Taxonomy and molecular phylogeny of three marine benthic species of <i>Haslea</i> (Bacillariophyceae), with transfer of two species to <i>Navicula</i>

<p>Using light, scanning and transmission electron microscopy, and SSU rDNA and <i>rbc</i>L gene sequencing, we investigated three marine benthic diatoms: <i>Haslea avium</i> Tiffany, Herwig <i>et</i> Sterrenburg; <i>H. feriarum</i> Tiffany <i>et</i> Sterrenburg and <i>H. tsukamotoi</i> Sterrenburg <i>et</i> Hinz collected from intertidal sediments in China. These are the first records of these three species from China. Our observations showed that the typical valve structure of <i>Haslea</i>, with an inner basal layer and an outer tegumental layer, and walls (saepes sensu Sterrenburg et al.) between them is not present in either <i>H. tsukamotoi</i> or <i>H. avium</i>. Moreover, the two species possess small helictoglossae, an internal apical thickened area and hooked terminal fissures reaching to the valve mantle, suggesting a close relationship with <i>Navicula tripunctata</i>, the type species of <i>Navicula</i> s.s. In molecular phylogenetic analyses, <i>Haslea</i> was polyphyletic, being divided into two separate clades: <i>H. feriarum</i> belonged to a clade that comprised only <i>Haslea</i> species, including the type <i>H. ostrearia</i>, while <i>H. tsukamotoi</i> and <i>H. avium</i> were within the <i>Navicula</i> clade. Therefore, we propose transferring <i>H. tsukamotoi</i> and <i>H. avium</i> to <i>Navicula</i> and suggest that the presence of continuous longitudinal strips on the external valve surface is not a synapomorphy, but rather a homoplastic character for <i>Haslea</i>.</p>