Australoneis J.M.Guerrero & Riaux-Gobin, 2021

Guerrero, José M., Riaux-Gobin, Catherine, Debandi, Juan I., Zacher, Katharina, Quartino, Maria Liliana & Campana, Gabriela L., 2021, Morphology of Australoneis gen. nov. and A. frenguelliae comb. nov. (Achnanthales, Bacillariophyta) from the Antarctic Peninsula, Phytotaxa 513 (2), pp. 81-98 : 93-95

Australoneis J.M.Guerrero & Riaux-Gobin gen. nov.

Description:—Frustules with up to five open, ligulate copulae. Valves elliptic to oblong-elliptic with round to cuneate apices. SV: Slightly concave valve face split in two zones by a zigzagged crista marginalis, transapically prolonged in raised marginal virgae. Marginal zone with triseriate to multiseriate striae. Mid-valve zone with bi- to triseriate striae and ornamented with a reticulate, embossed structure. Areolae round to reniform, occluded by hymenes with radial slits and mostly supported by one peg. Multiple pores at the end of each marginal stria, external openings rimmed and internally occluded by a domed hymen, on a shallow chamber-like depression. SVVC thick with short, pegged fimbriae. RV: Concave, with axial hyaline structures, internally raised, splitting the valve face in two zones. Marginal zone with multiseriate striae composed of irregularly arranged areolae. Mid-valve zone with multiseriate striae composed of bigger areolae, arranged in a quincunx pattern. Areolae round, occluded by hymenes with radial slits. Raphe straight, filiform, with distal simple endings, round and near the apices; proximal endings close and dropshaped, internally bent to opposite directions. Conspicuous helictoglossae. Axial area narrow; central area roundish and prominent. RVVC narrow and hollow, with undulated fimbria-like extensions. A second copula thick with no fimbriae.

Etymology:—The name refers to the austral (= southern) hemisphere, where the new genus is up to now restricted.

Generitype:— Australoneis frenguelliae (Riaux-Gobin & J.M.Guerrero) J.M.Guerrero & Riaux-Gobin comb. nov.

Australoneis frenguelliae (Riaux-Gobin & J.M.Guerrero) J.M.Guerrero & Riaux-Gobin comb. nov. LM Figs 1–35 ; SEM Figs 36–75 .

Basionym:— Campyloneis frenguelliae Riaux-Gobin & J.M.Guerrero in Riaux-Gobin et al. (2019a, p. 161–162, figs 54–59).

Epitype:— population from Potter Cove ( Western Antarctic Peninsula ), sample “Col 04, 14b” ( LPC 15910!). Herbarium of División Ficología “ Dr. Sebastián A. Guarrera ”, Museo de La Plata, Argentina .

Synonyms:— Cocconeis orbicularis Frenguelli & H.A.Orlando , nom. inval.

Cocconeis reticulata var. deceptionis Frenguelli & H.A.Orlando , nom. inval.

Habitat:—Marine, benthic.

Distribution:—Currently, A. frenguelliae is found in Antarctic marine environments and the South Pacific Ocean ( Chile).

TABLE 1. Main morphological features distinguishing the new genus Australoneis from the closely allied genera Cocconeis ,

Campyloneis , Xenococconeis and Amphicocconeis .

Remarks:—In view of the lack of raw type material available for SEM studies, we designate here the population from Potter Cove, sample “Col 04, 14b” (LPC 15910), as epitype of Australoneis frenguelliae .

Observed with LM, the combination of SV with a zigzagged structure splitting the valve face in a marginal sector with multiseriate striae and a mid-valve sector with a reticulate pattern and variably developed striae, and a RV with thick axial and transapical structures delimiting multiseriate marginal and mid-valve striae, easily permit the distinction of A. frenguelliae from other species of Cocconeidacean genera. The taxon illustrated in SEM (external SV view) by Majewska et al. (2014, fig. 2b) as Cocconeis sp. 1 , also from South Shetland Islands, with an indented crista marginalis splitting the valve face in two sectors, embossed transapical structures, 4–5 multiseriate striae in 10 µm and 35 × 23 µm in size (measured on the figure), most probably belongs to A. frenguelliae .

The distinctive morphological features of the new genus and those of the closely related Campyloneis , Cocconeis , Xenococconeis and Amphicocconeis are summarized in Table 1. Further studies combining morphological and molecular data could help to shed light on the taxonomic relationships between Australoneis and the other genera of Cocconeidaceae and thus clarify its phylogenetic position within the lineage of the Achnanthales .

Figures

FIGURES 1–29. LM images of Australoneis frenguelliae comb. nov. 1–2, 3–4, 24 from sample LPC 15911 (slide c, untreated); 12, 15–16, 28 from sample LPC 15910 (slide a, treated); 5–8, 10–11, 13, 17, 19–23, 27 from sample LPC 15908 (slide c, untreated); 9, 14, 18, 25–26, 29 from sample LPC 15908 (slides a and b, treated). 1–2. Complete frustule showing SV with hyaline structures splitting marginal and mid-valve striae (Fig. 1) and RV with filiform raphe and finely areolate mid-valve striae (Fig. 2). 3–14. Decreasing size series of SV. Note the variation in valve outline and in the extension of mid-valve striae. 15–29. Decreasing size series of RV. Note strong axial and transapical structures, raised axial area and prominent central nodule. Scale bar: 10 µm. Scale bar is the same for all LM figures.

