New species of Cyclodontina from Bahia , Brazil ( Gastropoda , Pulmonata , Odontostomidae )

A new species of pulmonate snail was recently collected in a small forest fragment in the city of Bom Jesus da Lapa, Bahia state, Brazil. Bahia is known for a high diversity of land snails and Bom Jesus da Lapa is an interesting locality, since it is close to the interface between two major Brazilian biomes: Cerrado and Caatinga. The new species is described as Cyclodontina tapuia sp. nov. and can be easily identified by its brown shell, conical spire, convex whorls, a sculpture comprised of strong ribs, and an aperture with four barriers: a median parietal tooth, a median palatal tooth, a median basal tooth and a strong columellar lamella. This discovery is also a reminder of how little the Brazilian continental molluscan fauna is known and of the urgency in studying and preserving the rich (though usually overlooked) fauna of the Caatinga.


ABSTRACT.
A new species of pulmonate snail was recently collected in a small forest fragment in the city of Bom Jesus da Lapa, Bahia state, Brazil.Bahia is known for a high diversity of land snails and Bom Jesus da Lapa is an interesting locality, since it is close to the interface between two major Brazilian biomes: Cerrado and Caatinga.The new species is described as Cyclodontina tapuia sp.nov.and can be easily identified by its brown shell, conical spire, convex whorls, a sculpture comprised of strong ribs, and an aperture with four barriers: a median parietal tooth, a median palatal tooth, a median basal tooth and a strong columellar lamella.This discovery is also a reminder of how little the Brazilian continental molluscan fauna is known and of the urgency in studying and preserving the rich (though usually overlooked) fauna of the Caatinga.
The semi-arid domains of the Caatinga were usually thought of as impoverished in terms of biodiversity, but they are simply understudied; recent works are revealing an astounding diversity of species across all main terrestrial and freshwater taxa, as well as many endemic species (Tabarelli & Silva, 2002).Simone (2006) already showed a wide variety of land snails for the region.However, there are proportionally few works on these animals and knowledge remains utterly incomplete; they are not even cited in the most recent accounts of the Caatinga's proposed biodiversity conservation measures (e.g., Silva et al., 2003).The more arid regions are often considered an adverse place for land snails, but it seems that the Caatinga may still hide many discoveries.
The shell dealer José Coltro Jr. and his team recovered some fresh land snail shells from the leaf litter of a forest fragment in the city of Bom Jesus da Lapa, eastern Bahia state, Brazil (Fig. 1 -7).
Etymology.Reference to the Tapuias, the region's native inhabitants.
Distribution.Known only from the type locality.

DISCUSSION
Cyclodontina is an endemic South American genus, occurring in Brazil, Paraguay, Uruguay and northern Argentina (Schileyko, 1999;Simone, 2006), but being especially diverse in central and northeastern Brazil, in the semi-arid domains of the Cerrado and Caatinga biomes (Simone, 2006).None of the conchological features of Cyclodontina tapuia sp.nov. is exclusive when compared to its congeners, but the set of diagnostic features makes the species readily identifiable.The species which share with C. tapuia the conical shell profile are (occurrences according to Simone, 2006) 8) by its smaller size, more convex whorls, and stronger ribs and apertural barriers.It differs from C. fasciata (Fig. 9) by the presence of ribs, more convex whorls, a more rounded aperture, the lack of a second basal tooth, and the positioning of the columellar lamella (closer to the parietal region).It differs from C. inflata (Fig. 10) by its more convex whorls, the presence of ribs, weaker and fewer apertural barriers and the lack of the channel-like structures on the borders of the aperture's parietal region.Finally, the remaining two species, C. maranguapensis and C. scabrella, are the ones that most closely resemble C. tapuia.Nevertheless, diagnosing C. tapuia sp.nov.remains rather simple: in comparison with C. maranguapensis (Fig. 11), C. tapuia sp.nov. is larger, has more (basal tooth present) and stronger apertural barriers and more convex whorls, with a very distinct geographic distribution; C. tapuia sp.nov.differs from C. scabrella (Fig. 12) by being wider and very conical (C.scabrella is more fusiform), having fewer apertural barriers, a more dorsally positioned columellar lamella, thinner and more spaced ribs, a much wider aperture, and by lacking the channel-like structures on the borders of the aperture's parietal region.
Bom Jesus da Lapa, the city where Cyclodontina tapuia sp.nov.was discovered, is located in eastern Bahia state (Fig. 1), on the banks of the São Francisco River, and is very interesting by being part of the Caatinga biome, but very close to the interface with the Cerrado biome.Vegetation is predominantly hypoxerophytic, but marked by stretches of deciduous forests (Sá et al., 2003).The climate is hot and dry (mean temperature 23.7°C, max.30.5°C, min.19.8°C), rain is extremely seasonal and irregular and the region is considered having a medium to high risk of drought (IBGE, 2014).It is common for shells of more arid places to be sturdier, with strong ribs and large apertural barriers (Goodfriend, 1986).These features are found in C. tapuia and it should be noticed that the region of Bom Jesus da Lapa is rich in limestone, which is an attractive (or even requisite) for snails with sturdy shells.Moreover, strong apertural barriers, usually thought of as protection from predators, may serve as a protection against desiccation in more arid climates, by reducing the area of evaporation (GiTTenberGer, 1996;PokrySzko, 1997).Judging by family's richness in the Brazilian semiarid regions (Simone, 2006), the odontostomids' typical apertural barriers could in fact be presently more related to the climate rather than to predation.
As previously stated, continental molluscs are not taken into account in environmental matters regarding the Caatinga, which is very troubling, since circa 20% of this environment is considered degraded (Sá et al., 2003).A proper knowledge of the species present in the Caatinga, their distributions and degree of endemicity are of utmost importance for future conservation efforts, since type localities and areas with many endemic species have priority according to the Brazilian law.