Hyalinella africana Wiebach, 1964

Wood, Timothy S., 2020, Review of freshwater Bryozoa (Phylactolaemata) of Central Africa with descriptions of two new species, Zootaxa 4820 (3), pp. 581-600 : 585

publication ID

https://doi.org/ 10.11646/zootaxa.4820.3.11

publication LSID

lsid:zoobank.org:pub:EEC6B089-AE6B-4479-919E-33A830357DBA

DOI

https://doi.org/10.5281/zenodo.4398075

persistent identifier

https://treatment.plazi.org/id/A85687C0-FFC2-9B29-FF3C-FE9D013940BA

treatment provided by

Plazi

scientific name

Hyalinella africana Wiebach, 1964
status

 

Hyalinella africana Wiebach, 1964 View in CoL

( Fig. 2 View FIGURE 2 a–c)

Hyalinella africana Wiebach, 1964: p. 32 View in CoL –34, text figs 24–26, pl. 11 (40–41).

Plumatella evelinae: Lacourt, 1968: 81–83 , pl. 11(e).

Material examined. Specimen Nos. 204 and 205 from Lukoma, Rwanda (both labeled “ Typus ”), No. 267 from Lake Mugesera, Rwanda, 33 km SE Kigali; and No. 439 from Lake Tanganyika. All specimens are well preserved with polypides extended ( Fig. 2a, b View FIGURE 2 ). No. 205 is probably in the best condition, consisting of three fairly large colonies .

Description. In his original description, Wiebach (1964) accurately described the spindle-shaped colonies growing around plant stems. The zooid body wall is clear, colorless, and soft ( Fig. 2a, b View FIGURE 2 ). Notable is what Wiebach described as the “common colonial ectocyst (forming) a hard-gelatinous mass, which is filled with fine detritus and epizoic unicellular organisms and over which the orifice of the individuals rises at intervals like a hump or fingertip.” In fact, in some of the preserved material the entire colonial mass has started to peel away intact from the plant stem. Wiebach described and illustrated (with photos) two types of floatoblasts: pycnoblasts and leptoblasts ( Wiebach 1964, figs. 23, 24). Unfortunately, among all three specimens I was able to find only a single floatoblast, in Specimen No. 267, not yet fully developed, corresponding roughly to Wiebach’s “pycnoblast” ( Fig. 2c View FIGURE 2 ). The two valves are about equally convex. The overall length = 311 μm, width = 195 μm; the dorsal fenestra length = 181 μm, width = 144 μm; ventral fenestra length = 19 μm, width = 162 μm.

Distribution. Known only from Rwanda and south to Lake Tanganyia.

Remarks. Wiebach worked under the assumption that many plumatellid species had two types of floatoblasts: robust pycnoblasts and more delicate leptoblasts. In the case of H. africana any such distinction is slight and can be attributed to normal variation. With the single remaining floatoblast, I separated the valves for detailed examination ( Fig. 2c View FIGURE 2 ) and isolated them in a small vial, now included in the larger vial with Specimen No. 267.

Although Wiebach described (but did not illustrate) sessoblasts in this species none could be found among any of the MRAC specimens. Assuming his written diagnosis is correct, the presence of sessoblasts would preclude accommodating this species in the genus Hyalinella . According to the current understanding, no sessoblasts are produced in this genus ( Wood et al. 2006). The thick gelatinous base suggests a possible affinity with Gelatinella toanensis (Hozawa & Toriumi, 1940) , but the validity of that genus remains questionable. At this time, I am reluctant to move the species to the already unwieldy genus Plumatella . Recognizing these difficulties, the species name, Hyalinella africana , should remain unchanged until more specimens become available.

Kingdom

Animalia

Phylum

Bryozoa

Class

Phylactolaemata

Order

Plumatellida

Family

Plumatellidae

Genus

Hyalinella

Loc

Hyalinella africana Wiebach, 1964

Wood, Timothy S. 2020
2020
Loc

Plumatella evelinae:

Lacourt, A. W. 1968: 83
1968
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