Thecal Pores Research Articles

Prorocentrum canariense sp. nov., a case of pseudo-cryptic speciation in the cosmopolitan dinoflagellate P. compressum (Prorocentrales, Dinophyceae).

The planktonic dinoflagellate Prorocentrum compressum is widespread in warm and temperate seas. A strain identified as P. cf. compressum BEA 0681B isolated from the island of Gran Canaria, NE Atlantic Ocean, showed a divergence in rDNA/ITS phylogenies with respect to P. compressum. The Canarian strain was oval, with an average length-to-width ratio of 1.35, smooth thecal surface with less than 150 thecal pores, including oblique pores, sometimes with a bifurcated opening. In contrast, P. compressum was rounder, with a length-to-width ratio < 1.2, with reticulate-foveate ornamentation and 200-300 pores per valve. We propose Prorocentrum canariense sp. nov. These species clustered as the most early-branching lineage in the clade Prorocentrum sensu stricto. Although this clade mainly contains planktonic species, the closer relatives were the benthic species P. tsawwassenense and P. elegans. Interestingly, P. compressum and P. canariense sp. nov. are widely distributed in temperate and warm seas without an apparent morphological adaptation to planktonic life. The formation of two concentric hyaline mucilaginous walls could contribute to this success. We discuss the use of Prorocentrum bidens to solve the nomenclature issue of P. compressum that was described citing a diatom as basionym.

Morphological and Phylogenetic Characterisation of Prorocentrum spinulentum, sp. nov. (Prorocentrales, Dinophyceae), a Small Spiny Species from the North Atlantic

Prorocentrum comprises dinophytes with several unique traits, including the presence of two large thecal plates and apical insertion of flagella. Species delimitation for many small and similar planktonic species is challenging, as SEM analyses and DNA sequence information of type material are rarely available. Based on a strain from the North Atlantic Prorocentrum spinulentum, sp. nov. is described here. Cells were small (9.0-12.8 µm long, 8.5-11.9 µm deep), oval to almost round in lateral view and moderately compressed. The ovoid nucleus was in median or slightly sub-median position on the cells ventral side. The plate surface appeared spiny in light microscopy with thecal pores visible in empty thecae. Electron microscopy revealed plates densely covered by relatively long spines and two size classes of thecal pores. The periflagellar area consisted of 8 platelets, and there was a prominent wing (ca. 1 µm wide and long) on platelet 1. The new species is distinct in DNA trees and embedded in the Prorocentrum shikokuense species group. It differs from the protologues of other small species of Prorocentrum by the unique combination of cell size and shape, the presence of long spines on the thecal plate surface and scattered thecal pores. The thorough morphological description of this species, representing a previously uncharacterised lineage within Prorocentrum, increases and improves our knowledge of the diversity within this important group of planktonic organisms.

Prorocentrum pervagatum sp. nov. (Prorocentrales, Dinophyceae): A new, small, planktonic species with a global distribution

SUMMARYProrocentrum comprises a unique group of dinophytes with several apomorphic traits, such as an apical insertion of flagella and the presence of two major, large thecal plates. Species delimitation is challenging, especially for morphologically very similar, small planktonic species. Contemporary analyses, including SEM studies and molecular phylogenetics of type material, are not available for many described species. Based on six strains isolated from Antarctic, subarctic and North Atlantic waters, Prorocentrum pervagatum sp. nov. is described. Prorocentrum pervagatum was small (12–16 μm long and deep), oval to round in outline, and moderately compressed. One small, pyrenoid‐like structure was faintly visible in some cells. Rod‐like, long trichocysts were present. Cells had one distinct apical spine (1.1–1.7 μm in length) visible in light microscopy. The plate surface appeared smooth in light microscopy with few pores located close to the plate margin visible in empty thecae. Electron microscopy revealed plates to be densely covered by small projections and two size classes of thecal pores. Cells had a row of mostly four large pores in apical‐ventral position on the right thecal plate. The periflagellar area consisted of eight small platelets. The apical spine was formed by platelet six. In molecular phylogenetics, P. pervagatum was part of a species group generally exhibiting small size and spiny thecal ornamentation, together with Prorocentrum cordatum and Prorocentrum obtusidens. The new species is distinct in DNA trees and differs from the protologues of other small species of Prorocentrum by the unique combination of size, shape (i.e. only moderately compressed or round), presence of a distinct apical spine, and position of thecal pores (i.e. located at the plate margins only). Its clear description and illustration may stimulate similar work of other small species of Prorocentrum, particularly including the re‐investigation of taxa with historical names collected at the corresponding type localities.

