﻿Further notes on the taxonomy of the land snail family Clausiliidae Gray, 1855 (Stylommatophora, Helicina) from Myanmar with description of two new species

﻿Abstract This study presents a complete species list of the door snails inhabiting Myanmar, updated to now include 33 taxa, and provides taxonomic notes together with a re-description of the shell, radula, and genitalia for 13 species and subspecies, including Oospiraphilippiana, the type species of the genus Oospira. The snails previously treated as subspecies or synonyms of Oospiragracilior and Oospiramagna are reclassified and recognized as distinct species. The lectotype of Oospirainsignis has been clarified and an illustration of the original type specimen provided. A long-overlooked species, Oospiraandersoniana, has been collected and redescribed herein. Two new species from the limestone karsts in the Salween River Basin are introduced: Oospiraluneainopsis Man & Panha, sp. nov. and Oospirazediopsis Man & Panha, sp. nov. A synoptic view of all clausiliid taxa known from Myanmar is presented along with taxonomic information and distributional records. Photographs of the type materials for all taxa are provided for further comparison or, if unavailable, photographs of the examined specimens or the original figure from the literature.


Introduction
Door snails are well-known land snails belonging to the family Clausiliidae Gray, 1855, and are easily recognized by their usually sinistral fusiform shell and their unique clausilial apparatus: clausilium, plicae and lamellae (Nordsieck 2007;Uit de Weerd and Gittenberger 2013). They are considered to have originated in western Eurasia during the Late Cretaceous before being dispersed worldwide, and now occur in the Ethiopian, Palearctic and Neotropical regions (Nordsieck 2007;Uit de Weerd and Gittenberger 2013). These snails have long fascinated researchers who studied their systematic and evolutionary history, particularly for European taxa (e.g., Giokas et al. 2005;Gittenberger et al. 2012;Koch et al. 2017;Fehér et al. 2018;Hausdorf 2022;Hausdorf and Neiber 2022;Sulikowska-Drozd et al. 2022).
Only two of the seven subfamilies of Clausiliidae have diversified in Southeast Asia: Phaedusinae Wagner, 1922 and Garnieriinae Boettger, 1926 (Uit de Weerd andGittenberger 2013). Their ancestors are believed to have colonized and diversified in SE Asia independently over nearly the same period (Nordsieck 2007;Uit de Weerd and Gittenberger 2013). These door snails are ground to arboreal dwellers (tree trunks) that tend to prefer karstic-associated habitats (Stoliczka 1871;Loosjes 1953). Within Indochina, Vietnam has the highest number of reported clausiliid taxa, with ca. 90 nominal species and subspecies in 33 genera and subgenera (Nordsieck 2011;Schileyko 2011;Páll-Gergely and Szekeres 2017;Bui and Szekeres 2019); in contrast, the clausiliids of other countries in Indochina are far less well documented. This is surprising especially in the case of Myanmar, which hosts 14 terrestrial ecoregions (Olson et al. 2001) and has twice the land area of Vietnam, but which has only 31 nominal species and subspecies from four genera (Grego et al. 2021;Szekeres et al. 2021a, b).
Knowledge of Myanmarese door snails was primarily reported during the colonial period in the 19 th century by the pioneering western naturalists (see Pholyotha et al. 2020;Man et al. 2022 for further history review). The 'Fauna of British India including Ceylon and Burma' by Gude (1914) was the first, and is still the most important, publication on Myanmarese clausiliids. This early-20 th century reference includes 19 nominal species and subspecies belonging to 'Clausilia Draparnaud, 1805' with various subgenera and 'sections' (Gude 1914). Later, three additional species from northern and south-eastern Myanmar were introduced in the mid-20 th and early-21 st centuries (Likharev 1962;Nordsieck 1973Nordsieck , 2002a. In 2007, Nordsieck published an updated global list and proposed a reclassification of nearly all known clausiliid species. Then, in 2021, he further published the diagnostic characters, drawings and photographs from the type species and representative materials for Asian Phaedusinae (Nordsieck 2007(Nordsieck , 2021. Regarding Myanmarese clausiliids, Phaedusa Adams &Adams, 1855 andOospira Blanford, 1872 stand out as the most species-rich genera in this family. Recently, Grego et al. (2021) and Szekeres et al. (2021a, b) reported that the door snail diversity of Myanmar included 27 nominal species and subspecies of three genera; however, these species are mainly recognized on shell features only.
Traditionally, shell morphology employs apomorphic characters for species recognition, including lamellae development, and the number and position of palatal plicae (i.e., Nordsieck 2007Nordsieck , 2021Uit de Weerd and Gittenberger 2013). Meanwhile, genital anatomy has been used to distinguish taxa when shell features alone are ambiguous (Pholyotha et al. 2020;Sutcharit et al. 2020a;Páll-Gergely and Szekeres 2020). Yet, the reproductive organs of clausiliids have received less attention, with only some scattered investigations in a few Indochinese species (Stoliczka 1871(Stoliczka , 1873Likharev 1962;Nordsieck 1973;Maassen and Gittenberger 2007;Páll-Gergely and Szekeres 2017). Nevertheless, recent studies on European taxa have shown that the genital organs and their internal sculpture, though highly variable, are helpful for more precise species identification (De Mattia et al. 2020, 2021Páll-Gergely and Szekeres 2020). Lately, Hwang et al. (2022) also discussed some characters involving the genitalia and shell sculpture that should be considered for further taxonomic work on clausiliids at the species level based on a molecular analysis of the genus Formosana Boettger, 1877. Prior to our recent study, all former studies on Myanmarese phaedusinids were based on shell characters, except for Oospira philippiana (Pfeiffer, 1847), O. decollata (Likharev, 1962), and O. malaisei Nordsieck, 1973; the genital anatomy of these three species was described, but only the external features were reported. Therefore, there is a need for more in-depth studies of the reproductive organs of these snails and Southeast Asian clausiliids in general.
Myanmar is actively promoting knowledge of its malacofauna, especially the material obtained under the framework of a joint project between the Forest Department of Myanmar, the Fauna and Flora International (FFI), and the Animal Systematics Research Unit (ASRU) of Chulalongkorn University, Thailand. This effort has already provided information regarding the distribution, habitat, and essential morphological characters (e.g., genitalia and radula) of the Myanmarese malacofauna, including the description of several new ariophantids and helicarionids taxa (Pholyotha et al. 2020(Pholyotha et al. , 2022Sutcharit et al. 2020a;Sutcharit and Panha 2021) and Streptaxidae (Sutcharit et al. 2020b;Man et al. 2022). In this context, the present study provides an up-to-date species list of the door snails from Myanmar, with taxonomic notes, and with a re-description of the shell, genitalia, and radula morphology of several species. In addition, two species from the limestone karsts in the Salween River Basin are described as new. Hopefully, this article will inspire young Myanmarese zoologists to take an interest in the land snails of their country.

