Leiostracus Albers, 1850 was established to allocate land snails from Central America and Northern South America. Currently, approximately 19 species are considered valid. However, for most of them, the internal morphology is unknown. Leiostracus obliquus was described as a species of Bulimus from the state of Bahia based on shell characters. Until now, knowledge of this species has been scarce. The discovery of ethanol-preserved specimens from MZSP of this species allowed us to characterize, for the first time, the internal anatomy of this species and update its distribution. The shell of L. obliquus has seven to eight whorls and a wide pale-pink disrupted band all over the teleoconch. The rachidian tooth is small rectangular, symmetric, with round edges, and without differentiated cusps. After comparing the anatomy and radular characters between the shells of L. obliquus and L. carnavalescus, we found remarkable similarities in the morphology and color pattern.

Anatomy, gastropods, land snails, Orthalicoidea, taxonomy

The land snails ascribed to the family Simpulopsidae Schileyko 1999 are characterized by shells with simple aperture, without teeth and the absence of a penial sheath (Breure 1979; Schileyko 1999). Currently, this family includes three genera: Rhinus Albers, 1860, Simpulopsis Beck, 1837, and Leiostracus Albers, 1850, which are distributed in Central America, South America, and West Indies (Schileyko 1999). The taxonomy of Simpulopsidae has changed over time; its internal phylogeny and evolutionary relationship with other lineages of Orthalicoidea remain uncertain (Breure and Romero 2012). This taxon was first established by Schileyko (1999) as Simpulopsini, a tribe of Bulimulidae. Bouchet and Rocroi (2005) and Bouchet et al (2017) sustained this taxonomic status, but Breure and Romero (2012) raised this group to family rank, based on a three-locus gene phylogenetic analysis.

Leiostracus was first established to allocate land snails from Central America and Northern South America (Guyana, Suriname, and Brazil) (Albers 1850). The original diagnosis of this genus included shell characters, i.e., oblong-conic shell with 7–8 whorls, peristome expanded, and columellar margin dilated. Breure (1979) and Schileyko (1999) included internal anatomy traits in the diagnosis of this genus, i.e., short flagellum, absence of penial sheath, and spermathecal duct dilated at the base and narrow at the top.

The taxonomic history of Leiostracus is controversial, different authors allocate this taxon in generic or subgeneric ranks and ascribe it to different families over time (Albers and Martens 1860; Pilsbry 1899; Breure 1978). Pilsbry (1899) and Thiele (1929), considered Leiostracus as a subgenus of Drymaeus Albers, 1850, due to similarities in shell morphology. Pilsbry (1899), was the one who restricted the name Leiostracus to some species of Drymaeus endemic to Brazil, whereas Zilch (1959–1960), raised Leiostracus to the genus level. Breure (1979), also considered Leiostracus as a genus with geographic distribution restricted to Guyana, Suriname, and Brazil. There has yet to be a consensus on the number of valid species in this genus. Herein, Breure (1978), considered 15 number of species as valid. One year later, the same author raised the number of valid species to 39, and included in the subgenera, Leiostracus and Pseudoxychona Pilsbry, 1930, all endemic to Brazil (Breure 1979). Schileyko (1999), probably following Breure (1979), mentioned the same number of valid species of Leiostracus, while Salgado and Coelho (2003), considered only twelve valid species.

Currently, approximately 19 species of Leiostracus are considered valid (Simone 2006; MolluscaBase 2022), including three species described in the last decade: Leiostracus fetidus Salvador & Cavallari, 2014 (from Canavieiras, Bahia, Brazil), Leiostracus faerie Salvador & Cavallari, 2014 (from Rio Doce, Espírito Santo, Brazil), and Leiostracus carnavalescus Simone & Salvador, 2016 (from Nanuque, Minas Gerais, Brazil) (Salvador and Cavallari 2014a, 2014b; Simone and Salvador 2016). The available information on Leiostracus species is fragmentary and scarce. For most of them, the internal morphology is unknown. The anatomy of the soft parts is described only for L. cinnamomeolineatus Moricand, 1841, L. demerarensis (Pfeiffer, 1861) (Breure 1978; Muratov and Gargominy 2011), and Leiostracus carnavalescus Simone & Salvador, 2016.

Leiostracus obliquus (Reeve, 1849), was initially described as a species of Bulimus Scopoli, 1777 from Bahia state, Brazil. Reeve (1849), did not mention the specific locality from where the type specimens were collected, and he established a diagnosis based entirely on the shell characteristics: “a pink shell of firm structure encircled with a conspicuous chestnut band around the last whorl” (sic.). So far, no other information besides the original description of this species is available. Dohrn (1883), ascribed L. obliquus to Bulimulus Leach, 1814, and designated six “varieties” based on the shell morphology and characteristics of the color bands, i.e.:

1. whitish without bands;
2. whitish, yellowish or reddish, with one band in the body whorl;
3. straw-yellow with rose broad bands and a brown band at the base of the body whorl or with a fine brown sutural line;
4. like the anterior but having a brown band around the umbilicus and two fine brown punctuated lines on the body whorl;
5. with four dark bands, the one upper the suture covering half of the whorls;
6. with four or five bands, the lowest around the umbilicus pale brown or dark, the other always dark, the uppermost and middle ones narrower and pale brown, the second lilac or rose, wider than the others, and frequently with a dark sutural line.