Two toxigenic Ostreopsis species, O. cf. ovata and O. siamensis (Dinophyceae), from the South China Sea, tropical Western Pacific

In the dinophyte genus Ostreopsis, seven out of 11 described species are known to produce various toxic compounds that were characterized in the palytoxins family. Species in the genus shared identical thecal plate patterns but differed in size, shape, and thecal plate ornamentation. Two species, O. cf. ovata and O. siamensis, have been reported from the Western Pacific, but information on toxin production is scarce. Here, we established nine strains of Ostreopsis from six localities in the South China Sea (SCS), covering the Gulf of Thailand, northern SCS (Hainan Island, Beibu Bay), and southern SCS (Peninsular Malaysia). Their morphology was examined by light and electron microscopy and the molecular phylogeny was inferred based on the LSU rDNA (D1-D3) and ITS rDNA sequences using maximum likelihood and Bayesian inference. Both O. cf. ovata and O. siamensis, albeit morphologically closely related, can be distinguished by a feature of the thecal pores with pronounced ridges in the latter. Molecular data further supported their species identity. Toxin production in the strains was examined by LC-MS/MS. O. cf. ovata strain T5PRBost02 was observed to produce Ovatoxin-k and Ovatoxin-j2 only; while Ostreocin-B and Ostreocin-D was produced by O. siamensis strain T10PRBost04. This is the first report confirming the production of palytoxins analogs in Ostreopsis species from the region.

A new potentially toxic dinoflagellate Fukuyoa koreansis sp. nov. (Gonyaulacales, Dinophyceae) from Korean coastal waters: Morphology, phylogeny, and effects of temperature and salinity on growth

To clarify an unspecified toxic Gambierdiscus-like species isolated from seawaters off Jeju Island, Korea, its morphology and molecular phylogeny based on the small subunit (SSU) and partial large subunit (LSU) rRNA gene sequences were examined. Cells were narrow in ventral view and broad in lateral view with a smooth surface. The round thecal pores were evenly distributed, with an average diameter of 0.41 µm. Cell depth, width and height were 51.7 ± 4.5 μm, 43.0 ± 4.2 μm and 55.0 ± 4.7 μm, respectively, and depth-to-width (D/W) and height-to-width (H/W) ratios were 1.1 ± 0.2 μm and 1.3 ± 0.02 μm, respectively. The nucleus was located in the hypotheca. Scanning electron microscope observations revealed that the cells displayed a plate formula of Po, 4′, 6′′, 6c, 6s, 5′′′ and 2′′′, and transmission electron microscope observation demonstrated that the cells contained crystal-like particles. Morphological features indicated that the unspecified Korean isolate belonged to the genus Fukuyoa, and based on the H/W and D/W ratios, the apical pore H/W ratio and thecal pore size, it could be differentiated from other Fukuyoa species. The phylogenetic analyses based on the SSU and LSU rRNA sequences revealed that the Korean isolate was nested within the genus Fukuyoa with high support, and it grouped with F. cf. yasumotoi isolated from Japan. Based on the morpho-molecular data, a new species, Fukuyoa koreansis sp. nov. is proposed. The maximum growth rate (0.254 d−1) of F. koreansis was observed at 25°C and a salinity of 25. The required levels of temperature and salinity for growth distinguished Fukuyoa koreansis from Gambierdiscus species.

