Urosolenia subtenuis Kociolek & Liu, 2016

Liu, Yan, Kociolek, J. P. & Fan, Yawen, 2016, Urosolenia and Acanthoceras species from Hainan Province, China, Phytotaxa 244 (2), pp. 161-173 : 167

Urosolenia subtenuis Kociolek & Liu , sp. nov. ( Figs 35–51 )

LM: frustules solitary, small, subcylindrical. Valve asymmetrical, conical, forming a slightly curved extension. Total frustule length: 66–89 μm, pervalvar length: 27–37 μm, width: 6–9 μm, extension length: 18–27 μm, girdle band density: 5–6 per 10 μm. SEM: valve areolae irregularly arranged, small and nearly round, 9–10 per 1 μm, with one or two round poroids located on the base of the extension ( Figs 45, 47 ) surrounded by irregular, rib-like structures ( Figs 45, 47, 49 ). Rib-like structures on the base of the extension do not extend to the valve. Girdle band width: 0.7–1.5 μm, with small, open areolae irregularly arranged, 7–9 per 1 μm. Imbrication line visible. Tip of the extension resembles a ligula surrounded by 2–3 teeth ( Figs 50, 51 ).

Type:— CHINA. Hainan Province: Orchid valley, unnamed stream, in sediments, Y. Liu & L. Li, 14 February 2012 (holotype: HANU!, individual in slide THGZ 2012015, here illustrated as Fig. 39 , isotype: COLO! JPK material no. 12HN15).

Etymology:— This species is named for its similarity with Rhizosolenia eriensis var. tenuis Hustedt (1942: 19)

Remarks:— Urosolenia obesa Freire, Tremarin & Ludwig in Tremarin et al. (2013: 3) shares some features with our species, such as the small frustule and the presence of two teeth and a ligula at the tip of the extension ( Tremarin et al. 2013). However, the ligula appears longer in our taxon and, in addition, our new taxon is narrower and has fewer bands per 10 μm than U. obesa . Urosolenia braunii ( Hustedt 1952: 367) Rott & Kling in Rott et al. (2006: 114) is also a small taxon in this genus, but it possesses a shaft of the extension that is variously ornamented ( Rott et al. 2006), which makes it quite distinct. Urosolenia parva Rott & McGregor in Rott et al. (2006: 117) and U. subtenuis differ by the former having denser bands per 10 μm, a variable number of poroids on the valve, a smooth process surface, absence of rib-like structures and an extension terminating with a long seta and two teeth ( Rott et al. 2006). Rhizosolenia eriensis var. tenuis is also similar to our new species. This taxon was reported from the Indomalayan Archipelago, in somewhat close proximity to Hainan Province. It should belong to the genus Urosolenia , but no detailed morphological research has been done on this taxon, and it has not been formerly transferred from Rhizosolenia to Urosolenia . The original description of Hustedt (1942) mentions only “Zellen zarter als bei der var. morsa , insbesondere sind die Borsten dünner.”, and the available light microscope pictures are from Simonsen (1987, plate 400: 1–6) without any description. Compared with our species, Rhizosolenia eriensis var. tenuis is shorter (based on our measurements from Simonsen’s pictures, total length of frustule: 41–49 μm, body length: 19–25 μm, process length: 10–13 μm, width: 6–7 μm; 9–11 cingula per 10 μm), slightly narrower, and has more cingula per 10 μm ( Hustedt 1942).

Figures

FIGURES 35–43: Urosolenia subtenuis, LM. Type material from Yalong vally forest park, Fig. 39 is of the holotype. Scale bar = 10 μm.

FIGURES 44–51: Urosolenia subtenuis, SEM. 44. External view of whole frustule, scale bar = 5μm. 45. External view of valve and bands, scale bar = 4 μm. 46. External view of bands areolae, scale bar = 5 μm. 47. External view of valve, showing the rib-like structure on the base of the extension (black arrow) and round poroids on the base between them (white arrow), scale bar = 2 μm. 48. External view of valve and bands with areolae, scale bar = 4 μm. 49. External view of valve, showing the rib-like structure on the base of the extension (black arrow), scale bar = 2 μm. 50, 51. Magnification of extension ends with 2–3 teeth and a ligula, scale bar = 500 nm.