The pelagophytes are a morphologically diverse class of marine heterokont algae defined by deoxyribonucleic acid (DNA) gene sequences, the presence of a multilayered, perforated theca (PT), and the novel role of the Golgi apparatus in the formation and secretion of the PT, as well as materials for the synthesis of the outer extracellular layers (e.g., cell walls and mucilage). We established clonal cultures of sand-dwelling pelagophytes collected from intertidal and subtidal locations at Heron Island on the Great Barrier Reef (GBR), Australia, and established phylogenetic trees based on nuclear 18S rDNA and plastid rbcL, psaA, psaB, psbA, and psbC gene sequences that led to the discovery of seven new species and several interesting range extensions. The new genus and species, Revolvomonas australis, is sister to Pituiglomerulus and Chrysocystis in the Chrysocystaceae (Sarcinochrysidales, Pelagophyceae). Additional new species are Sarcinochrysis kraftii, Sa. guiryi, Arachnochrysis pilardiaziae, A. cassiotisii, Sungminbooa capricornica, and Su. tropica; also identified and cultured from the GBR were Sa. marina, Aureoumbra geitleri, Chrysoreinhardia giraudii, Chrysocystis fragilisi, and the planktonic Pelagomonas calceolata. Revolvomonas was studied in detail and has several unusual features for sand-dwelling pelagophytes. In just three short collecting trips to Heron Island, we were able to isolate and identify over 40% of the pelagophyte genera discovered to date. This study substantiates the diverse nature of pelagophytes and suggests tropical reef sand may be a center for pelagophyte diversity.

We isolated into culture, along with their host cells (Desmidium, Spondylosum and Geminella), Stylococcus aureus and a previously undescribed taxon we name Stylococcus brevis sp. nov. The loricas of S. aureus were attached to the host cell with a long, thin stalk, and cells produced a long pseudopodium that often branched at the tip. Cells divided transversely, followed by daughter cell rotation of 90 degrees, giving the appearance of longitudinal division. One daughter cell was flagellate, escaped the mother lorica and swam to a host cell where it attached, producing a new lorica. The swimming cell had a long immature flagellum and short mature flagellum that were easily observed using a light microscope. Conversely, the loricas of S. brevis were anchored to the host cell with a short, thick stalk, and the cells produced a short pseudopodium. Stylococcus brevis cell division was the same as for S. aureus; however, its swimming cells had an extremely short mature flagellum that was visible by light microscopy only after chemical fixation. Molecular phylogenetic analyses using the 18S rRNA and rbcL genes showed that the two Stylococcus species were distinct species. Surprisingly, Stylococcus branched with Lagynion scherffelii (generitype) and L. ampullaceum, suggesting that these algae are congeneric, which supports the idea that the typical Stylococcus lorica morphology and stalk formation are a response to the host cell. We found no evidence suggesting that Stylococcus and Stylochrysalis are synonyms.

Brown algae are the only group of heterokont protists exhibiting complex multicellularity. Since their origin, brown algae have adapted to various marine habitats, evolving diverse thallus morphologies and gamete types. However, the evolutionary processes behind these transitions remain unclear due to a lack of a robust phylogenetic framework and problems with time estimation. To address these issues, we employed plastid genome data from 138 species, including heterokont algae, red algae, and other red-derived algae. Based on a robust phylogeny and new interpretations of algal fossils, we estimated the geological times for brown algal origin and diversification. The results reveal that brown algae first evolved true multicellularity, with plasmodesmata and reproductive cell differentiation, during the late Ordovician Period (ca. 450 Ma), coinciding with a major diversification of marine fauna (the Great Ordovician Biodiversification Event) and a proliferation of multicellular green algae. Despite its early Paleozoic origin, the diversification of major orders within this brown algal clade accelerated only during the Mesozoic Era, coincident with both Pangea rifting and the diversification of other heterokont algae (e.g., diatoms), coccolithophores, and dinoflagellates, with their red algal-derived plastids. The transition from ancestral isogamy to oogamy was followed by three simultaneous reappearances of isogamy during the Cretaceous Period. These are concordant with a positive character correlation between parthenogenesis and isogamy. Our new brown algal timeline, combined with a knowledge of past environmental conditions, shed new light on brown algal diversification and the intertwined evolution of multicellularity and sexual reproduction.

Summary The name Stenokalyx ( Chrysophyceae ) is not recommended for conservation against the name Stenocalyx ( Myrtaceae ). The name Mallomonas caudata is not recommended for conservation against the name M. fastigata ( Chrysophyceae ).

