Uncancylus concentricus ( Mollusca , Gastropoda , Ancylidae ) : New occurrence in state of Rio de Janeiro , Brazil

The freshwater pateliform pulmonate snails considered as Ancylidae are represented in South America by seven genera according to Santos (2003): Anisancylus Pilsbry, 1924; Burnupia Walker, 1912; Ferrissia Walker, 1903; Gundlachia Pfeiffer, 1849; Hebetancylus Pilsbry, 1913; Laevapex Walker, 1903 and Uncancylus Pilsbry, 1913. The knowledge about occurrence, distribution and systematic of these snails is poorly known in Brazil, although fundamental to studies concerning biodiversity, not only by the continental dimensions of the country, but also considering the reduced number of malacologists.

The freshwater pateliform pulmonate snails considered as Ancylidae are represented in South America by seven genera according to Santos (2003): Anisancylus Pilsbry, 1924;Burnupia Walker, 1912;Ferrissia Walker, 1903;Gundlachia Pfeiffer, 1849;Hebetancylus Pilsbry, 1913;Laevapex Walker, 1903 andUncancylus Pilsbry, 1913.The knowledge about occurrence, distribution and systematic of these snails is poorly known in Brazil, although fundamental to studies concerning biodiversity, not only by the continental dimensions of the country, but also considering the reduced number of malacologists.
According to the literature and data from scientific collections, U. concentricus was firstly described to Uruguay, in the vicinities of Montevideo.It is widely distributed, occurring from Costa Rica (Pilsbry 1920;Lanzer 1996) to the Patagonian region (Hylton-Scott 1963;Lanzer 1996;Santos 2003).In Brazil, it is found at Central-Western region (Thiengo et al. 2005), South and Southeast regions (Lanzer 1996;Santos 2003).
The records from Moricand (1845) to Bahia, van Benthem-Jutting (1943) to Rio Grande do Norte, Haas (1949a;b;1952) and Irmler (1975) to the Amazon region need to be confirmed, as previously assigned by Lanzer (1996).According to Santos (2003) it is not observed in North and Northeast regions.----------------Field work was conducted at Praia do Sul Biological Reserve, on the oceanic side of Ilha Grande (Figure 1), on 11 November 2006.This area is included in one of the last remnants of arboreal restinga in the state of Rio de Janeiro.The ancylids were found at a small stream (23°10'30" S, 44°18'13" W) in a swampy area, over decayed leaves.The snails were collected by three people using a handled metallic scoop for 15 minutes.
Live snails were transported with biotope water to the laboratory where, after stereomicroscope examination, we found the two specimens of U. concentricus together with 57 specimens of Gundlachia ticaga (Marcus & Marcus, 1962), the most widespread ancylid in the state of Rio de Janeiro (Thiengo et al. 2001;2002a;b;2004a;b;2006), already cited to Abraão village in Ilha Grande (Santos et al. 2007).These species were found living together in other places like Serra da Mesa dam (Thiengo et al. 2005).The shells fit well the genus diagnosis (Pilsbry 1913) with the typical protoconch bearing a pointed apex flexed to the right, well marked radial lines all over the shell and a yellow-amber periostracum with periostracal hairs (Figure 2); mantle with pigmentation concentrated at the left, right muscle scar moon-shaped, left muscle scar oval-shaped and the posterior one rounded (Lanzer 1996;Santos 2003).The elongated-oval shells measures, respectively, 2.95 mm length, 1.95 mm width and 0.7 mm height and 2.45 mm length, 1.55 mm width and 0.55 mm height (Figure 3).The specimens are deposited at the Malacological Collection of the Universidade do Estado do Rio de Janeiro (Col.Mol.UERJ 7372 a, b).---------- Haas (1953) reported Burnupia (Anisancylus) obliquus (Broderip & Sowerby, 1832) to Ilha Grande, a misidentification according Santos et al. (1999) because this species is restricted to Chile, Argentina and South Brazil (Lanzer 1996;Santos 2003).Anisancylus obliquus and U. concentricus are similar because of the elevated shell with projected apex flexed to right and teleoconch with well marked radial lines, differing by the shape of the muscle scars.Uncancylus concentricus have a moonshaped anterior right muscle scar whereas in A. obliquus it is elongated, almost reaching the medium of the mantle length; the posterior muscle scar is elliptical in U. concentricus and rounded in A. obliquus.The mantle pigmentation is scarce, sometimes more concentrated at the left side in U. concentricus (Figure 4A) whereas A. obliquus shows a dense pigmentation all over the mantle (Figure 4B), almost completely dark in some specimens (Santos 2000).More details about ancylids morphology in Santos (2003).It was not possible to examine Haas´s specimens (Haas 1953) to verify if they were in fact U. concentricus.

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The occurrence of these specimens at a so restricted habitat apart from the continental landmass could be explained by bird transport (Rees 1965;Green and Figuerola 2005).This record is the first about freshwater snails to the Praia do Sul Biological Reserve, extending the distribution of U. concentricus to Rio de Janeiro state and also of G. ticaga to Praia do Sul Biological Reserve.

Figure 1 .
Figure 1.Map of Ilha Grande, Rio de Janeiro, Brazil, showing the sampling point at Praia do Sul Biological Reserve.

Figure 2 .
Figure 2. Uncancylus concentricus.Photos of specimen Col. Mol UERJ 7372 b. (A) Dorsal view, (B) left lateral view, (C) right lateral view.White arrow shows the radial lines.Black arrow shows the pointed apex flexed to the right.Scale = 1mm.Photo by Antonio Carlos de Freitas.