Dohrn (1883), also synonymized Bulimus jeffreysi Pfeiffer, 1852, with L. obliquus, because both species are similar in shell morphology. Ancey (1901), transferred L. obliquus to Drymaeus and named two varieties: Drymaeus obliquus var. monozona Ancey, 1901 from Bahia and D. obliquus poecilogramma Ancey, 1901 from Minas Gerais. Breure (1978), designed the lectotype based on similarities with the specimen drawn by Reeve (1849), in the original description and synonymized the variety poecilogramma with L. obliquus. After that, Breure (1979), considered this variety as subspecies of Leiostracus (Leiostracus), while for Simone (2006), the two subspecies established by Ancey were synonyms of L. obliquus while giving no clear justification. The designation proposed by Breure (1978) is currently accepted, and Leiostracus (Leiostracus) obliquus is ascribed to the family Simpulopsidae.

During a taxonomic revision of Drymaeus species from Brazil, while analyzing material from two Brazilian malacological collections from Museu de Zoologia de São Paulo and Museu de Malacologia Maury Pinto de Oliveira of Universidade Federal de Juiz de Fora, we found specimens labelled as “Drymaeus sp.” and we noticed that they corresponded to Leiostracus obliquus. Therefore, this work aims to redescribe L. obliquus, providing detailed information on the shell sculpture and internal anatomy. Furthermore, we assessed the geographic distribution of this poorly known species. We also compared the new data to the available information on closely related species.

In the present work, we redescribe the species Leiostracus obliquus (Reeve, 1849), providing new information on shell micro sculpture, radular morphology, and anatomy of the soft parts. The striking similarities in shell morphology and color pattern between Leiostracus obliquus and L. carnavalescus, evidenced by comparison with the type material, the species original descriptions, and other specimens from malacological collections leads us to think that these are the same species. Notwithstanding, DNA analyses comparing L. obliquus specimens with L. carnavalescus type material are necessary to clarify these assumptions.

The material from Zoölogisch Museum of Amsterdam was donated by Dorhn and probably was used by him to describe varieties of L. obliquus (Dohrn, 1883) which are identical to the three color patterns described for L. carnavalescus. Moreover, the specimens herein identified as L. obliquus cannot be differentiated from L. carnavalescus through the anatomy of the soft parts and radular morphology.

Leiostracus obliquus was described from a single dry shell and since its description, records of this species are scant and outdated. L. obliquus is mentioned in the most recent Brazilian species lists by Salgado and Coelho (2003) and Simone (2006), but there are no more recent occurrences. Although most species of the genus have been documented for Bahia, Leiostracus vittatus (Spix, 1827) was the sole species of the genus that was reported in the inventory of Northeastern Brazil from Dutra-Clarcke and Souza (1991). Since then, records of this species have been virtually nonexistent, highlighting the importance of native species inventories, particularly, for imperiled areas such as Atlantic Forest.

Comparisons between the shells of the varieties from L. obliquus and L. carnavalescus showed remarkable similarities in morphology and color pattern. Concerning the “specimen #1” (MZSP 108010) from Mantena, Simone and Salvador (2016) mentioned: “…seem to belong to the same species as far as the conchological characters indicate.” This matched well with our material of L. obliquus, reinforcing the similarity of both species. The “variety 2” corresponds with the drawn specimen from the original description (Reeve 1849) and would be the typical form of L. obliquus, while the other varieties described by Dornh are identical to the shell color pattern mentioned by Simone and Salvador (2016). Furthermore, both species cannot be distinguished by their radula and reproductivesystem.

Color polymorphism refers to the occurrence of multiple discrete color phenotypes within the populations of the same species (White and Kemp 2016). The occurrence of color polymorphism is widespread in animals and usually has a genetic basis (Estévez et al. 2020). It may be associated with different biological functions such as sexual signaling, crypsis, and thermoregulation (Bond 2007). For land snails, crypticity and scape from predators may be the main advantages of color and color-band polymorphisms (Surmacki et al. 2013). Moreover, polymorphism can lead the number of species to be underestimated (Köhler and Burghardt 2016; Inkhavilay et al. 2017). Alternatively, on the other hand, it can also lead to the overestimation of diversity, in which individuals of the same species are described as belonging to distinct species, such as L. carnavalescus.

