Plumatella wiebachi, Wood, 2020

Wood, Timothy S., 2020, Review of freshwater Bryozoa (Phylactolaemata) of Central Africa with descriptions of two new species, Zootaxa 4820 (3), pp. 581-600 : 595-597

Plumatella wiebachi n. sp.

( Fig. 11 a–c, f, g)

Plumatella javanica: Wiebach, 1964: p. 12 –13, text-figs 5–8.

Material examined. Nos. 50-60, and 62, all collected 24 August 1937 in DR Congo at Lake Upemba at Mabwe , Haut Katanga Province, by Paul Brien; No. 56 is the designated holotype .

Etymology. The species name honors Fritz Wiebach (1904–1976), an enthusiastic bryozoologist who was among the first to recognize the valuable role of statoblast morphology in phylactolaemate taxonomy.

Description. The colony is tubular with short branches that occasionally grow over and across each other. The body wall is soft, transparent and colorless, becoming slightly amber in older regions; a raphe along the zooids is occasionally faintly visible. The few available floatoblasts have small, well spaced tubercles on the fenestrae ( Fig. 3c ). Dimensions are shown in Table 2. The dorsal fenestra is relatively large, with a length and width only 20–25% smaller than the ventral fenestra. The sessoblast is larger than the floatoblast, measuring 550–570 μm in length. The sessoblast frontal valve bears numerous small tubercles, each about 2 μm in diameter and increasing in height towards the periphery to reach a length exceeding 4 μm. The annulus is clearly reticulated and has a distinctive thickened rim

Remarks. The abundant material of this species has been divided among nine vials immersed in ethanol in a single large container. In his 1947 examination Lacourt called this “ Plumatella auricomis Annandale = Plumatella pseudostolonata Borg. ” It was Wiebach in 1964 who noticed a resemblance to Plumatella javanica Kraepelin, 1906 and re-labeled the specimens accordingly. The colonies are in excellent condition attached to plant stems, including many sessoblasts and a few floatoblasts ( Fig. 11c ).

Fortunately, unlike most other plumatellids, Plumatella javanica Kraepelin, 1906 , is a well documented species. Kraepelin (1906) provided a detailed description and left a good type specimen at the Zoologisches Museum in Hamburg (No. B-98). From this material Smith & Wood (1995) published the first SEM images of the floatoblast, which showed a dense formation of rounded tubercles on the fenestrae. Hirose & Mawatari (2011) provided a further description of P. javanica and SEM photos from Japan. More recent specimens from Thailand and Indonesia, now at the Natural History Museum (London), match Kraepelin’s syntype and include sessoblasts for the first time.

Together the Asian specimens present consistent features that can be considered diagnostic for Plumatella javanica . These include a fragile ectocyst that is often broken or torn, a prominent raphe, and a continuous, clear stripe along the raphe that expands to surround each zooid. While these features were all included in Kraepelin’s (1906) original description, they do not occur in the MRAC material. Even more diagnostic of the Asian P. javanica are the statoblast fenestrae which bear rounded tubercles so crowded that the points where they meet form deep pore-like holes clearly visible with SEM ( Hirose & Mawatari 2011). These are pits, not pores, and they do not actually penetrate the periblast. With light microscopy they appear either as dark spots or sharp points of light, depending on the focal plane. This optical illusion is most easily observed on separated valves viewed with substage lighting ( Fig. 11d ). Elsewhere among phylactolaemate species this feature is also seen only in Plumatella siamensis Wood et al., 2006 and a few Indian species (Wood, unpublished). The sessoblast of P. javanica , described here for the first time, bears large tubercles similar to those of the floatoblast. ( Fig. 11e ).They are rounded and densely crowded, leaving no space between them. The annulus is faintly reticulated and bears a finely toothed outer fringe.

By contrast, sessoblast tubercles of P. wiebachi n. sp. are smaller than those of P. javanica ( Fig. 11g ) and the annulus is wider.

Figures

FIGURE 3. Hyalinella punctata, Specimen No. 174 showing colony fragment on plant stem. Scale bar = 2 mm.

FIGURE 11. Plumatella wiebachi n. sp., Specimen No. 56. (a) Colony surrounded by sessoblasts, scale bar = 3 mm; (b) colony showing greater detail, scale bar = 1 mm; (c) floatoblast valves with dorsal valve on the left, scale bar = 100 μm; (d–g) com- parison of statoblasts in Plumatella javanica and Plumatella wiebachi n. sp. (d) P. javanica floatoblast fenestra showing optical points of light around each tubercle; (e) P. javanica sessoblast from the author’s personal collection from Thailand showing relatively large tubercles; (f) P. wiebachi n. sp. floatoblast fenestra showing the absence of such points of light; (g) P. wiebachi n. sp. sessoblast showing relatively small tubercles. Scale bars for figs. 11d–g = 100 μm.