The family Plectopylidae (Gastropoda, Pulmonata) in Laos with the description of two new genera and a new species

Abstract Previously only a single plectopylid species, Helix laomontana L. Pfeiffer, 1862 was reported from Laos. Here we erect Naggsia Páll-Gergely & Muratov, gen. n. for Helix laomontana based on the description of its reproductive anatomy and radula. Another species, Hunyadiscus saurini Páll-Gergely, gen. & sp. n. is described from Northern Laos based on conchological data. Helix (Plectopylis) andersoni Blanford, 1869, which is known from the Burmese-Chinese border region, is also classified within Hunyadiscus Páll-Gergely, gen. n. A third species, Gudeodiscus (Gudeodiscus) messageri raheemi Páll-Gergely & Hunyadi, 2015 is reported from Laos for the first time. The new localities represent the westernmost sites of the genus Gudeodiscus. The reproductive anatomy of the latter species is described.


Introduction
Land snails of the family Plectopylidae are widely distributed in East Asia, from Nepal to southern Japan (Gude 1899b, Páll-Gergely and Hunyadi 2013, Páll-Gergely et al. 2015b). The taxonomic system of the Plectopylidae was established by Gude (1899a), who recognized seven sections (Endothyra Gude, 1899a= Endothyrella Zilch, 1960, Chersaecia Gude, 1899a, Endoplon Gude, 1899a, Plectopylis Benson, 1860, Sinicola Gude, 1899a, Enteroplax Gude, 1899aand Sykesia Gude, 1897b. Two of these (Enteroplax and Sykesia = Ruthvenia Gude, 1911) are now classified in different families (Páll-Gergely and Hunyadi 2013). Recent investigation resulted in the redefinition of Gude's (1899a) genera as well as the description of three new genera (Gudeodiscus Páll-Gergely, 2013, Halongella Páll-Gergely, 2015and Sicradiscus Páll-Gergely, 2013. With these, plectopylids are now classified in eight genera (Páll-Gergely and Hunyadi 2013, Páll-Gergely et al. 2015a, 2015b. The single species reported from Laos to date was originally described as Helix laomontana L. Pfeiffer, 1862 (type locality: "Lao Mountains, Camboja") and was classified in Chersaecia by Gude (1899a). Revision of Endothyrella showed that Chersaecia had been treated as a catchall category and that it contained species with very diverse conchological characters (Páll-Gergely et al. 2015b). We transferred five species from Chersaecia to Endothyrella, mainly based on the ribbed protoconch and the absence of an apertural fold. In Chersaecia we retained only species that were similar to the type species, Plectopylis leiophis Benson, 1860, in terms of the presence of an apertural fold and the finely granulated (not ribbed) embryonic whorls. Helix laomontana, has also been excluded from Chersaecia, but could not be included into any other existing genus. Live collected specimens allowed the clarification of the taxonomic position of Helix laomontana. Another species, namely Helix (Plectopylis) andersoni W. Blanford, 1869 was also excluded from Chersaecia (see Páll-Gergely et al. 2015b). Although no ethanol-preserved specimens were available for anatomical study, its shell characters provide sufficient information to clarify its systematic status. Additionally, we report two other species from Laos, one being new to science.
For the nomenclature of lamellae (vertical parietal folds) and plicae (horizontal parietal folds and palatal folds) see Páll-Gergely et al. 2015b. Whenever possible, the internal lamellae and plicae were exposed by removing the shell wall at the appropriate part of the shells (inner view). If damaging the shells was not an option (too few shells available), the plicae were figured on the basis of their visibility through the shell wall (outer view). "Anterior" refers to the part or side of the armature closer to the aperture, "posterior" refers to the other side of the armature.
Ethanol-preserved specimens were dissected under a Leica stereomicroscope, equipped with a photographic camera. In the descriptions of the reproductive system, we used the terms "proximal" and "distal" in relation to the apical portion of the reproductive tract i.e. the ovotestis.