Taxonomy and toxicity of a bloom-forming Ostreopsis species (Dinophyceae, Gonyaulacales) in Tahiti island (South Pacific Ocean): one step further towards resolving the identity of O. siamensis.

Among dinoflagellates responsible for benthic harmful algal blooms, the genus Ostreopsis primarily described from tropical areas has been increasingly reported from subtropical and temperate areas worldwide. Several species of this toxigenic genus produce analogs of palytoxin, thus representing a major threat to human and environmental health. The taxonomy of several species needs to be clarified as it was based mostly on morphological descriptions leading in some cases to ambiguous interpretations and misidentifications. The present study aims at reporting a benthic bloom that occurred in April 2019 in Tahiti island, French Polynesia. A complete taxonomic investigation of the blooming Ostreopsis species was realized using light, epifluorescence and field emission electron microscopy and phylogenetic analyses inferred from LSU rDNA and ITS–5.8S rDNA regions. Toxicity of a natural sample and strains isolated from the bloom was assessed using both neuroblastoma cell-based assay and LC-MS/MS analyses. Morphological observations showed that cells were round to oval, large, 58.0–82.5 µm deep (dorso-ventral length) and 45.7–61.2 µm wide. The cingulum was conspicuously undulated, forming a ‘V’ in ventral view. Thecal plates possessed large pores in depressions, with a collar rim. Detailed observation also revealed the presence of small thecal pores invisible in LM. Phylogenetic analyses were congruent and all sequences clustered within the genotype Ostreopsis sp. 6, in a subclade closely related to sequences from the Gulf of Thailand and Malaysia. No toxicity was found on the field sample but all the strains isolated from the bloom were found to be cytotoxic and produced ostreocin D, a lower amount of ostreocins A and B and putatively other compounds. Phylogenetic data demonstrate the presence of this species in the Gulf of Thailand, at the type locality of O. siamensis, and morphological data are congruent with the original description and support this identification.

Amphidomataceae (Dinophyceae) in the western Greenland area, including description of Azadinium perforatum sp. nov.

ABSTRACTAzaspiracids (AZA) are lipophilic marine biotoxins associated with shellfish poisoning which are produced by some species of Amphidomataceae. Diversity and global biogeography of this family are still poorly known. In summer 2017 plankton samples were collected from the central Labrador Sea and western Greenland coast from 64° N (Gothaab Fjord) to 75° N for the presence of Amphidomataceae and AZA. In the central Labrador Sea, light microscopy revealed small Azadinium-like cells (9200 cells l−1). Clonal strains established from plankton samples and scanning electron microscopy of fixed plankton samples revealed at least eight species of Amphidomataceae: Azadinium obesum, Az. trinitatum, Az. dexteroporum, Az. spinosum, Az. polongum, Amphidoma languida, Azadinium spec., and a new species described here as Azadinium perforatum sp. nov. The new species differed from other Azadinium species by the presence of thecal pores on the pore plate. All samples, including cultured strains, filtered seawater samples, and solid phase adsorption toxin tracking (SPATT) samplers deployed during the expedition in a continuous water-sampling system (FerryBox), were negative for AZA. DNA samples and PCR assays were positive for Amphidomataceae from most stations, whereas species-specific assays for three toxigenic species were rarely positive (two stations for Az. poporum, one station for Am. languida). The results highlight the presence of Amphidomataceae in the area but the lack of toxins and low abundance of toxigenic species currently indicate a low risk of toxic Amphidomataceae blooms in Arctic coastal waters.

