Orthoseira variabilis Cefarelli, Guerrero & Vouilloud

Cefarelli, Adrián O., Guerrero, José M., Quartino, Liliana, Campana, Gabriela & Vouilloud, Amelia A., 2024, Orthoseira variabilis sp. nov., a new diatom from a snow patch in Potter Cove, King George Island, Antarctica, Phytotaxa 655 (1), pp. 37-53 : 39-47

Orthoseira variabilis Cefarelli, Guerrero & Vouilloud sp. nov. Figs 2–94

Description

LM ( Figs 2–48 ): Frustules cylindrical in girdle view ( Figs 2–14 ). Valve face flat to slightly convex, gently curving to the mantle, sometimes exhibiting both states in valves of the same frustule ( Fig. 7 ). Valve mantle with a step visible in some specimens ( Figs 6, 7 ). Mantle striae in parallel rows, sometimes dichotomise, continuous beyond the step up to a distinct, hyaline collum ( Figs 8, 9, 12, 14 ). Girdle bands ornamented with large poroids, arranged in one row or more scattered, in irregular rows ( Figs 3, 5, 9, 11–14 ). Valves disc-shaped, usually with scalloped outline when focused on the valve interior ( Figs 18, 23–30, 46–48 ). Central area hyaline and small, occupying approximately ⅕ to ¼ of the total valve diameter, irregularly shaped, with 3–4 carinoportulae. Valve face striae radiating out of central area, uniseriate in the middle and becoming branched near the margin, interspersed with shorter striae that arise distant from central area. Striae composed of conspicuous, round areolae ( Figs 15–20, 22–45, 47, 48 ). Marginal spines irregularly placed, present only in a few specimens ( Figs 14 , 47, 48 ).

SEM ( Figs 49–84 ): Externally , valve face varying from almost flat to convex ( Figs 49–54 ). Carinoportulae opening surrounded by raised rims forming incomplete semicircular collars ( Figs 55, 56 ). Central area ornamented with irregular silica ridges located between the carinoportulae ( Fig. 56 ). Valve face striae extending to the valve face/mantle junction ( Figs 51 , 61, 65 ). Areola openings surrounded by distinct rims, irregularly silicified and with small spinules ( Figs 56, 57 ) or forming a complete ring ( Fig. 58 ), sometimes both types of areolae occurring in the same valve. When present, spines simple, solid, conical and stellate at the base ( Figs 59, 60 ). Areolae more densely packed forming a sort of pore field at the valve face/mantle junction in most valves; at intervals, beneath the pore fields, mantle striae often bifurcated ( Figs 61, 65 ). On the mantle portion between the step and the collum, interstriae raised and areola openings between them round to apically elongated and without raised margins ( Figs 61, 62, 64, 65 ). Collum without perforations, in some specimens separated from the striated area by a circumferential smooth area ( Figs 61, 64 ).

Internally, valve face flat to slightly rounded towards the mantle. Shallow caverns at the valve face/mantle junction, in number of 5 to 8 per valve ( Figs 66–70, 72 ). In the areas between caverns interstriae distinctly raised and continuous from valve face to mantle ( Figs 68, 78 ). Caverns rather inconspicuous in some specimens ( Fig. 71 ). Carinoportula openings circular in outline, surrounded by an area of granular appearance and occluded by a silica covering ( Figs 73, 74, 77 ); a rosette-like occlusion visible when the covering is detached ( Figs 73, 74 ). Etched slits between the carinoportulae visible ( Figs 73, 74 ), although very faintly delineated in some specimens ( Fig. 75 ). Areolae occluded by stellate vela ( Figs 75, 77 ), except at caverns where no areola occlusion is visible ( Figs 76, 77 ). Smaller, unoccluded perforations are scattered among areola openings ( Figs 75–78 ).

