Predicting the distribution of Omalonyx ( Mollusca : Pulmonata : Succineidae ) species from literature review , museum databases and new sampling efforts in Brazil

Accurate distributional information is crucial for studies on systematics, biodiversity and conservation. To improve the knowledge regarding the geographical distribution of Omalonyx in South America, we present updated information based on data from a literature review, institutional collections and malacological surveys. All this information composed the dataset used to predict species distribution employing the Maximum Entropy Algorithm (MaxEnt). The model was run using data on species distribution, altitude and bioclimatic variables (WorldClim database). The model had consistent performance, and areas presenting similar conditions to areas where the species were recorded were considered areas of occurrence. The predicted occurrence areas included those that were already surveyed and those that are considered potential occurrence areas. The results demonstrate that the genus has widespread distribution in the Neotropical region and occurs in the tropical, temperate and arid regions of South America and Lesser Antilles. Omalonyx spp. were recorded in all South American countries and hydrographic regions. However, in some countries, there were only isolated records (ex: Colombia and Ecuador). Here, we also present the first record of Omalonyx spp. in four Brazilian States (Acre, Rondônia, Piaui, and Amapá). The genus was found in all hydrographic regions within Brazil and among 27 federative unities; it was absent from only two unities (Roraima State and Distrito Federal). This work contributes to the knowledge on Omalonyx spp. distribution and provides an important basis for the work of ecologists and taxonomists.


Introduction
The genus Omalonyx d'Orbigny, 1837 presents a reduced shell and represents one of the slug-like lineages within the family Succineidae (Patterson 1971, Tillier 1981, Barker 2001).The earliest fossil records of Succineidae were from the Tertiary of Europe and, currently, most of the diversity within the family occurs in the islands of the Pacific, in the Indian subcontinent and the Americas (Barker 2001).These Neotropical slugs are terrestrial, live on aquatic macrophytes or riparian vegetation and can also be found in humid soil (Garcia et al. 2012).They can act as agricultural plagues (Olazarri 1979, Garcia et al. 2012) and are agents in the control of water-cress (Poi de Neiff et al. 1977).They can also act as intermediate hosts of an avian trematode, Leucochloridium (Lutz 1921, Travassos 1928), in the wild and of the nematodes Angiostrongylus costaricensis and A. vasorum in the laboratory (Montresor et al. 2008, Mozzer et al. 2011).
To improve taxonomic knowledge on Omalonyx species, studies encompassing morphological and molecular data are essential.However, the first step to elucidating these questions is to acquire knowledge on species geographical distribution.Accurate geographical distributional information is crucial to solve systematics and biogeographic problems and to drive conservation efforts.Species-distribution models infer potential distribution from data on observed distribution and from environmental variables related to the sites where occurrences were recorded (Bradie & Leung 2017).These models assume that climate ultimately restricts a species' distribution and summarize it with a number of climatic variables within the known range of the species, generating a bioclimatic profile.They play an important role as first filters in assessing the potential distribution of each species, improving the success of future sampling efforts and providing initial insight into the bioclimatic tolerance of different species (Beaumont et al. 2005, Rubio & Acosta 2011).These tools have also been applied in several conservation biology studies to identify areas with high species richness and to predict effects of climate change on species' distributions (Araújo & Rahbek 2006, Costa et al. 2010, Vogler et al. 2013).
There are several methods to model species distribution, and they may use presence/absence, abundance or presence-only data.Usually, species records have limited coverage and consist of presence-only data (Elith et al. 2011).The Maximum Entropy Algorithm (MaxEnt) presents high performance for modeling presence-only data and is widely used to model species distribution (Bradie & Leung 2017).Here, we use this method to improve the knowledge on the geographical distribution of Omalonyx spp., assembling literature data with specimens either collected in our surveys, from malacological collections or donated by partner laboratories.These data on species presence and the associated bioclimatic variables were used to model species distribution, to investigate the main environmental factors related to the occurrence of Omalonyx species and to detect species with overlapping distribution areas.This work improves the knowledge on these slugs' distribution, providing information to propel advances in the morphological and molecular taxonomy of these neotropical succineids.

