﻿Redescription and geographical distribution of Leiostracusobliquus (Reeve, 1849) (Mollusca, Gastropoda, Simpulopsidae)

﻿Abstract 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. Leiostracusobliquus 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.


Introduction
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) 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, 1901from Bahia and D. obliquus poecilogramma Ancey, 1901from 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.

Morphology
Specimens were examined from the malacological collections of Museu de Zoologia de São Paulo (MZSP) and Museu de Malacologia Maury Pinto de Oliveira, Universidade Federal de Juiz de Fora (CMMPO). Images of the material deposited in the collections of the Academy of Natural Science of Philadelphia (ANSP) and the Zoological Museum of Amsterdam (ZMA) were also consulted. The species identification was based on the; shell morphology, original description of L. obliquus; and comparison with the images of the type material, besides the criteria proposed by Breure (1979) and the images provided by Simone (2006). Whole specimens examined were photographed using a Nikon D5300 digital SLR camera. Anatomical systems of ethanolpreserved specimens were dissected under a stereomicroscope Olympus SZX7, following the methodology proposed by Cuezzo (1997) and drawn with the help of a camera lucida. Measurements of the soft parts were expressed as a proportion of the length of the last whorl.
Radula and jaw were prepared for scanning electron microscopy, following the methodology described by Ploeger and Breure (1977). After being separated from the buccal mass, the radula and jaw were cleaned by immersion in a sodium hypochlorite solution, mounted on stubs, and metalized with 50 nm of gold. Details of the shell sculpture, jaw, and radula were obtained through scanning electron microscope FEI Quanta 250 at the Laboratório de Microscopia Eletrônica of the Universidade Federal de Juiz de Fora, Brazil (UFJF).

Occurrence records and distribution
To update the geographic distribution of L. obliquus, occurrence data were obtained from literature, and malacological collections consulted from the following sources: Global Biodiversity Information Facility (https://www.gbif.org), Sistema de Informação sobre a Biodiversidade Brasileira (https://www.sibbr. gov.br), the website of malacological collection of the Academy of Natural Science of Philadelphia (https://ansp.org). Despite the loss of the Museu Nacional do Rio de Janeiro's material in the fire of 2018, the information associated with specimens from this collection remained available on biodiversity databases. We decided to include the occurrence records for L. obliquus from this collection even though we could not confirm species identification, as these specimens were originally identified by Dr. Norma Campos Salgado, a renowned Brazilian malacologist. After removing duplicate records and records without specific localities, we obtained a total of 40 occurrence records, which were georeferenced using Gazetteers and Geolocation applications (https://geo-locate.org/web/WebGeoref.aspx). Layers corresponding to Brazilian biomes and administrative boundaries were obtained from Instituto Brasileiro de Geografia e Estatística (IBGE, https://www.ibge.gov.br). Distribution maps were constructed using QGis version 3.10.14-A Coruña (QGIS Development Team 2021).