The Cyanidiophyceae, an extremophilic red algal class, is distributed worldwide in extreme environments. Species grow either in acidic hot environments or in dim light conditions (e.g., “cave Cyanidium ”). The taxonomy and classification systems are currently based on morphological, eco‐physiological, and molecular phylogenetic characters; however, previous phylogenetic results showed hidden diversity of the Cyanidiophyceae and suggested a revision of the classification system. To clarify phylogenetic relationships within this red algal class, we employ a phylogenomic approach based on 15 plastomes (10 new) and 15 mitogenomes (seven new). Our phylogenies show consistent relationships among four lineages ( Galdieria , “cave Cyanidium ”, Cyanidium , and Cyanidioschyzon lineages). Each lineage is distinguished by organellar genome characteristics. The “cave Cyanidium ” lineage is a distinct clade that diverged after the Galdieria clade but within a larger monophyletic clade that included the Cyanidium and Cyanidioschyzon lineages. Because the “cave Cyanidium ” lineage is a mesophilic lineage that differs substantially from the other three thermoacidophilic lineages, we describe it as a new order (Cavernulicolales). Based on this evidence, we reclassified the Cyanidiophyceae into four orders: Cyanidiales, Cyanidioschyzonales, Cavernulicolales ord. nov., and Galdieriales ord. nov. The genetic distance among these four orders is comparable to, or greater than, the distances found between other red algal orders and subclasses. Three new genera ( Cavernulicola , Gronococcus, Sciadococcus ), five new species ( Galdieria javensis , Galdieria phlegrea, Galdieria yellowstonensis , Gronococcus sybilensis, Sciadococcus taiwanensis ), and a new nomenclatural combination ( Cavernulicola chilensis ) are proposed.

The pelagophytes, a morphologically diverse class of marine heterokont algae, have been historically united only by DNA sequences. Recently we described a novel perforated theca (PT) encasing cells from the Pelagophyceae and hypothesized it may be the first morphological feature to define the class. Here we consolidate that observation, describing a PT for the first time in an additional seven pelagophyte genera, including three genera new to science. We established clonal cultures of pelagophytes collected from intertidal pools located around Australia, and established phylogenetic trees based on nuclear 18S rDNA and plastid rbc L, psa A, psa B, psb A and psb C gene sequences that led to the discovery of three new species: Wyeophycus julieharrissiae and Chromopallida australis form a distinct lineage along with Ankylochrysis lutea within the Pelagomonadales, while Pituiglomerulus capricornicus is sister genus to Chrysocystis fragilis in the Chrysocystaceae (Sarcinochrysidales). Using fixation by high‐pressure freezing for electron microscope observations, a distinctive PT was observed in the three new genera described in this paper, as well as four genera not previously investigated: Chrysoreinhardia , Sargassococcus , Sungminbooa and Andersenia . The mechanism of PT formation is novel, being fabricated from rafts in Golgi‐derived vesicles before being inserted into an established PT. Extracellular wall and/or mucilage layers assemble exterior to the PT in most pelagophytes, the materials likewise secreted by Golgi‐derived vesicles, though the mechanism of secretion is novel. Secretory vesicles never fuse with the plasma membrane as in classic secretion and deposition, but rather relocate extracellularly beneath the PT and disintegrate, the contents having to pass through the PT prior to wall and/or mucilage synthesis. This study substantiates the diverse nature of pelagophytes, and provides further evidence that the PT is a sound morphological feature to define the Pelagophyceae, with all 14 of the 20 known genera studied to date by TEM possessing a PT.

SummaryThree names are recommended for conservation: Pseudokephyrion against Dinobryopsis and Kephyriopsis (Chrysophyceae), Phalacroma (Dinophyceae) against Phalacroma (Trilobita), and Discosphaera (Prymnesiophyta) against Discosphaera (Ascomycota). It is recommended that Actinostephanos (Bacillariophyta) and Actinostephanus (Gesneriaceae) be treated as homonyms.