Material and Methods
Literature data on Omalonyx was reviewed (until December 2016) in order to find records of its occurrence across the Neotropical region (see the topic literature review in the results).Institutions harboring preserved specimens were identified in the literature review and by onsite and virtual searching in institutional collections (Table 1), and information regarding the lot number and collection site was organized in two tables (Table 2 and 3).Donated specimens were also included in these tables (Table 2 and 3).
To investigate in detail the distribution of these slugs in Brazil, malacological surveys comprising all geographical regions (North, Northeast, Southeast, South and Central West) were conducted between 2006 and 2016 (permission from environmental agency: ICMBio/SISBIO no.12113-3).Specimens were manually collected from wet soil and vegetation in the vicinity of freshwater systems.Voucher specimens were deposited in the malacological collection of the Laboratório de Malacologia e Sistemática Molecular (LMSM), at Universidade Federal de Minas Gerais, Minas Gerais, Brazil.
All localities from the literature review, museums, collections, donations and our own malacological surveys were listed (Table 2 and 3) and plotted on a map (Figure 1) using the software ArcGIS 10.4 (ArcGIS Desktop 10.4 Geostatistical Analyst, Environmental Systems Research Institute ESRI, 2016).The geographic position of the localities and the information about South American hydrography and geography were cross-checked with Google Earth, Global Gazetteer, Hydro web (a hydrologic information system of Agência Nacional de Águas -ANA, the national water resources agency of the Environment Ministry, Brazil).Information regarding the hydrography of Austral South America was obtained from Bonetto (1994).
Morphological identification of specimens collected in our malacological surveys was based on characteristics of the reproductive system according to the following literature: O. convexus (Hylton-Scott & Lapuente 1968, Hylton-Scott 1971, Tillier 1981, Arruda & Thomé 2008b), O. unguis (Coscarelli & Vidigal 2011), O. matheroni, O. pattersonae and O. geayi (Tillier 1981).Specific identification provided in the papers (literature review) and on the labels (museum specimens) was also used in this work.Some of these records were not identified to species level and are designated Omalonyx sp.Until 1981, there were several species of Omalonyx, now recognized as synonyms.Throughout the text, species are designated according to Tillier (1981) and Arruda & Thomé (2008a, b), where synonyms for the six valid Omalonyx species can be found.However, when consulting the topic references, the reader will find the former designation.
Data of occurrence (Table 2 and 3) were used to model the species geographic distributions using one topographic variable (altitude) and the nineteen bioclimatic variables derived from the WorldClim database v. 1.4 as showed by Vogler et al. (2013)   Brasil e nas 27 unidades federativas; sendo ausente em apenas duas unidades federativas (Estado de Roraima e Distrito Federal).Esse trabalho contribui para o conhecimento da distribuição das espécies de Omalonyx e fornece uma importante base para trabalhos de ecólogos e taxonomistas.
Palavras chave: MaxEnt, modelagem de nichos, distribuição de espécies, Modelagem, Succineídeos, Neotrópico.LMSM 2573LMSM -2579LMSM , 2583LMSM , 2646LMSM -49, 2663LMSM , 2670LMSM , 2761LMSM , 2765LMSM -67, 2789LMSM -94, 2835LMSM , 2849LMSM -76, 2910LMSM , 2930, 3234, 3234 LMSM 1378LMSM -87, 2383LMSM , 2516LMSM , 2525LMSM , 2527LMSM , 2529LMSM , 2536LMSM , 2787LMSM , 2918LMSM , 2929, 3153-55, 3162-63, 3166, 3186, 3208-, 3153-55, 3162-63, 3166, 3186, 3208- Note: 1: Specimens from our malacological surveys in Brazil were deposited in LMSM and classified in the column source as "Survey"; Specimens that were donated by other researchers were deposited in LMSM and classified in the column source as "Donation"; 2: Hydrographic region numbers are according to Figure 1 and to the metadata information system of the water resources national agency -ANA -of the Environment Ministry, Brazil and to Bonetto 1994).1; 2: Specimens from our malacological surveys were deposited in LMSM and they were classified in the column source as "Survey"; Specimens that were donated by other researchers were deposited in LMSM and they were classified in the column source as "Donation".3: Hydrographic basin numbers are according to Figure 1 and to the metadata information system of the water resources national agency -ANA -of the Environment Ministry, Brazil and to Bonetto 1994); * Specimens from Chile that were previously identified as O. gayana, however, Tillier 1981 considered that this species belongs to the genus Succinea.To minimize the spatial autocorrelation of the bioclimatic variables and to determine which variables contributed more to the development of the model, a principal component analysis (PCA) was carried out in the areas of Omalonyx species occurrence.The resulting rasters were used to generate a potential distribution model for South America.The input parameters followed the MaxEnt (version 3.3.3k)(Phillips et al. 2004) default options except for the threshold rule, which was set as "minimum training presence".The resulting models were processed and reclassified using ArcGIS.A binary map (absence-presence) for the potential distribution of a species was generated considering the average map that represents the induced and adjusted habitat of each species.