Individual buccal masses were removed and soaked in 2 M KOH solution for 5 hours before extracting the radula, which was later preserved in 70% ethanol. Radulae and shells were directly observed without coating under a low vacuum SEM (Miniscope TM-1000, Hitachi High-Technologies, Tokyo).   under rocks in dry secondary forest under and above cliff, 1244 m a.s.l., 19°29.653'N, 102°24.470'E, leg. A. Abdou & I.V. Muratov, 16.11.2006, MNHN 2012 shells (some of them are broken/juvenile); Laos, Vientiane Province, Tam Chang, Vang Vieng, leg. Pongrat Dumrongrojwattana, 11.06.2009., PGB/1, WM/1. Reproductive anatomy. A single living specimen collected in Laos, was killed by drowning and was stored in 70 % ethanol. A part of the body was extracted from the shell and was examined anatomically. The inner parts of the genitalia, such as the gametolytic sac, the diverticulum and the spermoviduct could not be extracted.
The reproductive anatomy of Gudeodiscus messageri raheemi was figured in the original description (Páll-Gergely et al. 2015a). The two anatomically examined Vietnamese specimens differed from each other mainly in the length of the penial caecum. The Laotian specimen possesses a short caecum, similar to one of the Vietnamese specimens. The length of the caecum probably has minor taxonomic value because it varies considerably within species (see also G. phlyarius in Páll-Gergely et al. 2015a). The inner wall of the epiphallus of the Vietnamese specimens had three, rather low, longitudinal folds. In contrast, the Laotian specimen had a single thickened fold internally.
Remarks. Gudeodiscus (Gudeodiscus) messageri raheemi was described from Vietnam, where it inhabits the provinces Ninh Bình, Thanh Hóa, Sơn La, Hòa Bình and Nghệ An. The Laotian specimens agreed in shell morphology with the Vietnamese specimens. The new Laotian localities of Gudeodiscus messageri raheemi represent the westernmost record of the genus (Figure 14).
Ecology. This taxon inhabits primary or old secondary broad-leaved forests, in the humid microenvironments under leaves, logs, limestone rocks and in black soil accumulated inside limestone pockets. The live collected specimen co-occured with Garnieria mouhoti (L. Pfeiffer, 1862), a well-known species that is also associated with the moderate humidity of broad-leaved forests ( Figure 12).
Content. andersoni Blanford, 1869, saurini Páll-Gergely, sp. n. Diagnosis. Shell dextral, body whorl keeled or angulated; protoconch with spiral and radial lines, with the spirals being dominant; palatal plicae slightly sinuate; parietal wall with a single lamella and some additional plicae/denticles anteriorly and/or posteriorly. Internal anatomy unknown. See also Remarks. Differential diagnosis. Hunyadiscus gen. n. differs from all other plectopylid genera by the protoconch sculpture, which is characterized by both spiral and radial lines, the spirals being dominant. Moreover, all species of Gudeodiscus, Halongella and Naggsia gen. n. have a rounded body whorl, which is keeled in Hunyadiscus gen. n. The most similar genus to Hunyadiscus gen. n. is Sinicola, which also possess a keeled (shouldered) body whorl, and usually lacks the apertural fold. See also Table 1.
Etymology. The genus is dedicated to András Hunyadi, Hungarian malacologist and shell collector, who first called the attention of the first author on the necessity of revising the family Plectopylidae. The name Hunyadiscus is the combination of the family name Hunyadi and discus (Latin: disc), which refers to the shape of the shells.
Distribution. One species (H. saurini sp. n.) inhabits southern part of Northern Laos (exact locality unknown), the other species (H. andersoni) lives in southern Kachin state (Myanmar), at the bordering Chinese region ( Figure 15).
