Cosmarium margigranulatum F.M. Costa & C.W.N.Moura sp. nov. (Figs. 3, 15–18)

Diagnosis: —Cells as long as broad, median constriction deep, sinus closed, linear; semicells reniform, smooth median face, angles rounded covered by granules, apex slightly projected with three protrusions; cell oblong in apical view. Cell dimensions: length 36.8–41.3 μm, breadth 41.6–44.6 μm, breadth of isthmus 12.7–16.2 μm.

Holotype:— Material numbered (HUEFS 263036!) [pro parte], deposited at the Herbarium of the State University of Feira de Santana, population partially illustrated here (Figs. 3, 15–18).

Paratypes:— Material numbered (HUEFS 263040) [pro parte], deposited at the Herbarium of State University of Feira de Santana.

Type locality:— BRAZIL. Bahia: Camaçari, Camaçari-Mirim River, Lat. 12°42’23.1’’ S, Long. 38°15’27.2’’ W, 29 November 2019, F. M. Costa & J. T.X. Neto s/n (HUEFS 263036).

Habitat:— Periphytic on Eleocharis acutangula; water conductivity 0.04 mS. cm-1 (± 0.01); dissolved oxygen 7.6 mg.L- 1 (± 0.1); pH 7.3 (± 0.9); total dissolved solids 0.02 ppt (± 0.01); water temperature 28.3 ºC (± 1.3).

Etymology:— The specific epithet refers to the ornamentation composed of various granules located at the margins of semicells.

Differential diagnosis:— Cosmarium margigranulatum differs from the other species of Cosmarium by having a very distinct ornamentation: concentrated granules along the margins of the semicells, but lacking in the central region.

Morphologically, the newly described species resembles Cosmarium ornatum var. pseudolagoense Förster (1964: 399) . However, this latter variety differs by having a concentric ring of granules on the face of the semicells and short spines at the angles of the semicells.