Literature review
Inferences on the distribution of Omalonyx species have been made since its description, and it was assumed to be throughout South America east of the Andes (d'Orbigny 1837).This first inference was based on records from Bolivia and Paraguay (d 'Orbigny 1835a'Orbigny , 1837)).However, at that time (1837), the name Omalonyx was used as the subgenus Succinea (Omalonyx) unguis.Later, Omalonyx was used at the genus level (Herrmannsen 1849).In addition to the publications of d'Orbigny other species were described at that time as showed below.In the next century, Patterson (1971) extended the distribution of the genus to several West Indies islands and Central America.However, the basis for this conclusion was not clearly demonstrated.After that, Tillier (1981) demonstrated the occurrence of Omalonyx species in all South America east of the Andes and the Lesser Antilles.His conclusion was based on preserved specimens from malacological collections that did not include significant sampling material from Brazil, although there were already records on the presence of Omalonyx spp. in the country years before (e.g., Moricand 1836, Gibbons 1879).In fact, Tillier (1981) studied animals from only eight localities in Brazil, and four of these could not be clearly located and were excluded from his study.In this work, Tillier also discusses the origin and evolution of South American and Juan Fernandéz Islands (Chile) succineids.He suggests that the southeast region of Brazil is the center of Omalonyx radiation once three species can be found in this region (O.unguis, O. matheroni and O. brasiliensis).Details on the records of Omalonyx occurrence in the Neotropics are given below in the subsections "Omalonyx in Brazil" and "Omalonyx in other South American countries and Lesser Antilles".

Literature review: Omalonyx in Brazil
The first record of Omalonyx in Brazil was made in the 19 th century in the Northeastern region (Moricand 1836) on a lake in Bahia State named "la Digue" or "le Baril".The specimens were identified as O. unguis.Hidalgo (1869) also identified as O. unguis specimens collected by Paz and Martinez in Bahia State.Two years later, the same author (Hidalgo 1872) stated that Paz and Martinez collected those specimens at "Lago Dique" (Dike Lake), Salvador, Bahia.We suppose that the specimens cited by Moricand (1836) and Hidalgo (1869Hidalgo ( , 1870) ) were collected in an urban lake known since the colonial period as "Dique do Tororó".Gibbons (1879) identified two different species of Omalonyx in Bahia State, O. unguis and O. matheroni.However, no other information about the locality was provided, and the morphology described in Gibbons ( 1879) is not compatible with O. unguis; thus these records were not included in Table 2. Omalonyx convexus was described by Martens (1968) as Succinea convexa from specimens collected in Porto Alegre, Rio Grande do Sul State, in southern Brazil (type locality), and it was later included in the genus Omalonyx (Arruda & Thomé 2008b).The map provided by Arruda and Thomé (2008b) shows overlapping distribution of O. convexus and O. unguis in the Argentinean region of the Paraná River basin (in Figure 1 the Paraná River basin is included in the Del Plata hydrographic region) and adjacent localities in Uruguay.Omalonyx brasiliensis was described by Simroth (1896) based on specimens collected by H. von Ihering in Rio Grande do Sul State.
