Abstract
The freshwater snail Gundlachia ticaga (Marcus & Marcus, 1962) is widely distributed in Brazil, but its morphology has been poorly studied. We compared the shell morphology of samples from four sites (Vila do Abraão, Vila de Provetá, Parnaioca and Praia do Sul) in Ilha Grande (Angra dos Reis, state of Rio de Janeiro) in order to evaluate differences within and among four populations. We used nine morphometric characters representing shell size and shape. To analyze shell morphology we considered aperture shape, sculpture of teleoconch, apex carving and position. The resulting dataset was correlated by Pearson´s linear correlation and shell differences among populations were tested using ANOVA and Discriminant Function Analysis. The results showed that there is significant variation among populations concerning shell shape and morphology. Shells from preserved localities (Praia do Sul and Parnaioca) and shells from highly modified environments (Vila do Abraão and Vila de Provetá) were the most similar to each other. Results from the visual assessment and from the discriminant analysis were almost identical. The shell indices are the most important variables in the differentiation of samples. The observed variation corroborates the hypothesis that G. ticaga displays phenotypic plasticity, which may lead to wrong identifications. Narrower shells with an elongate aperture could be misidentified as Ferrissia Walker, 1903 and, broader shells with a roundish aperture could be wrongly identified as Burnupia Walker, 1912. We confirmed that the absence of radial lines is not a good diagnostic character for G. ticaga. The analysis of the apical micro-sculpture and soft parts is essential for a correct identification.
Highlights
Shell morphometry is a useful tool in mollusc taxonomy and ecology (CIPRIANI 2007)
Gundlachia ticaga (Marcus & Marcus, 1962) is a basommatophoran without a coiled shell (HUBENDICK 1978), in the family Ancylidae sensu lato, whose members are limpetshaped and small (3 to 15 mm in length), occurring mainly in lentic environments adhered to aquatic plants, branches and leaves of decayed riparian vegetation, or rocks (LANZER & VEITENHEIMER-MENDES 1985, SANTOS 2003)
The morphology of G. ticaga has only been described in the original description of the species (MARCUS & MARCUS 1962), and subsequently by OHLWEILER & LANZER (1993), LANZER (1996) and SANTOS (2003)
Summary
Shell morphometry is a useful tool in mollusc taxonomy and ecology (CIPRIANI 2007). In studies of freshwater snails, it has been used to discriminate between species (WULLSCHLEGER & JOKELA 2002), to recognize intraspecific morphological variation (CHIU et al 2002), and to associate shell variations with environmental conditions (MACMAHON & WHITEHEAD 1987, WULLSCHLEGER & JOKELA 2002) and geographical distribution (PFENNINGER et al 2003). Gundlachia ticaga is widely distributed, mainly in southeastern (SANTOS 2003) and central-western regions of Brazil (THIENGO et al 2005). It is the most frequent ancylid in freshwater ecosystems of the state of Rio de Janeiro (THIENGO et al 1998, 2001, 2002a,b, 2004a,b, 2006), being recently recorded for Praia do Sul Biological Reserve, Ilha Grande (SANTOS et al 2009). The morphology of G. ticaga has only been described in the original description of the species (MARCUS & MARCUS 1962), and subsequently by OHLWEILER & LANZER (1993), LANZER (1996) and SANTOS (2003). We conducted morphometric analyzes and compared samples from four different freshwater environments in Ilha Grande, southeastern Brazil, to better determine the range of variation and thereby improve species delineation
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