Plumatella pirassununga, Wood & Okamura, 2017

Wood, Timothy S. & Okamura, Beth, 2017, New species, genera, families, and range extensions of freshwater bryozoans in Brazil: the tip of the iceberg?, Zootaxa 4306 (3), pp. 383-400 : 390-391

Plumatella pirassununga n. sp.

( Figs. 5 , 6)

Plumatella javanica sensu Wiebach, 1970: 356 –357, pl. 1, figs. 4a, 4b, 5a, 5b, not Plumatella javanica Kraepelin, 1906 , fig. 16.

Material examined. Holotype: ZUEC BRY 10 , colony growing on wood, collected 28 January 2016 by B. Okamura at Santa Fé Lake ( Site 7), 21°57'47"S; 47°27'39"W, (see Table 2)

Etymology. Specific name honors Pirassununga, the nearest city to the type locality.

Description. The colony is open and repent, entirely attached to the substratum. The ectocyst is lightly sclerotized but well encrusted, giving it a velvety appearance ( Fig. 5 ). A weak raphe is evident throughout the colonies.

Statoblasts are shown in Fig. 6, dimensions are provided in Table 3. In lateral view the statoblast is asymmetrical with a nearly flat dorsal valve and highly convex ventral valve (Fig. 6c). Dorsal and ventral fenestrae are similar in size and shape (Fig. 6a, b). Fenestra tubercles on the dorsal valve are sharply defined and well spaced (Fig. 6a); on the ventral fenestra the tubercles become increasingly crowded towards the center (Fig. 6b). The annulus of both valves reveals convex contours of each air chamber, giving it a lumpy appearance. The suture is minutely crenulated (Figs. 6d). This feature shows up well in SEM photos, but it can also be seen in light microscopy as a minutely jagged edge, especially on the dorsal valve.

Remarks. In some ways the floatoblast this species resembles Plumatella javanica Kraepelin, 1906 from Java, and it may have been mistaken for P. javanica by Wiebach 1970 in specimens from the Amazon Basin. In both species the floatoblasts are similar in overall dimensions, and in having large fenestrae and heavy tuberculation. The colonies are also similar, both being flat and repent with a fragile ectocyst.

SEM photos of the type specimen of P. javanica (see Smith & Wood 1995, Fig. 1 ) correspond well with SEM photos by Wood et al. 2006b (their Fig. 20) and Hirose & Mawatari 2011a (their Fig 3 C, D). In every case the domed fenestra tubercles are formed very close together in a manner seen in no other species except Plumatella siamensis Wood, Anurakpongsatorn & Mahujchariyawong, 2006 ( Wood et al. 2006b). In both species, the densely packed tubercles are also surrounded by several deep, pore-like dimples. These features may be considered partially diagnostic for both species. Plumatella siamensis is further characterized by the absence of a fully-formed capsule ( Wood et al. 2006b).

However, there are significant differences between floatoblasts of those species. The fenestra tubercles of P. pirassununga n. sp. are much smaller than those of P. javanica (diameter 3.6 µm compared to 5 µ) and are well separated, especially on the dorsal valve. This uncommon separation is also seen in Plumatella bushnelli Wood, 2001 and sharply distinguishes P. pirassununga n. sp. from P. javanica . Since Wiebach (1970) apparently limited his observations to statoblast dimensions it is very possible that his “ P. javanica ” was in fact the new species, P. pirassununga n. sp. The situation may be clearer as more material becomes available.

Distribution. Unknown beyond the single site where this species was collected.

FIGURE. 6. Plumatella pirassununga n. sp. Scanning electron microgtraphs of statoblasts, scale bar = 100 µm. a) Dorsal valve; b) Ventral valve, c) Lateral view of showing asymmetry; d) Detail of ventral valves showing crenulated margin, scale bar = 30 µm.

Figures

FIGURE 1. Map showing collection sites in Brazil; a) General location of collection sites; b) Collection sites in Pará State: 1 — Verde Lake, 2 — Tapajós River, 3 — Juá Lake, 4 — Jari Channel, 5 — Downstream of dam on Curuá-Unã River; c) Collection sites in São Paulo State: 7 — Santa Fé Lake on campus of Universidade de São Paulo at Pirassununga, 8 — Aguapé Lake.

FIGURE 3. Natanella natans n. comb. a) Portion of the colony showing four developing nautizooids (arrows), scale bar = 1 mm; b) Magnified image of a developing nautizooid, scale bar = 0.2 mm; c) Hibernaculum, scale bar = 0.1 mm.

FIGURE 5. Plumatella pirassununga n. sp. Colony showing recumbent branches and several statoblasts inside, scale bar = 2 mm.