Chaetoceros mannaii, Li & Boonprakob & Gaonkar & Kooistra & Lange & Hernández-Becerril & Chen & Moestrup & Lundholm, 2017

Li, Yang, Boonprakob, Atchaneey, Gaonkar, Chetan C., Kooistra, Wiebe H. C. F., Lange, Carina B., Hernández-Becerril, David, Chen, Zuoyi, Moestrup, Øjvind & Lundholm, Nina, 2017, Diversity in the Globally Distributed Diatom Genus Chaetoceros (Bacillariophyceae): Three New Species from Warm-Temperate Waters, PLoS ONE (e 0168887) 12 (1), pp. 1-38 : 33-34

Chaetoceros mannaii

Cells of C. mannaii are ultrastructurally similar to field material identified as C. lorenzianus from Thailand, Mexico and Japan ([ 12, 36], own observations). Compared to the original description of C. lorenzianus , C. mannaii has large poroids on the setae, 0.7±0.2 μm long, the largest among strains of section Dicladia examined by us, and readily visible in LM. They are more closely spaced (12.3±1.6) than in the type material of C. lorenzianus (7.2±1.7), and smaller than those of the Mexican ([ 12], pl. 23, figs 3 and 4) and Japanese material ([ 36], pl. VI, fig 7) tentatively identified as C. lorenzianus , where poroids of 1 μm or more were illustrated. In addition, the apertures of C. mannaii are hexagonal, compared to the more quadrangular apertures of C. lorenzianus (compare Figs 11C, 11d , 16A and 16B ) [ 8]. Chaetoceros mannaii also differs in having a smaller apical axis, 5.7–12.9 μm, compared to 20–43 μm in C. lorenzianus [ 8], 13–25 μm in the Mexican material [ 12] and around 30 μm (with a variation of 10–

80 μm) in the Japanese material [ 36].

Cells of C. mannaii are otherwise characterized by heavily silicified frustules and a distinct furrow above the basal ring of the mantle ( Fig 11F , arrowheads). The terminal cell of C. mannaii carries a relatively long and distinct external tube of the rimoportula ( Figs 11E, 11F and 12C ). An external tube was not observed in C. decipiens , C. laevisporus and C. mitra ( Figs 2F , 8E and 14G ), and a very short one was present in C. elegans ( Fig 5D and 5E ). This character still needs to be explored in C. lorenzianus .

Resting spores were not observed in C. mannaii although several attempts were made to induce spore formation.

Figures

Fig 2. Chaetoceros decipiens. LM (A and B), TEM (C, D, H-J) and SEM (E-G). A-E: Seta structure of lectotype MIC5366 (A), strains P14B3B (B) and D10 (C–E), showing the 4–6 sided seta with poroids and small spines. F: Terminal valve with fringes (arrowheads); strain D10. G: Silica warts on the basal ring of the mantle; strain D10. H: Annulus, costae and poroid pattern on intercalary valve; strain P10E5. I: Terminal valve showing rimoportula without external process (arrowhead); strain D10. J: Girdle bands; strain D10. A and B scale bars, 10 μm. C–J scale bars, 2 μm. doi:10.1371/journal.pone.0168887.g002

Fig 5. Chaetoceros elegans sp. nov. SEM (A–E) and TEM (F and G). A: Terminal valve view with external process of rimoportula and poroids on valve face; strain MC1048. B and C: Intercalary cells demonstrating large apertures and valve faces; strain M1 (B), strain MC1048 (C). D and E: Terminal valves with central processes (arrowheads) and silica ear-like structures (arrows in D) in strain YL7. F: Annulus, costae and poroid pattern near intercalary valve centre; strain YL7. G: Parallel rows of poroids on the mantle; arrowhead indicates ring-shaped constriction; strain YL7. A–E scale bars, 5 μm. F and G scale bars, 2 μm. doi:10.1371/journal.pone.0168887.g005

Fig 8. Chaetoceros laevisporus sp. nov. LM (A–C), SEM (D and E) and TEM (F). Fig A: Part of a chain showing constrictions (arrows) between mantle and girdle, and V- shaped protrusion (arrowhead) located centrally on the terminal valve; strain N7. B: Dividing chain showing seta divergence; strain DY1. C: Structure of terminal seta; strain DY1. D: Chain in girdle view showing cells and apertures; strain N7. E: Terminal valve with rimoportula without external process (arrowhead); strain N7. F: Valve views of intercalary (upper) and terminal valves (below); strain N7. A, C, D scale bars,20 μm. B scale bar, 100 μm. E and F scale bars, 5 μm. doi:10.1371/journal.pone.0168887.g008

Fig 11. Chaetoceros mannaii sp. nov. LM (A and B), SEM (C and E) and TEM (D and F); strain N1. A: Straight chain showing seta divergence and constrictions (arrows) between the mantle and the girdle. B: Oval valve face. C and D: Intercalary cells, with ear-like structures (arrowheads in D) at the bases of setae in heavily silicified frustule. E and F: Terminal valves, with ear-like structures at the seta bases (arrowheads in E) and distinct constriction above the ring (arrowheads in F). A scale bar, 20 μm. B–F scale bars, 5 μm. doi:10.1371/journal.pone.0168887.g011

Fig 12. Chaetoceros mannaii sp. nov. LM (A), SEM (B) and TEM (C–F); strain N1. A and B: Setae with oval poroids. C: Terminal valve showing valve structure and rimoportula with external projection. D: Poroids and costae on the mantle. E and F: Girdle bands with poroids. A scale bar, 10 μm. B scale bar, 5 μm. C–F scale bars, 2 μm. doi:10.1371/journal.pone.0168887.g012

Fig 14. Chaetoceros mitra. LM (A), SEM (B, C, F, G) and TEM (D, E, H–J); strain P10A1. A–E: Setae showing round-oval poroids and spines, using different microscopy techniques. F: Intercalary valves showing wing-like structures (arrowhead), and furrows above the basal ring of mantle (arrows). G: Terminal valve showing rimoportula without external tube (arrowhead), furrow above the basal ring of mantle (arrows) and fringe (curved arrow). H: Intercalary valve face. I and J: Girdle bands. A scale bar, 10 μm. B, C, F–H scale bars, 5 μm. D, E, I, J scale bars, 2 μm. doi:10.1371/journal.pone.0168887.g014

Fig 16. Lectotype material of C. lorenzianus from the Grunow Collection. A: Intercalary valves with oval-hexagonal aperture and some fusion of the basal parts of the setae. B: Intercalary seta poroids visible under the LM. Scale bars are 10 μm. doi:10.1371/journal.pone.0168887.g016