First report on okadaic acid production of a benthic dinoflagellate Prorocentrum cf. fukuyoi from Japan

SUMMARYThe consumption of bivalves contaminated with diarrhetic shellfish toxins (DSTs) such as okadaic acid and dinophysistoxins has caused serious economic hardship to shellfish industries worldwide including Japan. Several benthic species of the genus Prorocentrum have been confirmed to produce DSTs. There have been no published studies of Japanese strains of Prorocentrum species that include a three‐way characterization of morphological characteristics, molecular phylogenetic data, and toxin profiles. In the present study, a benthic Prorocentrum strain isolated from Japanese temperate shallow water (depths &lt; 3 m) was characterized using morphological, phylogenetic, and toxicological methods. Cell size of the Japanese Prorocentrum strain KSK4P was 27.2 ± 1.3 μm in length, 22.4 ± 0.9 μm in width, and had a length‐to‐width ratio of 1.22 ± 0.04. The thecal surface was smooth and covered with large and small thecal pores lying in rows, and the pores were lacking in the central area of the theca. The right theca had a deeply excavated periflagellar area that was narrow V‐shaped. Nine platelets and two wings were in the periflagellar area. These morphological features of the strain KSK4P are similar to those of P. fukuyoi. Phylogenetic trees based on the LSU rDNA D1/D3 sequences revealed that the strain KSK4P forms a new subclade F2f belonging to P. fukuyoi complex (subclade F2). The sequence analysis revealed that the strain KSK4P (subclade F2f) diverges from a subclade F2e to which the strain used for the description of P. fukuyoi belongs. Based on the results of morphological and phylogenetic analyses of the strain KSK4P, the strain was designated as P. cf. fukuyoi. The results of the LC/MS/MS analysis revealed that the strain KSK4P produced okadaic acid (1.5–2.7 fg cell−1). This is the first report that a strain belonging to the P. fukuyoi complex can produce okadaic acid.

Reliable determination of Prorocentrum micans Ehrenb. (Prorocentrales, Dinophyceae) based on newly collected material from the type locality

ABSTRACT The Prorocentrales are a unique group of dinophytes based on several apomorphic traits, but species delimitation is challenging within the group. The type species of Prorocentrum, namely P. micans, cannot be determined unambiguously, as important characters are not preserved in the original material collected in the first half of the 19th century. Water samples were taken at the type locality of P. micans in the Baltic Sea off Kiel (Germany) and strains with a morphology consistent with the protologue were established. An in-depth morphological analysis was performed, illustrating minute traits such as the periflagellar platelets and three different types of thecal pores. rRNA sequence data allowed for molecular characterization of the species. The newly collected material of P. micans was used for epitypification with the result that the type species of Prorocentrum can now be determined unambiguously.

Occurrence of Ostreopsis lenticularis (Dinophyceae: Gonyaulacales) from the Archipiélago de Revillagigedo, Mexican Pacific

From December 2016 to May 2017, 22 phytoplankton surface samples were collected with a 20-μm mesh net at three islands of the Archipiélago de Revillagigedo (Partida, Socorro and San Benedicto), Mexican Pacific. The sites depth was approximately 20–80 m; the surface water temperature was 21–27 °C. The potentially toxic benthic dinoflagellate Ostreopsis lenticularis was present in all the samples. Cells had a lenticular to broadly oval shape, 65–100 μm long and 50–80 μm wide. The taxonomy of the genus Ostreopsis has been unclear due to equivocal ascribing some taxonomic features among species. The identification of specimens from the archipelago was made based on the most important taxonomic characteristics: the thecal plates, the presence of two types of thecal pores (larger and smaller), and the lack of cingulum undulation. The studied cells are compared with O. cf. siamensis, O. labens and O. marina. This is the first record of the species in the archipelago waters.

