Cosmarium abbreviatiforme 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 : 3-6

Cosmarium abbreviatiforme Van Westen et Coesel sp. nov. ( Figs 5 , 15–20 )

Cells slightly broader than long, deeply constricted. Sinus linear, closed to about half-way, then much dilated. Semicells in frontal view elliptic-hexagonal with broadly rounded angles, in lateral view globose, in apical view elliptic. Cell wall apparently smooth but faintly scrobiculate in high magnification, provided with widely spaced, fine pores. In apical view a characteristic line of pores crossing the semicell broadwise, in the very centre flanked by two additional pores on both sides resulting in a hexagonal pattern of pores. Chloroplast with a single pyrenoid.

Dimensions: length 12.5–15 μm, breadth 13–16.5 μm, thickness 6.3–8.1 μm, isthmus 3.3–4.1 μm.

Type:— THE NETHERLANDS. Drenthe: oligo-mesotrophic pool in estate Schepping in Holthe near Beilen, 52.8435° N, 6.5447° E, between mosses, pH 7.4, conductivity 27 μS cm-1. Van Westen, 22 September 2016 (holotype L! Hugo de Vries Lab 2018.02, preserved as a fixed natural sample).

FIGURES 9–14. 9 – 11. Closterium cynthiaforme . 12 – 14. Cl. joostenii . Scale bar = 10 μm.

Differential diagnosis:—As its name already indicates, C. abbreviatiforme resembles C. abbreviatum Raciborski (1885: 83 , pl. 10: 13) as described from Poland. Main difference is in the shape of the lateral angles: about rectangular in C. abbreviatum , broadly rounded in C. abbreviatiforme , as well as in the shape of the semicell apex: concavetruncate in C. abbreviatum , convex-truncate in C. abbreviatiforme . Thus, semicell outline in C. abbreviatiforme is about elliptic rather than hexagonal. Next to that, cell dimensions in C. abbreviatiforme are smaller than those in the nominate variety of C. abbreviatum . C. abbreviatum var. minus (West et G.S. West) Willi Krieger et Gerloff (1969: 242 , pl. 42: 18) in its turn has smaller dimensions than C. abbreviatiforme and, like the nominate variety of C. abbreviatum , is characterized by rectangular lateral angles.

Cosmarium abbreviatiforme is found in several locations in the south-west of the province of Drenthe in shallow pools on sandy soil in nature restauration areas. The pools are fed by rainwater, with some influence of ground water. pH 5–8, conductivity 20–40 μS cm-1.

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 15–26. 15–20. Cosmarium abbreviatiforme (19, 20. SEM microphotographs). 21–26. Cosmarium kouwetsii (24–26. SEM microphotographs). Scale bar = 10 μm.