Staurastrum exlooënse Van Westen et Coesel, Van Westen et Coesel, 2018

Van Westen, Marien C. & Coesel, Peter F. M., 2018, Taxonomic notes on desmids from the Netherlands II, with a description of six new species, Phytotaxa 385 (1), pp. 1-12 : 8

Staurastrum exlooënse Van Westen et Coesel sp. nov. ( Figs 4 , 41–46 )

Cells broader than long, deeply constricted. Sinus widely open and acute-angled. Semicell body subfusiform, the apical angles produced to form rather long, slightly diverging processes. Apex of the semicell body with two elevated, bidentate verrucae. Processes tipped with 3 stout spines and furnished with acute granules and denticulations arranged in indistinct concentric series, the dorsal denticulations being larger than the ventral ones. Semicells in apical view 3- radiate with straight sides, the angles produced to form processes . Semicell body ornamented with a hexagonal ring of emarginate verrucae, rest of the body free of granules.

Dimensions (including processes): length 22–24 μm, breadth 43–50 μm, isthmus 6.4–8 μm.

Type:— THE NETHERLANDS. Drenthe: pool in Exloerkijl near Exloo, 52.8903° N, 6.9314° E, in plankton, pH 8.7 conductivity 340 μS cm-1. Van Westen, 19 July 2010 (holotype L! Hugo de Vries Lab 2018.05, preserved as a fixed natural sample).

Etymology:—The species is named after the village near the type location.

Differential diagnosis:—The above-diagnosed Staurastrum species resembles given forms of St. anatinum Cooke et Wills ( Cooke 1881: 92, pl. 139: 6), in particular St. anatinum var. curtum G.M. Smith (1922: 354 , pl. 12: 6–7) and to a lesser extent St. anatinum var. denticulatum G.M. Smith (1924: 95 , pl. 75: 21–25). Both of those varieties, however, have larger cell dimensions and lack, in apical view, the marked hexagon of emarginate verrucae on the semicell body. As for that latter feature, there is more resemblance with St. floriferum West et G.S. West (1896: 267) as depicted in Florin (1957). Apart from a somewhat questionable identification by Florin, St. floriferum is characterized by more slender processes relative to the semicell body. According to Coesel & Meesters (2013: 62–63), the highly polymorphic species St. anatinum most likely includes a number of separate species, not only differing in morphology but also in ecology. In view of that, we decided to describe St. exlooense as a new species.

Ecology and geographical distribution: —In Exloerkijl, and later on near Ter Apel in the province of Groningen, this species was found in a meso-eutrophic, rather large water body.

Figures

FIGURES 1–8. 1. Closterium joostenii. 2. Closterium cynthiaforme. 3. Staurastrum subcomptum. 4. Staurastrum exlooënse.5. Cosmarium abbreviatiforme. 6. Cosmarium kouwetsii. 7. Zygospore of Cosmarium spierense with adhering gametangial cells. 8. Cosmarium spierense.

FIGURES 41–52. 41–46. Staurastrum exlooënse (45, 46. SEM microphotographs). 47–52. Staurastrum subcomptum. (fig. 47 and 48 are different views of the same cell. (50–52. SEM microphotographs). Scale bar = 10 μm.