Cocconeis dirupta var. dirupta Gregory
- Dataset
- Distribution of the genus Cocconeis (Bacillariophyceae) along the Seogwipo coast of Jeju Island, South Korea
- Rank
- VARIETY
Classification
- kingdom
- Chromista
- phylum
- Bacillariophyta
- class
- Bacillariophyceae
- order
- Achnanthales
- family
- Cocconeidaceae
- genus
- Cocconeis
description
Description: Valves broadly elliptical, 9 – 23 μm long, 5 – 14 μm wide. SV: sternum narrow to broadly lanceolate, fusiform, sometimes slightly retracted in the middle. Transapical striae radiate, crossed by hyaline and longitudinal rows, 15 – 22 in 10 μm, one median stria often shorter on one or both side of the central area. RV: raphe slightly sigmoid. Sternum narrow and straight. Central area not developed or extended as transversely narrrow fascia, not reaching to the margins. Transapical striae radiate, 24 – 28 in 10 μm.
discussion
Remarks: The specimens described herein have valve outlines that are more elliptical rather than round-elliptical to discoid, as described for the lectotype designated by Riaux-Gobin et al. (2016). C. dirupta is distinguished from C. dirupta var. flexella by the straight axial area in the SV. In the literature, Cocconeis dirupta corresponds to two forms: one having large valves with a wide sternum (Kobayasi & Nagumo 1985, Riaux-Gobin et al. 2016) and the other having valves with a strong retraction in the middle of the sternum (Witkowski et al. 2000, Lobban et al. 2012). This species has a wide range in length and width dimensions, and both forms were found in the present study. The identifications were conducted according to the large forms designated by Hustedt (1933), and the small retracted forms by Lobban et al. (2012). The retracted forms collected in local areas have smaller dimensions, 9 – 17 μm long and 5 – 9 μm wide. In the smaller forms, transapical striae are abruptly denser at apices. This taxon was reportedly common along oceanic coasts (Witkowski et al. 2000), and in tropical coasts (Riaux-Gobin et al. 2011, Lobban et al. 2012). Here, frequent on seaweeds of the Seogwipo coast of South Korea.