Morphological And Phylogeny Of Three New Species Of Naviculoid Diatom

Three new diatom species,Microcostatus hainanensis Tan,Gao&Chen sp.nov.,Microcostatus shantouensis Tan,Gao&Chen sp.Nov.,Staurophora shantouensis Tan,Gao&Chen sp.nov.,and a strain of Olifantiella muscatinei were described from sandy environments,which was collected from Xixiu beach,Hainan province(March 2018),Qingao Bay and Jinting Bay,Guangdong province(four quarters of 2019-2020),China,respectively,using light microscope scanning,electron microscope and transmission electron microscope.At the same time,a phylogenetic tree was constructed based on SSU rDNA and rbcL genes of two Microcostatus species and Olifantiella muscatinei to study the taxonomic status of genus Microcosfatus and Olifantiella.The main results are as follows:1.M.hainanensis was discovered at Xixiu Beach,Haikou City,Hainan Province.It is the first brackish species of genus Microcostatus in China and the second brackish species of genus Microcostatus.M.hainanensis is usually small size(less than 20 μm),each cell has two plastids,close to the girdle.The key diagnostic features of the species include the valves elliptical to lanceolate,blunt end;raphe filiform and slightly curved;striae forming macroareolae are external occluded by hymene;macroareolae extends to the junction of the valve and the mantle,and only a few short striae on the edge of one side of valve at the middle,forming a large hyaline areas;two longitudinal depressions on both sides of the raphe,with radial transapical costae,microcostae are barely visible,and conopeum is absent.2.M.shantouensis was discovered at Qingao Bay,Nanao Island,Shantou City,Guangdong province,is the second brackish species of Microcostatus found in China after M.hainanensis,and the third brackish species of genus Microcostatus.M.shantouensis is small,about half size smaller than M.hainanensis.Cells have two plastids,close to valve.The key diagnostic features of the species are as follows:valve elliptic-lanceolate,blunt end;raphe simple,straight,filiform;striae are composed of macroareolae,occluded externally by hymene;striae are parallel at middle of the valve,and slightly radial near the apices;conopeum is present,taking about 60%-70%of valve width,distributed with irregular puncta;two deep grooves lying at both marginal of the valve,with transapical costae.Mantles are relatively deep,possess a row of macroareolae corresponding to the macroareolae on the valve.3.O.muscatinei was discovered at Qingao Bay,Nanao Island,Shantou City,Guangdong province.Its basic characteristics are as follows:cells small,solitary,and each cell has a plastid;valve flat,elliptic to elliptic-lanceolate,rounded to protracted end;striae are equidistant,composed of a macroareolae,parallel to the radial;axial area is straight and narrow;central area is slightly enlarged,with a long elliptic slightly curved foramen;raphe is straight and simple;marginal canal formed a circle around the valve,evenly arranged,top and bottom with a supported siliceous skeleton covered by porous hymene;a hemispherical nodular structure was found at the middle of raphe on internal valve;buciniportula was composed of two low hollow structures.4.A phylogenetic trees of two species of Microcostatus and O.muscatinei were constructed based on SSU rDNA and rbcL genes,revealed that Microcostatus belonged to a clade that comprised of genera Sellaphora and Fallacia,indicating that genus Microcostatus belonged in the Sellaphoraceae.However,M.hainanensis and M.shantouensis have 2 plastids,while genus of Sellaphoraceae e.g.Sellaphora and Fallacia have 1 plastid,indicating broader phylogenetic relationship in this family.Olifantiella belonged to a clade that comprised Neidium,Scoliopleura and Diadesmi,indicating that genus Olifantiella belonged in the Neidiineae,which is belonged in the Naviculales,but the position of the family is not clear,and more evidence is needed to support it.5.S.shantouensis was discovered at Jinting Bay,Shanwei City,Guangdong Province.It was also found in Qingao Bay,Nanao Island,Shantou City.The basic characteristics of this species are as follows:valve linear lanceolate or elliptic lanceolate,end slightly protracted,no constriction in the middle;raphe simple,and slightly curved;external central raphe endings is close to each other which is in the shape of a small water drop,slightly curved to one side of the valve;distal raphe endings is hook-like shaped,bent in the same direction;internal proximal raphe endings bent in the same direction,terminal fissures forming a slight helictoglossa located on the silicon thickened area;axial area is narrow;central area expanded forming an obvious stauros reaching the valve margins,sometimes residual 1-2 shortened striae;striae are composed of small round areolae,uniseriate,continuous,slight radial,absent at terminal area;terminal area silicified internally,with a transapical hyaline.