In the 20 th century, specimens of Omalonyx infected by Leucochloridium, an avian trematode, were found by Lutz (1921) in the surroundings of the institute where he used to work in Rio de Janeiro city, Rio de Janeiro State.The author also reported that this slug is abundant in the north of Brazil.This trematode was also found in birds from Mato Grosso and used in the experimental infection of Omalonyx (Travassos 1928).Both of these works have a parasitological focus, and the specific identification of the slug was not provided.Haas (1939) registered O. unguis for the State of Pernambuco but did not specify the locality.Parodiz (1957) recorded O. unguis in Brazil but did not include the locality.He also mentioned the occurrence of O. unguis in Porto Alegre (Rio Grande do Sul State) and observed its similarity to O. convexus.Based on specimens from the MCZ (lot number unavailable), Parodiz (1963) registered the occurrence of Omalonyx in Rio de Janeiro (O.unguis) and Camaquã, Rio Grande do Sul.The specimens from Camaquã were later identified as O. convexus (Arruda & Thomé 2008b).Lange de Morretes (1949) recorded O. brasiliensis and O. unguis in Vila Nova (Bahia State) and O. matheroni in Santarém (Pará State).In a taxonomical review using specimens from institutional collections, Tillier (1981) studied animals from eight localities in Brazil.Three of them were easily identified: Santarém and Alenquer in Pará State, and Rio de Janeiro in Rio de Janeiro State.The other four localities, due to insufficient labeling information, could not be precisely located.Two of them were only superficially specified: "Brazil" Pernambuco State and Praya (=Praia) Grande (Rio de Janeiro State).The other two localities could not be identified: Santa Amélia, Amazonas and "Makthlawara" (BMNH 1929.10.2.6.22).This author also mentioned the occurrence of Omalonyx in Porto Alegre, Rio Grande do Sul State, and cited Martens (1868) and Simroth (1896), who also recorded O. brasiliensis in this State (Tillier 1981).The distribution of Omalonyx in Brazil was revisited by two authors whose results were similar to those of Lange de Morretes (1949).First, Salgado & Coelho (2003)  Several South American and Lesser Antilles countries are included in the distribution area of the genus Omalonyx (Figure 1, Table 3).The occurrence of O. unguis in Paraguay and Bolivia was reported by d 'Orbigny (1835a'Orbigny ( , b, 1837)).On this occasion, the author did a complete textual description of the external appearance of the animal and specified the collection sites: the flooded margins of Paraná River, near Corrientes, and the swamps of Moxos Province in Bolivia.Corrientes is a city on the riverbank of the Paraná River in Argentina, very close to the frontier with Paraguay, which is defined by the Paraná River itself.Later, Asunción, in Paraguay, was considered to be the type locality for O. unguis (Arruda & Thomé 2008b).
Omalonyx matheroni was described from individuals collected in Guadeloupe, Lesser Antilles (Potiez & Michaud 1835).Tillier (1981) studied specimens he collected or borrowed from institutional collections that were from several localities including the Lesser Antilles, Guiana, Suriname, French Guyana, Ecuador, Paraguay, Argentina and Peru (Table 3).Omalonyx occurrence in South American countries has been well documented by several authors: Argentina (Arruda & Thomé 2008a, b); Brazil (see above the topic geographic distribution of Omalonyx in Brazil); Colombia (Vera-Ardila 2008); Uruguay (Olazarri 1979, Scarabino 2003, Arruda & Thomé 2008b.);French Guiana (Tillier 1981, Arruda et al. 2016); Ecuador (Hermann & Dundee 1967, Tillier 1981, Arruda et al. 2016); Suriname (Tillier 1981, Arruda et al. 2016) Venezuela (Martens 1873, Baker 1925, 1926, Escarbassiere 1993); Guyana (Gibbons 1879, Tillier 1981); Peru (Tillier 1981, Ramirez, 1991;Ramirez et al. 2003) and Paraguay (Hylton-Scott & Lapuente 1968).Parodiz (1963) listed Omalonyx specimens from Paraguay, Argentina and Bolivia that were deposited in different institutional collections.Cazzaniga (1985), based on a bibliographic review, concluded that the known distribution area for O. unguis is southern Brazil, northern and eastern Argentina, Uruguay, Paraguay, and Bolivia and