Morphology and molecular phylogeny of Ostreopsis cf. ovata and O. lenticularis (Dinophyceae) from Hainan Island, South China Sea

SUMMARYThe genus Ostreopsis contains benthic and potentially toxic species that are distributed in tropical and temperate regions. In this study, we present the first report of observations of Ostreopsis cf. ovata and O. lenticularis in Chinese waters. Isolates were characterized morphologically based on LM and SEM, and phylogenetic analyses were conducted by sequencing the LSU rDNA (D1–D3), ITS region (ITS1‐5.8S‐ITS2) and SSU rDNA. The morphology of O. cf. ovata Hainan strains was similar to the original description of O. ovata, despite differences in cell size. The morphology of O. lenticularis Hainan strains was similar to the original description, although both deviations of cell dimensions and different kinds of thecal pores were observed. The plate formula for the Ostreopsis Hainan strains was arranged in Kofoid's system tabulation of Po, 3′, 7′′, Vp, Rp, 1p, 5′′′, 2′′′′. The O. cf. ovata and O. lenticularis Hainan strains showed close relationships with strains collected from the Pacific Ocean based on the sequences of both LSU rDNA and ITS region. The genetic differences (p‐distances) of SSU rDNA sequences of the Ostreopsis cf. ovata Hainan strain were 0.0096 and 0.0447 different from those of a Malaysian strain and a South Korean strain, respectively. This work identifies the first occurrence of Ostreopsis with the morphology and phylogeny of Hainan strains in Chinese waters.

Ostreopsis fattorussoi sp. nov. (Dinophyceae), a new benthic toxic Ostreopsis species from the eastern Mediterranean Sea.

The new benthic toxic dinoflagellate, Ostreopsis fattorussoi sp. nov., is described from the Eastern Mediterranean Sea, Lebanon and Cyprus coasts, and is supported by morphological and molecular data. The plate formula, Po, 3', 7″, 6c, 7s, 5‴, 2'''', is typical for the Ostreopsis genus. It differs from all other Ostreopsis species in that (i) the curved suture between plates 1' and 3' makes them approximately hexagonal, (ii) the 1' plate lies in the left half of the epitheca and is obliquely orientated leading to a characteristic shape of plate 6″. The round thecal pores are bigger than the other two Mediterranean species (O. cf. ovata and O. cf. siamensis). O.fattorussoi is among the smallest species of the genus (DV: 60.07±5.63μm, AP: 25.66±2.97μm, W: 39.81±5.05μm) along with O.ovata. Phylogenetic analyses based on the LSU and internal transcribed spacer rDNA shows that O.fattorussoi belongs to the Atlantic/Mediterranean Ostreopsis spp. clade separated from the other Ostreopsis species. Ostreopsisfattorussoi produces OVTX-a and structural isomers OVTX-d and -e, O. cf. ovata is the only other species of this genus known to produce these toxins. The Lebanese O.fattorussoi did not produce the new palytoxin-like compounds (ovatoxin-i, ovatoxin-j1 , ovatoxin-j2 , and ovatoxin-k) that were previously found in O.fattorussoi from Cyprus. The toxin content was in the range of 0.28-0.94pg·cell-1 . On the Lebanon coast, O.fattorussoi was recorded throughout the year 2015 (temperature range 18°C-31.5°C), with peaks in June and August.

Alexandrium diversaporum sp. nov., a new non-saxitoxin producing species: Phylogeny, morphology and sxtA genes

Species of the PST producing planktonic marine dinoflagellate genus Alexandrium have been intensively scrutinised, and it is therefore surprising that new taxa can still be found. Here we report a new species, Alexandrium diversaporum nov. sp., isolated from spherical cysts found at two sites in Tasmania, Australia. This species differs in its morphology from all previously reported Alexandrium species, possessing a unique combination of morphological features: the presence of 2 size classes of thecal pores on the cell surface, a medium cell size, the size and shape of the 6″, 1′, 2⁗ and Sp plates, the lack of a ventral pore, a lack of anterior and posterior connecting pores, and a lack of chain formation. We determined the relationship of the two strains to other species of Alexandrium based on an alignment of concatenated SSU-ITS1, 5.8S, ITS2 and partial LSU ribosomal RNA sequences, and found A. diversaporum to be a sister group to Alexandrium leei with high support. A. leei shares several morphological features, including the relative size and shapes of the 6″, 1′, 2⁗ and Sp plates and the fact that some strains of A. leei have two size classes of thecal pores. We examined A. diversaporum strains for saxitoxin production and found them to be non-toxic. The species lacked sequences for the domain A4 of sxtA, as has been previously found for non-saxitoxin producing species of Alexandrium.

