Cocconeis coreana

Cocconeis coreana R. Jahn & B. M. Suh sp. nov.

Holotype. Slide B 40 0041501a, Botanic Garden and Botanical Museum Berlin, from the strain D119_029. Fig. 2F (SV; Fig. 2B RV) represents the holotype. SEM-stub deposited as B 40 0041501b. For molecular material and data see “Materials and Methods” and Supplementary Table S1.

Type locality. DPR Korea, Myohyangsan, Hyangsanwaterfalls, Sep 17, 2014, collected by Byung Moon Suh & Regine Jahn.

Registration. http://phycobank.org/102187.

Etymology. We are referring to the entire Korean Peninsula since this taxon was found in clean freshwaters in North and South Korea.

Description by LM (type strain only, Fig. 2). Valve outline is generally slender elliptical (Fig. 2A) but sometimes round elliptical (Fig. 2B), apices are obtusely rounded (length [AA]: 25.5-59.3 µm; width [TA]: 14.1-36.6 µm [n = 34]). The number of striae on both valves are similar but the individual punctae are different. The RV shows punctate striae with 18-24 rows per 10 µm and 15-24 areolae in 10 µm. The SV shows short dash-like striae with 18-24 rows per 10 µm and 9-12 areolae per 10 µm. The striae on both valves are parallel at the center and radiate near the apices; the striae of the SV seem to be in bundles of 2-5 striae (Fig. 2E-H). The RV shows a pronounced round central area (Fig. 2A-D). Only the RV has a rim of several rows of areolae at the valve mantle as a continuation of the striae separated by a submarginal hyaline rim (for details see SEM). In addition, the RV has a conspicuous valvocopula with irregular spaced clamp-like fimbriae (for details see SEM). Raphe is filiform and straight, axial area very narrow; sternum axial area very narrow. Concerning alive cells, in one strain we documented a single c-shaped plastid with serrated edges and a pyrenoid (Fig. 1A-C) and in two strains we observed auxospore formation (Fig. 1D-G) (not for the type strain).

Description by SEM (Figs 7-11). RV: The valve face is flat with a concave mantle separated by a pronounced (Fig. 8A & C). Striae are made up of round to slightly elliptical uniseriate areolae which are small (about 0.25 µm) and regularly spaced, increasing in size from the axial area towards the valve margin and the apices (Fig. 7E), forming a pronounced central area of about 6 rows of areolae length (AA) and 3 areolae wide on each side of the raphe ends (TA) (Fig. 7A-C). Internally, the areolae are occluded by round lattice-structured hymenes with short slits around the margin and tiny perforations in the middle (Figs 7D, 8B & D). On the mantle, the uniseriate valve face striae continue as uniseriate rows of two to four, generally three areolae (Fig. 7A-C); at each pole there is a gap of these mantle areolae (Fig. 7E). Externally, the raphe is straight, filiform, proximal raphe endings are slightly drop-like expanded (Fig. 7A-C). Internally, the proximal raphe fissures are bent to opposite sides (Fig. 8A & C); distal raphe endings are straight and end in weakly elevated helictoglossae on the hyaline rim (Fig. 8A & C). Valvocopula is open; long, slender and heavily silicified clamp-like fimbriae (without papillae and furrows) seem to be attached to the hyaline rim and are irregularly spaced at every 4th to 7th stria, or 3 to 5 clamps per 10 µm (Figs 8A & 10F).

SV: The valves are thicker than the RV (compare Figs 7D & 9G). The valve face is flat to slightly convex with a short mantle (Fig. 9A). Striae are made up of dash-like regular uniseriate areolae, undifferentiated unto the valve edge (Fig. 10A & D); internally they are rounded (Fig. 9D & F) whereas externally they are slit-like of different openness (Fig. 10B & E). Areolae are occluded by elongated lattice structured hymenes of about 0.7 µm length by 0.13 µm width with marginal slits and tiny holes in the center; the hymenes lie towards the outer side but not completely externally (Figs 9E, G & 10B). The sternum is very thin and sometimes shows the mark of a ghost raphe (Fig. 10A). The valvocopula is open with no visible fimbriae (Figs 9B & 10C; the fimbriae and valvocopula seen in Fig. 9C are from the RV). We also observed auxospore formation in SEM (Fig. 11) with remnants of incunabula (Fig. 11A & B) but apparently no perizonium.

Comparison to related taxa. With its largest length of almost 60 µm and width of up to a 43 µm C. coreana is generally bigger than C. placentula var. placentula (sec. Jahn et al. 2009, figs 28-43). Nevertheless, their length to width ratios overlap, with C. coreana having a broader ratio (see morphometric values in Table 1). The RV of C. coreana looks like a replica of C. placentula with generally similar numbers of striae and areolae, becoming larger towards the pronounced hyaline rim; also the numbers of areolae of the mantle below the hyaline rim are similar with about 3 (2-4 for C. coreana and 3-4 for C. placentula) per row but there is a gap at both poles in C. coreana (Fig. 7A-C) in contrast to continuing areolae in C. placentula (Jahn et al. 2009, figs 37 & 39). Further, in C. coreana the numbers and spacing of the longer clamp-like fimbriae of the raphe valvocopula are similar but there seem to be no small fimbriae in C. coreana (Figs 8A & 9C) in contrast to C. placentula (Jahn et al. 2009, fig. 42). The size of the central area around the drop-like proximal raphe ends is pronouncedly bigger in C. coreana (Fig. 7A-C) than in C. placentula (Jahn et al. 2009, figs 37 & 39). As expected for the genus Cocconeis, the biggest differences are found in the SV concerning numbers of the dash-like striae, size of the areolae and size of the sternum: C. coreana has a narrow sternum and closely spaced areolae of the size 0.6 µm by 0.2 µm externally (Fig. 10C); C. placentula has a broad sternum and widely spaced long and very thin areolae of the size of up to 1.5 µm by 0.05 µm externally (Jahn et al. 2009, figs 40 & 41).

Comparing C. coreana to C. lineata (sec. Romero and Jahn 2013, figs 2-8) is problematic since the only available data is from one strain without auxospores. C. lineata has a higher length to width ratio (see morphometric values in Table 1) which means that C. lineata is smaller and slenderer in comparison to C. coreana. The mantle of the RV of C. lineata shows 2-3 rows of areolae with a gap at the poles as C. coreana. The length to width ratios and the numbers and density of the SV areolae are similar in C. coreana and C. euglypta (sec. Romero and Jahn 2013, figs 9-18) (see morphometric values in Table 1). In C. euglypta the hyaline rim is barely visible externally and the raphe mantle areolae rows are only 2 in C. euglypta.

With 2.6-2.87% for rbcL and 6.1% for 18SV4 C. coreana has the lowest p-distance with the strain UTEX FD23 named C. placentula, but 4.0-4.1% for rbcL and 7.4% for 18SV4 to the epitype of C. placentula var. placentula (see detailed values in Tables 2 & 3).

• Author
  R.Jahn and B.M.Suh 2020
• Length Range
  25.5-59.3 µm
• Width
  14.1-36.6 µm
• Striae in 10µm
  18-24 raphe valve, 18-24 rapheless valve