Cosmarium pentachondrum Børgesen (1891: 39)

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 : 187

Cosmarium pentachondrum Børgesen (1891: 39) ( Figs 11–13 )

Cell dimensions: length 25–27 μm, breadth 20–22 μm, isthmus 10–12 μm.

Habitat characteristics: River; quiet and warm waters, associated to filamentous algae.

Material examined: HUEFS 244148.

Notes: This is a very rare species, known only in southeastern Brazil (Rio de Janeiro, São Paulo), and it was not reported over 70 years ago. Cosmarium pentachondum was described by Børgesen based on an apparently unique specimen collected in the municipality of “Moji” ; Biolo (2016), however, noted that Børgesen did not specify in which of the three areas currently known as Moji (Mogi das Cruzes, Mogi Guaçu, or Mogi Mirim in São Paulo State) the sample was collected .

This species is mainly characterized by having semicircular semicells, eight undulations on the lateral margins, granular cell walls with 5 large granules in the mid-region of the semicell. Due these features, this species might be confused with Cosmarium itatiayae Willi Krieg. (1950: 41) , which differs by having 18 granules per semicell and larger cell dimensions (length 37 μm, width 32 μm, isthmus 12 μm), whereas C. pentachondrum has ca. 13 granules per semicell and smaller cells.

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.