Cosmarium heptangulare Lacoste de Díaz (1972:212)

Ramos, Geraldo José Peixoto, Santos, Maria Aparecida Dos & Moura, Carlos Wallace Do Nascimento, 2021, Taxonomic notes on some Cosmarium species (Desmidiaceae, Zygnematophyceae) from Brazil, Phytotaxa 483 (3), pp. 291-299 : 292-293

Cosmarium heptangulare Lacoste de Díaz (1972:212) ( Figs 3 , 22–26 )

Cell dimensions: 18–22 μm long, 18,5–22 μm wide, isthmus 6–7 μm wide.

Material examined:— BRAZIL. Pantanal dos Marimbus, Andaraí, Bahia State. Sample: HUEFS 241798 .

Habitat: —This taxon was found associated with periphyton of Utricularia foliosa . EC 0.07 (± 0.03 mS cm-1), DO 6.6 (± 0.3 mg L- 1), pH 6.6 (± 0.6), TDS 0.03 (± 0.01), T 27.6 (± 0.2 ºC), WT 0.7 (± 0.14 m).

Note:—This species was originally described by Lacoste de Díaz (1972) based on samples gathered in Valinhos, São Paulo, Southeastern Brazil. This was the only record of this species till now. Almost 50 years later, it was found again in Brazil, but now in Bahia, Northeast region.

The cell outline (7–8 angled), as well as wide and straight apices are the main morphological features of this species. The SEM analysis revealed that the cell wall is slightly scrobiculate (pock marked pattern) ( Fig. 26 ).

Another feature which we consider relevant in this species is the apical view, which is oblong. Somewhat similar species such as Cosmarium lapponicum ( Borge 1913:19) , and C. fontigenum Nordstedt ( Wittrock & Nordstedt 1878: 71) have elliptical cells when observed in apical view.

Figures

FIGURES 1–8. Line drawings. 1. Cosmarium boeckii var.areolatum 2. C. clepsydra var. incrassatum 3. C. heptangulare 4. C. kanetsunae 5. C. pygmaeum 6. C. trinodulum 7. C. trinodulum var. brasiliense 8. C. trinodulum var. pilgeri.

FIGURES 9–32. LM and SEM. 9–15. Cosmarium boeckii var. areolatum: LM (9–12), SEM (15), frontal view (9, 10, 15), lateral view (11, 12), apical view (13, 14), 16–21. C. clepsydra var. incrassatum: frontal view (16–19), lateral view (20), apical view (21), 22–26. C. heptangulare: LM (22–25), SEM (26), frontal view (22–23, 26), lateral view (24), apical view (25), 27–32. C. kanetsunae: frontal view (27–28), lateral view (29, 30), apical view (31, 32). Scale bar: 10 μm, except Fig. 15 (5 μm).