Nitzschia incurva Grunow, 1878

Lobban, Christopher S. & Witkowski, Andrzej, 2023, Marine benthic diatoms of Guam: new records, Dictyoneis apapae sp. nov., and updates to the checklist, Micronesica 2023 (2), pp. 1-75 : 12

Nitzschia incurva Grunow Figs 75–78

Syn.: Nitzschia lorenziana Grunow in Cleve & Grunow (nom. illeg.)

Ref. illus.: Navarro 1982, pl. 35, fig. 4; Poulin et al. 1990, p. 87, figs 67, 68, 71, 72 ( SEM); Witkowski et al. 2000, p. 392, pl. 210, figs 24, 25, pl. 211, fig. 3, pl. 212, figs 1–3 (all as N. lorenziana )

Samples: GU58G-4A, GU44I-1, GU44Z-15

Dimensions: Length 18.5 µm, width 7.4 µm; striae 20 in 10 µm.

Diagnostics: Weakly sigmoid in girdle view, keel eccentric except in long-rostrate apices, striation bold in LM because of external costae between the striae; central striae biseriate towards to keel, triseriate towards the margin ( Fig. 78 ), becoming rings of pores with central row of pores and diminishing towards apex ( Fig. 77 ). Eccentric keels of the two valves are on opposite sides of the frustule (nitzschioid, not hantzschioid) ( Figs 77, 78 ). Keel canal is closed except for circular fenestrae ( Fig. 77 ).

Comments: Guiry (2017) explains why lorenziana is illegitimate and provides the earlier synonym. The ultrastructure of our specimens clearly matches SEM images in Poulin et al. (1990). It is apparently a brackish/estuarine species, with wide temperature tolerance (from Gulf of St. Lawrence to Florida + Guam). Abundant in Vietnam and Indonesia (Witkowski, unpubl.). Lopez-Fuerte et al. (2010: p. 63, pl. 37, fig. 21) show var. subtilis Grunow from Mexico and list the nominate variety. Nitzschia incurva somewhat resembles N. gaoi Bing Liu, S. Blanco & B.Q. Huang (2019) , but that has small conopeal canals and uniseriate striae. Lobban & Ashworth (2022b) did not transfer N. gaoi or their own N. maiae Lobban, Ashworth, Calaor & E.C.Theriot to Homoeocladia because of maintaining a narrow definition of the morphology of Homoeocladia and noted some other species in the region with doubtful formation of a conopeal canal that also have T-shaped external costae (one shown in Lobban 2023a, figs 4F, G).

Figures

Figures 71–80. Moreneis, Nitzschia and Olifantiella. SEM except Fig. 71. Figs 71–74. Moreneis hexagona. Fig. 71. Valve in LM (DIC). Fig. 72. Valve exterior, showing isolated pores at the Voigt faults (arrows). Fig. 73. Valve exterior detail showing central raphe endings characteristic of the genus and c-shaped areolae. Fig. 74. Valve interior. Figs 75–78. Nitzschia incurva. Figs 75, 76. Guam voucher frustules at different angles. Figs 77, 78. Yap specimens showing interior and details of areolae. Figs 79, 80. Olifantiella mascarenica frustule showing the characteristic buciniportula (arrow). Scale bars: Fig 75 = 10 µm, Figs 71, 72, 74, 76, 77 = 5 µm, Figs 73, 78 = 2 µm, Figs 79, 80 = 1 µm.