Natanella natans, 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 : 387-388

Natanella natans n. comb.

( Fig. 3 )

Hislopia natans Wood et al., 2006b , pp. 108–110, figs. 49–52

Material examined. Holotype: CUMZ No. 3152, collected 6 March 2005 by T. Wood, Huai Chan Reservoir , 35 km NE Sa Kaeo, Sa Kaeo Province , Thailand, 13°59.2’N, 100°26.8’E. Other material examined: ZUEC BRY 57 , Santa Fé Lake (Site 7), 21°57'47"S; 47°27'39"W, (see Table 2), growing on a piece of PVC pipe; NHMUK (not yet accessioned), collected 28 August 2011 by B. Okamura, oxbow lake on Kinabatangan River near Sandakan, Sabah, Borneo, 5° 28.840’ N; 118° 15.448’ E.

Etymology. Latin adjective, natans , swimming, alluding to the unusual motile zooids characteristic of this genus and species. The species name is retained from the original designation of Hislopia natans .

Description. Colonies form a diffuse, sparsely branching network composed of spindle-shaped zooids joined end to end with occasional side branches ( Fig. 3 a). Zooids are flattened and attached firmly to the substratum, with mean length of 860 µm long and width of 380 µm (n = 20; SD length = 12; SD width = 4), and a length to width ratio of 2–3.5. The lophophore bears 12–14 tentacles. The simple gut consists of a narrow esophagus leading progressively to a small gizzard, a large stomach and a small distal area for the temporary storage of digested remains. The hibernaculum is shorter and broader than the standard zooid, with thickened walls and one or more dark portals marking the site of its former attachment to the colony ( Fig. 3 c). Dorsolateral lobe-like extensions of certain zooids develop into nautizooids ( Fig. 3 a,b) which eventually detach and swim away under the power of an extended lophophore.

Remarks. There is no evidence of cyphonautes larvae in this species. Instead, it seems likely (but not yet confirmed) that nautizooids are the products of sexual reproduction, developing directly from fertilized ova in the maternal zooid.

This species resembles and sometimes co-occurs with Hislopia species. Both N. natans n. comb. and Hislopia spp. produce zooids in linear series, each zooid can develop a lateral branch on either side, the entire colony is adherent to the substratum and free branches occur rarely, mostly under very crowded conditions. N. natans n. comb. and Hislopia spp. differ in the following ways:

Zooid morphology: length to width ratio is <2 in Hislopia and> 2 in N. natans n. comb.;

Tentacle number: Hislopia zooids typically have 16–20 tentacles, N. natans n. comb. zooids have 12–14;

Nautizooids: Natanella natans n. comb. colonies normally bear numerous nautizooids in various stages of development, especially in older parts of the colony; Hislopia has no such nautizooids and releases fertilized ova directly into the water where cyphonautes larvae develop.

Distribution. This is a tropical species known so far from only five far-flung sites worldwide, including three in Thailand ( Wood et al. 2010), one in Borneo (River Kinabatangan), and now one in São Paulo, Brazil. The latitudinal range extends so far from 13° N ( Thailand) to 23° S ( Brazil).

Figures

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.