Sampling and morphological studies
This study was conducted within the MoU (Letter No. 0092) framework between the Forest Department, Ministry of Natural Resources and Environmental Conservation and Forestry, Myanmar and FFI from 2015 to 2016. Specimens were collected throughout northern and southern Myanmar ( Fig. 1; Table 1) by the ASRU members and are deposited in the Chulalongkorn University Museum of Zoology (CUMZ), Thailand. Living snails were photographed and euthanized following standard two-step method protocols. The snails were immersed in 5% ethanol and then preserved in 70% (v/v) ethanol for anatomical studies (American Veterinary Medical Association 2020). Species identifications were based on the original descriptions, supplemented with Gude (1914), Nordsieck (2002bNordsieck ( , 2007, Grego et al. (2021) and Szekeres et al. (2021a, b). Specimens were also compared with available reference collections and type material.
Shell dimensions (height and width), whorl count, coloration and sculpture were assessed from intact adult shells. The parietal wall of the last whorl of one to three shells was removed to observe the shape, size, thickness and numbers of plicae and lamellae, and clausilium morphology. The terminology used for the clausilial apparatus and genitalia in this description is modified from Gude (1914), Loosjes (1953), and Nordsieck (2007Nordsieck ( , 2021, as shown in Fig. 2. In addition, when ethanol-preserved specimens were available, the genitalia of one to five snails of each species were dissected and observed under an Olympus SZX2-TR30 stereoscopic light microscope.  Table 1. The shells, clausilial apparatus and genitalia were then imaged using a digital camera (DSLR D850-Nikon) and a stereo microscope with Cell's Imaging Software. The buccal masses were removed, and the radulae were soaked in 10% (w/v) NaOH, and then cleaned in distilled water. Radulae were photographed under scanning electron microscopy (SEM; JEOL, JSM-6610 LV). Table 1. Shell measurements of clausiliid species examined in this study. The numbers listed with collection localities correspond to the map in Fig. 1. Asterisks indicate incomplete (apex broken; not decollated) shells. SH: shell height; SW: shell width. Species no., locality no., and CUMZ no.

Number of specimens
Ranges, mean ± S.D. in mm SH/SW ratio

Number of whorls Shell height Shell width
Two nominal species names described as new to science in this work are attributed to the first and last authors (Man and Panha). Thus, a complete citation of the authorship is "Man and Panha in Man et al.".  Albers (1860: 275). Diagnosis. Shell fusiform, more or less turreted, spire attenuated and shell surface with fine wavy to oblique striations. Palatal plicae short mostly, middle plicae weak to developed and 3 to 7 in number. Superior lamella low, connected to or separated from spiralis, and distinct at transition to spiralis. Inferior lamella spirally ascending and ending close to superior lamella from aperture view. Subcolumellaris visible or invisible in frontal view. Clausilium plate lateral side, rounded and broad.

Anatomical
External features. Animal covered with reticulated, dark gray skin; tentacles short; body and tail with paler color on lateral margin of foot; foot moderately elongated, posteriorly obtusely pointed.
Remarks. Nordsieck (2002b) compiled all the Southeast Asian Phaedusinae and summarized their diagnostic characteristics. Although Phaedusa and Loosjesia Nordsieck, 2002 are recognized as having spirally ascending inferior lamella, Phaedusa possesses shorter or weaker palatal plicae with the inferior lamella more narrowly spiral; in contrast, Loosjesia possesses longer and more developed palatal plicae, and much more spiral inferior lamella. Phaedusa closely resembles the Indian Cylindrophaedusa Boettger, 1877(Gittenberger et al. 2019. In the most recent generic classifications and species accounts by Grego et al. (2021) and Szekeres et al. (2021a, b), the genus Phaedusa from Myanmar is comprised of eight species, of which only three species were collected and re-described herein.  -Zilch 1954: 34, pl. 3, fig. 46. Nordsieck 1974. Grego et al. 2021: 27. Szekeres et al. 2021a fig. 11a Fig. 4A, B), CUMZ 13033 (40 specimens in ethanol), JG-C2881 (2 shells). Description. Shell fusiform, turreted, translucent, and pale yellowish brown; spire acute. Shell surface with thin and dense oblique striations; suture distinct. Whorls 11-13½, little convex, regularly growing and attenuated to apex, last whorl somewhat compressed. Aperture obliquely rounded to pear-shaped, basis rounded and narrowing towards parietal sinus; peristome slightly protruded, thickened, and expanded. Superior lamella low, continuous with spiralis, and very low at transition to spiralis to almost separated. Inferior lamella spirally ascending, close to superior lamella and ending at peristome. Subcolumellaris emerged and only visible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, three: first plica strong and longest; second plica very weak and close to first plica; third plica oblique from subcolumellaris and sometimes almost connected to second plica. Palatal plicae not visible without cracking shell. Clausilium plate lateral side, broad, rounded and slightly thickened at tip. Genitalia (n = 5). Atrium (at) short; penis (p) muscular, cylindrical, and gradually narrower towards epiphallus. Epiphallus (ep) muscular, cylindrical, ca. same as penis length and size, and gradually widening to proximal end. Penial retractor muscle (pr) attached proximally to epiphallus. Vas deferens (vd) slender, and shortly bounded at atrium and penis junction (Fig. 5A). Internal sculpture of penis smoothsurfaced and with 3 to 5 longitudinal folds (Fig. 5B); at transition from penis to epiphallus with irregularly corrugated and wrinkled folds that randomly split and merge (Fig. 5C). Internal sculpture of epiphallus with large papillae arranged in oblique rows (Fig. 5D).
Vagina (v) slender at junction of atrium, then bulging at connection of free oviduct (fo) and distal part of pedunculus (dpb), and almost as long as free oviduct. Distal part of pedunculus large, long, and basally stouter; diverticulum (db) slender, nearly equal to dpb length; proximal part of pedunculus (ppb) large, long, measuring ~ 3/4 of diverticulum length, and bursa copulatrix (bb) ovoid (Fig. 5A).
Radula. Each row contains ~ 47 teeth with half-row formula: central-(lateral)marginal teeth (1-(11-12)-23). Central tooth symmetrically tricuspid; mesocone large with pointed tip; ectocones triangular and located near the base. Lateral teeth asymmetrically bicuspid with small and pointed ectocone located at base; endocone large with pointed tip. Marginal teeth with asymmetrical tricuspids starting at approximately tooth number 11 or 12; mesocone large with dull tip; endocone and ectocone with small and pointed tips. Marginal teeth gradually reduced in size and becoming multicuspid marginally (Fig. 6A).
Distribution. Phaedusa shanica is collected from probably nearby the type locality and likely restricted in Myanmar. It appears to be quite abundant in the limestone hills based on the high numbers collected in our samplings.
Remarks. Phaedusa shanica is very similar to P. theobaldi (Blanford, 1872) in having two or three palatal plicae which tend to connect at the second and third plicae. Phaedusa theobaldi (Fig. 19M) can be distinguished by its less turreted shell, coarser striations, darker horny color, superior lamella and spiralis separated, and not emerged subcolumellaris. These two species are difficult to distinguish at first sight; additional materials from the type locality and the genitalia of P. theobaldi, are required to elucidate the relationship between these two species.
Our specimens slightly differ from the type specimen in having three separated palatal plicae, or sometimes second and third plicae well developed and connected (Fig. 4B). According to Nordsieck's (1974: fig. 6) drawing, the lectotype SMF 62260 has only two almost connected first and second palatal plicae, while the probable paralectotype as stated in Gude (1914: fig. 112) has palatal plicae pattern similar to the specimens examined herein. Therefore, we assume that the distinct or indistinct second plica might be attributed to morphological variation. Shell variations among the examined materials for P. shanica were observed, including slender to regular fusiform shell, oblique to subquadrate aperture, and the third plica may be well developed and reach to the second plica (Fig. 4B).
In addition, Phaedusa lypra (Mabille, 1887) from Shan State also resembles this species in shell form; however, P. lypra has a blunter spire, less turreted shell, and wider aperture sinus (Szekeres et al. 2021a: fig. 10f ). Phaedusa burmanica (Gude, 1914) and P. bocki menglunanensis (Luo, Cheng & Zhang, 1998) from Shan State differ from P. shanica in having a larger shell, five distinct palatal plicae that can be seen from outside of shell, wavier and coarser shell surface, and clausilium with a hook (Fig. 4). Regarding the genitalia, P. shanica possesses more simple and smooth longitudinal folds and reticulated papillae in the epiphallus, while P. burmanica has strongly wavy, irregularly dense, and crowded longitudinal folds along the epiphallus with a distinct fold near the vas deferens (Fig. 5).
2 Phaedusa burmanica (Gude, 1914 Description. Shell fusiform, turreted, translucent, and pale chestnut-brown; spire acute. Shell surface glossy with thin and dense striations; suture distinct. Whorls 12-13, little convex, regularly growing and attenuated to apex; last whorl compressed. Aperture vertically subquadrate, basis rounded and narrowing towards parietal sinus; peristome slightly protruded, thickened, and expanded. Superior lamella low, continuous with spiralis, and very low at transition to spiralis. Inferior lamella spirally ascending, close to superior lamella and ending at peristome. Subcolumellaris emerged, and visible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, distinctly five: first plica strong, longest, and nearly connected to principalis anteriorly; second and fifth plicae almost equal and slightly strong; third and fourth plicae weakest and almost not visible. Palatal plicae visible through translucent shell. Clausilium plate lateral side, broad, rounded and with hook. Genitalia (n = 1). Atrium (at) short and slender; penis (p) muscular, cylindrical, broadest at middle part and gradually narrower towards epiphallus. Epiphallus (ep) muscular, cylindrical, ca. same length and size as penis, gradually enlarging to proximal end. Penial retractor muscle (pr) attached proximally to epiphallus. Vas deferens (vd) slender, and shortly bounded at atrium and penis junction (Fig. 5E). Internal sculpture of penis smooth-surfaced and slightly wavy with ca. four longitudinal folds (Fig. 5F). Internal sculpture of epiphallus generally defined as two parts: region near penis with wavy longitudinal folds, then gradually becoming more densely crowded towards proximal epiphallus; region near vas deferens with strong folds and papillae arranged in oblique rows (Fig. 5G).
Vagina (v) slender at junction of atrium, then bulging at connection of free oviduct (fo) and distal part of pedunculus (dpb), and almost as long as free oviduct. Distal part of pedunculus large, long, basally stouter, and broadest near entrance of diverticulum; diverticulum (db) large, as long as dpb; proximal part of pedunculus (ppb) large, measuring ~ 1/2 diverticulum length, and bursa copulatrix (bb) ovoid (Fig. 5E).
Distribution. Apart from the type locality, this species is widely known from Bhamo, Kachin State (Gude 1914) to Shan State and the Mandalay Region in Myanmar (Grego et al. 2021).
Remarks. Phaedusa bocki menglunanensis from Shan State can be distinguished from this species by its inferior lamella less spirally ascending, palatal plicae longer, obliquely arranged and more spaced between them, shell surface finer and more curved striations, aperture vertically quadrate, and subcolumellaris distinctly visible in frontal view. Phaedusa bocki thompsoni Grego & Szekeres, 2021 also differs from this species in having a more vertical aperture, acute spire, and palatal plicae more on dorsal side (see Szekeres et al. 2021a: fig. 9f ).
Variation was observed among the examined specimens in having the superior lamella and spiralis either separated or connected.  Table 2 Hemiphaedusa menglunanensis Luo et al., 1998: 34, fig  12 and 13 nearly flattened, regularly increasing, and attenuated to apex. Aperture vertically subquadrate, basis rounded and narrowing towards parietal sinus; peristome protruded, expanded and little reflexed. Superior lamella low, continuous with spiralis, and low at transition to spiralis. Inferior lamella spirally ascending, slightly horizontal before reaching peristome and close to superior lamella. Subcolumellaris emerged, ending at peristome margin, and clearly visible in frontal view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, four or five: first plica distinct, longest, and nearly connected to principalis anteriorly; second plica ~ 1/2 of first plica length and remaining plicae oblique, equally spaced, and shorter. Palatal plicae visible through translucent shell. Clausilium plate lateral side, broad, rounded, and with hook. Distribution. Phaedusa bocki menglunanensis was originally described from Yunnan Province, China, which is near the borders with Vietnam and Laos. It was recently found in Shan State, along the Mekong River near the border with Laos (Szekeres et al. 2021a).

