Discovery of a novel brown algal genus and species Setoutiphycus delamareoides (Phaeophyceae, Ectocarpales) from the Seto Inland Sea, Japan

Hiroshi Kawai,Takeaki Hanyuda

doi:10.1038/s41598-021-93320-7

Abstract

We describe a new genus and species of brown algae from the Seto Inland Sea, Japan. This species is similar to Delamarea in gross morphology and anatomy, but distinctive in having longer thalli with rare branching and shorter cortical cells. In culture, pluri-zoids derived from plurilocular zoidangia on the erect thalli developed into filamentous gametophytes bearing ectocarpoid plurilocular zoidangia, but also formed parenchymatous erect thalli of sub-sympodial growth similar to Trachynema often having branches, and formed lateral and terminal plurilocular zoidangia. Molecular phylogenies using concatenated chloroplast and mitochondrial gene sequences showed the new alga nested in the clade composed of ectocarpalean genera with diffuse growth, parenchymatous thalli, and multiple chloroplasts, but this species is distinctive. Therefore, we propose Setoutiphycus delamareoides gen. & sp. nov. for this new alga, and provisionally place it in Chordariaceae, Ectocarpales. The Seto Inland Sea repeatedly dried during sea level regressions during glacial periods, and the present sea level recovered after the last glacial maximums (LGM), ca. 10,000 years ago. Therefore, it is unlikely that the species evolved within this area. Its distribution in the area may be explained as a remnant population that survived in refugia in southern Japan during the LGM.

Highlights

The higher rank taxonomy of brown algae (Phaeophyceae) has been considerably revised in the last few decades, especially in certain orders, by the application of life history studies and molecular phylogenetic analyses[1,2,3,4,5]
Plurilocular zoidangia were formed by subdivisions of cortical cells (Fig. 2i), conical to lanceolate, often with protruding locules at the distal end of well-developed zoidangia (Fig. 2j) and becoming longer than the cortical cells (Fig. 2i), up to 120 μm by 72 μm
As to the genus level taxonomy of parenchymatous members of Ectocarpales, morphological features of sporophytes such as the gross morphology, growth mode, thallus constructions and shape of cortical cells and plurilocular zoidangia have been used for defining the genera (Table 1)

Summary

Introduction

The higher rank taxonomy of brown algae (Phaeophyceae) has been considerably revised in the last few decades, especially in certain orders, by the application of life history studies and molecular phylogenetic analyses[1,2,3,4,5]. Within the Ectocarpales, genus and species level taxonomies of the members with terete, parenchymatous thalli having multiple chloroplasts have been relatively well documented because of their recognizable macroscopic thalli, distinctive anatomical features applicable to taxonomic comparisons, and the substantial number of studies using unialgal cultures elucidating their life histories and early development. We describe, based on morphology and molecular phylogenetic studies, a new terete parenchymatous species belonging to Ectocarpales s.l., and discuss its family level taxonomy

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Conclusion