Cosmarium regnesiforme Van Westen & Coesel, 2021

Van Westen, Marien C. & Coesel, Peter F. M., 2021, Taxonomic notes on desmids from the Netherlands IV, with a description of another five new species, Phytotaxa 522 (3), pp. 240-248 : 246-247

Cosmarium regnesiforme Van Westen & Coesel spec. nov. ( Figs. 8 , 21, 22, 23 , 36, 37 )

Diagnosis: Cells about as long as broad with a rather deep, widely V-shaped to U-shaped sinus. Semicells in frontal view triangular with deeply concave apex and downward bent apical angles. Semicell margin furnished with some six blunt dentations: two on either side of the apical indentation, usually two on each lateral side. Lateral parts of the semicell with a variable number (1-4) of scattered intramarginal dentations. Apical view elliptical-fusiform with on either side a blunt dentation near the poles. Semicells in lateral view subcircular. Chloroplast with a single, central pyrenoid.

Dimensions: cell length 7–10 µm, breadth 7.5–10.5 µm, L/B =0.8–1.1, thickness 4–5 µm, isthmus 3.5–4.5 µm

Type:— THE NETHERLANDS. Drenthe: moorland pool Kliplo near Dwingeloo, 52.834545 ° N, 6.438517° E, in Sphagnum squeezing, pH 6.9 conductivity 26 µS cm- 1. Van Westen, 27 June 2015 (holotype L! Hugo de Vries Lab 2021.05, preserved as a fixed natural sample and represented by our fig. 8) .

Differential diagnosis:—As its name indicates, C. regnesiforme resembles C. regnesi described by Reinsch (1867, p. 116, pl. 22AIII: 1–5). Main difference is in the shape of the semicell: triangular instead of rectangular. Concomitant to that, apical angles are bent downward giving the impression of drooping shoulders. Although the species C. regnesi is known for its multiformity, morphological variability mainly concerns its pattern of granulation ( West & West 1908; Förster 1982). In view of the essentially different shape of our above described algal form we are of opinion that it deserves the status of a separate species. The find of a similar form on several locations in the Dutch province of Drenthe and near Ambleside in the English Lake District renders it likely that it does not concern an incidental aberration.

Morphological details:—With respect to the ornamentation pattern of C. regnesiforme as revealed in scanning electron microscopy a remarkable dentate character of the bigger granules can be observed (figs 36, 37). As a similar feature is to be seen in SEM pictures of C. regnesi (fig. 38) a common characteristic of the C. regnesi kinship group is likely. Although the dentations in question look like acutely shaped mucous extrusions they actually are minute spines.

Figures

FIGURES 1–8. Drawings 1. Cosmarium grantii (from Eexterveld, province of Drenthe, the Netherlands). 2. C. palatiniforme. 3, 4. C. neonotabile (no 4 from Holmers, province of Drenthe, the Netherlands). 5. C. neocrenatum. 6. C. sphagnicola. 7. C. sphagnicoliforme (with zygospore). 8. C. regnesiforme.

FIGURES 18–23. LM photographs. 18–20. Cosmarium palatiniforme (from Holmers). 21–23. C. regnesiforme (21, 23 from Dwingelderveld, province of Drenthe, the Netherlands, 22 from type location). Scale bar = 10 µm

FIGURES 30–38. SEM photographs. 30. Cosmarium grantii (from Eexterveld). 31. C. neocrenatum (from Iceland). 32. C. neonotabile (from Holmers). 33. C. palatiniforme (from type location). 34. C. sphagnicola (from Eexterveld). 35. C. sphagnicoliforme (from type location). 36, 37. C. regnesiforme (from type location). 38. C. regnesi (Zeijen, province of Drenthe, the Netherlands). Figures 30–33: Scale bar = 10 µm, Figures 34–38: Scale bar = 5 µm