Remarks.
No preserved specimens were found for examination of the genitalia. This subspecies and samples of P. bocki thompsoni collected from the same geographical range have a similar shell morphology, but P. bocki thompsoni has invisible subcolu- Figure 5. Genital anatomy of A-D Phaedusa shanica, specimen CUMZ 13033 A whole reproductive system B internal sculpture of penis C transition from penis to epiphallus D internal sculpture of epiphallus and E-G Phaedusa burmanica, specimen CUMZ 13035 E whole reproductive system F overview internal sculpture of penis and epiphallus G internal sculpture of proximal epiphallus. Yellow arrows indicate approximate transitional position from penis to epiphallus. mellaris in frontal view, blunter and turreted spire, and whorls after antepenultimate whorl rapidly attenuated (see Szekeres et al. 2021a: fig. 9f ). However, the holotype of P. bocki thompsoni from Thailand possesses a subcolumellaris that is visible in frontal view, and four to seven plicae that become shorter and somewhat diffuse towards the base (Szekeres et al. 2021b: fig. 2d). More materials are required for comparison to determine whether the differentiating characters are consistently distinct between these two subspecies.
Diagnosis. Shell short to long fusiform, shell surface smooth to with striated ridges, spire blunt to attenuated, whorls few to numerous (6-13). Palatal plicae short to long, mostly developed and 3-10 in number. Superior lamella developed, usually connected to spiralis, distinct or indistinct at transition to spiralis. Inferior lamella steeply ascending and somewhat ending distant from superior lamella in aperture view. Subcolumellaris usually invisible in frontal view; clausilium plate lateral to ventral side and usually narrow.
External features. Living animals possess reticulated skin; dark gray head; short tentacles; body and tail pale to dark brownish; foot moderately elongated, posterior nearly rounded to bluntly pointed.
Remarks. Oospira is the most species-rich genus of the Phaedusinae, and more than a hundred species have been reported from a broad range in Southeast Asia (MolluscaBase 2022). Nordsieck (2002b) united two previously recognized genera, Acrophaedusa Boettger, 1877 and Pseudonenia Boettger, 1877 to form Oospira based on their shared steeply ascending inferior lamella, normal clausilium plate, and mostly palatal plicae form. Perhaps this grouping causes Oospira to become widely diverged in shell shape from ovate to fusiform, dark brown to pink, and different aperture shapes which is thought to be a homoplasy. A phylogenetic analysis of phaedusinids genera from Japanese and some southeast Asian taxa, especially from Vietnam, was not in line with traditional taxonomy probably due to parallel or convergent evolution (Motochin et al. 2017;Mamos et al. 2021). However, none of the Indochinese taxa, including Oospira, were explored in this phylogenetic work.
Based on shell morphology, we have divided Oospira from Myanmar into two species groups comprised of those with (i) short and ovate fusiform shells and (ii) long and slender fusiform shells. The short and ovate fusiform group includes the species believed to be Oospira s.s. (type species Clausilia philippiana Pfeiffer, 1847), while the long and slender fusiform group assumed to be the species previously known as 'Pseudonenia Boettger, 1877' (type species Clausilia javana Pfeiffer, 1841).