Coccolithophores are well-known haptophytes that produce small calcium carbonate coccoliths, which in turn contribute to carbon sequestration in the marine environment. Despite their important ecological role, only two of eleven haptophyte plastid genomes are from coccolithophores, and those two belong to the order Isochrysidales. Here, we report the plastid genomes of two strains of Ochrosphaera neapolitana (Coccolithales) from Spain (CCAC 3688 B) and the USA (A15,280). The newly constructed plastid genomes are the largest in size (116,906 bp and 113,686 bp, respectively) among all the available haptophyte plastid genomes, primarily due to the increased intergenic regions. These two plastid genomes possess a conventional quadripartite structure with a long single copy and short single copy separated by two inverted ribosomal repeats. These two plastid genomes share 110 core genes, six rRNAs, and 29 tRNAs, but CCAC 3688 B has an additional CDS (ycf55) and one tRNA (trnL-UAG). Two large insertions at the intergenic regions (2 kb insertion between ycf35 and ycf45; 0.5 kb insertion in the middle of trnM and trnY) were detected in the strain CCAC 3688 B. We found the genes of light-independent protochlorophyllide oxidoreductase (chlB, chlN, and chlL), which convert protochlorophyllide to chlorophyllide during chlorophyll biosynthesis, in the plastid genomes of O. neapolitana as well as in other benthic Isochrysidales and Coccolithales species, putatively suggesting an evolutionary adaptation to benthic habitats.

SummaryThe name Peridinium splendor‐maris (Blepharocysta splendor‐maris) is not recommended for conservation with the proposed conserved type. The name “Alexandrium” Halim (Dinophyceae) could not be recommended for conservation because it is not a validly published name. The name Gracilariopsis is recommended for conservation. The name Chara flexilis (Nitella flexilis) is not recommended for conservation with the proposed conserved type.

The relationships among the Aurearenophyceae, Phaeothamniophyceae, Phaeophyceae and Xanthophyceae lineages of the Heterokontophyta SI clade are not well known. By adding previously unexamined taxa related to these classes in a five gene phylogeny (SSU rRNA, atpB, psaA, psaB, rbcL), we recovered an assemblage of taxa previously unrecognized. We propose the class Phaeosacciophyceae class. nov., that includes Phaeosaccion collinsii, Phaeosaccion multiseriatum sp. nov., Phaeosaccion okellyi sp. nov., Antarctosaccion applanatum, Tetrasporopsis fuscescens, Tetrasporopsis moei sp. nov., and Psammochrysis cassiotisii gen. & sp. nov. We re-examine the literature for Chrysomeris, Nematochrysis, Chrysowaernella and the invalid name "Giraudyopsis" and conclude some taxa in previous studies are misidentified or misnamed, i.e. Chrysomeris and Chrysowaernella, respectively. We also show that Nematochrysis sessilis var. vectensis and Nematochrysis hieroglyphica may belong in the recently described class Chrysoparadoxophyceae. The phylogenetic relationships of Phaeobotrys solitaria and Pleurochloridella botrydiopsis are not clearly resolved, but they branch near the Xanthophyceae. Here we describe a new class Phaeosacciophyceae, a new order Phaeosacciales, a new family Tetrasporopsidaceae, a new genus Psammochrysis and four new species.

Summary The names Microtheca and Anuraea octoceras are not recommended for rejection.

Alkenone-derived paleotemperature reconstruction holds great promise in lake environments. However, the occurrence of multiple species of alkenone-producing haptophyte algae in a single lake can complicate the translation of alkenone unsaturation to temperature if each species requires an individual temperature calibration. Here, we present the first systematic monitoring of two alkenone-producing haptophytes throughout the course of a seasonal cycle in Lake George, North Dakota, using a combined approach of DNA sequencing and alkenone lipid characterization. Field sampling revealed a nonoverlapping haptophyte succession, with both an early and late season haptophyte bloom event. Culturing experiments demonstrated that the two haptophyte species responsible for these blooms had statistically similar alkenone-temperature responses, although the culture-based calibrations were distinct from the in situ calibration. Bloom timing of each haptophyte species corresponded to surface-water temperatures that differed by more than 10 degrees C, revealing that changes in bloom intensities for each species will skew the sediment-inferred temperatures to a different stage of the growth season. These results highlight the importance of accounting for bloom timing when interpreting alkenone-derived temperatures in sediment cores, especially in lakes that experience large seasonal fluctuations in water column temperature and salinity.

SummaryThe name Amphidoma (Dinophyceae) is not recommended for conservation as being of feminine gender and with a conserved type because the feminine gender is already established, and because there is no known evidence to show that the existing type (A. acuminata) is not congenric with A. nucula, the type proposed for conservation. The name Heterocapsa (Dinophyceae) is recommended for conservation with a conserved type. Two requests for binding decisions were considered, Cosmarium geminatum and C. gemmatum (Streptophyta), and Trigonium (Bacillariophyta) and Trigonum (Streptophyta). The NCA did not consider the names concerned sufficiently similar to be confused and recommended that they not be treated as homonyms.

