Nitzschia tarangensis Lobban, 2021

Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, Phytotaxa 508 (3), pp. 235-265 : 257-259

Nitzschia tarangensis Lobban , sp. nov. Figs 103–110 .

Diagnosis:— Differing from other conopeate Nitzschia spp. in the following combination of characters: linear valve with rib along the edge of the valve depression, valve-face areolae small, transapically oval; small pores in peri-raphe zone; apical keel extension present; raphe bordered by ribs.

* Incorrectly typed in their table 1 as 46–45.

Description:— Frustules spathulate in girdle view. Valves linear, 109–194 long, 10–12 µm wide ( Figs 103–104 ), striae 46 in 10 µm, comprising uniseriate rows of oval pores ( Figs 105–109 ). Striae nearest to the apex with few vimines ( Fig. 105, 108 arrow). Fibulae irregularly spaced, 2 in 10 µm (8–10 in 40 µm) ( Figs 103, 105 ). Conopeum 2.1 µm broad with straight margins; raphe bordered by prominent ribs and with a distinctive wave near the apex (going up over keel extension); prominent rib along the edge of the valve depression ( Figs 106, 107 ). Peri-raphe area with 1–2 rows of small, circular pores (unlike the valve face areolae, but probably like those in the valve-depression), more near apex; in most specimens ( Fig. 107 ) there was one row on one side, adjacent to the inner edge of the conopeum, and 1–3 on the other side, adjacent to the raphe rib. Externally areolae on valve face oval transapically elongated; a prominent hyaline zone along the valve border. Internal views were distinguished from similar species on the criterion of periraphe pores visible in keel. Areolae changed from oval to circular foramina in the valve depression; position of the external rib marked by a row of longer foramina ( Figs 108–110 ). No longitudinal break in the striae along the fibulae insertions ( Fig. 110 ). Copulae not positively distinguished from several similar species because valve characters were hidden or unclear.

Holotype hic designatus:— Specimen at 11.0 mm E, 7.3 mm S of mark on slide 512, deposited at ANSP, accession # ANSP-GC20095 . Fig. 103 . Registration: http://phycobank.org/102765.

Type locality:— Yap , Tarang (“ O’Keefe’s Island ”), 9.525027 N, 138.1324 E; subtidal sediments from 15 m depth, sample Y26 C. C.S. Lobban and M. Schefter, 25 Sep. 1988 .

Etymology:— Named for Tareng (O’Keefe’s Island) in Colonia Bay, Yap where it was discovered.

Comments:— The asymmetry in the rows of pores in the peri-raphe zone has not been seen before in conopeate Nitzschia , but it is the combination of characters that defines the species. Other spathulate species include N. spathulata Brébisson ex. W. Smith 1853: 40 and N. spathulatoides Lobban, Ashworth, Calaor & E.C.Theriot 2018: 227 . Species with a rib along the edge of the valve depression include N. dagmannii Lobban, Ashworth, Calaor & E.C.Theriot 2018: 223 , and N. electrae Lobban, Ashworth, Calaor & E.C.Theriot 2018: 228 . Another species with ribs bordering the raphe is N. jordanii Lobban, Ashworth, Calaor & E.C.Theriot 2018: 213 ( Table 3). Nitzschia tarangensis resembles N. distans var. tumescens Grunow in Cleve & Grunow 1880: 87 but as described in Peragallo & Peragallo (1897 –1908, p. 284, pl. 73, figs 1, 2), that form is distinguished from the nominate variety only in having slightly spathulate apices, and from N. spathulata only in the more distant fibulae (1–3 vs 3–5 in 10 µm). Given the need for ultrastructural characters to sort out species in this group ( Lobban et al. 2019), the new species cannot be assigned to N. distans var. tumescens .

Figures

FIGURES 103–110. Nitzschia tarangensis. SEM except Fig. 103 DIC, all from Y26C. Fig. 103. Holotype specimen, valve view. Fig. 104. Whole valve in SEM, external view. Fig. 105. Internal view of valve fragment showing fibula density (details in Figs 109, 110). Fig. 106. External aspect of apex showing keel extension (long arrow), broad hyaline border of valve (short arrow), and numerous apical pores (arrowhead). Fig. 107. Mid portion of valve showing ribs along edge of valve depression (arrow) and each side of the raphe, and differing pattern of peri-raphe pores on opposite sides of the raphe (arrowheads). Figs 108–110. Internal views of valves showing apices (different valves) and a mid-portion. Arrow on Fig. 108 points to keel extension, arrow on Fig. 109 points to rimate striae near apex. Arrow on Fig 110 points to line of elongate foramina under the rib along the edge of the valve depression. Arrowheads on Figs 108–110 point to periraphe pores visible in the keel. Scale bars: Fig. 105 = 20 µm, Figs 103, 104 = 10 µm, Figs 106–109 = 5 µm, Fig. 110 = 2 µm.