Oospira species group with short and ovate fusiform shell
In Myanmar, this group is comprised of five species, four of which were collected and examined, while O. vespa (Gould, 1856) was not. Description. Shell ovate-fusiform, opaque, and chestnut-brown color; spire blunt. Shell surface nearly smooth or with very thin striations; suture distinct. Whorls 5-6½, convex, regularly growing and bluntly attenuated to apex. Aperture obliquely pearshaped, basis broader and narrowing towards parietal sinus; peristome detached, thickened, expanded and little reflexed. Superior lamella developed, continuous with spiralis, and low at transition to spiralis. Inferior lamella steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged, and only visible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, 7-9: first plica strong and longest; following plicae shorter, parallel, nearly equal in length, gradually reduced towards anterior. Clausilium plate lateral side, slightly broad and rounded at tip. Genitalia (n = 5). Atrium (at) short and slender; penis (p) muscular and cylindrical. Epiphallus (ep) muscular, cylindrical, ca. same length and half of the diameter of penis and broadest at middle part. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) slender, and shortly bounded at atrium and penis junction (Fig. 8A). Internal sculpture of penis consists of two parts: region near atrium ~ 1/3 of penis length with series of irregular transverse folds, chevron-shaped; region near epiphallus becoming smooth surface and relatively thick with 5-7 longitudinal folds (Fig. 8B). Internal sculpture of epiphallus with elevated papillae arranged in oblique rows (Fig. 8C).
Vagina (v) thick and very short, ~ 1/3 of free oviduct (fo) length. Distal part of pedunculus (dpb) large and long; diverticulum (db) long, ~ 2× length and slightly larger diameter than dpb; proximal part of pedunculus (ppb) slender, ca. equal in length to diverticulum, and bursa copulatrix (bb) with distinct ovate shape (Fig. 8A). Radula. Each row contains ≥ 39 teeth with half-row formula: central-(lateral)marginal teeth (1-(11-12)-19+). Central tooth unicuspid with rounded to blunt tip. Lateral teeth bicuspid: endocone large and rounded tip; ectocone very small, pointed tip and located near the base. Marginal teeth asymmetrically tricuspid starting at approximately tooth number 11 or 12: mesocone large and curved to blunt tip; endocone small and located near tip of mesocone; ectocone triangular, pointed tip and located near the base. Outermost teeth have been lost during the preparation process (Fig. 15A).
Distribution. In Myanmar, this species is reported from Kayin, Mon and Tanintharyi (Gude 1914;Szekeres et al. 2021a, b). In addition, the records outside Myanmar are from Kanchanaburi Province, Thailand (Szekeres et al. 2021b), and further in Andaman Islands, but mentioned as dubious record (see Szekeres et al. 2021a: 177). In this survey, three populations were collected from isolated limestone karsts in Salween River Basin with relatively high abundance.
Remarks. Oospira stoliczkana can be distinguished from O. philippiana by its elongate ovoid shell, pale color, and higher numbers of plicae. In terms of the genital organs, the male internal sculpture of O. philippiana has thicker and denser corrugated folds near the atrium than in O. stoliczkana (Fig. 10F). Moreover, O. vespa can be differentiated from this species by having an acute spire, aperture more oblique and broader, whorls more expanded.
Among the examined specimens, those from the Pha Boang Cave population (24 shells) have larger and darker shells with more widely spaced and up to nine developed palatal plicae. In contrast, specimens from the Kayon Cave (21 shells) and Saddan Cave (15 shells) populations are uniform in terms of a smaller shell and seven closer and weaker plicae (Table 1). No specimens were found at the type locality 'Mergui' [Myeik]; but Szekeres et al. (2021b) reported material from Tanintharyi Region. Instead, multiple populations with high abundance were collected in the vicinity of Salween River Basin in this present study ( Fig. 1; Table 1). This agreed with Stoliczka's (1871: 175)   Description. Shell oblong-ovate, translucent, and brownish; spire rounded and almost flatted to apex. Shell surface with fine and distinct striations; suture wide and distinct. Whorls 5-5½; penultimate whorl rapidly growing and largest; last whorl compressed and narrower. Aperture obliquely pear-shaped, basis rounded and narrowing towards parietal sinus; peristome detached, thickened, slightly expanded, and not reflexed. Superior lamella sharp, oblique, continuous with spiralis, and low at transition to spiralis. Inferior lamella steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged and invisible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, five: first plica longest; following four plicae parallel, equal in length and spacing, and slightly reduced towards anterior. Clausilium plate lateral side and narrow.
Genitalia (n = 2). Atrium (at) short and slender; penis (p) muscular and cylindrical. Epiphallus (ep) muscular, cylindrical, ca. same length and half diameter of penis, and broadest at middle part. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) slender, and shortly bounded at atrium and penis junction (Fig. 8D). Internal sculpture of penis consists of two parts: region near atrium and ~ 1/2 of penis length with series of irregular transverse folds, chevron-shaped; region near epiphallus becoming smooth, with 5-7 slightly wavy longitudinal folds (Fig. 8E). Internal sculpture of epiphallus with elevated papillae arranged in oblique rows (Fig. 8F).
Distribution. Oospira bulbus has only been reported from Myanmar and is possibly endemic in the limestone hills along the lower course of Attaran River. The specimens examined herein were collected near the type locality.
Remarks. Oospira ovata can be separated from this species by its a smoother striated shell, attenuated spire and usually seven plicae. In terms of the genital organs, the male internal sculpture of O. ovata has longer V-shaped folds in the region near the atrium and rounded papillae in epiphallus than this species. Although O. bulbus has a similar shell form to Atractophaedus pyknosoma (Gittenberger & Vermeulen, 2001) from Vietnam, A. pyknosoma has a narrower spire, visible subcolumellaris in frontal view, peristome reflected with nearly double lip and first palatal plicae shorter than the following plicae (see Gittenberger and Vermeulen 2001: figs 1-10). Description. Shell ovate or pupiform, opaque and chestnut-brown; spire blunt. Shell surface nearly smooth or with very thin growth lines; suture distinct. Whorls 5-5½ convex, rapidly growing; penultimate and antepenultimate whorls equally broad and rounded to apex. Aperture obliquely pear-shaped, basis rounded and narrowing towards parietal sinus; peristome detached, thickened, expanded and little reflexed. Superior lamella well developed, continuous with spiralis and low at transition to spiralis. Inferior lamella steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged and only visible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, six or seven: first plica strong and longest; following plicae short, parallel, equal in length and gradually reduced towards anterior. Clausilium plate lateral side and narrow.
Genitalia (n = 1). Atrium (at) short and slender; penis (p) muscular and cylindrical. Epiphallus (ep) muscular, cylindrical, ~ 1.5× diameter of penis, and broadest close to penis. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) slender and shortly bounded at atrium and penis junction (Fig. 10A). Internal sculpture of penis consists of two parts: region near atrium, ~ 2/3 of penis length with moderately thick transverse folds arranged in V-shaped rows; region near epiphallus with smooth surface and four or five longitudinal folds (Fig. 10B, C). Internal sculpture of epiphallus with rounded papillae arranged in oblique rows (Fig. 10D).
Radula. Each row contains ~ 61 teeth with half-row formula: central-(lateral)marginal teeth (1-(12-13)-26). Central tooth unicuspid with dull tip. Lateral teeth bicuspid; endocone large with curved to dull tip; ectocone very tiny to small and pointed tip. Marginal teeth asymmetrically tricuspid starting at approximately tooth number 12 or 13: mesocone large and dull tip; ectocone and endocone small with pointed tips. Outer marginal teeth increasingly asymmetrical and shorter than inner marginal teeth (Fig. 15B).
Distribution. At present, O. ovata is only known from Myanmar. Many shells were collected in this study; it is likely endemic to the valley of Attaran River.
Remarks. Oospira ovata and O. philippiana are generally similar in shell morphology, but O. ovata has a more expanded spire. The male internal sculpture of O. ovata has longer V-shaped folds in the region near the atrium and rounded papillae pattern in epiphallus, whereas O. philippiana has shorter V-shaped folds and more elevated and pointed papillae in epiphallus.  Description. Shell elongate ovoidal, glossy, translucent, and horny brown; spire blunt. Shell surface with very thin striations to smooth surface; suture wide and distinct. Whorls 6-6½, convex, regularly growing and bluntly attenuated to apex. Aperture obliquely pear-shaped, basis rounded and narrowing towards parietal sinus; peristome  following four plicae parallel and equal in length, and remaining plicae shorter, closer, gradually reduced towards anterior. Clausilium plate lateral side and slightly broad at tip.
Genitalia (n = 1). Atrium (at) short and slender; penis (p) muscular and cylindrical. Epiphallus (ep) muscular, cylindrical, slightly longer by 1.5× diameter of pe- Figure 10. Genital anatomy of A-D Oospira ovata, specimen CUMZ 13045 A whole reproductive system B internal sculpture of penis C transition from penis to epiphallus D internal sculpture of epiphallus and E-H Oospira stoliczkana, specimen CUMZ 13047 E whole reproductive system F internal sculpture of penis G transition from penis to epiphallus H internal sculpture of epiphallus. Yellow arrows indicate approximate transitional position from penis to epiphallus. nis, and broadest at proximal part. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) slender, and shortly bounded at atrium and penis junction (Fig. 10E). Internal sculpture of penis consists of two parts: region near atrium, ~ 1/4 length of penis with irregular transverse fleshy folds arranged in nearly V-shaped rows (Fig. 10F); region near epiphallus becoming smooth with oblique longitudinal folds (Fig. 10G). Internal sculpture of epiphallus with elevated papillae arranged in nearly oblique rows (Fig. 10H).
Distribution. This species is known from Mon State, along with its type locality in Tanintharyi Region; no reports have been made outside Myanmar to date (Szekeres et al. 2021a Some of the examined specimens had a thin and translucent shell, with more distinct palatal plicae.
Genitalia (n = 5). Atrium (at) short and slender; penis (p) long, slender, and shortly narrower at transition to epiphallus. Epiphallus (ep) slender, ca. same length as penis, slightly smaller diameter, and broadest at middle. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) thin and shortly bounded at penis (Fig. 13A). Internal sculpture of penis with smooth surfaces and five or six thin longitudinal folds (Fig. 13B). Internal sculpture of epiphallus with irregular corrugated pattern (Fig. 13D) and sometimes with distinct irregular transverse fold and papillae arranged in oblique rows.

