Plumatella pseudostolonata Borg, 1940

Wood, Timothy S., 2020, Review of freshwater Bryozoa (Phylactolaemata) of Central Africa with descriptions of two new species, Zootaxa 4820 (3), pp. 581-600 : 591-592

Plumatella pseudostolonata Borg, 1940

( Figs 8 a–c)

Plumatella pseudostolonata Borg, 1940: p. 34 –43, text-fig. 1, pls 1, 2.

Plumatella longigemmis Lacourt, 1968: p. 76 .

Stolella indica Wiebach, 1964: p. 22 .

Material examined. Nos. 46-47 collected May, 1937 in DR Congo, on rocks in a stream near Weka, northwestern Kongo Central , by Edmund Dartevelle; No. 48 collected January 1938 in DR Congo underneath a floating leaf of a water plant on on the Island of Mateba in the Congo River , Kongo Central Province, by Edmund Dartevelle .

Description. Little remains of the holotype colony described and illustrated by Borg (1940). The largest fragment, on a rock in No. 46, shows a narrow, unbranched tube with four zooids in series ( Fig. 8a ). The ectocyst is without color and bears a distinct raphe. Nothing in the specimen suggests an elongated, stolon-like zooid. Floatoblasts are missing; however, photos of two floatoblast valves from Borg (1940) are reproduced here in Fig. 8b . The average dimensions cited by Borg (1940 are 383 μm long and 222 μm wide. An intact sessoblast displays a broad annulus without reticulation or other markings ( Fig. 8c ); sessoblast tubercles become smaller and more widely spaced towards the annulus.

Distribution. Kongo Central Province in DR Congo.

Remarks. The MRAC specimens reveals little useful information. The floatoblast photos provided by Borg (1940) also are limited since we cannot be certain whether the valves shown are dorsal or ventral. However, it is clear that the annulus extends far beyond the capsule (fig. 8c). As a result, the capsule length is only 56-63% of the total floatoblast length. In P. philippinensis , P. marlieri , and most other plumatellids that value is around 80% or more. In Africa it is lower only in P. emarginata and P. bombayensis Annnandale, 1908 where is there a comparable disparity between the length of the whole floatoblast and that of the capsule. The wide sessoblast annulus ( Borg, 1940, fig. 3) and the apparent absence of a strong reticulation on the ventral floatoblast fenestra rule out P. bombayensis as the identity of Borg’s species. For these reasons, I consider this specimen to be either a valid species or else it is Plumatella emarginata . The question may be resolved with additional field work.

Figures

FIGURE 8. Plumatella pseudostolonata, Specimen No. 46. (a) Colony fragment on rock, scale bar = 2 mm; (b) ventral (?) floatoblast valves, modified slightly from Borg (1940) to show the fenestrae more clearly; (c) detail of sessoblast showing wide, unmarked annulus and tubercles on frontal valve, scale bar = 50 μm.