FIGURES 30–35. LM images of Australoneis frenguelliae comb. nov. Sample LPC 15911 (slide c, untreated). SV at different focus levels showing SVVC still in place. Note short pegged SVVC fimbriae (arrows). Scale bar: 10 µm.

FIGURES 36–44. SEM images of Australoneis frenguelliae comb. nov. 36–39, 41 from sample LPC 15910 (untreated); 40, 42–44 from sample LPC 15908 (treated). SV external views. 36. Valve in face view. Note crista marginalis and transapical raised structures. 37. Valve in face view and underlying detached fimbriate SVVC (arrow). 38. Detail of the valve apex. 39. Detail of valve margin showing multiple pores at the end of the stria (arrow) above the shallow furrow (arrowhead) delimiting valve face from valve mantle. 40. Detail of nonareolate mid-valve zone showing embossed transapical structures (arrow) and scattered small pores (arrowheads). Note the numerous small silica warts covering the valve face. 41. Mid-valve short stria showing pegged areolae. 42. Areola of marginal stria occluded by hymen with radial slits and supported by one peg. 43. Detail of valve margin showing multiple pores with rimmed openings (arrow). Note that some of the areolae are round and with hymenes not pegged (arrowheads). 44. Detail of the marginal pores showing rimmed to shortly conical external openings (arrows). Scale bars: 200 nm (Figs 42, 44), 500 nm (Figs 41, 43), 1 µm (Fig. 39), 2 µm (Figs 38, 40), 5 µm (Figs 36–37).

FIGURES 45–54. SEM images of Australoneis frenguelliae comb. nov. 45, 47, 49 from sample LPC 15908 (treated); 46, 48, 50–51, 54 from sample LPC 15910 (untreated); 52–53 from sample LPC 15908 (untreated). SV internal views. 45, 47, 49. SV without copulae. Note the variable extension of the mid-valve striae. 46. Detail of an elliptic, bi- to triseriate mid-valve stria. 48. Detail of a roughly triangular, multiseriate marginal stria. 50. Areolae of marginal stria occluded by hymenes with radial slits. 51, 54. Detail of the valve margin showing pores occluded by domed hymenes and lying in shallow marginal chamber-like depressions (arrows). 52. SV with SVVC still in place. Note pegged fimbriae lying on the raised virgae (arrows). 53. Detail of the valve apex showing the open SVVC (arrow). Scale bars: 200 nm (Figs 46, 50), 500 nm (Fig. 48), 1 µm (Figs 51–54), 5 µm (Figs 45, 47, 49).

FIGURES 55–63. SEM images of Australoneis frenguelliae comb. nov. 55–57, 61–63 from sample LPC15910 (untreated); 58–60 from sample LPC 15908 (treated). RV external views. 55, 57. Complete frustules showing cingulum composed of at least 5 copulae. Note in zigzag hyaline axial area in the RV delimiting a concave mid-valve zone and a raised marginal zone. 56. Detail of Fig. 55 showing the marginal rim surrounding RV (arrow) and ligulate copulae (arrowheads). 59. Valve face. Note the different areola sizes and arrangement between marginal and mid-valve zones. 58. Detail of valve apex showing distal raphe ending terminating in a large and round pore. 60. Detail of the central area showing proximal raphe endings relatively close to each other and with tear-shaped pores. 61. Detail of the valve marginal zone showing striae with multiple, randomly arranged areolae and slightly concave virgae. 62. Round areolae of marginal striae. 63. Detail of the areolae occluded by hymen perforated by slits of different lengths. Scale bars: 200 nm (Figs 62–63), 1 µm (Figs 58, 60–61), 2 µm (Fig. 56), 5 µm (Figs 55, 57, 59).

FIGURES 64–71. SEM images of Australoneis frenguelliae comb. nov. 64–65, 67, 69 from sample LPC 15910 (untreated); 66, 70–71 from sample LPC 15908 (treated); 68 from sample LPC 15911 (untreated). RV internal views. 64. Valve with partially broken RVVC, open at one pole (arrow). 66. RV showing raised axial structures and marginal virgae. 68. Tilted valve showing flat virgae at mid-valve and more raised marginal virgae, more prominent towards the margin (arrows). 65. Detail of raised axial structure and marginal virgae. Note undulated RVVC with fimbria-like undulations attached to the virgae (arrowheads) and a second, flat copula (arrow). 67. Detail of valve margin showing broken, hollow RVVC (arrowhead) with “fimbriae” attached to the raised virgae (arrow). 69. Round areolae occluded by hymen perforated by radial slits. 70. Detail of the valve apex showing distal raphe ending with prominent helictoglossa. 71. Detail of the prominent central nodule showing proximal raphe endings bent in opposite directions. Scale bars: 200 nm (Fig. 69), 1 µm (Figs 65, 67, 70–71), 5 µm (Figs 64, 66, 68).

FIGURES 72–75. SEM images of Australoneis frenguelliae comb. nov. 72–74 from sample LPC 15911 (untreated); 75 from sample LPC 15910 (untreated). RV internal views with parts of the copulae still in place. 72. Second copula, open at one pole (arrow). 73–74. Valves showing broken, hollow RVVC (arrowheads) and thicker, no fimbriate copulae (arrows). 75. Detail of the valve in Fig. 64 with partially broken SVVC. Note unbroken portion to the left (arrow) and broken portion to the right, showing the hollow, tubular nature of the SVVC (framed arrowhead) and wavy “fimbriae” attached to virgae (arrowheads). Scale bars: 2 µm (Figs 74–75), 5 µm (Figs 72–73).