Plumatella ruandensis Wiebach, 1964

(Fig. 9 a–c)

Plumatella ruandensis Wiebach, 1964: p. 15, pl. 4 (13–15).

Plumatella casmiana Lacourt, 1968: p. 54 .

Material examined. No. 206, type specimen, collected 6 June 1952 in Rwanda at Lake Burera, 60 km NNW Kigali, Northern Province, Burera District, by Hubert Damas .

Description. Colonies have grown completely around narrow stems like a sheath. The soft ectocyst is colorless and transparent (Fig. 9a). While the colonies are tubular many tubules are firmly adhered to each other. Floatoblasts are less than 400 μm in length (Table 2), lightly tuberculated, and show a clear size difference between dorsal and ventral fenestrae (Fig. 9b). Scanning electron microscopy reveals that cells of the annulus are individually highly convex (Fig. 9c). Sessoblasts have a wide annulus that is faintly reticulated; the frontal valve bears fine tubercles.

Distribution. The species is known only from its type locality in Rwanda.

Remarks. The specimen is in excellent condition, including abundant floatoblasts and sessoblasts.