Radula.
Each row contains ≥ 39 teeth with half-row formula: central-(lateral)marginal teeth (1-(11-12)-19). Central tooth tricuspid with large and triangular mesocone, and ectocones very small and pointed tips. Lateral teeth bicuspid: endocone large and triangular; ectocone very small and pointed tip. Marginal teeth asymmetrically tricuspid starting at approximately tooth number 11 or 12: endocone small located near the tip; mesocone large and dull to blunt tip; ectocone with triangular shape, pointed tip and located near the base (Fig. 15C).
Distribution. Oospira gouldiana is the most abundant species of the genus in Myanmar, occurring mainly in the south-eastern part of the country. This species was abundant at seven limestone outcrops in Kayin State (Fig. 1, Table 1). It was recorded from Bago, Kayin, Mon, and Tanintharyi in Myanmar, and the distribution was later expanded to include parts of Thailand (Gude 1914;Szekeres et al. 2021a, b).
Remarks. Oospira gouldiana specimens from Taung Lay Cave are quite similar to O. malaisei from Kachin State in terms of shell form. But O. malaisei (Fig. 17C) shows a more vertical and broader aperture, reflected peristome, closely and rapidly attenuated apical whorls, and inferior lamella more straight ascending at peristome. In contrast, Taung Lay Cave specimens have an oblique and rounded aperture, less reflected peristome, regularly attenuated whitish apical whorls and inferior lamella more spirally ending at peristome. Anatomically, O. malaisei possesses an epiphallus of ~ 1/2 the penis length, while in O. gouldiana epiphallus and penis have almost equal lengths (see Nordsieck 1973: fig. 26).
Oospira gouldiana also shares a similar shell morphology with O. insignis exhibiting a regularly attenuated spire with whitish apical whorls, palatal plicae five, and a broad pear-shaped aperture. Nevertheless, O. gouldiana has a more attenuated spire, more parallel palatal plicae, aperture more vertical, and less glossy than O. insignis. In addition, this species can easily be separated from O. shanensis by its pale color, shorter and oblique palatal plicae, inferior lamella more spirally and closely ascending from spiralis and superior lamella. Oospira penangensis differs from this species by its less ventricose, narrower, and more vertical subquadrate aperture, inferior lamella ending straight at peristome and weaker superior lamella from apertural view.
Oospira gouldiana is highly variable in terms of shell color and shape. The typical form was found in the Bardai and Kaw Ka Thaung populations, showing a yellowish to pinkish color with a regular fusiform shape (Fig. 11A, D), while the Taung Lay population have a slenderer shell and the Waiponla population have a more bulging shell (Fig. 11E, F). In addition, the arrangement of palatal plicae shows much variation among the populations. For instance, the Bardai population has irregularly or obliquely arranged plicae (nearly vertical), Kaw Ka Thaung population has parallelly arranged plicae, while the Waiponla and Lun Nga populations have very weak and short parallelly arranged palatal plicae. Furthermore, a very short plica (dot-like) located near the anteriormost palatal plicae next to subcolumellaris is also observed in the Bardai population.
Except for the Sadhdan, Taung Lay, and Rathye Pyan populations, for which genitalia could not be examined, the remaining populations are similar in external genital morphology, with only slightly differing thickness of the longitudinal folds of the internal sculpture of the penis being observed. However, these four populations inhabit a very small geographical area, hence we attribute this minor difference to morphological variation. Description. Shell fusiform, translucent, and pale yellowish brown color; spire regularly attenuated. Shell surface glossy and almost smooth surface; suture impressed and distinct. Whorls 9-10, little convex, regularly growing and attenuated to apex. Aperture pear-shaped, and basis broader and narrowing towards parietal sinus; peristome protruded, little thickened and expanded. Superior lamella developed, continuous with spiralis, and indistinct at transition to spiralis. Inferior lamella steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged and invisible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, 3-5 (usually 3): all plicae very strong, parallel, equal length, spacing, and one or two small plicae sometimes present in middle and at lowest. Clausilium plate lateral side and narrow.
Genitalia (n = 5). Atrium (at) short and slender; penis (p) almost cylindrical and shortly narrower at transition to epiphallus. Epiphallus (ep) cylindrical, ca. same length and diameter as penis. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) thin and shortly bounded at penis (Fig. 13E). Internal sculpture of penis with smooth surfaces and with relatively thickened four or five longitudinal folds (Fig. 13F, G). Internal sculpture of epiphallus with large and scattered papillae arranged obliquely to irregularly spaced rows (Fig. 13H).
Distribution. Currently O. andersoniana is only known from Tanintharyi Region, Myanmar.
Remarks. This species was described based on two shells collected by the Scottish zoologist, John Anderson (1833Anderson ( -1900, approximately from southern Myanmar, and an illustration was included in the original publication (Möllendorff 1882;Alcock 1902). Then, it was re-described and suggested to be very similar to O. gouldiana by Gude (1914). Despite the type specimen being mentioned in the type catalogue of the Clausiliidae in the Naturmuseum Senckenberg by Zilch (1954), this nominal species seems mysterious and is, therefore, listed as uncertain (taxon inquirendum) in Mol-luscaBase (2022). The type specimens of this species are presumably lost. However, Möllendorff (1882) provided a very detailed description and illustration of the species. Our newly collected specimens from the Tanintharyi Region have a thinly striated shell, smooth surface, thin peristome, mostly nine whorls and three palatal plicae, which matches well with the diagnostic characteristics of this species.
In this survey, Oospira andersoniana and O. stoliczkana were collected from the same locality in the Tanintharyi Region. These two species are similar in possessing a nearly smooth shell glossy surface, thin peristome, pale yellowish color, and less developed inferior lamella. However, O. stoliczkana exhibits a shorter, blunt spire, broader clausilium and several palatal plicae (from 8 to 10).
Compared with the other congeners, Oospira andersoniana can be distinguished from O. insignis, O. gouldiana, and O. magna by its less ventricose shell, smoother surface and pale color, peristome and inferior lamella weaker, and palatal plicae longer and more uniformly arranged. In contrast, O. insignis possesses oblique palatal plicae, more ventricose and darker colored shell, while O. gouldiana has a ventricose shell, spire more attenuated and with whitish apical whorls, inferior lamella more bent, aperture thicker and broader, and palatal plicae closer and more oblique. In addition, O. magna can be distinguished from O. andersoniana by having a finely and densely striated shell surface, inferior lamella well developed, clausilium in ventral position, and palatal plicae longer and more ventral (nearly horizontal). In terms of the genitalia, O. andersoniana has a short male organ, internal penis with large longitudinal folds and epiphallus with a distinct reticulated papillae pattern. In contrast, O. gouldiana and O. magna possess slender and longer male organs, internal penis with thinner and denser longitudinal folds, and epiphallus with irregularly arranged reticulated papillae patterns. Furthermore, O. limborgi Grego & Szekeres, 2021, also described from the Tanintharyi Region, shares some characteristics with this species in having the same number of palatal plicae, nearly triangular aperture, glossy and pale yellowish color (see Szekeres et al. 2021a: fig. 7c).
Shell variation was observed with respect to a small and short plica between the first and second palatal plicae. Description. Shell fusiform, translucent, yellowish brown and 3-4 white apical whorls; spire regularly attenuated. Shell surface nearly smooth to with thin growth lines; suture deep and distinct. Whorls 10-11, convex, regularly growing and attenuated to apex. Aperture oval-pear-shaped, less oblique, basis broader and narrowing towards parietal sinus; peristome protruded, thickened, and slightly expanded. Superior lamella developed, continuous with spiralis, and indistinct at transition to spiralis. Inferior lamella well developed, steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged and invisible in oblique view. Principalis running along ventral-lateral side and anterior end visible through oblique apertural view. Palatal plicae ventral-lateral, 4-6 (usually 4): first plica strong and longest; second and third plicae short, parallel, oblique, and equal in length; fourth plica longer and stronger than middle plicae. Clausilium plate ventral side and narrow.
Genitalia (n = 1). Atrium (at) short and relatively large; penis (p) almost cylindrical and shortly narrower at transition to epiphallus. Epiphallus (ep) slender, ca. same length as penis and smaller diameter. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) almost same diameter as epiphallus and shortly bounded at penis (Fig. 14A). Internal sculpture of penis with smooth surface and ca. four or five thin longitudinal rows (Fig. 14B), and folds slightly enlarged near epiphallus (Fig. 14C). Internal sculpture of epiphallus with large papillae arranged in oblique rows (Fig. 14D).
Distribution. Oospira magna is only recorded from the southern part of the country to the limestone area of the Salween River Basin in Mon and Kayin States, Myanmar.
Remarks. Originally, Oospira magna was proposed as a subspecies of O. gouldiana based on its distinct less ventricose shell and seven palatal plicae (Gude 1914). Later Szekeres et al. (2021b) recognized this as a morphological variation within the variable species, O. gouldiana. From our recent field survey, several specimens were collected, and their shell morphology matched well with the diagnostic characters of O. magna. Although O. magna is highly similar to O. gouldiana in shell form, it can be distinguished mainly by having a less ventricose shell, almost uniform and ventrally longer palatal plicae, more developed inferior spiral lamella, aperture less oblique, last whorl more compressed, spiralis starting deeply ventral, and clausilium ventrally seated. In genitalia, O. gouldiana exhibits a long distal part of pedunculus almost the same length as the proximal part of pedunculus and an internal sculpture of epiphallus with a thin and irregular corrugated pattern. These differences in the shell and genitalia characters are greater than the intraspecific variation and those characters were not observed as a morphological variation among the O. gouldiana populations examined; therefore, we have raised O. magna to a distinct species. Oospira zediopsis sp. nov. differ from O. magna by its a more ventricose shell with a smoother surface, apical whorl rapidly attenuated, dark reddish color, clausilium and palatal plicae laterally seated, and inferior lamella straight ascending. Description. Shell fusiform, opaque, and dark yellowish color; 5-6 apical whorls rapidly attenuated. Shell surface glossy and almost smooth; suture impressed and distinct. Whorls 12½-13, last four whorls regularly growing and then rapidly attenuated to apex. Aperture obliquely or elliptical, basis oblique and broadest and narrowing towards parietal sinus; peristome attached, thickened, and expanded. Superior lamella developed, continuous with spiralis and indistinct at transition to spiralis. Inferior lamella steeply ascending, anterior end weakly visible in apertural view, very distant from superior lamella and ending at peristome. Subcolumellaris emerged and visible in oblique view. Principalis running along ventral-lateral side and anterior end visible through oblique apertural view. Palatal plicae ventral-lateral, five: equally spaced, fourth plica curved most, two middle plicae equally shorter than first and fourth; fifth plica can only be seen when shell is opened. Clausilium plate lateral side, broad, rounded and with hook.
Genitalia (n = 2). Atrium (at) small and short; penis (p) almost cylindrical and gradually narrower at transition to epiphallus. Epiphallus (ep) cylindrical and ca. same length and diameter as penis. Penial retractor muscle (pr) attaches proximally to epiphallus. Vas deferens (vd) very thin and shortly bounded at penis (Fig. 14E). Internal sculpture of penis with 3 to 4 large corrugated longitudinal folds (Fig. 14G). Internal sculpture of epiphallus with finely reticulated pattern arranged on two or three large longitudinal folds (Fig. 14H).
Distribution. This species is presently only known from Shan State, Myanmar.
Remarks. Among all the Myanmar's Oospira species studied herein, this is the only species with a clausilium hook (Fig. 12F), and the clausilium plate is broader than in all other congeners. The presence of the hook in other phaedusinid taxa has been documented and is assumed to provide an advantage in trapping air bubbles to avoid drowning (see Páll-Gergely and Szekeres 2017).
Oospira sardicola can be distinguished from O. shanensis by having paler glossy yellowish color, wider and less oblique aperture, and less ventricose shell (Szekeres et al. 2021b). This species can clearly be recognized from O. gouldiana and O. magna by its more ventricose shell, inferior lamella straight ascending and reduced to the peristome and clausilium more rounded, broader, and in lateral position. Moreover, O. shanensis has a relatively short male organ, epiphallus larger than the penis, diverticulum narrower to the proximal end, and the internal sculpture is distinctly different from O. gouldiana and O. magna.
Oospira mongmitensis, O. sardicola, and O. shanensis were recorded from Shan State. All of them are similar in possessing distinct palatal plicae which can be seen through the shell, but different in their pale to dark color, more or less bulging shell and aperture oblique to nearly vertical (Szekeres et al. 2021a, b). Furthermore, O. sardicola and O. mongmitenis have distinct sutural papillae. These three species; O. mongmitensis, O. sardicola, and O. shanensis from Shan State are notably different from their congeners from southern Myanmar showing anterior end of inferior lamella reduced at peristome.
Etymology. The specific name luneainopsis is a compound of 'lun-eain', which in the Myanmar language refers to a bobbin used for traditional Myanmar weaving, and the Greek suffix -opsis meaning 'having the appearance of or like'. It refers to the bobbin shape of the shell of this species.
Description. Shell ovate-fusiform, decollated, opaque, pinkish brown; spire blunt. Shell surface smooth to with fine growth lines on last whorl, denser near suture and last whorl neck subquadrate; suture impressed and distinct. Whorls 7-8, convex, regularly growing, and bluntly attenuated to apex. Aperture nearly round; peristome detached, thickened, expanded and little reflexed. Superior lamella developed, continuous with spiralis, and slightly low at transition to spiralis. Inferior lamella steeply ascending, distant from superior lamella and ending at peristome. Subcolumellaris emerged and invisible in oblique view. Principalis running along lateral-dorsal side and anterior end visible through oblique apertural view. Palatal plicae lateral, four: first and fourth plicae strong and longest; remaining plicae parallel and equal length; sometimes tiny lowest plica present. Clausilium plate lateral side, narrow and slightly pointed at tip.
Distribution. Oospira luneainopsis sp. nov. is only known from the type locality.