Cingulum consisting of at least four open and fimbriate copulae ( Figs 63, 65 , 84 ). Valvocopula with a thickened pars interior ( Figs 79–81 ), a row of axially elongated large poroids on its advalvar margin and irregular rows of small poroids in its middle part ( Figs 62–65 , 80, 81 ). The rest of the copulae ligulate ( Figs 62–65 , 82, 83 ), with a row of small poroids in the advalvar margin and poroids scattered or arranged in somewhat irregular rows perpendicular to pervalvar axis.

Morphometric data:

Valve diameter: 11.0–36.5 μm (x = 20.0 μm, n = 154). Valve stria density: 16–24 in 10 µm (x = 19, n = 119). Valve areola density: 15–23 in 10 µm (x = 18.5, n = 100). Mantle height: 7.5–15.5 μm (x = 11.0 μm, n = 31). Mantle stria density: 18–27 in 10 µm (x = 23.5, n = 68). Mantle areola density: 20–31 in 10 µm (x = 22.5, n = 51). Valvocopula exterior width: x = 5.10 µm (n = 22). Density of valvocopula elongated poroid: 13–18 in 10 µm (x = 15.5, n = 31).

Type: — ANTARCTICA, King George Island/Isla 25 de Mayo , Potter Cove coast (62.2464° S, 58.6796° W), snow patch. LPC 13325 , February 15, 2017. (Holotype designated here, specimen positioned in England Finder D39/3, slide 13325(1)!, illustrated in Figs 24, 25 ).

Etymology: The specific epithet “ variabilis ” refers to the high variability in several morphological features exhibited by the new species.

Ecology and associated diatom flora: Orthoseira variabilis was found in dusty snow and associated with mosses in a circumscribed coastal area. The accompanying flora is mostly composed of taxa usually living in aerophilic environments such as several species of Chamaepinnularia Lange-Bertalot & Krammer (in Lange-Bertalot & Metzeltin 1996: 32), Humidophila (Lange-Bertalot & Werum) R.L. Lowe & al. (2014: 352) , Luticola D.G.Mann (in Round et al. 1990: 670), together with Hantzschia amphioxys (Ehrenberg) Grunow (in Cleve & Grunow 1880: 103) and Pinnularia borealis Ehrenberg (1843: 420) , among others. Marine diatom species such as Fragilariopsis curta (Van Heurck) Hustedt (1958: 160) , F. cylindrus (Grunow ex Cleve) Helmcke & Krieger (1954: 17) , Pseudogomphonema kamtschaticum (Grunow) Medlin (in Medlin & Round 1986: 216), Shionodiscus gracilis (Karsten) Alverson, Kang & Theriot (2006: 259) and S. gracilis var. expectus (VanLandingham) Alverson, Kang & Theriot (2006: 259) were also observed denoting a marine influence presumably through wind and sea spray aerosol.

Remarks: Some specimens exhibited on their valve faces patches of smooth areas ( Figs 52, 58 ) that were interpreted as two layers of silica deposition, the upper one being responsible for the spiny rims and rings that surround the external areola openings.

Some initial valves and initial cells were observed ( Figs 85–94 ), with clearly convex valve face ( Figs 85–87 ), more irregularly arranged striae composed of rimmed areolae, an irregularly-shaped, somewhat bilobate central area, and numerous (up to eight) carinoportulae with incompletely developed collar ( Figs 88–94 ). Crawford (1981) described initial valves as structurally similar to vegetative valves except that they are hemispherical in shape, without distinction between valve face and mantle, and lack spines. He illustrated in his figs 52-55 initial valves of Orthoseira sp. that also exhibit a central area with two groups of carinoportulae. Similarly, Roemer & Rosowski (1980) documented hemispherical initial valves of Orthoseira (= Melosira ) roeseana with multiple (4–10) carinoportulae which are reduced to 3–4 in vegetative valves.

