Fernando Gómez

A dinoflagellate identified as Prorocentrum dentatum, P. shikokuense or P. donghaiense is responsible of massive harmful events. Blooms of a species identified as P. shikokuense have been recently reported in the Mediterranean Sea, and an exotic origin, tentatively introduced by ballast waters from Asia, has been hypothesized. The molecular data based on the small-, large subunit, and internal transcriber spacers ribosomal RNA gene (SSU-, LSU-, ITS rRNA) sequences confirmed P. shikokuense in the Mediterranean Sea. The Mediterranean ribotype is identical to a subtropical North Atlantic ribotype, and with slight divergence from the numerous sequences from the Pacific Ocean. To revisit the relationship between P. shikokuense (=P. donghaiense) and P. obtusidens, we provide the first micrographs of P. dentatum and P. obtusidens, the latter collected from the type locality. Our observations indicate that P. dentatum, P. obtusidens, and P. shikokuense are three different species. Their diagnostic morphological characters are: Prorocentrum dentatum is 44–60 μm long, leaf-shaped, pointed and central posterior end, conspicuous anterior shoulder; P. obtusidens is 33–41 μm long, irregular parallelepiped, almost paralel valve margins, eccentric and pointed posterior end, moderate anterior shoulder; and P. shikokuense is 25 μm long, sunflower seed-shaped, round and centric posterior end, inconspicuous anterior shoulder.

The noctilucoid dinoflagellates have been investigated in the open waters of the Mediterranean Sea. Kofoidinium spp., Spatulodinium spp. and Scaphodinium mirabile were found in nearly all the stations. The genera Craspedotella, Leptodiscus, Petalodinium and Pomatodinium were recorded for the first time in the eastern Mediterranean basin. An undescribed small species of Kofoidinium (40–60 μm in diameter) with a pointed extension represented about 1/3 of the genus records. The monotypic character of the genus Spatulodinium needs to be reconsidered because numerous specimens differed from the type species. One of these undescribed species showed a distinctive hyposome and an extremely long tentacle (up to 1600 μm long). A leptodiscacean that showed an arrowhead-shaped contour is found for the first time in the Mediterranean Sea. There is a considerable diversity of noctilucaceans yet to be described.

The dinoflagellate generaOxytoxum and Corythodinium that account for more than fifty species are widespread in warm oceans. These genera have been considered synonyms and thecal plate designations varied among authors. Several planktonic and sand-dwelling genera have been placed within the Oxytoxaceae. We obtained the first molecular data based on small subunit (SSU) rRNA gene sequences ofOxytoxum and Corythodinium, including the type species (O. scolopax and C. tessellatum) and C. frenguellii and C. cristatum. The three species of Corythodinium branched together a strong support [bootstrap (BP) of 98%]. This formed a sister clade with moderate support (BP 75%) with O. scolopax that supported the generic split. Oxytoxaceae should exclusively remain for Oxytoxum and Corythodinium, as an independent group, unrelated to any other known dinoflagellate. Oxytoxum was characterized by spindle-shaped cells with an anterior narrow epitheca, an apical spine and little cingular displacement. Corythodinium exhibits relatively broad cell shapes, with wider epitheca and greater cingular displacement, and an obovate or pentangular anterior sulcal plate that noticeably indented the epitheca. This suggested the need of new combinations for species that were described as Oxytoxum and possessed the characteristics of Corythodinium.

The molecular phylogeny of the sand-dwelling dinoflagellate Planodinium striatum was investigated from isolates collected in the NE English Channel. In the SSU rRNA gene phylogeny, the sequences of Planodinium clustered with the type species of Plagiodinium, P. belizeanum, and more distantly related to Plagiodinium ballux. Although the SSU rRNA gene sequences of Planodinium showed a high percentage of identity (96%) with partial sequences of species of Podolampas (~1200 base pairs), the SSU rRNA gene phylogenies did not show a relationship with the clade of the Podolampadaceae (Podolampas, Blepharocysta, Roscoffia), neither with the sequences of the sanddwelling genus Cabra. The SSU rRNA gene sequences of Plagiodinium belizeanum and P. ballux showed a low percentage of identity (96%) clustering in separate clades in the SSU rRNA gene phylogeny with Planodinium. The morphology of P. ballux and its generic type differed in the plate arrangement and the morphology of the cingulum, amongst other features. Based on the morphological and molecular differences, we propose the new genus Chrysodinium gen. nov. for P. ballux, with the re-interpreted thecal plate formula Po 3’ 1’’ 7c 2s 5’’’ 1’’’’.

