Revision of the carnivorous snail genus Discartemon Pfeiffer, 1856, with description of twelve new species (Pulmonata, Streptaxidae)

Abstract Twelve new species of the streptaxid snail genus Discartemon Pfeiffer, 1856 are described from southern Thailand and western Malaysia, D. afthonodontia sp. n., D. circulus sp. n., D. deprima sp. n., D. discadentus sp. n., D. discamaximus sp. n., D. expandus sp. n., D. flavacandida sp. n., D. kotanensis sp. n., and D. megalostraka sp. n. from southern Thailand, as well as D. conicus sp. n., D. epipedis sp. n. and D. triancus sp. n. from western Malaysia. All 15 previously described species are revised and commented upon based on examined material. Streptaxis paradiscus Möllendorff, 1900 is considered a junior subjective synonym of the type species D. discus (Pfeiffer, 1853). Details of the genital anatomy of twelve species, and the radula and pallial system, are provided for the first time. An identification key is provided.


Introduction
The Streptaxoidea is divided into two sister families, Streptaxidae Gray, 1860and Diapheridae Panha & Naggs, 2010(Sutcharit et al. 2010). The superfamily is thought to have originated on the Laurasian continent during the Mesozoic era (Rowson et al. 2010). The Streptaxidae are carnivorous land snails occurring in tropical and subtropical areas from South America to Africa and Asia (Bruggen 1967, Schileyko 2000, Sutcharit et al. 2010. Most appear to be active predators feeding on other snails or other soil invertebrates, and may also be cannibalistic (Gray 1860, Blanford and Godwin-Austen 1908, Benthem Jutting 1954, Berry 1963. Streptaxids are particularly diverse in Africa, with hundreds of described species (Bruggen 1967, Winter and Gittenberger 1998, Rowson et al. 2010, Rowson and Tattersfield 2013. They are also diverse in Southeast Asia, comprising more than 130 nominal species in 15 genera (Blanford and Godwin-Austen 1908, Benthem Jutting 1954, Zilch 1960, Richardson 1988, Schileyko 2000, Siriboon et al. 2013.
The shell has traditionally been emphasized in streptaxid taxonomy (Tryon 1885, Kobelt 1905, 1906, Benthem Jutting 1954. As in many stylommatophorans, the reproductive organs have also proven to be useful in discriminating taxa at the generic and specific levels (Stoliczka 1871, Berry 1963, 1965, Schileyko 2000, Siriboon et al. 2013). To date, six generally accepted Southeast Asian genera, Discartemon Pfeiffer, 1856, Oophana Ancey, 1884, Perrottetia Kobelt, 1905, Haploptychius Möllendorff, 1906and Indoartemon Forcart, 1946, have been critically dissected, investigated and illustrated, providing additional anatomical diagnostic and systematic characters (Stoliczka 1871, Berry 1963, 1965, Schileyko 2000, Siriboon et al. 2013. The genus Discartemon can be distinguished from other Southeast Asian streptaxid genera by having a flattened to subglobose-heliciform shell with the last whorl not being axially distorted from the columellar axis (Kobelt 1906, Benthem Jutting 1954, Zilch 1960, Richardson 1988, Schileyko 2000. Discartemon species are all larger than those of Platycochlium Laidlaw, 1950, a genus from Borneo whose anatomy is not known, and do not share the riblets on slopes of umbilicus, spaced transverse ridges, and continuous peristome. Knowledge of the genital anatomy of Discartemon is currently limited to D. stenostomus Benthem Jutting, 1954 as studied by Berry (1965). The genitalia show a short penis with a blunt appendix and a penial sheath along its whole length. The internal penial wall has cornified ridges but no penial hooks apart from a single large "stylet" in the apex of the penis.
This present study aims firstly to provide shell and anatomical descriptions for characterization and identification within the genus Discartemon, including new species The second aim is to revise the previously described species. The third aim is to record and discuss the geographic distribution of the genus.
Material examined. This species was described from specimens from the H. Cuming collection. The number of specimens was not indicated, but only one set of measurements was given in the original description. Only one specimen from the H. Cuming collection at NHMUK has Pfeiffer's handwriting on the species name label. It is identical to the illustration and measurements in Pfeiffer (1854: 394, 395, pl. 145, figs 15-17) and is designated here as the lectotype to stabilize the name: NHMUK 20130684 (Fig. 4A Description. Shell. Shell flattened, white and translucent; whorls 6-6½; spire flattened with distinct suture. Shell surface glossy, smooth with growth lines and varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, regularly expanded; umbilicus very wide, shallow and showing all preceding whorls. Aperture semi-ovate; peristome discontinuous, thickened, expanded and reflected; apertural dentition with only one parietal lamella ( Fig. 4A-C).