that the presence of O. unguis in the west of Argentina is known only in Tucumám (Hylton-Scott 1971) and Catamarca Provinces.The latter represents a new record made by Cazzaniga (1985) himself.Arruda & Thomé (2008b) showed that the distributions of O. convexus and O. unguis overlap in the Argentinean area of the Paraná River hydrographic region and adjacent localities in Uruguay.Gutiérrez Gregoric et al. ( 2013) recorded the occurrence of Omalonyx sp. in Misiones Province, Argentina using data from the La Plata Museum Mollusk Collection, literature and his own field work.For further literature data about Omalonyx occurrence in Argentina see Table 3.There are some records of Omalonyx in Chile (Odhner 1922, Letellier et al. 2003, 2014), and some of them are recent.However, in 1981, Tillier studied specimens from Chile that were identified as O. gayana and stated that, despite its limaciform shape, the species belongs to the genus Succinea.The recent records from Chile (Letellier et al. 2003(Letellier et al. , 2014) ) do not include a description of the specimens nor any discussion on this taxonomic issue related to Chilean succineids.Thus, we suppose that the specimens are in fact Succinea gayana.
The distribution of the genus in the Lesser Antilles is also well documented.Succinea haliotidea Mittre 1841 was found in Martinique by Mittre (Tillier 1981).However, Tillier (1981) did not include this species in the genus Omalonyx, and indicates that they do not even belong to the family Succineidae once neither he nor Fischer found any Omalonyx in Martinique.Therefore, we did not include Martinique within the occurrence area of Omalonyx.Hermann & Dundee (1967) studied Omalonyx from Sta. Lucia and Antigua, both in the Lesser Antilles.Other authors have also worked in this region.Patterson (1971) and Tillier (1981) studied specimens from Antigua, and Robinson et al. (2009) recorded the occurrence of Omalonyx in several localities in Dominica.Arruda et al. (2016) showed new records of O. geayi and extended the range of distribution of this species in South America to include Suriname, Ecuador, and Bolivia.All references and localities are in Table 3.

Records from institutional collections
Based on data of Brazilian institutional collections obtained through literature, museum databases or onsite research, we verified 21 records for the genus in the North region of the country, 28 in the Northeast, four in the Central West, 33 in the Southeast and 31 in the South (Table 2).Specimens were found in eight Brazilian institutional collections (INPA, MCP, MCNZ, MZSP, MNRJ, UFS, ZUECA and CMIOC).Among the institutional collections that were visited, two of them did not present specimens belonging to the genus (MIRR and MPEG) in (Table 1).Brazilian specimens of Omalonyx were also registered in six foreign institutional collections (ANSP, FMNH, BMNH, ZMB, MNHN, and MCZ).We also investigated the presence of Omalonyx in other South American countries and Lesser Antilles using engines for virtual searching in databases from Brazilian (CMIOC, MCP, MZSP, MNRJ) and foreign institutional collections (ANSP, BMNH, USNM, CM, MACN, MLP) (Table 3).

Malacological surveys in Brazil
Specimens of Omalonyx were sampled across Brazilian hydrographic regions, and the sites were classified above according to the presence or absence of Omalonyx spp.(Table 2 and 5).

Surveyed sites with Omalonyx spp. presence
Specimens were collected in all Brazilian geographic regions, and we found Omalonyx in three States of the South region (Rio Grande do Sul, Santa Catarina, Paraná) where six localities were sampled, one State in the Southeast region (Minas Gerais) where seven localities were sampled, two States in the Central-west region (Mato Grosso, Mato Grosso do Sul) where four localities were sampled, five States in the Northeast region (Piauí, Ceará, Rio Grande do Norte, Pernambuco and Bahia) where nine localities were sampled, and five States (Acre, Amazonas, Pará, Rondônia and Amapá) in the North region where 15 localities were sampled.Among these localities, we made new records for four Brazilian States: Acre, Rondônia, Amapá and Piauí.All coordinates for 41 surveyed sites are listed in Table 2 and indicated in the map (Figure 1).

