic plates. Different variations of the epithecal plate pattern were observed in P. bolmonense population, involving the division or the fusion of pre-existing plates. Only one other Protoperidinium species, P. vorax, is known to possess only three cingular plates, but the thecal plate arrangement is not exactly the same. The relationship with other congeneric species and the position within the genus are discussed. From an ecological point of view, P. bolmonense was present in spring, in an oligo-mesohaline range of the salinity, which is not usual for Protoperidinium species. Because of the hypereutrophic conditions pertaining in the lagoon, the phytoplankton was abundant with dominant Planktothrix agardhii (cyanoprokaryota) and other autotrophic species. So, the latter might represent an important source of food for some marine heterotrophic dinoflagellates, especially those that can tolerate brackish water. In such environments, where large amounts of phytoplankton species are mixed, the identification of small dinoflagellates can be tedious. Scanning electron microscopy is very useful, and a simple method is described to isolate, prepare and observe a few dinoflagellate cells.

Morphology, ultrastructure and feeding behaviour of Protoperidinium vorax sp. nov. (Dinophyceae, Peridiniales)

Protoperidinium vorax sp. nov. is a small heterotrophic dinoflagellate with a plate formula of Po, X, 4′, 3a, 7′′, 3C, 5S, 5′′′, 0p, 2′′′′. P. vorax has an ortho-hexa thecal plate arrangement. Its peculiar features are the presence of only three cingular plates and the marked extension of the second intercalary plate (2a), which abuts the second precingular plate (2′′). TEM sections revealed the presence of a large sac pusule, several convoluted vesicular structures and electron-dense accumulation bodies scattered in the cell periphery. These accumulation bodies probably represent the Periodic Acid-Schiff (PAS) bodies, which fluoresce yellow–green under blue light excitation. P. vorax is a pallium feeder and was observed feeding on diatoms of different sizes. When fed with the chain-forming diatom Skeletonema pseudocostatum under non-limiting food concentrations, doubling rates up to 1.28 divisions d−1 were recorded. Ingestion rates of 35.95 cells dinoflagellate−1 h−1 and clearance rates of 18.34 µl dinoflagellate−1 h−1 were reached, the highest ever recorded for a small-sized dinoflagellate. These data support the hypothesis that small heterotrophic species might contribute to diatom bloom decay.

MORPHOLOGY AND ECOLOGY OF GLENO‐DINIUM ARMATUM LAVENDER (DINOPHYCEAE)

Faust, M. A.1 and Kuosa, H.2 1Department of Systematics Biology, NMNH, Smithsonian Institution, Suitland, MD 20746; 2Finnish Institute of marine Research, Helsinki, Finland FIN‐00931Light and scanning electron microscopy were used to examine the morphology of Glenodinium armatum Levander, a small armored dinoflagellate from the Tvärminne Archipelago, Baltic Sea, Finland. This species is an important dinoflagellate in coastal rock pools. Cells are small, ovate, and dorso‐ventrally flattened. The cell surface is rugose with small round pores. The plate tabulation is: Po, x, 4', 2a, 7'', 6C, 5S, 5''', 2''''. Two intercalary plates are hexagonal and adjacent. Epitheca conical and hypotheca round and two antapical spines are present. The cingulum wide, slightly displaced and descending, and comprised of six cingular plates. Sulcal platelets are five and do not reach the antapex. Often in the hypotheca, a red horseshoe‐shaped stigma is present. Large nucleus situated posteriorly. Chloroplast golden brown and discoid. We suggest that G. armatum is a valid species with clear differences to Peridinium umbonatum Stein (syn. P. inconspicuum Lemmermann), but that it has not been always correctly identified. A new emended description is presented.

TOWARD AN ASSESSMENT ON THE TAXONOMY OF DINOFLAGELLATES THAT PRODUCE CALCAREOUS CYSTS (CALCIODINELLOIDEAE, DINOPHYCEAE): A MORPHOLOGICAL AND MOLECULAR APPROACH

In recent years an unified classification system for both fossil cysts and extant dinoflagellate species has been proposed. This classification has prompted investigations aimed at testing the phylogenetic validity of the distinctive morphological characters of both vegetative cells and cysts. We have focused on a group of dinoflagellates that produce calcareous resting cysts, which are abundant in marine neritic and oceanic waters and form wide fossil deposits. Extant species are included in the genera Scrippsiella, Ensiculifera, and “Pentapharsodinium” (subfamily Calciodinelloideae), which are distinguished by the number and/or shape of the cingular plates of their planktonic vegetative stages. On the other hand, the classification of fossil cysts is based on the morphology of the calcareous covering and on the orientation of crystals. In this study we combine the information derived from morphological traits of both motile stages and cysts with that obtained from nucleotide sequence analysis of the ribosomal DNA internal transcribed spacers (ITS). We also describe the vegetative cell produced by the calcareous cyst Calcigonellum infula and a new variety, Scrippsiella trochoidea var. aciculifera var. nov. Molecular analyses confirm the monophyletic origin of the genus Scrippsiella, whereas the “Pentapharsodinium” and Ensiculifera species are grouped together in another monophyletic cluster. The coupled morphological and molecular approach supports the taxonomic value of some of the characters of the planktonic stage, such as the cingular plate number. On the other hand, it questions the validity of other morphological characters of both vegetative and encysted stages. Our data provide a phylogenetic classification of these dinoflagellates; however, they also open a debate that would imply a redefinition of the characters to be used for the circumscription of the subfamily Calciodinelloideae.