Remarks. Many plectopylid species belonging to the genera Endoplon, Endothyrella, Gudeodiscus, Halongella, Plectopylis, Sicradiscus possess two parietal lamellae (anterior and posterior). Other species, however, possess only a single one. In most cases it is possible to decide that the single lamella is homologous with either the anterior or the posterior lamella, because there are "remains" of the other lamella. For example, in some Gudeodiscus species (e.g. G. multispira [Möllendorff, 1883]), there are some small denticles in position of the anterior lamella, anterior to the well-developed, curved lamella. This indicates that the curved lamella is homologous with the posterior lamella. In contrast, in the genera Sicradiscus and Endothyrella, many species have small denticles on the posterior side of the single lamella. This suggests, that the single, well developed lamella is homologous with the anterior lamella (Páll-Gergely and Asami 2016). Hunyadiscus andersoni also has two small denticles on the posterior side of the lamella, one above, one below. This suggests that the single lamella of H. andersoni is homologous with the anterior lamella. The single lamella of Hunyadiscus saurini sp. n. is, on the other hand, probably homologous with the posterior lamella, because it has a strongly curved shape, and has a lower plica positioned anteriorly, which is, when present, situated under the anterior lamella in Gudeodiscus species. These hypotheses suggest that the two species of Hunyadiscus have remarkably different parietal plication (Fig. 11). Description. Shell flat, angulated, light brown or corneous; ventral side of the body whorl keeled around the moderately wide, very deep umbilicus; protoconch spirally striated, radial ribs are mostly visible on its first whorl only; teleoconch equally ornamented with fine ribbing and spiral striae, resulting in rough, irregular reticulated surface on the dorsal side; ventral side also reticulated, but much weaker than the dorsal surface; 7.5-8.5 slowly increasing whorls separated by shallow suture; near the sutures the riblets sometimes supported with fine folds of the periostracum; aperture rounded, with white, slightly expanded and thickened apertural rim; callus slightly elevated, sharp, slightly S-shaped and forms two canals upon junction with the lip. The parietal side was examined in one specimen (SMF 150117), whereas the palatal plicae is examined in specimens of the SMF and the NHM. Parietal wall with one curved horizontal lamella with occasionally an elongated upper plica, which is in con-tact with the lamella; there are two small denticles on the posterior side of the lamella, these are in weak contact with the lamella; palatal side with eight horizontal plicae, first near the suture is small, the second is even smaller; the last also short and close to the lower suture and the penultimate resembles the second denticle; remaining four plicae between the first and last two are long and slim.
Differential diagnosis. This species differs from large Chinese Gudeodiscus species (and Naggsia laomontana) by the keeled margin of the shells. It is much larger than all Sinicola species. The largest Sinicola species, S. fimbriosa (Martens, 1875) does not have a callus and has a stronger apertural margin.
Distribution. The species is known from Northern Burma and Western Yunnan. Hoetone (Hutung Village) and Bhamo are located in Kachin Provinces, whereas Ava is in Mandalay Province (all in Burma/Myanmar). The Kakhyen Hills are situated on the Chinese (Yunnan) and Burmese (Kachin) border.

Diagnosis.
A dextral, medium-sized or large species with a relatively sharp upper keel and a blunt lower keel on the body whorl. On the parietal wall there is a single oblique lamella with a horizontal plica below it.
Description. The shell is yellowish or corneous (the type material consists mainly of weathered shells). The protoconch is very large, with regular riblets and spiral lines; the radial and spiral lines are approximately of the same strength. The 5.25-6 whorls are separated by a shallow suture. The umbilicus is wide but moderately deep. The body whorl has a prominent upper keel and a less conspicuous lower keel. The apertural margin is slightly thickened. The parietal callus is blunt, not well developed and is only clearly apparent in older specimens.
Three shells were opened. On the parietal wall there is a single curved lamella that is oblique, its upper end situated much more anteriorly than the lower end. A short, but thick vertical plica is situated below and anteriorly of the lamella. On the palatal wall there are six more-or-less parallel plicae, with some additional short plicae. The most prominent additional plica is situated above the posterior end of the last plica. The fifth plica is usually S-shaped.
Differential diagnosis. Hunyadiscus saurini sp. n. is smaller than H. andersoni, its keel is situated higher (this results a more angular body whorl), has weaker parietal callus, a lower horizontal plica on the parietal wall which is absent in H. andersoni. Naggsia laomontana has a rounded body whorl and weaker spiral striation on its protoconch.
Etymology. The species is named in honour of the French geologist and malacologist Edmond Saurin (1904Saurin ( -1977 who collected it. Type locality. Laos, Pa Hia (Ancienne province Tran Ninh).

Distribution. This species is known only from Southern Laos.
Remarks. This new species shows considerable diversity in terms of shell size. However, the other shell characters are stable within and between samples.
