Gyrosigma cf. obscurum (W. Smith) Griffith et Henfrey

Al-Handal, Adil Y., Torstensson, Anders & Wulff, Angela, 2022, Revisiting Potter Cove, King George Island, Antarctica, 12 years later: new observations of marine benthic diatoms, Botanica Marina (Warsaw, Poland) 65 (2), pp. 81-103 : 94

Gyrosigma cf. obscurum (W. Smith) Griffith et Henfrey ( Figure 81 )

Literature: ( Krammer and Lange-Bertalot 1986, p. 299, fig. 116: 1, 2; Patrick and Reimer 1966, p. 346, pl. 24, fig. 7).

Description: Length 144–170 µm, width 9–11 µm, transverse striae 28–30 in 10 µm.

Remarks: There has been controversial debate on whether this species belongs to Gyrosigma or Pleurosigma ( Reid 2004; Sterrenburg 1993, 2003) based on the angle of striae crossing in the center of the valve. The transverse striae which cross the apical axis at 90° can be easily seen under LM but the oblique striae were very difficult to resolve. According to Reid (2004), molecular analysis supports placing this species in Gyrosigma which is followed here. The observed specimens matched well the description of G. obscurum but as this species is considered freshwater, doubt arose. According to Sterrenburg (2003), marine records of this species were inaccurate.

Ecology and distribution: This species appeared in large numbers in Potter Cove but have not been observed in previous collections.

Figures

Figures 79–92: Marine benthic diatoms in Potter Cove, King George Island, Antarctica, summer 2015. (79) Gyrosigma arcuatum. (80) Gyrosigma fasciola. (81) Gyrosigma cf. obscurum. (82) Pleurosigma eudon var. kerguelensis. (83) Pleurosigm diversestriatum. (84) Pleurosigma strigosum. (85) Amphora gourdonii. (86) Amphora marina. (87, 88) Amphora sp. 1. (89) Amphora sp. 2. (90) Cylindrotheca closterium. (91, 92) Fragilariopsis cylindrus.