Rhoicosphenia kloseri E.W. Thomas & R. Ligowski, 2016

Thomas, Evan W. & Ligowski, Ryszard, 2016, Rhoicosphenia kloseri, a new isopolar Rhoicosphenia (Bacillariophyta) species from the Antarctic with comparison to other isopolar Rhoicosphenia, Phytotaxa 265 (1), pp. 50-58 : 51-53

Rhoicosphenia kloseri E.W. Thomas & R. Ligowski , sp. nov. ( Figs 1–104 )

Frustules flexed in girdle view. Valves isopolar in valve view, linear with rounded apices, 9–27 μm long, 2.7–3.8 μm wide. Frustules heterovalvate, one valve concave with long raphe branches (R-valve), one valve convex with shortened raphe branches (D-valve). R-valve raphe straight, proximal raphe ends expanded externally, distal raphe ends curved in same direction externally, ending in helictoglossae internally. Axial area narrow, central area expanded laterally to margins. Striae strongly radiate at center of the valve and radiate throughout, 11–13 in 10 μm, composed of round areolae, 20 in 10 μm. D-valve raphe 1.0–2.5 μm long at each pole, external proximal ends straight, not inflated externally, external distal ends straight, terminating in helictoglossae internally. Striae parallel throughout, 9–13 in 10 μm, composed of round areolae, 20 in 10 μm. Both valves with short pseudoseptum at each apex. R-valve with condensed areolae at each pole, 3 per 1 μm. LM observations, living cells ( Figs 1–2 ): in unprepared slides, the living cells detached from the substrate are commonly visible in girdle view. Cells contain one lobed chloroplast. Cleaned frustules ( Figs 3–60 ), girdle view ( Figs 3–8 ): frustules are bent and very slightly wedge shaped. Bending is uniform and has the shape of the arc of a circle. Polar pseudosepta stretch up to 1/4 on the concave valve length and usually up to 1/5 of on the convex dorsal valve. One row of pores (14 – 17 in 10 μm) is present on the epicingulum and hypocingulum. Concave (R-valve) ( Figs 9–34 ): valve shape differs as the length of the valve increases. Striae close to the central area are irregular and less dense than striae close to the poles. In the central area of the valve there usually are no striae. However, on some valves longer than 20 μm, striae are present in the central area ( Figs 25, 26, 28, 31, 33, 34 ). Convex valve (D-valve) ( Figs 35–60 ): axial area very narrow. Striae can be irregular both in the middle of valve ( Figs 36, 40, 41, 43, 44, 52 ) and near the central raphe ending ( Figs 39, 43, 53, 54, 57 ). SEM observations, girdle view Figs 61–66 : at the poles of both valves the striae are more closely spaced than in the central part of the valves. The row of pores on the cingulum on concave valve is more or less straight and the pores at the poles are elongated, whereas the row of pores on the cingulum at the R-valve is curved, and the pores at the poles are also elongated. On frustules of different length, the number of more closely spaced striae at the poles is more or less equal (5–6), while the number of remaining striae vary from 3 ( Fig. 61 ) to 15 ( Fig. 65 ). Concave valve, external view ( Figs 67–77 ): the striae are radiate along the valve forming a narrow axial area. Striae are composed of round areolae; there is only one row of areolae along the axial area and they are elongated. The raphe slits terminate in the central area as drop shaped pores. As the raphe approaches the apices, it bends and then another small branch abruptly hooks back towards the center of the valve. The central area is expanded to the valve mantle with the exception of larger cells, in which shorter striae are located in the central area ( Figs 73, 74, 76 ). Concave valve, internal view ( Figs 78–84 ): arms of the slits are located asymmetrically. The internal central raphe endings are hooked in the same direction. Convex valve, external view ( Figs 85–94 ): axial area is narrow. Striae are parallel and irregular over the length of the valve. The central raphe endings are drop shaped. The raphe slits end at the poles in a curved terminal fissure. Convex valve, internal view ( Figs 95–104 ): proximal raphe endings are hooked in the same direction. One valve was found without a pseudoseptum ( Figs 102–104 ) which allows for the documentation of the raphe terminating in helictoglossae.

Type:— SOUTH SHETLAND ISLANDS. King George Island: Potter Cove (62.14 o S, 58.46 o W), epiphytic on G. confluens . Sample BRM R 1272 (holotype: BRM! Zu10/68, illustrated in Fig. 29 ).