The village "Pa Hia" or "Pah Hia" is located 100 km south from Xieng-Khouang, the capital of Tran Ninh Province (see Saurin 1953: 113). However, the exact locality could not be determined (Nordsieck 2002, Páll-Gergely 2014, Páll-Gergely 2015c. A geological report (Marutani 2006), mentioned the name "Ban Namthong" in brackets after "Pa Hia". The two names are probably identical, but the origin of this information could not be traced. Marutani (2006) gave the following GPS coordinates for Ban Namthong: 19.05000°N, 103.28330°E. This location is situated approximately 75 km southwest from Xiangkhoang city. Google Earth placed "Ban Namthong" 7.6 km in southwest direction (18° 59'N, 103° 16'E), which agrees with the 1:50.000 map printed by the National Geographic Directorate, Vietnam, in 1965. We provisionally identify the village Pah Hia with Ban Namthong, because we could not locate the name Pah Hia on the maps available to us. Content. Naggsia laomontana (L. Pfeiffer, 1862). Diagnosis. Shell flat, widely umbilicated, body whorl rounded; protoconch with dense, regular, slightly waved ribs with extremely fine spiral striation. Epiphallus ab-sent, diverticulum and gametolytic sac are both very short, but diverticulum is still shorter than the gametolytic sac. Cusp of central tooth missing, only basal plate of central tooth present. Marginals bicuspid.
Differential diagnosis. Naggsia gen. n. differs from the genera having ribbed embryonic whorls (Endothyrella, Gudeodiscus, Halongella, Sicradiscus, Sinicola) by the absence of an epiphallus and the presence of a very short diverticulum. Moreover, although the protoconch of Naggsia gen. n. is ribbed, the ribs (radial lines) are not straight, as in the other genera, but are somewhat wavy. Naggsia gen. n. differs from the genera without a ribbed protoconch (Chersaecia, Endoplon, Plectopylis) by the presence of regular, slightly waved ribs on the embryonic whorls. The latter genera are insufficiently known anatomically. Plectopylis bensoni Gude, 1914(mentioned as P. achatina Pfeiffer, 1845 and P. cyclaspis Benson, 1859 have a well-developed epiphallus (Stoliczka 1871). Interestingly, these Plectopylis species have a relatively short and thickened diverticulum, which is somewhat similar to that of Naggsia laomontana. Similarly to Naggsia laomontana, Chersaecia simplex Solem, 1966 lacks the epiphallus (see Solem 1966), but it at has no diverticulum, which is well developed in Naggsia. See differential diagnosis under Hunyadiscus and Table 1.
Etymology. The new genus is dedicated to Fred Naggs (NHM) in acknowledgement of his help with our studies on the Plectopylidae.
Distribution. Northern Laos (Figure 15). Remarks. The anatomy of Naggsia laomontana is rather similar to that of Plectopylis in the short diverticulum and to Chersaecia in the absence of epiphallus. The shell characters, namely the ribbed protoconch and the reduced parietal plication is similar to the genera Endothyrella, Gudeodiscus, Halongella, Sicradiscus and Sinicola. The radula of Naggsia laomontana shows similarities with those of Gudeodiscus (Veludiscus), Halongella and Plectopylis (see Stoliczka 1871, Páll-Gergely et al. 2015a) in terms of the small central tooth and the simple marginals. In contrast, the central tooth of Endothyrella, Gudeodiscus (Gudeodiscus), Sicradiscus and Sinicola species is large (as large as or larger than the ectocones of the first laterals), (Páll-Gergely et al. 2015a, 2015b, and the marginals are tricuspid or even quadricuspid. Before examining ethanol-preserved Naggsia laomontana specimens, we considered grouping the plectopylid genera into two tribes, namely one with a ribbed, and another with a smooth or granulated protoconch. The examination of Naggsia laomontana revealed that the character states considered to be primarily important do not allow the placement of Naggsia gen. n. in any of the two groups, and that the character states rather show a mosaic structure across genera.   l., 19°44.966'N, 101°59.496'E, leg. A. Abdou, I.V. Muratov, 28.11.2006., MNHN 2012 (some of them broken/juvenile).