Genital organs. Atrium (at) short; penis (p) long and slender. Penial sheath (ps) thin, extending about half to third-fourths of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting at distal end of penial sheath (Fig. 11A). Vas deferens (vd) passes through a very short part of penial sheath before entering into penis distally (Fig. 11B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction. Vagina (v) long, cylindrical, about two thirds of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) short; oviduct (ov) enlarged and folded. Prostate gland inconspicuous and bound to oviduct. Talon (ta) small. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 11A).
Pallial system. Excretory system typically sigmurethran and without mantle gland. Heart (h, auricles and ventricle) located left of kidney (on right in Fig. 11C). Pulmonary cavity approximately three times longer than broad. Pulmonary vein (puv) and venation on lung roof distinct and well developed. Kidney (k) very short, located at posterior of pulmonary cavity. Ureter (ur) sigmoid, closed tube arising from apex of kidney, extending along right side of kidney, recurving adjacent to rectum (rt). Anus (a) adjacent to pneumostome (pn) on mantle collar.
Remarks. The type specimen discovered in the H. Cuming collection at NHMUK elucidates two issues. Firstly, Streptaxis paradiscus Möllendorff, 1900 has been recognized as a separate species in many works (Möllendorff 1900, Gude 1903, Kobelt 1906, Benthem Jutting 1954, Zilch 1960, Schileyko 2011. However, based on the type specimens, D. discus and S. paradiscus are identical in all shell characters. Therefore, we officially place Streptaxis paradiscus as a junior subjective synonym of D. discus. Second, D. discus had an unknown type locality and range (Pfeiffer 1851: 252). From the new material and the type locality of S. paradiscus, the distribution of this species is demarcated to several localities in the area of Da Nang, Vietnam (Schileyko 2011).
Remarks. The shell of this species is clearly distinct from all other recognized species. Shell flattened, with a concave spire and distinct suture. Shell surface smooth, varices present; whorls regularly coiled. Last whorl rounded with keel below periphery, rapidly expanded; umbilicus very wide, concave and showing all preceding whorls. Aperture triangular with long and narrow sinulus, peristome thickened and little reflected. Apertural dentition with one parietal, one palatal and one columellar lamella ( Fig. 4D) (Fulton 1899, Kobelt 1906, Marwoto 2008. The distribution of D. planus seems to be outside the ranges of all other Discartemon species, and is probably restricted to the limestone karst in the south of Sulawesi (Fulton 1899, Sarasin and Sarasin 1899, Laidlaw 1929, Bruggen 1972, Marwoto 2008). It does not closely resemble any other streptaxid genus more closely than Discartemon. However, the very wide umbilicus showing all preceding whorls and surrounded with a keel, with a long and narrow adapical sinulus, may indicate that D. planus comprises a distinct lineage within Discartemon. Both Bruggen (1972) and Marwoto (2008) discussed the possibility that it required a separate genus or subgenus, but anatomical or molecular evidence are desirable to support this assertion. (Collinge, 1902) http://species-id.net/wiki/Discartemon_sykesi Figs 4E, F, 23
Remarks. The distinguishing characters of this species are the flattened shell and spire with a distinct suture. Shell surface nearly smooth with thin growth lines, varices present; following whorls regularly coiled. Last whorl angular, intermediately expanded; umbilicus very wide and showing all preceding whorls. Aperture semi-ovate with sinulus; peristome thickened, expanded and reflected; apertural dentition with only one parietal lamella (Fig. 4E).
Vagina (v) short and stout, about half of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) long and thick; oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, very short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 11D).
Vaginal wall generally with smooth surface of longitudinal vaginal folds (Fig. 17E).
Remarks. Discartemon nummus was described from Tale Sap (= Lake or Lagoon), Singgora (= Songkhla). In this study, living snails were found at an isolated limestone hill near the lake in Phatthalung, about 60 km north of the type locality.
Having the smallest shell size clearly discriminates D. nummus from all congeners. It is similar to D. discus, which has a larger shell and a peripheral keel, lacks a sinulus, and has a semi-ovate aperture with a straight parietal lamella. Discartemon nummus can be distinguished from D. khaosokensis in having a flattened spire, the last whorl regularly expanded, a triangular aperture, and a Y-shaped parietal lamella.
