Climaconeis 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 : 246

Climaconeis tarangensis Lobban , sp. nov. Figs 45–49 .

Diagnosis:— Curved species without craticular bars or stauros, differing from Climaconeis riddleae A.K.S.K. Prasad 2003: 14 in its lower stria density (20 vs 24–27 in 10 µm) and regular apically rectangular areolae.

Description:— Living cells not observed. Valves arcuate, 121–124 µm long, 4.5 µm wide at center, gradually tapering to 3.0 µm just before the weakly capitate apices, 3.5 µm wide ( Fig. 45 ). Striae 20–21 in 10 µm, parallel except convergent near apices and radiating around the apex; areolae apically rectangular ( Figs 46–49 ). Raphe biarcuate ( Fig. 45 ), the raphe slit partially covered by an irregular flap along the ventral side ( Figs 46, 47 ). External central raphe endings turned slightly ventral, terminal endings nearly straight. Internal raphe with a rib along one side, helictoglossa at the apex ( Figs. 48, 49 ). Copulae with two rows of apically-oriented pores similar to those on the valve ( Figs 46, 47 ).

Holotype hic designatus:— Specimen at 9.0 mm E, 6.4 mm S of the mark on slide 512, deposited at ANSP, accession # ANSP-GC20095 . Fig. 45 . Registration: http://phycobank.org/102760.

Type locality:— F.S.M. Yap State: Tarang (“ O’Keefe’s Island ”), 9.525 N, 138.132 E; subtidal sediments from 15 m depth, sample Y26 C. C.S. Lobban and M. Schefter, 25 September 1988 .

Etymology:— Named for the type locality.

Comments:— This species is very similar to C. riddleae , which has been recorded from Guam ( Lobban et al. 2011) and Chuuk (Park et al. in prep.), but Prasad (2003) described the areolae of that species thus: “squarish or subrectangular poroids… [sometimes] slightly apically elongated, especially at the apices.” In C. tarangensis the areolae are distinctly apically elongate even in the central part of the cell. Prasad’s images show a row of somewhat larger, square areolae along the ventral side of the raphe sternum (the same side that bears the silica flaps). While the differences in stria density and areola shape are small, it has become clear in this genus that such details must be taken into account in discriminating species [e.g., in distinguishing C. mabikii J.Park, Khim & J.H.Lee 2016: 592 from C. undulata ( Meister 1932: 41) Lobban, Ashworth & E.C.Theriot 2010: 295 – Park et al. 2016]. For C. tarangensis , with C. riddleae known from the region, it is especially clear that the differences cannot be dismissed as geographic variation between Atlantic and Pacific Ocean basins.

Figures

FIGURES 45–49. Climaconeis tarangensis. Fig. 45. Holotype, Y26C, DIC. Figs. 46–49. SEMs of valves from same sample. Fig. 46. Exterior central portion, also showing copulae. Fig. 47. External apical portion; note silica flap along one side of raphe. Fig. 48. Interior central portion. Fig. 49. Internal apical portion showing helictoglossa and convergent striae. Scale bars: Fig. 45 = 10 µm, Figs 46–49 = 2 µm.