Gyrosigma tenuissimum var. gundulae Hargraves & Sterrenburg 2014, var. nov.
Creators: name: Sterrenburg, Frithjof A. S.
name: Haan, Myriam De
name: Herwig, Wulf E.
name: Hargraves, Paul E.
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Chromista
Bacillariophyta
Bacillariophyceae
Naviculales
Pleurosigmataceae
Gyrosigma
Gyrosigma tenuissimum
Gyrosigma tenuissimum var. gundulae hargraves &amp; sterrenburg

description: Gyrosigma tenuissimum var. gundulae Hargraves & Sterrenburg var. nov. (Figs 28–36)   
As the species, but valves larger and more robust.  
 Type:— USA. Indian River Lagoon, Florida (BRM ZU 8 /74! holotype = fig. 28, coordinates 6.7 East, 10.0 South; collection Sterrenburg #721, isotype; collection Hargraves, isotype).   
 As G. tenuissimum, with comparable striation (Fig. 28, 30) but much more robust and larger: 159–190 µm long and 9.5–11 µm wide. With respect to G. tenuissimum var. tenuissimum, valve much broader at apices (Figs 32, 34), with presence of small accessory apical pore (Fig. 32, arrow). Externally, central raphe fissures (Figs 33) identical to G. tenuissimum var. tenuissimum. Some external areolar fissures of adjacent rows show tendency to fuse, forming the letter V (Fig. 33), as in G. tenuissimum. Internal raphe fissures show sideways twisting (Fig. 35).   
 Central bars around internal central raphe node markedly variable in their degree of silification but are often vestigial, reduced to 4 small “knobs” of silica (Figs 35 and 36). The extreme resolution of the special LM technique used reveals that one central bar (the lower in Fig. 30) may also consist of a continuous sharp ridge, the other (upper in Fig. 30) being reduced to two separate “knobs”, which matches the aspect seen in Fig. 7 of G. tenuissimum var. tenuissimum.   
 Etymology:— The epithet refers to the long-term support of the first author’s diatom studies by his spouse.   
 Habitat:—Found at temperatures of 21.9–30.5° C and salinities of 26.2–38.9 PSU; typical spring and summer conditions. The Indian River Lagoon is quite shallow (Hargraves & Hanisak, 2011), so that the presence of this taxon in plankton samples is not by itself indicative of a planktonic habitat.   
 Distribution:—Subtropical Indian River Lagoon, East coast of Florida: widespread (but rare).   
 Observations:— The vestigial central bars (4 “knobs”) match the situation in a specimen from the Adriatic illustrated in Höbel & Sterrenburg (2011: Fig. 12) that conforms to G. tenuissimum. The central bars are highly variable in shape in both G. tenuissimum and the variety described here. Deposition of silica is a quantitative process and marked variation in the solidity of the central bars is common in the genus. Probably the basic shape in the taxa discussed is as in Fig. 7 and 30, reduction leading to the aspect as in Figs 35 and 36.
description: Published as part of 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), pp. 71-80 in Phytotaxa 172 (2) on pages 76-78, DOI: 10.11646/phytotaxa.172.2.2, http://zenodo.org/record/5142351