Etymology:— Named in honor of Dr. Heinz Klöser, naturalist, ecologist, marine diatomist, and friend.

Taxonomic remarks and differential diagnosis:— Rhoicosphenia kloseri is most easily distinguished from the other isopolar Rhoicosphenia by its narrow valves, 2.7–3.8 μm in width. At its longest, R. kloseri that we observed and documented are 27 μm with a width of 3.8 μm. At its smallest, the type of R. adolfii is 21 μm with a width of 4.5 μm. This means that the smallest R. adolfii is wider than R. kloseri of comparable size, a key feature in demonstrating how narrow the valves of R. kloseri are when compared to other isopolar Rhoicosphenia . A comparison of the morphometric features of R. kloseri to the other isopolar Rhoicosphenia taxa, R. genuflexa , R. adolfii , and R. pullus , is presented in Table 1.

Distribution:— Known from various localities in the South Shetland Islands from epiphytes on Georgiella confluens . Rhoicosphenia kloseri is found also on the seabed in shallow sublittoral at depths ranging from 2 to 25 meters.

Figures

FIGURES 1–8. Rhoicosphenia kloseri, light microscope (LM). Girdle view. Fig. 1 is from sample 2009/194. Fig. 2 is from sample 2009/178, and Figs 3–8 are from sample BRM R1272. Figs 1–2. Living cells. Note the single chloroplast inside the cells. Figs 3–8. Size diminution series of cleaned cells. Note the slightly heteropolar cells and how the frustules bend regularly in the shape of the fragment of a circle. Scale bar = 10 μm.

FIGURES 9–34. Rhoicosphenia kloseri, LM. View of the concave R-valve. Size diminution series from sample BRM R1272. Note that striae close to the central area are irregular and less dense than at poles. Note the lack of striae in the central area, however sometimes striae are present. Note the differences in the shape between specimens. Scale bar = 10 μm.

FIGURES 35–60. Rhoicosphenia kloseri, LM. View of the convex D-valve. Size diminution series from sample BRM R1272. Note the irregular striae appearing alternately on both sides of the valve. Note the denser striae along the branches of the raphe. Scale bar = 10 μm.

FIGURES 61–66. Rhoicosphenia kloseri, scanning electron microscope (SEM). Girdle view. 61–65. Size diminution series. On frustules of different length the number of more closely spaced striae at the poles is more or less equal (5–6), while the number of remaining striae vary from 3 (Fig. 61) to 15 (Fig. 65). 66. Frustules after vegetative division. Scale bars: Figs 61, 63, 64, 66 = 5 μm, Fig. 62 = 3 μm, Fig. 65 = 8 μm.

FIGURES 67–84. Rhoicosphenia kloseri, SEM. 67–77. External view of the R-valve. 78–84. Internal view of the R-valve. 67–73. External view of size diminution series. Note the pores in the first column along the raphe are larger in diameter than the remaining pores. 74. External view of valve and their basal pole (Fig. 75) central area (Fig. 76) and head pole (Fig. 77). Note the same endings of raphe at poles and drop shape endings at the central area. 78–83. Internal view of size diminution series. 84. Central area with raphe hooked in the same direction. Scale bars: Figs 67, 68, 78, 79 = 3 μm, Figs 69– 71, 80, 81, 83 = 5 μm, Figs 72, 73, 82 = 8 μm, Fig. 74 = 10 μm, Figs 75–77, 84 = 2 μm.

FIGURES 85–104. Rhoicosphenia kloseri, SEM. 85–94. External view of the D-valve. 95–104. Internal view of the D-valve. 85–91. External view of diminution series. On frustules of different length the number of more closely spaced striae at the poles is more or less equal (5–8), while the number of remaining striae vary from 8–22. 92. External view of frustule, its head pole (Fig. 93) and its foot pole (Fig. 94). 95–101. Internal view of diminution series. Note irregular striae and different striae on opposite sides of the valve. 102. Internal view of frustule without short pseudoseptum at each apex (Figs 103 and 104). Note the raphes terminating in helictoglossae at each pole. Scale bars: Figs 85, 88, 89, 95–99 = 5 μm, Figs 86, 87, 92, 103, 104 = 3 μm, Figs 90, 100, 102 = 8 μm, Figs 91, 101 = 10 μm, Figs 93, 94 = 1 μm.