Institutional acronyms MCZ
Museum Redescription. Shell (Figs 2A-D, 3). Shell perforate, pyramidally ovate, umbilicated, thick. Shell height from 21.87 to 30.81 mm (Table 1); seven or eight whorls slightly convex. Protoconch 1½ whorls, white to pale pink, with wellmarked regular striation (Fig. 3A). Teleoconch sculptured with delicate spiral striae (Fig. 3C), with a single narrow dark-brown line in the last whorl, surface with regular and shallow striae. Spire high, ~ 3/5 of the shell length. Second whorl with two forms of sculpture, oblique irregular striations in the upper part, irregular striations in the middle part, and spiral lines, with punctuations in the lower part (Fig. 3B-D). The transition between protoconch and teleoconch well marked. Aperture broad, oblique, ovate to subovate. Outer lip and columella   broadly reflected (Fig 2A). Suture well-marked, simple, slightly oblique, with a thin purple-brown line (Fig. 2B). Body whorl, white to pale cream; wide pale-pink disrupted band all over the teleoconch ( Fig. 2A-C). Peristome widely expanded in adult specimens (Fig. 2C). Body whorl ~ 2/5 of the shell length, rounded; umbilicus narrow, partially covered by the peristome; periumbilical area pale cream (Fig. 2D). Radula (Fig. 3F-H). Approximately 75 teeth per row. Mean number of teeth per half row (except for central tooth) 37. Each radular row disposed linearly on the same level (Fig. 3E). Rachidian tooth small (~ 4/5 of the length of laterals), rectangular, symmetric, with round edges, without differentiated cusps (Fig. 3F); basal plate almost trapezoidal; cutting edge slightly round. Lateral teeth asym-metrical, bicuspid, basal plate wider, weakly arched towards the median region, and with cutting edge, ½ the size of the rachidian tooth (Fig. 3G). First lateral tooth with conspicuous inner cuspid; base wider than the apical part. The size of the lateral teeth decreases gradually towards the outer area. Basal-lateral cusp appears in the third or fourth teeth and becomes more distinct in the marginal teeth. Marginal teeth with four cuspids, mesocone well developed, with a bicuspid cutting edge, endocone relatively reduced, bicuspid or tricuspid (Fig. 3H).
Pallial system (Fig. 4A). Mantle border simple, thick. Rectum narrow, walls thick. Primary ureter along the rectal side of the kidney up to the top of the lung cavity. Secondary ureter, wide and slender, parallel along the entire left side of the rectum. Mantle cavity short, ~ 1/4 of the body whorl. Kidney elongated, narrowly triangular, thin, ~ 1/3 of the pallial cavity in length, with ~ 7 lobes, the anterior lobe at the level of the auricle slightly longer. Pericardial cavity on the left side of the kidney, at the columellar margin of the posterior end of the pallial cavity, near the same length as the kidney. Auricle elongate, ~ 1/3 of the triangular ventricle. Pulmonary vein visible in the mantle roof, almost as long as the pallial cavity, oblique in the anterior 1/2, converging to the pneumostome region along with the ureter and rectum. Slender vessels visible on both sides of the pulmonary vein, at the distal portion of the pallial system.
Genital system (Fig. 4B-D). Ovotestis with three or four branches of enlarged digitiform acini, each branch with more than 20 simple acini. Hermaphroditic duct tubular, very sinuous, thick, folds itself in an S-shape. Albumen gland small, slightly elongated (Fig. 4B, C). Spermoviduct, bursa copulatrix and penial complex with approximately the same length when distended. Bursa copulatrix elongated (~ 1/3 larger than spermoviduct), thin. Bursa sac slightly elongated terminally, lying on the concave face of the spermoviduct. Prostate long, with numerous tubular-acini, in the columellar surface of the spermoviduct. Penial complex long, club-shaped, phallus subcylindrical, penis with a sheath. Phallus-epiphallus transition unrecognizable externally. Insertion of the vas deferens subterminal. Flagellum present, subcylindrical, short, ~ 1/10 of penial complex length. Insertion of the bursa copulatrix and penial complex into the free oviduct at the same level. Genital atrium very short, ~ 1/10 of spermoviduct length. Spermatheca well-differentiated, sinuous, lying at the superior third of the albumen gland.
Remarks. The shell characters of the specimens from MZSP, identified here as L. obliquus matched with the original description made by Reeve (1849) and the lectotype designed by Breure (1978) (Fig. 6A, C, Table 1). After comparing our specimens with the material from several malacological collections, we concluded that L. obliquus is very similar to Leiostracus carnavalescus Simone & Salvador, 2016. Both species are medium-sized (24.5 mm ± 2.7 in L. obliquus whereas in L. carnavalescus 24.4 mm ± 1.3) (Table 1), presenting conical-oval shells, with a typical brown line on the base of the body whorl (Fig. 6A), 7-8 whorls, and outer lip widely reflected. In the original description of L. carnavalescus, Simone and Salvador (2016) provided two images of a specimen from Mantena, whose shell characteristics match the original description of L. obliquus. We also observed notable similarities between Dorhn's "varieties" and the three color patterns described for L. carnavalescus, all of them exhibiting a brown  (Reeve, 1849), anatomy A ventral view of the pallial system dissected out, showing the inner face of ventral view B detail of albumen gland showing internal lobs C ventral view of the reproductive system without ovotestis D dorsal view of the reproductive system. Abbreviations: ag, albumen gland; bc, bursa copulatrix; ca, carrefour; fl, flagellum; ga, genital atrium; hd, hermaphrodite duct; k, kidney; mb, mantle border; pe, pericardium; pr, prostate; pur, pulmonary roof; pv, pulmonary vein; re, rectum; spo, spermoviduct; sur, secondary ureter; vd, vas deferens; ur, ureter. Scale bar: 2 mm (A-D).
band on the base of the body whorl mentioned by Dohrn (1833) and Pilsbry (1899) for L. obliquus (Fig. 6B, D). The holotype of L. carnavalescus is identical to Dorhn's "variety 2" (Fig. 6B; Dohrn 1833: fig. 11). The paratypes #1 and #2 (MZSP 106179 and M`ZSP 106178, respectively) of L. carnavalescus are similar to Dorhn's "variety 4", presenting pinkish bands and fine lines of brown spots ( Fig. 6B; Dohrn 1833 date: fig. 15). Dorhn's "variety 3" (Fig. 6B; Dohrn 1833: fig.  13) is similar to "specimen #2" of L. carnavalescus from Sooretama (Fig. 6D), both present yellowish shells, with wide pinkish bands, a brown band at the base of the body whorl, and a thin brown sutural line. Lastly, Dorhn's "variety 5" (Fig. 6B; Dohrn 1833: fig. 14) is similar to the paratype #3 (MZSP 106179) of L. carnavalescus. Both presents wide dark bands with a fine brown line of punctations. Dohrn (1883) did not specify where the material analyzed by him was deposited. Nonetheless, we found two lots donated by Dorhn and identified as L. obliquus from Brazil, housed in the Zoölogisch Museum of Amsterdam (ZMA 385620; ZMA 385621). We believe this material could be part of the specimens used by Dorhn to establish those color varieties of L. obliquus. The shell from ZMA 385620 is similar to Dorhn's "variety 3", while the shells from ZMA 385621 are similar to Dorhn's "variety 1" and "variety 2". The analysis of these specimens also confirmed the similarities between L. obliquus and L. carnavalescus. The radulae of both species are identical: the rachidian tooth is rectangular, symmetric, without differentiated cusps and the basal plate is almost trapezoidal; cutting edge slightly round; lateral teeth bicuspid and weakly arched to- wards the median region ( Table 2). The anatomy of the reproductive system is also identical in both species (mainly the presence of the penis sheath and the morphology of the penis complex).
On the other hand, L obliquus differs from L. cinnamomeolineatus in the morphology of the radula: in L. obliquus the rachidian tooth is nearly round, while in L. cinnamomeolineatus it is triangular (Table 2). However, this variation may be the result of age and/or diet. Considering the anatomy of the reproductive system, both species can be differentiated by the shape of the flagellum, which is longer and slender in L. obliquus, and inverted U-shaped and less tapered flagellum in L. cinnamomeolineatus, as well as by the shape of the bursa copulatrix reservoir, which is claviform in L. obliquus and globose in L. cinnamomeolineatus (Table 2). 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 reproductive system.
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 pallial system, 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.