Remarks. This species is known only from the type locality. The shell is flattened and semi-transparent and has a concave spire with a distinct suture. Shell surface with transverse ridges that diminish below periphery, with varices present; whorls regularly coiled. Last whorl angular with a strong peripheral keel, rapidly expanded; umbilicus very wide, showing all preceding whorls. Aperture semi-ovate with narrow sinulus; peristome thin and expanded; apertural dentition of only one parietal lamella (Fig. 4H).
Diagnosis. This new species can be distinguished from D. discus and D. sykesi by having transverse ridges that diminish below the periphery, and having an apertural dentition with five lamellae. In comparison, D. sykesi has a smaller shell and D. discus has a higher spire. The genitalia of D. discus have a short penis, penial sheath and free oviduct, and long vagina while D. discadentus sp. n. has a very long penis, penial sheath and free oviduct, and short vagina. Discartemon discadentus sp. n. differs from D. nummus and D. khaosokensis in having a larger shell with higher spire, in lacking a peripheral keel, and in usually having five apertural lamellae. The last whorl of D. khaosokensis is rapidly expanded, while D. nummus has a regularly expanded last whorl and Y-shaped parietal lamella. The genitalia of D. discadentus sp. n. differ from those of D. nummus in the long and slender penis, penial wall with reticulated folds, and long penial hooks located on conical penial papillae.
Description. Shell. Shell flattened, white and translucent; whorls 6; spire only slightly elevated; suture distinct. Shell surface glossy with transverse ridges that diminish below periphery; varices present. Embryonic shell large, about 2½ whorls, with smooth surface; following whorls regularly coiled. Last whorl angular, intermediately expanded; umbilicus very wide and showing all preceding whorls. Aperture semi-ovate; peristome discontinuous, thickened and expanded. Apertural dentition usually with one strong parietal, one palatal, one small basal and one strong columellar lamella. A small supracolumellar lamella is sometimes present (Fig. 4I).
Genital organs. Atrium (at) short; penis (p) very long and slender. Penial sheath (ps) thin, extending about five-sixths of penis length; penial sheath retractor muscle very thin (psr), originating at genital orifice wall and inserting distally on penial sheath ( Fig. 12A). Vas deferens (vd) passes through a very short part of penial sheath before entering into penis distally (Fig. 12B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.
Vagina (v) short, about one seventh of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) convoluted and distally long and thick; oviduct (ov) enlarged and folded. Prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about four times longer than the length from talon to branching point of seminal vesicle (Fig. 12A).
Distribution. This species seems to be restricted to limestone areas in Suratthani Province, Thailand. Tam Khuha, Kanchanadit District, is an isolated limestone hill about 40 km southeast of the type locality and Wat Tam Wararam, Phanom District, is in the limestone mountains near Ratchaprapa Dam, about 70 km southwest of the type locality.
Remarks. This species shows variation in shell size and the presence of the infrapalatal, upper palatal and supracolumellar lamellae. Some specimens from Phanom, Suratthani (CUMZ 3571, 3582) possess an upper palatal and supracolumellar lamella, and an infrapalatal lamella is present in one paratype shell (CUMZ 6003). Populations from Tam Khuha, Suratthani (CUMZ 6004) exhibit a relatively smaller shell size (width about 11 mm). This new species is apparently rare and only extensive searching revealed living animals.
Other material examined. Tam Kobe, Phangnga: CUMZ 3669, 6197. Type locality. Tam Namphud, Phangnga, Thailand, 8°27'46.8"N, 98°32'30.5"E. Diagnosis. The characters distinguishing D. discamaximus sp. n. from D. sykesi and D. khaosokensis are the larger shell with flattened to concave spire, the transverse ridges present near the suture, and the lack of a sinulus. Discartemon discamaximus sp. n. has similar shell morphology to D. discus and D. discadentus sp. n., but is distinguished by having the transverse ridges present only near the suture and the last whorl rapidly expanded. Discartemon discadentus sp. n. also has five apertural lamellae.
Description. Shell. Shell flattened, white and translucent; whorls 7, spire flattened to concave, with distinct suture. Shell surface glossy with transverse ridges near suture and varices present. Embryonic shell large, about 2½ whorls, with smooth surface; following whorls regularly coiled. Last whorl angular, rapidly expanded; umbilicus very wide and showing all preceding whorls. Aperture semi-ovate; peristome discontinuous, expanded and reflected; apertural dentition with one parietal lamella (Fig. 5A).
