Hislopia corderoi Mané-Garzón, 1960

(Fig. 2)

Hislopia corderoi Mané-Garzón, 1960: pp. 213–216, figs. 1–3

Hislopia lacustris sensu Bonetto & Cordiviola,1963: pp. 82–85, fig. 2, not Hislopia lacustris Carter, 1858.

Material examined. ZUEC BRY 0 1, Tapajós River (Site 2a), 2°26'30"S; 54°53'38"W, colony on wood; Preto Lake (Site 2b), 2°26'31"S; 54°53'59"W, colonies on leaves and wood; Tapajos River (Site 2c), 2°26'19"S; 54°54'54"W, colonies on plastic bottles and aluminum can; Cuná-Unã Dam (Site 5a), 2°26’30"S; 54°53'38"W, colony on wood; ZUEC No. BRY 0 6, Cuná-Unã River (Site 5b), 2°48'54"S; 54°53'38"W, colony on wood; and Verde Lake (Site 1), 2°48'54"S; 54°53'38"W, colonies on tree trunk and plastic (see Table 2).

Description. Zooids are flattened and firmly adherent to the substratum. They are joined end-to-end in linear series with frequent lateral and bilateral branching (Figs. 2 a, c, d). The dorsal orifice is surrounded by a squarish chitinous rim with a single spine at each corner. As zooids age the chitinous rim becomes taller, forming a distinct peristome, and the sides peel back as flat scale-like protuberances. Dorsal body spines seem to occur most often on older zooids, often in pairs to form a double row (Fig. 2 e). Hibernaculae form directly from functional zooids as the walls thicken, the polypide degenerates, and the internal space fills with yolky cellular material (Fig. 2 b)

Remarks. Hislopia corderoi was the most commonly encountered bryozoan species during this brief survey of the waters around Santarém (Table 2). It occurred mostly on submerged wood but was also found on plastic bottles and packaging. Typically multiple colonies occurred in close proximity.

The issue of dorsal body spines that define H. corderoi has been contentious. In his original description, Mané- Garzón (1960) considered dorsal body spines to be diagnostic of the new species, clearly distinguishing it from previously described hislopiids from China, Thailand, Cambodia, India, and elsewhere in Asia. The type species of this genus, H. lacustris, had been described and illustrated with only a small spine at each of the four corners of the peristomial orifice (Carter 1858). Subsequent Hislopia species were distinguished on the basis of zooid shape, zooid color, the frequency of branching, the shape of the developing bud, and the presence or absence of orificial spines (Marcus 1984), but not body spines. By the time Mané-Garzón described H. corderoi in Uruguay, Bonetto and Cordiviola (1963) had already been collecting what they identified as Hislopia lacustris from the Paraná River. They had noted a variable number of dorsal body spines and assumed these were normal features of the species. In his Hislopia material from the Amazon River, Wiebach (1967) found body spines ranging from 0 to 24. He also noted that spines occurred on young zooids and even on developing buds. Wiebach (1967) considered the presence of any dorsal body spines as diagnostic for H. corderoi, but recognized that some colonies of H. corderoi may lack spines. This would mean that Bonetto and Cordiviola (1963) may have been mistaken, and that H. lacustris has yet to be confirmed from South America.

During the final preparation of this paper, DNA sequence data revealed that Hislopia specimens from Sites 1 and 2 were genetically distinct. Morphologically the zooids from Site 1 had spines ranging from prominent to very small, while those from Site 2 seemed smooth. Spiny material from Site 4 allied genetically with the Site 1 group. This work was done by Andrea Waschenbach (NHMUK). Further details and the significance of her finding will be explored at a later time.

Distribution. Brazil: Amazonas River, Tapajós River; Uruguay: Uruguay River at Nueva Palmira; Argentina: middle and Upper Paraná River.