As we mentioned above, the species now ascribed to Leiostracus were allocated to different genera of Orthalicoidea in the past (Albers and Martens 1860; Pilsbry 1899; Ancey 1901; Breure 1979; Schileyko 1999), and these taxonomic attributions relied solely on the shell morphology. However, there is enough evidence of the separation of Leiostracus from other genera, which is supported by both shell and anatomical characters (Breure 1978; Schileyko 1999). Leiostracus can be distinguished from Bulimulus by its elongated shell and protoconch sculpture with wavy, or radial wrinkles, sometimes with granulations or reticulate on the lower part, while the latter exhibits regular oblique striation on the upper part and spiral irregular corrugate lines. Despite some superficial similarities, the shells of Drymaeus and Leiostracus can be clearly separated. According to Breure (1979), in Leiostracus, the shell is more conical, sometimes presenting a keeled or angled body whorl, with a higher spire and 7–8 whorls, while Drymaeus presents an oval shell shape, with a lower spire, and 5–6 whorls. In Drymaeus, the protoconch shows a reticulate sculpture, whereas the protoconch in Leiostracus has spiral striations. Considering the pallialsystem, the conspicuity of the pulmonary vein and secondary vessels is distinct in Leiostracus and the other genera. In species of Leiostracus, the pulmonary vein is well developed, and secondary vessels are moderately developed. In species of Bulimulus, the pulmonary vein and the secondary vessels are strongly developed, while Drymaeus species show veins weakly to moderately developed with the adrenal ureter partly open or veins strongly developed and the adrenal ureter varying from open to closed. Some differences are also found in the genital apparatus of these genera. In Leiostracus, the penis sheath is absent, while in Drymaeus, the absence or presence of a penis sheath can be observed in different species. In Bulimulus, the penis is swollen in the distal part and usually covered by a proximal sheath (Breure 1979).

Leiostracus obliquus differs from all other species of the genus due to its conical-oval shell, with a brown line on the base of the body whorl, a reflected apertural lip and by presenting a fine brown sutural line, which is an uncommon trait among species of this genus. This species can be distinct from L. cinnamomeolineatus due to the presence of spiral brown lines and the absence of a sutural line in the shell. Shell dimension is also different, with the shell of L. obliquus being slightly larger (~ 23 mm, with 7–8 whorls) compared to the shell of L. cinnamomeolineatus (~ 21.5 mm, with 6 2/3 whorls).

Our findings suggest that Leiostracus obliquus may be endemic to Brazil, where it is primarily found in Atlantic Forest areas. In the original description, Reeve (1849), mentioned the type locality was the state of Bahia, without giving a specific location where the material was found. The geographical distribution of this species remained largely unknown as subsequent authors (Pilsbry 1899; Ancey 1901; Breure 1978) mentioned records for the states of Minas Gerais, Bahia, and Espírito Santo, without reference to the specific localities. Dohrn (1883), mentioned that the material analyzed by him was collected in the headwaters of the Mucury River, eastern Minas Gerais, which corresponds to the locality mentioned in the original label of the material ZMA 385621, i.e., “Mucury, Brasilis”. Herein, most of the occurrence records of. L. obliquus associated with malacological collections corresponded to localities in the Southeast of Brazil. According to Simone (2006), the genus Leiostracus occurs in Bahia and Minas Gerais states. Other species also occur in the Southeast, with scarce records for Espírito Santo, Rio de Janeiro, and São Paulo states. In this regard, the compilation of occurrence records for L. obliquus made in this work, extends the known distribution of this genus in Brazil. According to our results, most of the records of L. obliquus corresponded to the Atlantic Forest, one of the most threatened biomes in South America, with more than 85% of its original area deforested (Ribeiro et al. 2009). Land snails have a limited potential for dispersal and rely on their surroundings to survive and reproduce (Baur and Baur 1988; Barahona-Segovia et al. 2019). Thus, they are among the most threatened animal groups globally. In Brazil, the scarcity of information on taxonomy, ecology, and distribution of native species of land snails, hampers the efforts in determining their conservation status and, consequently, to foment legal protection measures for land snail species occurring in the Atlantic Forest, one of the most threatened biomes and with more than 85% of the original area deforested, threatening many plant and animal species with extinction.

The authors would like to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) for granting a fellowship to MIPFM. We are grateful to Jonathan Ablett, Natural History Museum of United Kingdom and Macy Hafner, Academy of Natural Science of Philadelphia for providing images of the specimens of L. obliquus, Pedro Loureiro, and Laboratório de Microscopia Eletrônica da Universidade Federal de Juiz de Fora - Brazil, for their support during MEV imaging.

We deeply appreciate all comments provided by the editor, Edmund Gittenberger, and the two anonymous reviewers to whom we are thankful. Their recommendations significantly enhanced the quality of this paper.