Ostreopsis cf. siamensis and Ostreopsis cf. ovata from the Atlantic Iberian Peninsula: Morphological and phylogenetic characterization

Individuals of Ostreopsis, a genus containing potentially toxic species which affects human health, were collected during summer-autumn 2010 and 2011 from 17 sites located along the Atlantic coast of the Iberian Peninsula, a temperate area which during summer presents contrasting seawater temperatures. Ostreopsis cells were obtained by shaking macroalgae collected from rocky-shore areas bordering accessible beaches. Isolated strains and field samples were analyzed for morphological and phylogenetic characterization where sequences of the ITS1-5.8S-ITS2 region of the rDNA delineated two different species fitting Ostreopsis cf. ovata and Ostreopsis cf. siamensis. By means of calcofluor staining and scanning electron microscopy, it was observed that field samples of both species exhibited a wide and overlapping range of dorsoventral as well as width values. Those cells presented 11–18 pores/100μm2 and were also similar concerning plates shape and size. The main differential feature between the two species was the presence of two sizes of thecal pores (0.07–0.13μm and 0.15–0.39μm) in Ostreopsis cf. siamensis and one size (0.24–0.56μm) in Ostreopsis cf. ovata. A comparison of field vs. cultured cells indicated that field isolates presented larger cells than in culture.

First occurrence of the genus Ostreopsis (Dinophyceae) in the Sea of Japan

Abstract Preliminary studies on dinoflagellates epiphytic on macrophytes in a bight of Peter the Great Bay, Sea of Japan revealed the presence of two species of the genus Ostreopsis, O. cf. ovata and O. cf. siamensis. Morphometric features, such as the length of the pore plate, and thecal ornamentations were used for species identification. The two species differed from each other in cell size and the length of the pore plate. Cells of O. cf. ovata were smaller in length and width, with a dorsoventral diameter of 36–60 μm and a width of 24–45 μm, in comparison with the cells of O. cf. siamensis, which were 63–78 μm in dorsoventral diameter and 36–54 μm in width. Cells of O. cf. siamensis are slightly flattened in comparison with O. cf. ovata; the dorsoventral to anteroposterior diameter ratio varied from 1.9 to 2.7 for O. cf. ovata and from 1.8 to 3.5 for O. cf. siamensis. The length of the pore plate in O. cf. ovata (6.3–8.3 μm) is shorter than that in O. cf. siamensis (11–13 μm), while the diameter of the thecal pores in O. cf. ovata and O. cf. siamensis overlapped markedly (0.12–0.25 μm and 0.16–0.20 μm, respectively). The two species were present from August to October at water temperatures of 7–25°C on almost all macrophytes collected. The maximum abundance of Ostreopsis spp. reached 10,970 cells g-1 dry weight in late September at a water temperature of 9°C. This is the first occurrence of the genus Ostreopsis in Russian waters, which are characterized by cold temperatures during the winter season.