Etymology. The specific epithet "discamaximus" is derived from the Latin "discus" meaning "disc" and "maximus" meaning "large or broad".
Distribution. This new species is known from limestone karst near Phanganga Bay reaching about 100-400 meters amsl, surrounded by the Phuket mountain range.

Discartemon circulus
Description. Shell. Shell flattened, white and translucent; whorls 5½-6, spire flattened, with a distinct suture. Shell surface glossy with weak transverse ridges and varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, regularly expanded; umbilicus very wide, deep and showing all preceding whorls. Aperture sub-quadrangular; peristome discontinuous, thin and expanded. Apertural dentition with one parietal, one palatal, one small basal, one small columellar and one small supracolumellar lamella (Fig. 5C).
Etymology. The specific epithet is from the Latin "circulus" meaning "circle". It refers to the appearance of this new species when seen from the apex.
Distribution. This species is known only from the type locality, an isolated limestone hill which reaches about 200 meters amsl, about 20 km southwest of Tai Rom Yen National Park.
Remarks. Apparently rare and extensive searching revealed no living examples. Diagnosis. This species closely resembles D. sykesi, but is distinct in having a concave spire and strong peripheral keel on the last whorl. Compared with D. khaosokensis, D. deprima sp. n. has a smaller shell with weaker transverse ridges, and the last whorl intermediately expanded. Discartemon deprima sp. n. differs from D. nummus by having a larger shell, a concave spire, and one straight parietal lamella. It differs from D. circulus sp. n. and D. expandus sp. n. in having a concave spire, the last whorl intermediately expanded with a strong peripheral keel, and in having only one parietal lamella and a sinulus. In addition, D. expandus sp. n. has transverse ridges that diminish below the periphery, and has a thin and widely expanded peristome. C holotype CUMZ 6246 with apertural dentition, and D paratype CUMZ 3665 E, F Discartemon deprima sp. n. E holotype CUMZ 6247 with apertural dentition, and F paratype CUMZ 3573 G, H Discartemon expandus sp. n. G holotype CUMZ 6248 with apertural dentition, and H paratype CUMZ 3664.

Discartemon deprima
Description. Shell. Shell flattened, white and semi-transparent; whorls 5, spire concave with a distinct suture. Shell surface glossy with weak transverse ridges that diminish below periphery and appear again near peristome; varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular with strong peripheral keel, intermediately expanded. Umbilicus very wide and showing all preceding whorls. Aperture semi-ovate with sinulus; peristome discontinuous, thin, expanded and reflected. Apertural dentition with only one parietal lamella (Fig. 5E).
Etymology. The specific epithet "deprima" is derived from the Latin "deprimo" meaning "depress". It refers to the depressed spire of this new species.
Distribution. This species is known from the east coast of Chumphon, on an isolated limestone hill reaching about 200 meters amsl, and from a more southerly locality in Patthalung, a limestone hill complex reaching about 200-400 meters amsl.
Remarks. There is some variation in this species in the discontinuous peristome and the presence of a sinulus. The samples from Patthalung (CUMZ 3670, 2 shells) have a continuous peristome and lack a sinulus. Currently, no living examples have been found.
Type locality. Klong Hoy, Suratthani, Thailand, 8°57'18.1"N, 98°48'30.7"E. Diagnosis. Discartemon expandus sp. n. differs from D. discus and D. sykesi in its smaller shell with transverse ridges, intermediately expanded last whorl, and widely expanded peristome. In addition, a sinulus is absent in D. discus. Discartemon expandus sp. n. can be distinguished from D. khaosokensis by having a flattened spire, an angular and intermediately expanded last whorl, and a widely expanded peristome. Compared with D. discadentus sp. n. and D. discamaximus sp. n., D. expandus sp. n. has a smaller shell with strong transverse ridges, a sinulus and a widely expanded peristome. Moreover, D. discadentus sp. n. has five apertural lamellae, and D. discamaximus sp. n. has a rapidly expanded last whorl.
Description. Shell. Shell flattened, white and semi-transparent; whorls 5½-6, spire flattened with a distinct suture. Shell surface glossy with transverse ridges that diminish below periphery; varices present. Embryonic shell large, about 2-2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, intermediately expanded; umbilicus very wide, deep and showing all preceding whorls. Aperture semi-ovate with narrow sinulus; peristome discontinuous, thin and widely expanded. Apertural dentition of only one parietal lamella (Fig. 5G).