Diagnosis.
A dextral, medium-sized or large species with a rounded body whorl, and no apertural fold. On the parietal wall there is a single curved lamella.
Description. The yellowish, sometimes pink or light brown shell is dextral, almost flat with the apex slightly elevated. The 5.5-6 whorls are separated by a moderately deep suture. The protoconch is very densely, regularly ribbed, with extremely fine spiral lines across the ribs. The teleoconch is irregularly ribbed; the space between the ribs is greater than on the protoconch. The lip is only slightly thickened and reflexed. There is an elevated, but blunt parietal callus, which has two shallow channels at the meeting point with the parietal part of the lip.
Four specimens were opened. On the parietal wall there is a single curved lamella without additional plicae. On the palatal wall there are seven horizontal plicae. The first, (situated near the suture) is short, undivided, not inclined, sometimes having a short denticle slightly lower than its posterior end. The second plica is slightly indented in place opposing the parietal curved lamella just before it becomes dichotomously bifurcated posteriorly, with its lower posterior arm slightly inclined away from the suture. The third, fourth and fifth exhibit an increasing tendency to be divided opposing the parietal lamella and inclined posteriorly away from the suture. The sixth is strongly, equally divided, having both parts equally inclined posteriorly away from the suture. The last one, unequally divided, consists of a long, not inclined anterior part and short, inclined posterior part.
Differential diagnosis. Naggsia laomontana resembles Gudeodiscus species in having the single parietal lamella, rounded body whorl and densely ribbed protoconch.  The protoconch of N. laomontana however reveals a unique surface structure, the riblets are comprised of slight waves that do not stand as regularly as those of Gudeodiscus. Gudeodiscus species that usually have a somewhat elevated spire, more whorls, two horizontal plicae in front of the parietal lamella, and simple (undivided) palatal plicae.

Characters of the genital structure
Penis long, its distal part is more slender than the proximal part, internally with 5-6 longitudinal folds aligned next to each other; only one of the folds reach the proximal end of the penis, the others are shorter; the penial wall (outside of the folded area) is wrinkled; the wrinkles are stronger near the distal end of the penis; many small, flat, lenticular calcareous granules were found in the penis lumen; epiphallic differentiation was not detected; retractor muscle slightly thinner than penis, shorter than it and connected to the apical end of penis; vagina shorter than half of penis; vas deferens has thick coiled portion just after coming out of spermoviduct, connects to vaginal wall and forms part of penial wall, reaching the middle of the proximal part of penis; diverticulum short, oval, gametolytic sac with relatively thick, cylindrical stalk and thickened, rather quadrangular sac; there were five, well-developed embryos in the uterus.
Radula (Figure 10). Radula elongated, but not very slender; the basal plates of the centrals are present, but their cusps are absent; the teeth are arranged in rows; each row contains 18-19 teeth, the first nine are laterals, the remaining are marginals, but it is rather difficult to decide which teeth are the last laterals and the first marginals; lateral teeth stand in straight rows which are perpendicular to the central column; marginals stand in anteriorly pointed, slightly oblique rows; endocones of laterals are rhomboid, rather blunt; ectocones are small, pointed, triangular; endocones of marginals are slender ovoid, blunt; the ectocones are small, pointed, triangular.
Distribution. The species was described from "Lao Mountains, Camboja". We have seen material with more detailed geographical data only from the central part of Northern Laos (around Luang Prabang). In the collection of the Natural History Museum London, a single shell of Ch. laomontana is present with the locality "China" (NHMUK 20110363, Salisbury Collection Ex Beddome Ex Canon Hoisley coll. 1918;see Páll-Gergely and Hunyadi 2013). Its occurrence in China is not verified and the locality is possibly wrong. Ecology and behaviour. This species can be found in primary or old secondary broad-leaved forests, but it inhabits some peculiar habitats as well. It can survive droughts as well as periodical floods and can be found in large numbers near waterfalls (Kuang Si waterfall, for example, is one very popular collecting spot) ( Figure 13). Unlike most terrestrial snails that start to crawl when placed in water, snails of this species, when under water, retract deep into the shell, which is probably an adaptation that helps to survive frequent floods.