LONG STALKED EOCRINOIDS IN THE BASAL MIDDLE CAMBRIAN KAILI BIOTA, TAIJIANG COUNTY, GUIZHOU PROVINCE, CHINA

Long-stemmed eocrinoids are limited to two species in the basal Middle Cambrian Kaili Biota, which occupies the middle portion of the Kaili Formation, Taijiang County, Guizhou Province, China. The Kaili Biota contains preserved soft-bodied organisms shared with either the Chengjiang Fauna (Southwest China) or the Burgess Shale Fauna (British Columbia) or with both. Echinoderms are preserved as limonitic external molds that produce excellent latex casts. Sinoeocrinus lui Zhao et al., 1994 has a complex ontogenetic development, which is described in terms of morphology of holdfast, number of thecal plate circlets, addition and morphology of thecal pores, ambulacral arrangement, and number of brachioles relative to thecal height. Because of the complex ontogeny the following species are now seen to be synonymous with S. lui: S. curtobrachiolus Zhao et al.,1994; S. lepidus Zhao et al., 1994; S. longus Zhao et al., 1994; S. minus Zhao et al., 1994; Paragogia globosa Zhao et al., 1994; and Curtoeocrinus guizhouensis Zhao et al., 1994. A second and rare eocrinoid of undetermined familial and ordinal placement, Balangicystis rotundus n. gen. and sp., has an unusually long holdfast and poreless thecal plates with prominent radial ridges. Sinoeocrinus lui and Balangicystis rotundus inhabited the outer shelf in disaerobic fine-grained shales and mudstones. Megascopic infauna in their community is not present.

Morphology of Prorocentrum minimum (Dinophyceae) in the Baltic Sea and in Chesapeake Bay: Comparison of Cell Shapes and Thecal Ornamentation

Prorocentrum minimum (Dinophyceae) is a red tide-forming toxin-producing planktonic microalga from coastal waters worldwide. In this study, the morphology of natural and cultured populations of P. minimum was examined to investigate whether the species can be split morphologically into more species. The diacritical features of cell shape and size, ornamentation of thecal plates, and architecture of the apical pore area and intercalary band were studied from scanning and light micrographs. Cell size of P. minimum is similar in Baltic Sea samples and a culture from the Chesapeake Bay, USA. Cell shape varies from triangular to oval-round including intermediate forms in valve view. The thecal surface is covered by evenly distributed short spines, while the circular thecal pores are mainly situated near the valve margin. The intercalary band is rim-like, striated and covered with short evenly distributed spines. The architecture of the apical pore area is ornate and more complex than previously pointed out. It is V-shaped, located on the right valve in a shallow depression and accommodates a large elongated flagellar pore, and a small round auxiliary pore. Four distinct apical features are present: next to the auxiliary pore there is a curved collar, and adjacent to the flagellar pore arise a forked double tooth, a short single tooth, and a ridged edge near the left valve margin. Our study suggests that the ornamentation of the apical pore area of P minimum is independent of cell shape or growth place, and it is considered a stable morphological character of this cosmopolitan morphospecies.

Prorocentrum nux sp. nov. (Dinophyceae), a small planktonic dinoflagellate from the Mediterranean Sea, and discussion of P. nanum and P. pusillum

A new Prorocentrum species was discovered in the Gulf of Naples (Mediterranean Sea) and is described in the present study as P. nux Puigserver & Zingone sp. nov. Prorocentrum nux is small (6.3–9.0 μm long, 5.3–10.0 μm wide, and 5.3–10.7 μm deep), irregularly oval in valve view, and lacks an apical spine. Unlike most Prorocentrum species, its cells are not laterally compressed, owing to the marked convexity of the valves and to the overgrowth of the intercalary bands. The thecal plates are thin and smooth, with a few pores of two different sizes near the valve margins. Seven platelets are arranged around the flagellar pore. Two parietal chloroplasts are present, each having a pyrenoid without a visible starch shield. The nucleus is located posteriorly. A pusule is present close to the flagellar bases. Numerous trichocysts were observed both within the cell and discharged outside it. In the genus Prorocentrum, two other small-celled species have been described, viz. P. nanum and P. pusilium; the latter has sometimes been considered a synonym of the former. However, based on their original descriptions and on other published information, P. nanum and P. pusillum are quite distinct from each other and from P. nux, with respect to cell shape, and the size and location of the thecal pores. Unlike P. nux, both P. nanum and P. pusillum are described as having a thick theca and a laterally flattened cell body. We reexamined the only existing culture material classified as P. nanum, viz. UTEX LB 1008, derived from the Plymouth 184 strain and originally identified as Exuviaella pusilla. This material has consistently been misidentifiedand has the same distinctive characters as P. nux.