Modeling of species distributions
The potential distribution of each species is indicated in the maps (Figure 2) where different colors and color densities are related to different probabilities of occurrence of suitable conditions for their presence.The environmental model applied here agrees with the data on species distribution (Figure 1) and supports geographic constraints on the species.Some species presents overlapping ranges of distribution.This is the case for O. matheroni, O. pattersonae and O. geayi, which tend to occur in tropical areas within the northern half of South America (Figure 2A, B and C) and for O. convexus and O. unguis, which tend to occur in temperate areas in the southern half of South America (Figure 2 D and E).Omalonyx matheroni, O. pattersonae and O. geayi present moderate probability of occurrence in a vast area within northern South America, merged with intermittent areas of high probability of occurrence (Figure 2A, B and C).Omalonyx convexus and O. unguis present a smaller area of occurrence; however, there are many regions of high probability of occurrence.
There was a high probability of occurrence of O. matheroni in the Lesser Antilles, in the central region of South America (hydrographic region 5 and 10), in the Atlantic coast (hydrographic region nine), and in the south of South America (hydrographic region 13) (Figure 2A).These areas are predominantly tropical; however, there are also some temperate areas.
Omalonyx pattersonae showed a high probability of occurrence in tropical and arid regions (Figure 2B) in hydrographic region one, two and three (at isolated points in arid regions within hydrographic regions two and three) and in hydrographic regions six, seven and eight (in tropical and arid regions).Moderate probabilities of occurrence of O. pattersonae were observed in hydrographic regions nine and five (tropical region), where discontinuous areas of high probability of occurrence were observed in the Amazonian region (tropical and arid region) (Figure 2B).
Omalonyx geayi is a predominantly tropical species that can also occur in arid areas with high probability of occurrence within hydrographic regions one, two, three, four and five (Figure 2C).In hydrographic region five there are several small areas of high probability of occurrence merged in a vast area of moderate probability.There are areas of moderate probability of occurrence of O. geayi in hydrographic regions six, seven and 13.
Temperate areas along the southeast of South America present the highest probability of O. convexus occurrence.Areas with high probability of occurrence are within hydrographic regions 10, 12 and 13 (Figure 2D).There is moderate probability of occurrence in a vast area of hydrographic region 10 and in small areas within hydrographic regions 11 and 13.
Temperate areas in the southeast of South America that presented high probability of O. unguis occurrence includes hydrographic regions 10, 11, 12 and 13 (Figure 2E).Some areas within tropical (hydrographic regions five, nine and 10), arid (hydrographic region 11) and temperate areas (hydrographic region 14 and Malvinas Islands) were considered to have moderate probability of occurrence.
The PCA analysis resulted in three layers with highest eigenvalues that better explain the relationship between the variables in the selected study area.The most representative variables within these PCA-analysis axes were BIO4 (Temperature seasonality), BIO12 (Annual precipitation), and Altitude.As a consequence, the modeling of the species of Omalonyx was strongly influenced by these three variables, and their potential distribution was mainly determined by them.2), the records for O. pattersonae and O. geayi are sparser (Figure 1).Omalonyx geayi was known to occur only in Kaw Swamp, French Guiana, the type locality (Tillier 1981).However, new records published recently expanded its distribution to Ecuador, Bolivia, Suriname and some localities in Brazil (Arruda et al. 2016).In this work, we recorded O. pattersonae for the first time in three hydrographic regions in North and Northeast of Brazil.There is one state in Brazil (Amazon State) where all three of these species occur at sites that are very close.