Figures

FIGURES 2–14. Orthoseira variabilis sp. nov. LM. Frustules in girdle view. Note mantle step (Fig. 7, black arrow) and marginal spines (Fig. 14, white arrowheads). Figures marked with “=” are the same frustules with a different focus. Scale bar: 10 µm (Scale bar is the same for Figs 2–13).

FIGURES 15–48. Orthoseira variabilis sp. nov. LM. Specimens in valve view. Figs 24–25: Holotype. Figs 46–48. Same specimen in three different focus levels; note the marginal spines. Figures marked with “=” are the same valves with a different focus. Scale bar: 10 µm (Scale bar is the same for Figs 15–45 and for Figs 46–48).

FIGURES 49–60. Orthoseira variabilis sp. nov. SEM. Specimens in external view. Figs 49–54. Whole valve views; the arrow in Fig. 52 indicates a patch of smooth area. Figs 55–59. Details of valve surface, showing carinoportulae (Figs 55–56), areolar structure (Figs 56–58), a patch of smooth area (Fig. 58) and marginal spines (Fig. 59, white arrowheads). Fig.60. Mantle view; note the conic spines at the margin (black arrowheads). Figs 55 and 57 are details of Fig. 53; Fig. 55, rotated. Fig. 56 is a detail of Fig. 54, rotated. Fig. 58 is a detail of Fig. 52, rotated. Fig. 59 is a detail of Fig. 50. Scale bar: 10 µm (Figs 49–54), 5 µm (Fig. 60), 2 µm (Figs 55–59).

FIGURES 61–65. Orthoseira variabilis sp. nov. SEM. Specimens in girdle view. Fig. 61. Valve with pore field (arrow) and raised interstriae on the mantle. Note the collum (white arrowhead) separated from the mantle striae by a smooth area (black arrowhead). Figs 62–65. Whole frustules; note the presence of pore fields, step and collum in the mantle, and the cingulum composed by open, ligulate copulae. Collum (white arrowhead) and smooth area of the mantle (black arrowhead) are also indicated in Fig. 64. Fig. 63 is a detail of Fig. 62, rotated. Scale bar: 10 µm.

FIGURES 66–78. Orthoseira variabilis sp. nov. SEM. Specimens in internal valve view. Figs 66–72. Whole valve views. Note valves with shallow or inconspicuous caverns (arrows). Figs 73–78. Details of valve surface, showing areolar structure, carinoportulae, etched slits (Figs 73–74, arrows), and shallow caverns (Figs 76–78); note small unoccluded perforations among the areolae (arrowheads). Fig. 75 is a detail of Fig. 71, rotated. Fig. 76 is a detail of Fig. 72. Fig. 77 is a detail of Fig. 70. Fig. 78 is a detail of Fig. 66. Scale bar: 10 µm (Figs 66–72), 2 µm (Figs 73–78).

FIGURES 79–84. Orthoseira variabilis sp. nov. SEM. Girdle elements. Fig. 79. Valvocopula with internal silica thickening attached to valve. Fig. 80. Detached open valvocopula. Fig. 81. Broken frustule in internal view showing valve and attached valvocopula with thickened pars interior and poroids. Fig. 82. Open, ligulate copula. Fig. 83. Detail of a copula showing ligula. Fig. 84. Detail of a copula showing tiny poroids and fimbriae. Scale bar: 10 µm (Figs 79–80, 82), 5 µm (Figs 81, 83), 2 µm (Fig. 84).

FIGURES 85–94. Orthoseira variabilis sp. nov. Figs 85–92. LM. Initial cells. Figs 85–87. Girdle view. Figs 88–92. Valve view. Figs 93–94. SEM. Initial valve. Fig. 93. General view. Fig. 94. Detail of central area of specimen in Fig. 93, rotated; note the numerous and incompletely developed carinoportulae. Figures marked with “=” are the same valves with a different focus. Scale bar: 10 µm (Figs 85–93; scale bar is the same for Figs 85–92), 5 µm (Fig. 94).