Origin and phylogeny of Guyniidae (Scleractinia) in the light of microstructural data

The set of skeletal characters of the Recent azooxanthellate coral Guynia annulata Duncan, 1872 is unique among extant scleractinians and encompasses: (a) undifferentiated septal calcification centers (in most extant scleractinians calcification centers are clearly separated); (b) completely smooth septal faces (septa of almost all extant scleractinians bear granular ornamentation); (c) deeply recessed septa in respect to the epithecal rim in the adult coralla (in adults of the majority of extant scleractinians the relationships between septa and wall are the reverse); and (d) an aseptal part of the initial ontogenetic stage, just above the basal plate (almost all known scleractinians have a septate initial coralla). Skeletal features of five other extant traditional guyniids are typical of other caryophylliines (and of Scleractinia). However, the wall types present in different species of traditional guyniids exceed limits traditionally attributed to one caryophylliine family: i.e., Stenocyathus and Truncatoguynia have a marginothecal wall like the Flabellidae, whereas Schizocyathus and Temnotrochus usually have an entirely epithecal wall, as in Gardineriidae (Volzeioidea). Moreover, Pourtalocyathus and Schizocyathus show intraspecific variation in distribution of septal calcification centers (separated vs. non-separated) and in wall types (epithecal vs. consisting of large spherulite-like bodies). These major differences in skeletal architecture form the basis for a new, threefold taxonomical subdivision of the traditional guyniids: (1) Guyniidae Hickson, 1910, containing only monospecific Guynia with an epithecal wall, and septa with non-separated calcification centers; (2) Schizocyathidae fam.n., groups Microsmilia Schizocyathus, Pourtalocyathus, Temnotrochus, which have an epithecal wall and septa with usually well-separated calcification centers; and (3) Stenocyathidae fam.n. with Stenocyathus and Truncatoguynia which have a marginothecal wall and septa with well-separated calcification centers. Despite differences in the basic architecture of the skeleton, all taxa attributed to these families have ‘thecal pores’ formed by selective dissolution of the skeleton. I propose two hypotheses for evolutionary relationships among Guyniidae, Schizocyathidae, and Stenocyathidae: (1) Hypothesis A: the three families are not phylogenetically related and ‘pores’ originated independently in different scleractinian lineages: e.g., Guyniidae may represent distant zardinophyllid or gigantostyliid descendants, Schizocyathidae may be a volzeioid offshoot, whereas Stenocyathidae may be a flabellid descendant; (2) Hypothesis B: the three families are phylogenetically related and ‘thecal pores’ are synapomorphic for the clade (superfamily Guynioidea). Additional approaches, such as anatomical observations, molecular studies on guyniid DNA sequences, and in-depth studies on scleractinian biomineralization will be necessary to test these hypotheses.

Reinstatement of the genus Exuviaella (Dinophyceae, Prorocentrophycidae) and an assessment of Prorocentrum lima

Arguments are presented for splitting the genus Prorocentrum (sensu Dodge) by reinstating the genus Exuviaella Cienkowski defined by Exuviaella marina Cienkowski. The reason for making this separation is that new information has become available for species included in Exuviaella and Prorocentrum. Species of Exuviaella are relatively large marine prorocentroids, primarily benthic in habit. There is no obvious apical spine or tooth and thecal spines are absent. Thecal pores are associated with mucocysts, and species of Exuviaella elaborate complex polyether secondary metabolites (DSP-type toxins) that are unknown in other prorocentroids. Recent molecular phylogenetic data strongly support a separation of genera. In addition to Exuviaella lima (as Prorocentrum lima sensu Dodge), two other species, Prorocentrum maculosum M.A. Faust and Prorocentrum hoffmannianum M.A. Faust, are transferred to Exuviaella. This genus may contain additional species described in Prorocentrum, but further information is required before transfers can be made.