The other three species (O.unguis, O. convexus, O. brasiliensis) are concentrated in the south of South America.Among these species O. unguis reaches the most northern positions.This species was even found outside its distribution range (Lesser Antilles, Bolivia, Peru and in Ceará State, in the Northeast of Brazil).Omalonyx convexus records are very concentrated (Figure 1) and are restricted to sites where high or intermediate probability of occurrence was predicted (Figure 2B).However, there are some exceptions, and the species was also recorded in the north shore of Venezuela and in the Northeast of Brazil (Sergipe State).Until now, O. brasiliensis was known only from its type locality in Rio Grande do Sul State, Brazil.Despite all the surveying efforts already concentrated in Rio Grande do Sul State (Figure 1), O. brasiliensis was never found again since its description and the species remain known only for the type specimens from an unspecified site that could be related to hydrographic region 10 or 12 (Figure 1).Thus, O. brasiliensis remains to be rediscovered.This is a large State where O. convexus is widespread (Table 2, Figure 1); thus, both species may occur in sympatry.
There are several records from literature review, museums and collections that were not identified to species level and are designated Omalonyx sp.They were not used to model species distribution.These records are widespread throughout South American hydrographic regions (e.g., five, seven, nine and 10) and should also be carefully analyzed in future studies.On the other hand, some records identified to species level seem to be inconsistent (e.g., O. convexus was recorded for the Northeast of Brazil) and should be revised.All the records situated outside the area predicted for the species distribution should be carefully investigated.We suppose that the lack of taxonomists dealing with this group is the main cause for the great amount of records identified to genus level.On the other hand, the lack of training and the subtle morphological differences among species must be a cause of misidentification.These problems contribute to gaps in the knowledge regarding Omalonyx distribution (Tillier 1981, Coscarelli & Vidigal 2011).
Brazil is the best-sampled region in South America.Here, based on our malacological surveys, new records were made in Acre, Rondônia, Piaui, and Amapa.However, despite the absence of records even after intensive surveys in some administrative unities (Roraima, Tocantins and Distrito Federal) (Table 5), the genus was registered in all Brazilian hydrographic regions.There were no records for the central area of Tocantins River hydrographic region (surveyed sites: Palmas and other surrounding areas such as Lagoa da Confusão and Porto Nacional).However, the genus was present in the upper part of the hydrographic region (comprising Goiás and Pará States; Figure 1 and Table 2).Distrito Federal is an administrative unity that encompasses a small area when compared to the Brazilian States, and within this small area, there are the frontiers of three hydrographic regions: Tocantins River, São Francisco River and Del Plata.Despite its proximity to Goiás State where we found Omalonyx sp., there were no records in Distrito Federal (surveyed sites: the margins of Paranoá Lake, in Brasília, and in Brazlândia, all of them in the upper Del Plata hydrographic region where the genus is widely distributed; Figure 1).In Roraima State, northern Brazil, despite the surveying efforts (23 records of absence) no record was made.Roraima is within the Amazon River hydrographic region in which Omalonyx is widely distributed (Figure 2).However, all these negative localities are in the northeastern quadrant of Roraima, which is characterized by unusual vegetation, a seasonally flooded savannah, locally called "Lavrado" (Barbosa et al. 2007), which may have some ecological features that prevent Omalonyx spp.colonization.Future sampling efforts should focus on areas within these States that were not investigated until now.Considering that Omalonyx spp.occur in the hydrographic regions that cover these States, the absence of records is probably due to insufficient sampling effort.
In South America Omalonyx species were found in all hydrographic regions (except hydrographic regions one and 14) and countries.However, there were only isolated records in Colombia, Ecuador and Chile, indicating the need for more sampling effort in these areas (Figure 1).However, the occurrence of this genus in Chile must be further investigated due to different point of views regarding the identification of the Chilean slug-like succineids (Tillier 1981).The record from Chile (Letellier et al. 2014) should be carefully investigated since Tillier (1981) considered that the species recorded in Chile, O. gayana, belongs to the genus Succinea.In fact, Chile is separated from the other South American countries by the Andes mountain range, which is the major water divider in South America.d'Orbigny (1837) stated that the genus occurs only on the east side of the ridge, and until now, there is no evidence suggesting otherwise.Our results agree with those from d' Orbigny (1837) and Tillier (1981).Bioclimatic analysis proved to be a valuable tool for gaining insight into the geographical distribution of a species, especially when few records are available (i.e., O. geayi and O. pattersonae).Predictions showed that O. matheroni and O. geayi are tropical species.Omalonyx pattersonae usually occurs in arid regions; however, its distribution moderately extends over tropical areas.However, the prediction of O. geayi to hydrographic region 13 (temperate and very cold area) could be related to low numbers of records.In fact, bias can occur if species are insufficiently sampled.Thus, climatic envelopes may generate incomplete results, and the accuracy of predicted distributions will be decreased (Beaumont et al. 2005).