Remarks.
No ethanol preserved specimens were available for anatomical study. This species can be distinguished from O. gouldiana, O. magna, and O. zediopsis sp. nov. by its small size, decollated, fewer whorls, roundish aperture, more spiral inferior lamella, and equal palatal plicae. This new species is clearly distinct from O. decollata by its spiral inferior lamella visible from aperture, smoother shell, pink color, and more bulging whorls.
Etymology. The specific name zediopsis is a compound word; 'zedi' is one of several terms in the Myanmar language that refer to a stupa or pagoda, and the Greek suffix -opsis means 'having the appearance of or like'. It refers to the Myanmar pagoda-like shell shape of this species.  Diagnosis. Shell fusiform, with four to five white apical whorls, and nearly smooth shell surface. Inferior lamella straight ascending or almost flattened, palatal plicae lateral, equally oblique, superior lamella distinct at transition to spiralis, and clausilium plate lateral side and less bent inwards. Description. Shell fusiform, opaque, and chestnut-brown color; 4-5 apical whorls white and rapidly attenuated. Shell surface smooth to with very thin growth lines; suture impressed and distinct. Whorls 10-11, convex, regularly growing, and attenuated to apex. Aperture obliquely pear-shaped, and basis rounded; peristome slightly protruded, large, relatively thickened and slightly expanded. Superior lamella developed, connected to spiralis and slightly low at transition to spiralis. Inferior lamella steeply first and fourth plicae strongest and longest; remaining plicae parallel and equal length; fifth plica smallest. Clausilium plate lateral side and narrow.
Distribution. This species is only known from the type locality with plentiful shells collected.

