Cosmarium diamantinum G.J.P.Ramos & C.W.N.Moura, 2019

Ramos, Geraldo José Peixoto, Costa, Fabiana De Matos, Santos, Maria Aparecida Dos & Moura, Carlos Wallace Do Nascimento, 2019, Taxonomic novelties, new records, and rare species of desmids from the Chapada Diamantina region, Brazil, Phytotaxa 391 (3), pp. 185-196 : 186-187

Cosmarium diamantinum G.J.P.Ramos & C.W.N.Moura , sp. nov. ( Figs 2–6 )

Cells somewhat longer than wide; semicells subtriangular, with a deep median constriction; sinus distinctly open; lateral margins divergent; upper margin straight to slightly rounded, semicells elliptic in apical view, semicells in lateral view with a widely oblong outlines; semicell wall covered with sharp granules arranged in 3 slightly curved rows near the apices, median region smooth, with 1 row of granules in the isthmus region. Zygospores not observed. Cell dimensions: length 36–38 μm, width 32–35 μm, isthmus 10–12 μm.

Holotype: material numbered ( HUEFS 244147 !) deposited at Herbário da Universidade Estadual de Feira de Santana , population illustrated here in LM ( Figs 2-6 ).

Etymology: The epithet refers to diamond, main mineral from Chapada Diamantina region.

Type locality and habitat characteristics: Collected at Pico das Almas, Rio de Contas , Bahia state, Brazil. Lat. 13º 31’ 20” S, Long. 41º 55’ 56” W. Sample collected by A. V. F. Lima s/n ( HUEFS 244147 ) on 01 May 2011. Cosmarium diamantinum occurred in an ephemeral puddle in the mountain ;

Notes: The new species is similar to Cosmarium furcatum Kurt Först. & F.Eckert (1964: 391) , though the latter differs by having a pair of bifurcated spines at the angles, in addition to a uniformly ornamented cell wall, and being half the size of the former. Due to the angular spines, Förster (1964) had difficulty accommodating the species in the genus Cosmarium when it was first described, suggesting that it might be some representative of another genus, such as Staurastrum .

The ornamentation pattern of Cosmarium diamantinum is interesting, with slightly curved rows of sharp granules near apices, whereas the mid-region of the semicell lacks ornamentation. In addition, it presents an ornamentation formed by a row of granules in the region of the isthmus, which is well detached in the lateral view ( Fig.5 ).

Figures

FIGURES 2–27. Cosmarium diamantinum (2–6): ventral view (2–4), lateral view (5) apical view (6); Cosmarium dimaziforme var. concavum (7–10): ventral view (7), lateral view (8) apical view (9), cell division (10); Cosmarium pentachondrum (11–13): ventral view (11), lateral view (12) apical view (13); Euastrum bahiense (14–16): ventral view (14), lateral view (15) apical view (16); Euastrum croasdaleae var. incrassatum (17–20): ventral view (17,18), lateral view (19) apical view (20); Euastrum duplicato-verrucosum (21–25): ventral view (21,22), lateral view (23) apical view (24), zygospore (25); Euastrum octogibbosum (26–27): LM (26), SEM (27). Scale bar 10 μm.