The occurrence records and the predictions both indicated that O. convexus and O. unguis have largely overlapping distributions in temperate areas within southern South America.These results are in accordance with those from Arruda & Thomé (2008b) and Coscarelli & Vidigal (2011).However, the distribution of O. convexus is constrained to temperate regions while O. unguis is well represented in tropical, temperate and arid regions indicating that the latter presents a broader tolerance range for environmental variables and is adapted to different bioclimatic conditions.
Considering the extension and the great diversity of habitats in the neotropical region and the wide occurrence area of Omalonyx species, bioclimatic models can be used to extrapolate information on species distribution if the high cost of field surveys in such a vast area is unfeasible.Information on the distribution of Omalonyx species will help to improve the taxonomic and biogeographic studies on these slug-like gastropods.

Figure 1 .
Figure 1.Updated distribution of the genus Omalonyx across Neotropical region.The coloured areas represent different hydrographic regions and their respective numbers.The solid black line indicates the borders among South American countries and within Brazilian administrative regions.The species records were represented by colours dots: red = O. matheroni; blue = O. convexus; green = O. unguis; yellow = O. geayi, purple = O. pattersonae, black = O. brasiliensis; gray = do not identified until species level, or Omalonyx sp. and gray circle with black border = Specimens from Chile that were previously identified as O. gayana.The stars represents the records made in our surveys, the circles represents literature or museums data and the cross symbol represents the samples that were donated by other researchers.Details about each sample are on tables 2 and 3. Hydrographic regions are indicated by numbers: 1) Pacific Coast; 2) Caribbean sea; 3) Orinoco River; 4) Amapá-Esequibo; 5) Amazon River; 6) Tocantins River; 7) North Atlantic; 8) São Francisco River; 9) Eastern Atlantic; 10) Del Plata; 11) Border strip of the Brasilica (North) and the Chilean-Patagonian (South West) Subregion; 12) Eastern; 13) Chilean-Patagonian Subregion of the Pacific Versant; 14) Chilean-Patagonian Subregion of the Atlantic Versant.

Table 4
).The classifications of climate were based on Koppen-Geiger climate classification types for South America (Peel et al. 2007).Maps for the distribution of O. matheroni, O. pattersonae, O. geayi, O. convexus and O. unguis were produced.

Table 1 .
Institutions harbouring specimens of Omalonyx found after literature review, visits and virtual search in collections databases.Tecnologia da Pontifícia Universidade Católica do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.MCNZ Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.MCZ Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, United States of America.

Table 2 .
Records of Omalonyx in Brazil based on literature data, institutional collections, and our own malacological surveys.

Table 4 .
Bioclimatic variables used in models development.
(Arruda et al. 2016) (2011) 2012)et al. 2006, Montresor et al. 2008)Omalonyx species genus in a review about Brazilian land snails but did not cite any locality.After that,Simone (2006)cited the occurrence of O. brasiliensis in Rio Grande do Sul State and considered the occurrence area for the genus Omalonyx to be from Bolivia to Patagonia.Several other records were made in Brazil, including Minas Gerais(Oliveira & Almeida 2000, Arruda et al. 2006, Montresor et al. 2008)and São Paulo State(Arruda et al.Cantanhede et al. 2014)in the northeast; and Amazonas State in the North(Pimpão 2007, Garcia et al. 2012).Coscarelli & Vidigal (2011)investigated the distribution of O. unguis in Brazil and included new records for this species.Recently, new records for O. geayi extended the distribution range of this species in northern South America including Brazil(Arruda et al. 2016).The presence of Omalonyx was recorded in several Brazilian States representing all geographic regions (Table2).All data and details (i.e., species and coordinates) on species distribution in Brazil were included in Table2and are shown in Figure1.