Remarks.
No ethanol preserved specimens were available for anatomical study. Oospira gouldiana can be distinguished from O. zediopsis sp. nov. by its less ventricose shell, denser and stronger striations, more spiral inferior lamella, palatal plicae and clausilium more ventrally positioned, and principalis not visible from the aperture view. Likewise, O. shanensis can be differentiated from this new species by wider spacing between spiralis and inferior lamella, anterior end of inferior lamella reduced at peristome, longer palatal plicae, attached peristome, and clausilium wider and with a hook. Furthermore, O. zediopsis sp. nov. can be differentiated from O. insignis by its more attenuated spire, narrower and more oblique aperture, shorter and more equal palatal plicae.

Discussion
Among the 33 clausiliid taxa recorded from Myanmar, 13 species are redescribed here based on the shell, genitalia, and radular morphologies, including two new species. The remaining 20 species are known from literature, and images of the type specimens, authenticated specimens or original illustrations are provided for further comparison (Figs 18,19). All examined clausiliid genitalia in Myanmar show simple male organs (penis, epiphallus, penial retractor muscle, and vas deferens) and these differ mainly in the length of penis, diverticulum, and pedunculus. Internally, the epiphallus is more variable with two or three patterns on the surface, and different numbers of simple longitudinal folds in penis. The genitalia of the recently reported Phaedusa bhutanensis Nordsieck, 1974 from Bhutan is similar to the Myanmar Phaedusa species examined in this study in having a distinctly long diverticulum, pedunculus and developed male organs (see Gittenberger et al. 2019: figs 27b, 28, 29). Overall, the external shell morphology, including shape, size, whorl number, and color is useful in recognizing the Myanmar clausiliids at first glance.
In Myanmar, Oospira is one the most diverse stylommatophoran genera. It comprises 20 species of which ten are redescribed herein, including the type species, O. philippiana. Based on the shell, clausilial apparatus and genital morphology, the genus is generally divided into two groups: (1) short and ovate fusiform shell group (including type species), and (2) long and slender fusiform shell group. The first group tends to have palatal plicae reduced towards the anterior, inferior lamella straight ascending and superior lamella distinct from spiralis at its transition point, a well-developed penis, diverticulum, and proximal of pedunculus almost similar in length, internal wall of epiphallus with equally and obliquely arranged papillae, and internal wall of penis consists of two shapes: oblique V-shaped near atrium and transitioning to longitudinal folds near epiphallus. The second group possess palatal plicae that are not reduced towards the anterior, inferior lamella more spirally ascending (S-shape) and superior lamella indistinct from spiralis at it transition point, slender to narrowly cylindrical penis, generally diverticulum longer than proximal of pedunculus in length, internal wall of epiphallus with irregularly arranged papillae, and internal wall of penis consists of longitudinal folds throughout the entire chamber. Additionally, the central tooth of group (1) has a more rounded cusp than group (2), which has a triangular shape and pointed cusp. These differences in shell and clausilial apparatus between the two groups rather agree with the diagnostic characters of the Pseudonenia Boettger, 1877 (see Gude 1914). However, further supporting evidence and the morphological and anatomical information of its type species are needed to elucidate and resolve the taxonomy of these groups.
Although the clausiliids seem evenly distributed throughout Myanmar, Phaedusa is distributed in the northeast to southwest, while Oospira occurs widely along the northernmost to the southernmost parts of the country ( Fig. 1; Table 1). Based on our surveys, the southern part of Myanmar, including Kayin and Mon States and the Tanintharyi Region, has the largest number of species recorded, and seven species are assumed to be endemic to this area. Allopatric speciation caused by massive and isolated limestone karsts in the topography of the Salween River Basin and the Tenasserim Range possibly plays an important role in the high endemicity of clausiliids. Recent studies on streptaxid and helicarionid snails have shown a similar pattern (Sutcharit et al. 2020a;Man et al. 2022;Pholyotha et al. 2022). However, alternative forces of sympatric speciation and resource partitioning cannot be ignored. For example, O. andersoniana and O. stoliczkana in Tanintharyi are sympatric based on this study. The lower abundance of one species compared to the co-occurring species may reflect the high level of competition (Table 1).
Despite the numbers of the Myanmar clausiliids are increasing, the taxonomic placements of some species are still questionable, for example, Oospira gouldiana and O. insignis which are morphologically highly variable and have overlapping distributions. Previous studies have attempted to reveal their differentiation, but this remains ambiguous (Stoliczka 1872;Gude 1914;Szekeres et al. 2021a, b). This work, therefore, provides baseline information for future studies, especially with respect to the phylogenetic interpretation of the short and ovate shell group that is endemic in Mon State and the long and slender shell group, with its wider distribution from Shan State to Kayin State and the Tanintharyi Region.

