Gyrosigma baculum Herwig & Sterrenburg, 2014

Sterrenburg, Frithjof A. S., Haan, Myriam De, Herwig, Wulf E. & Hargraves, Paul E., 2014, Typification and taxonomy of Gyrosigma tenuissimum (W. Sm.) J. W. Griffith & Henfr., comparison with Gyrosigma coelophilum N. Okamoto & Nagumo and description of two new taxa: Gyrosigma tenuissimum var. gundulae var. nov. and Gyrosigma baculum sp. nov. (Pleurosigmataceae, Bacillariophyta), Phytotaxa 172 (2), pp. 71-80 : 76

Gyrosigma baculum Herwig & Sterrenburg , sp. nov. (Figs 24–27)

Valve linear, 82–92 µm long, 5.5–6.0 µ wide, transverse striae circa 18–19 in 10 µm, longitudinal striae circa 35–37 in 10 µm, raphe sternum staff-shaped in its apical portion.

Type:— ITALY, Cala Gonone , Sardinia ( BRM ZU 8 /35!, holotype, coordinates 7.4 East, 4.6 South = Fig. 24; Fig 25 is another specimen from the same slide, isotype; collection Herwig, isotype; collection Sterrenburg # 712, isotype) .

Valves very delicate, 82–92 µm long, 5.5–6.0 µm wide, practically parallel-sided and straight for most of their length, becoming sigmoid near acute apex. Raphe sternum straight except near apices, where it first curves to dorsal side and then recurves on a strongly eccentric and sigmoid course. Striation (Fig. 26): transverse striae circa 18–19 in 10 µm, longitudinal striae circa 35–37 in 10 µm, becoming irregular at the apices (Fig. 27). No hyaline central area visible, central raphe node minute and elongated.

Etymology: —The specific epithet baculum (“staff”) is chosen to describe the typical reversed curvature of the raphe sternum at the apices.

Habitat:—Littoral-marine, benthic.

Distribution:— Type locality only.

Observations:— Gyrosigma baculum differs from G. tenuissimum in two independent characters: the different course of the raphe sternum and stria density. Gyrosigma baculum somewhat resembles Gyrosigma uncinatum Ricard (1975: 209 , fig. 3) in valve contour and raphe sternum course but G. uncinatum has much coarser (15 in 10 µm) transverse striae, a value incompatible with the stria density of G. baculum . No type specimens for Gyrosigma uncinatum have been deposited in PC. No specimens have been isolated for G. baculum for SEM examination as it is very rare in the type material, but the LM findings of raphe sternum course and stria densities already permit separation from the described species.