Amphidiniopsis is one of the most specious genera of sand-dwelling dinoflagellates. However, its systematic position and the affinities to other genera remain unresolved. We obtained the first SSU rDNA sequences of two species of Amphidiniopsis, A. hirsuta and A. swedmarkii collected from the French coasts of the English Channel. In the corresponding SSU rDNA phylogeny, the sand-dwelling Amphidiniopsis spp., Thecadinium dragescoi, Herdmania litoralis and the planktonic Archaeperidinium (= Protoperidinium) minutum formed a strongly supported clade (100% bootstrap support), with a Scrippsiella-like species occupying a basal position. This clade branched close to families of Peridiniales such as Calciodinellaceae (Scripssiella), Podolampadaceae (Podolampas, Roscoffia), Heterocapsaceae (Heterocapsa) and other peridinioids. The members of the clade of Amphidiniopsis are placed in the family Amphidiniopsidaceae, within
the Peridiniales.

The North Sea and the English Channel are regions with a long tradition of plankton studies, where the colony-forming haptophyte Phaeocystis globosa dominates the spring phytoplankton blooms. Among its predators, we investigated an abundant unarmored dinoflagellate (~3000 cells per liter) in the North Sea in May 2019. It has been reported in the literature as Gymnodinium heterostriatum or G. striatissimum, and often identified as Gyrodinium spirale. Phylogenetic analyses using the small-, large subunit- and Internal Transcriber Spacers of the ribosomal RNA (SSU-, LSU-, ITS rRNA) gene sequences indicate that our isolates clustered within the Gyrodinium clade. The new sequences formed a sister group with sequences of the freshwater taxon Gyrodinium helveticum, being one of the infrequent marine-freshwater transitions in the microbial world. This isolate is the first characterized member of a clade of numerous environmental sequences widely distributed from cold to tropical seas. This common and abundant taxon has received several names due to its morphological plasticity (changes of size and shape, often deformed after engulfing prey) and the difficulty in discerning surface striation. We conclude that the priority is for the species name Gymnodinium heterostriatum Kofoid & Swezy 1921, a new name that was proposed for Gymnodinium spirale var. obtusum sensu Dogiel 1906. The species Gyrodinium striatissimum (Hulburt 1957) Gert Hansen & Moestrup 2000 and Gymnodinium lucidum D. Ballantine in Parke & Dixon 1964 (=G. hyalinum M. Lebour 1925) are posterior synonyms. We propose Gyrodinium heterostriatum comb. nov. for Gymnodinium heterostriatum.

Dinoflagellates (Alveolata, Dinophyceae) are protists with a truly remarkable diversity in lifestyles (free-living, parasites and mutualistic symbionts), habitats (marine, freshwater, plankton, benthos), and trophic modes (heterotrophic, plastid-containing). Here dinoflagellates are used to evaluate biases in the availability of molecular markers in relation to the variety of functional and ecological characteristics of protists. A large number of dinoflagellate sequences are available in GenBank, at least one for 56% of the 264 described genera. The most common marker is the small ribosomal subunit ribosomal DNA (49%). At the species level, SSU rDNA or the large subunit rDNA are available for 15% of the 2,386 described species. Availability of sequences of the internal transcribed spacers (ITS) and cytochrome oxidase I (COI) show a strong bias towards cultivable species. Relative to trophic mode, while about half of the known dinoflagellates are heterotrophic, only 12% of them have been sequenced compared to 29% of the plastid-containing species. For the COI marker availability is 10 times greater for plastid-containing compared to heterotrophic species. Freshwater species are underrepresented (13%) relative to the marine forms (22%). A high proportion of benthic species have been sequenced (46%) reflecting interest in Symbiodinium and harmful epiphytic taxa. Most of the relatively few described mutualistic species have been sequenced (> 80%). In contrast, only 17% of the described parasitic species have been sequenced, and most of the available sequences were not identified at the species level. In recent years, new species have been described mostly from coastal blooms or cultures. These studies are favored by the availability of abundant material for detailed studies of ultrastructure and multi-gene molecular phylogenies. Many methods are difficult to apply for the scarce specimens available from the open ocean. The requirement of these protocols, easy to apply with cultured species, is an obstacle in our knowledge of the open ocean diversity because it discourages studies based on sparse material. Consequently, in recent years descriptions of new species from the open ocean have declined considerably.