Alphabetical list of additional clausiliid taxa recorded from Myanmar
Below is an alphabetical list of 20 clausiliid species and subspecies belonging to the genera Cylindrophaedusa, Indonenia Ehrmann, 1927, Oospira, and Phaedusa that have been reported to occur in Myanmar, but that were not found during this study. The usages of each taxon name are provided in Grego et al. (2021) and Szekeres et al. (2021a, b). The original combination of the taxon name with reference to pages, plates, and/ or figures that made the names available is mentioned. The type locality mentioned in the original publication and the distribution record in Myanmar is included. If possible, the modern name and/or regional names of the type locality are provided in square brackets. In addition, the unique name-bearing types (syntype, holotype, and lectotype) are illustrated; only for those that were unavailable or could not be located, the paratypes or paralectotypes or a representative specimen are given. Where necessary, remarks are given on the status of its nominal taxon, type specimens, and other necessary information. Distribution. In Myanmar, this species is known from Schegoo (presumably Shwegu), Bhamo City in Kachin State; no further materials have been reported from Myanmar after its mention in Tapparone-Canefri (1889) and Gude (1914).  fig. 8, pl. 2, fig. 8. Szekeres et al. 2021a: 165, fig. 4d.
Distribution. This species is probably endemic to Rakhine State, Myanmar.
3 Oospira decollata (Likharev, 1962 fig. 6b, c. Distribution. In Myanmar, this species is known from Rakhine State and Ayeyarwady Region, and also reported from the Bago Region (Gude 1914). In addition, O. fusiformis was recorded from 'Zwekabin Hill near Mawlamyine', which the current administration defines as Zwekabin Mountain in Hpa-an District, Kayin State; however, it was noted as dubious by Szekeres et al. (2021a: 171).
Remarks. Blanford (1865) described this species based on a single specimen and also noted that the examined specimen was an immature shell because the shell was thin, and the peristome not continuous. Later, Blanford (1872) provided a re-description based on a fully adult specimen received from W. Theobald that had a thickened, expanded, and continuous peristome.
The specimen identified as Oospira insignis Szekeres et al. (2021a: 172, fig. 7a) is similar to O. fusiformis (Fig. 18I) in terms of shell morphology. Blanford (1872) also knew these similarities and suggested uniting the two species; however, further evidence from the shell and genitalia from topotypic specimens will be necessary to verify their species status.  Remarks. Hanley and Theobald (1870) introduced this species as a variety of O. insignis but did not provide a description. Later Gude (1914) treated it as a separate species and made a complete re-description. We treat this taxon as a distinct species, following Gude (1914), because it clearly differs from O. insignis s.s. in being less ventricose, with blunt spire, and the aperture nearly triangular that is broader at its basis; however, no materials for this species have been recollected since the original description.

Distribution.
In Myanmar, this species is originally known from Dawei, Tanintharyi Region. Subsequent records were from Mon and Kayin states in Myanmar, and the range was further extended to include Tak and Kanchanaburi provinces in Thailand (Gude 1914;Szekeres et al. 2021a, b). Remarks. Oospira insignis was the first clausiliid discovered from Myanmar, introduced by A.A. Gould based on specimens from the American missionary and naturalist Francis Mason (1799-1874). In the original description, Gould (1843) did not clearly state the number of examined specimens or the type specimen deposition. Later, Gould (1844) re-described this species with an illustration. When Johnson (1964) catalogued Gould's type specimen, he clearly designated the lectotype USNM 117120 as the unique name-bearing type. However, Nordsieck (2007: pl . 1, fig. 1) and Nordsieck (2021: pl . 1, fig. 6) illustrated a specimen BM(NH) 1996183 [=NHMUK] from the Cuming collection and used the term 'lectotype', but this seems invalid; recently, Szekeres et al. (2021a) designated this specimen as the lectotype. This specimen lot NHMUK 1996183a ex. Cuming collection consisted of three shells with no clear evidence that they originated from Gould's collection. Although Johnson (1964) catalogued Gould's type specimens in the Museum of Comparative Zoology, Harvard University, he stated that some unlocated types might presumably be deposited in the NHM, London, because Gould brought some specimens to compare to the Cuming collection. Presum-ably, Nordsieck (2007) and Szekeres et al. (2021a) may have overlooked the previous lectotype designated by Johnson (1964), which clearly stated that the specimen USNM 117120 ex. Lea collection ex. Gould's collection consists of a single shell as the lectotype. Therefore, the USNM 117120 specimen is the sole name-bearing type of this species. The latter restriction of the lectotype by Nordsieck (2007) and Szekeres et al. (2021a) is invalid (ICZN, 1999: Art. 74.1). Additionally, the specimen NHMUK 1996183 is potentially a part of Gould's type series and is here recognized as the possible paralectotype. Distribution. In Myanmar, this species is known only from Tanintharyi Region. Distribution. This species was introduced from Kachin State, and no subsequent materials have been recorded from Myanmar. Recently, provisionally classified specimens belonging to this species were reported from Mae Hong Son Province in Thailand (Szekeres et al. 2021b). In addition, it was further reported from Yunnan, China, and included in a molecular analysis (Hwang et al. 2022 fig. 116. Oospira vespa- Szekeres et al. 2021a: 180, fig. 9c.

Distribution.
In Myanmar, this species is known from Tanintharyi Region and Salween Valley (Sykes, 1893).
Remarks. Oospira vespa is the second clausiliid species introduced by Gould (1856). It was described based on a collection by the American naturalist, F. Mason, from Tavoy, British Burma. In the original publication, Gould (1856) provided only a brief description, without the arrangement and morphology of plicae, illustration, or number of examined specimens. Later, Johnson (1964) catalogued Gould's type specimens and found two specimens, which validly designated a specimen lot MCZ 169455 as the lectotype, which is figured herein (Fig. 17D).
While describing Oospira stoliczkana from Myanmar, Sykes (1893) re-described O. vespa based on a specimen from 'Salwin Valley'. Then, it was re-described based on Gould's original type series (Gude 1914). Between the two species, O. vespa can be distinguished from O. stoliczkana by having a more acute spire, and only five or six palatal plicae. In contrast, O. stoliczkana possesses a blunt spire, and 8 to 10 palatal plicae. Distribution. In Myanmar, this species is only known from Shan State.
Distribution. In Myanmar, this species is only known from Rakhine State and no further materials have been mentioned to date.

Distribution.
In Myanmar, this species is known from Shan State and Mandalay Region (Grego et al. 2021). Phaedusa lypra has a wide geographical distribution, ranging from China to Thailand, Vietnam, and India (Szekeres et al. 2021a). Distribution. In Myanmar, this species was first known from Bago Region. Later, the range was expanded records from Rakhine and Kayah States in Myanmar and from Thailand (Gude 1914;Grego et al. 2021;Szekeres et al. 2021b). Fig. 19N Phaedusa bocki thompsoni Grego & Szekeres in Szekeres et al. 2021b: 46, fig. 2d. Type locality: "Doi Tung, Chiang Rai Province, Thailand".

Distribution.
In Myanmar, a single specimen was recorded in Shan State (Szekeres et al. 2021a). This subspecies was originally described from northern Thailand with several specimens.  Szekeres et al. 2021a: 157, fig. 2d.

Distribution.
In Myanmar, this species is only known from Bago Region.