Pelagophytes (Heterokonta) are a morphologically diverse class of marine algae historically united only by DNA sequences. We established clonal cultures of sand‐dwelling pelagophytes collected from intertidal pools around Australia. Phylogenetic trees based on nuclear 18S rDNA and plastid rbcL, psaA, psaB, psbA, and psbC sequences revealed two new genera, Gazia and Glomerochrysis, related to Aureoumbra in a distinct lineage within the Sarcinochrysidaceae (Pelagophyceae). The three new species (Gazia saundersii, Gazia australica, and Glomerochrysis psammophila), along with an Australian strain of Aureoumbra geitleri, are characterized by dominant benthic stages that differ significantly from one another, while occasionally producing classic heterokont zoospores. The benthic stage of Ga. saundersii has a novel development not observed in any other colonial alga, consisting of large, spherical colonies (up to 140 μm in diameter) containing c. 2,500 cells that eventually differentiate and segregate into a large number of daughter colonies that are subsequently liberated. Alternatively, colonies may differentiate into a mass of zoospores that escape and settle to develop into new colonies. In Gl. psammophila, cubic packets of cells form large sticky clusters that bind sand together, while Ga. australica and A. geitleri are unicellular species. Using fixation by high‐pressure freezing, a distinctive perforated theca was observed by TEM in all genera of this lineage, and we hypothesize this unique covering may be the first morphological feature to characterize most, if not all, pelagophytes. This study substantiates the diverse nature of sand‐dwelling pelagophytes as well as their mechanisms for thriving in a dynamic habitat.

Melting summer snow in the Austrian Alps exhibited a yellowish bloom that was mainly comprised of an unidentified unicellular chrysophyte. Molecular data (18S rRNA and rbcL genes) showed a close relationship to published sequences from an American pond alga formerly identified as Kremastochrysis sp. The genera Kremastochrysis and Kremastochrysopsis are morphologically distinguished by the number of flagella observed with the light microscope, and therefore we assigned the Austrian snow alga and an American pond alga to the genus Kremastochrysopsis. Transmission and scanning electron microscopy revealed that swimming cells had two flagella oriented in opposite directions, typical for the Hibberdiales. Molecular phylogenetic analyses showed that both new species were closely related to Hibberdia. Kremastochrysopsis ocellata, the type species and only known species, has two chloroplasts per cell and the zoospores have red eyespots. Our two organisms had only a single chloroplast and no zoospore eyespot, but their gene sequences differed substantially. Therefore, we described two new species, Kremastochrysopsis austriaca sp. nov and Kremstochrysopsis americana sp. nov. When grown in culture, both taxa showed a characteristic hyponeustonic growth (hanging below the water surface), whereas older immotile cells grew at the bottom of the culture vessel. Ecologically, Kremastochrysopsis austriaca sp. nov., which caused snow discolorations, had no close phylogenetic relationships to other psychrophilic chrysophytes, for example, Chromulina chionophilia, Hydrurus sp., and Ochromonas‐like flagellates.

Dictyochophyceae (silicoflagellates) are unicellular freshwater and marine algae (Heterokontophyta, stramenopiles). Despite their abundance in global oceans and potential ecological significance, discovered in recent years, neither nuclear nor organellar genomes of representatives of this group were sequenced until now. Here, we present the first complete plastid genome sequences of Dictyochophyceae, obtained from four species: Dictyocha speculum, Rhizochromulina marina, Florenciella parvula and Pseudopedinella elastica. Despite their comparable size and genetic content, these four plastid genomes exhibit variability in their organization: plastid genomes of F. parvula and P. elastica possess conventional quadripartite structure with a pair of inverted repeats, R. marina instead possesses two direct repeats with the same orientation and D. speculum possesses no repeats at all. We also observed a number of unusual traits in the plastid genome of D. speculum, including expansion of the intergenic regions, presence of an intron in the otherwise non‐intron‐bearing psaA gene, and an additional copy of the large subunit of RuBisCO gene (rbcL), the last of which has never been observed in any plastid genome. We conclude that despite noticeable gene content similarities between the plastid genomes of Dictyochophyceae and their relatives (pelagophytes, diatoms), the number of distinctive features observed in this lineage strongly suggests that additional taxa require further investigation.