The morphology of strains of Skeletonema Greville emend Sarno et Zingone was examined in LM, TEM, and SEM and compared with sequence data from nuclear small subunit rDNA and partial large subunit rDNA. Eight distinct entities were identified, of which four were known: S. menzelii Guillard, Carpenter et Reimann; S. pseudocostatum Medlin emend. Zingone et Sarno; S. subsalsum (Cleve) Bethge; and S. tropicum Cleve. The other four species were new: S. dohrnii Sarno et Kooistra sp. nov., S. grethae Zingone et Sarno sp. nov., S. japonicum Zingone et Sarno sp. nov., and S. marinoi Sarno et Zingone sp. nov. Skeletonema species fell into four morphologically distinct groups corresponding to four lineages in the small subunit and large subunit trees. Lineage I included S. pseudocostatum, S. tropicum, S. grethae, and S. japonicum. All have external processes of the fultoportulae with narrow tips that connect with those of sibling cells via fork‐, knot‐, or knuckle‐ like junctions. Lineage II included only the solitary species S. menzelii. Lineage III comprised S. dohrnii and S. marinoi. This latter pair have flattened and flared extremities of the processes of the fultoportulae, which interdigitate with those of contiguous valves without forming knots or knuckles. Lineage IV only contained the brackish water species S. subsalsum. Some species also differ in their distribution and seasonal occurrence. These findings challenge the concept of S. costatum as a single cosmopolitan and opportunistic species and calls for reinterpretation of the vast body of research data based on this species.

Seventy-five diatom strains isolated from the Beaufort Sea (Canadian Arctic) in the summer of 2009 were characterized by light and electron microscopy (SEM and TEM), as well as 18S and 28S rRNA gene sequencing. These strains group into 20 genotypes and 17 morphotypes and are affiliated with the genera Arcocellulus, Attheya, Chaetoceros, Cylindrotheca, Eucampia, Nitzschia, Porosira, Pseudo-nitzschia, Shionodiscus, Thalassiosira, and Synedropsis. Most of the species have a distribution confined to the northern/polar area. Chaetoceros neogracilis and Chaetoceros gelidus were the most represented taxa. Strains of C. neogracilis were morphologically similar and shared identical 18S rRNA gene sequences, but belonged to four distinct genetic clades based on 28S rRNA, ITS-1 and ITS-2 phylogenies. Secondary structure prediction revealed that these four clades differ in hemi-compensatory base changes (HCBCs) in paired positions of the ITS-2, suggesting their inability to interbreed. Reproductively isolated C. neogracilis genotypes can thus co-occur in summer phytoplankton communities in the Beaufort Sea. C. neogracilis generally occurred as single cells but also formed short colonies. It is phylogenetically distinct from an Antarctic species, erroneously identified in some previous studies as C. neogracilis, but named here as Chaetoceros sp. This work provides taxonomically validated sequences for 20 Arctic diatom taxa, which will facilitate future metabarcoding studies on phytoplankton in this region.

A new photosynthetic planktonic marine dinoflagellate, Azadinium dexteroporum sp. nov., is described from the Gulf of Naples (South Tyrrhenian Sea, Mediterranean Sea). The plate formula of the species, Po, cp, X, 4', 3a, 6″, 6C, 5?S, 6‴ and 2″″, is typical for this recently described genus. Azadinium dexteroporum is the smallest rep-resentative of the genus (8.5 μm average length, 6.2 μm average width) and shares the presence of a small antapical spine with the type species A. spinosum and with A. polongum. However, it differs from all other Azadinium species for the markedly asymmetrical Po plate and the position of the ventral pore, which is located at the right posterior end of the Po plate. Another peculiarity of A. dexteroporum is the pronounced concavity of the second intercalary plate (2a), which appears collapsed with respect to the other plates. Phylogenetic analyses based on the large subunit 28S rDNA (D1/D2) and the internal transcribed spacer (ITS rDNA) support the attribution of A. dexteroporum to the genus Azadinium and its separation from the other known species. LC/MS-TOF analysis shows that Azadinium dex-teroporum produces azaspiracids in low amounts. Some of them have the same molecular weight as known compounds such as azaspiracid-3 and -7 and Compound 3 from Amphidoma languida, as well as similar fragmentation patterns in some cases. This is the first finding of a species producing azapiracids in the Mediterranean Sea.

The type material of Skeletonema costatum (Greville) Cleve was reexamined with the aims of providing an EM description of the species and clarifying which of the recently recognized Skeletonema Greville species, if any, deserves the epithet costatum. Two permanent mounts and two loose samples from the same collections from Hong Kong Bay were examined. Two distinct Skeletonema species were found in all materials. Based on the original description and on the observation of the lectotype, it was concluded that the most abundant morph in the type material is S. costatum. Cells were heavily silicified and 5-16 lm in diameter. The external processes of the fultoportulae in the terminal valves were open tubules with claw-shaped tips. The intercalary fultoportulae processes were closed flattened tubules with a pore at their base, each attached to two processes of the sibling valve (1:2 junction). The rimoportula had a long process and was located marginally in all valves. The second morph in the type material was described as Skeletonema grevillei Sarno et Zingone sp. nov. Cells were delicate, 4-7.5 lm in diameter, and formed short colonies. The fultoportulae processes in the terminal valves were open tubes having narrow tips with truncated or spiny margins. In the intercalary valves, they formed knuckle-like generally 1:1 junctions. A scallop-work of silica bridges joined the bases of the processes. The rimoportula was marginal in all valves. Neither S. costatum nor S. grevillei match any Skeletonema species that have been recently analyzed by combined morphological and molecular approaches.

Azadinium dexteroporum is the first species of the genus described from the Mediterranean Sea and it produces different azaspiracids (AZA). The aims of this work were to characterize the toxin profile of the species and gain structural information on azaspiracids produced by the A. dexteroporum strain SZN-B848 isolated from the Gulf of Naples. Liquid chromatography-mass spectrometry (LC-MS) analyses were carried out on three MS systems having different ion source geometries (ESI, TurboIonSpray®, ESI ION MAX) and different MS analyzers operating either at unit resolution or at high resolution, namely a hybrid triple quadrupole-linear ion trap (Q-trap MS), a time of flight (TOF MS), and a hybrid linear ion trap Orbitrap XL fourier transform mass spectrometer (LTQ Orbitrap XL FTMS). As a combined result of these different analyses, A. dexteroporum showed to produce AZA-35, previously reported from A. spinosum, and six compounds that represent new additions to the AZA-group of toxins, including AZA-54 to AZA-58 and 3-epiAZA-7, a stereoisomer of the shellfish metabolite AZA-7. Based on the interpretation of fragmentation patterns, we propose that all these molecules, except AZA-55, have the same A to I ring system as AZA-1, with structural modifications all located in the carboxylic side chain. Considering that none of the azaspiracids being produced by the Mediterranean strain of A. dexteroporum is currently regulated by European food safety authorities, monitoring programmes of marine biotoxins in the Mediterranean area should take into account the occurrence of the new analogues to avoid an underestimation of the AZA-related risk for seafood consumers