Lineaperpetua gen.nov.:a new diatom genus in the Thalassiosirales supported by morphology and molecular data

Based on a combination of morphology and molecular data of ribosomal DNA genes,a new diatom genus Lineaperpetua gen.nov.Yu,You,Kociolek&Wang is described.The features that help define Lineaperpetua at the level of genus include:a tangentially undulated valve face;continuous cribra areolae on the valve interior consisting of pores arranged as strips;single rimoportula located inside the ring of marginal fultoportulae.Additionally,phylogenetic analysis based on nuclear small subunit(SSU)rDNA sequences and nuclear large subunit(LSU)rDNA gene placed the three strains of L.lacustris in a single,monophyletic clade at a considerable sequence distance from the other genera(Thalassiosira,Conticribra,Planktoniella,Shinodiscus,and other genera)belonging to Thalassiosirales.Despite the similarities with some species of Thalassiosira,Conticribra,and Spicaticribra,the suite of features found in Lineaperpetua differentiate it from these other genera.These molecular data and morphological characters suggest an affinity of the new genus to the Thalassiosiraceae.

Two new Stephanodiscaceae species(Bacillariophyta)from SW China

Two new freshwater centric diatom species were described from the southwest of China based on light and scanning electron microscopy.Pliocaenicus weixiense sp.nov.has a transversely undulate valve face,marginal fultoportulae situated at the end of the hyaline strips,central fultoportulae forming a ring positioned in a circular pattern,each with 3-4(usually 3)satellite pores,and a single rimoportula located at the base of the inner distal end of the costa.Tertiarius aspera sp.nov.has an uneven valve face with small granules that may be present on the marginal area and valve mantle,marginal fultoportulae situated on each costa close to the margin of the valve,6-7 central fultoportulae forming a ring near the valve center each with two satellite pores,and one rimoportula located on the valve face/mantle junction in the middle of costa on the internal valve.T.aspera sp.nov.is the first reported extant species in the genus.This study played an important role in studying the taxonomic status and ecological information of the genus,and the establishment of the two new taxa will help demonstrate the unique nature of freshwater diatom flora in the southwest of China.

Morphological comparison and molecular marker screening of three Skeletonema species found in Changjiang(Yangtze)River Basin

In our recent investigations of diatom diversity,we studied three species,namely,Skeletonema costatum,Skeletonema subsalsum,and Skeletonema potamos.Although they have been found frequently in Changjiang(Yangtze)River Basin,their morphological and molecular identification is difficult in taxonomy.Therefore,to integrate morphological and molecular biological approaches,we compared systematically their morphological characters and performed phylogenetic analysis.Twelve strains of Skeletonema were collected and isolated from Shanghai and Jiangsu,China,and their morphological characteristics were examined by light microscopy(LM)and the scanning electron microscopy(SEM).Based on morphological comparison,we determined that S.potamos is easy to distinguish from the other two species.The heavily silicified areolae,undulated or cleft distal ends of terminal fultoportula processes(TFPPs),absence of basal pores of fultoportula processes(FPPs),the rootlike protrusions of FPPs,and no interlocking connection are the stable characteristics that can be used to identify S.potamos.However,there are only two features that can distinguish S.costatum from S.subsalsum,namely the location of terminal rimoportulae(TRPs)and the distal shape of TFPPs.In addition,we amplified and sequenced nine common genetic markers from the strains,from which 101 sequences were obtained,constructed phylogenetic trees based on the nine genes and evaluated that seven genes can be used to identify S.potamos,and revealed that S.subsalsum is the closest known relative of S.costatum,and only ATP synthetase beta-subunit gene(atp B)is able to distinguish them from each other,which strongly support that it is an effective molecular marker for Skeletonema.This work provided a theoretical basis for the taxonomic study of Skeletonema.

Morphological and phylogenetic analysis of a new Melosira species and revision of freshwater Melosira in China

Melosira is one of the most common diatom genera found in freshwater ecosystems.There are many freshwater species of Melosira,of which M.varians is the most common.In our investigation of periphytic diatoms in the Jinsha River,China,a new species,M.capsularum sp.nov,was characterized in combined morphological and molecular approaches.M.varians was also analyzed using molecular data.The new species is similar to M.varians,M.moniliformis,M.nummuloides,and M.lineata in morphology.The cells are capsular and join to filaments by mucilage pads that are secreted on the valve face and united into pairs by their cingula.The valve face is domed and covered with small granules,and the valve mantle edge has a milled appearance.The two strains of M.capsularum are in a single clade obviously away from other Melosira species,as determined in phylogenetic analysis based on nuclear small subunit(SSU)rDNA sequences and the chloroplast-encoded rbc L gene.Thus,the results of morphological comparisons and phylogenetic analysis based on molecular data provide strong evidence that M.capsularum is a new species,thereby increasing the total number of recognized freshwater diatom species in China.In addition,we have systematically reclassified the freshwater Melosira that have been recorded in China.