Etymology. The specific epithet "expandus" is derived from the Latin "expandi" meaning "expand". It refers to the expanded peristome of this species.
Distribution. The species is known only from the type locality and extensive searching revealed no living examples.
Remarks. Some variation has been observed in the spire, which is slightly convex rather than flattened in some specimens, and in the distinctness of the suture.  6B; 3 shells).
Remarks. The original descriptions included informative figures (Morgan 1885a, b), and subsequently Benthem Jutting (1954: fig. 2) published excellent figures of topotype specimens. These allow unambiguous recognition of this species. Shell depressed-heliciform with a flattened spire. Shell surface with transverse ridges that diminish below periphery and varices present; following whorls regularly coiled. Last whorl rounded and regularly expanded; umbilicus widely open and deep. Aperture triangular with sinulus, and apertural dentition with one parietal and one palatal lamella (Fig. 6B).

Discartemon hypocrites
Radula. Each row consists of 43 teeth with formula (21)-1-(21). Central tooth very small and triangular with a pointed cusp. Lateral and marginal teeth undifferentiated, unicuspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 22C).
Genital organs. Atrium (at) long and thick. Proximal penis (p) with short and stout penial appendix (pa) about two-thirds of penis length; distal penis slender (Fig. 12C). Penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 12C). Vas deferens (vd) passes through about a quarter of penial sheath length before entering into penis distally (Fig. 12D). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.
Vagina (v) short. Gametolytic duct (gd) enlarged and stout at base, and suddenly tapering to small and long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) proximally large with equivalent diameter to vagina, tapering to smaller tube distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long and thick seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 12C).
Vaginal wall with reticulated vaginal folds (Fig. 18E). Distribution. This species is known from several limestone hills in Perlis, Malaysia.
Remarks. Discartemon hypocrites can be distinguished from D. plussensis, D. leptoglyphus and D. platymorphus by the apertural dentition with one sinuous parietal, one columellar, and one supracolumellar lamella. The latter three species exhibit one straight parietal and one palatal lamella. In addition, D. plussensis has a lower spire, an inflated last whorl and a sinulus; D. leptoglyphus has transverse ridges over the entire shell; and D. platymorphus has a larger shell and lower spire. Discartemon hypocrites also differs from D. leptoglyphus in having a slender penis with short and stout penial appendix, the vas deferens passing through about a quarter of penial sheath length, the pointed penial hooks located on laterally-flattened penial papillae, and the vagina having reticulated folds.  NHMUK 1939.4.13.22, from Perak, Malaysia, and B topotype CUMZ 6009 with apertural dentition C, D Discartemon hypocrites C holotype ZMA 3.34.017, and D topotype CUMZ 6011 with apertural dentition E, F Discartemon leptoglyphus E holotype ZMA 3.54.019, and F specimen CUMZ 6007, from Ipoh, Perak, Malaysia with apertural dentition G, H Discartemon platymorphus G holotype ZMA 3.54.022, and H paratype ZMA 3.54.023.  Fig. 6F).
Vagina (v) short, about one-third of penis length. Proximal gametolytic duct (gd) enlarged, stout; distally a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Proximal free oviduct (fo) enlarged then tapering to smaller tube distally. Oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small and club shaped. Hermaphroditic duct (hd) bearing long and thick seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 13A).
Vaginal wall generally smooth (Fig. 18L). Distribution. This species is known from the limestone mountains around the type locality in Perak, Malaysia.
Remarks. Compared with D. platymorphus, this species differs in having a smaller shell, with transverse ridges appearing on the entire shell and a more inflated last whorl. Discartemon leptoglyphus can be distinguished from D. stenostomus by having a depressed-heliciform shell with lower spire, transverse ridges on the entire shell, the last whorl angular, and apertural dentition of one straight parietal lamella. In addition, the penial appendix in D. leptoglyphus is relatively much longer than that shown for D. stenostomus (see Berry 1965). Material examined. Holotype ZMA 3.54.022 (fragmented) (Fig. 6G). Paratype ZMA 3.54.023 (2 shells).

Discartemon platymorphus
Remarks. The shell is depressed-heliciform with the spire only slightly convex and with a distinct suture. The shell surface has transverse ridges that diminish below the periphery, and varices are present. The following whorls are regularly coiled. Last whorl rounded, regularly expanded; umbilicus widely open and deep. Aperture tri-angular; peristome discontinuous, thickened, expanded and little reflected; apertural dentition of one parietal and one palatal lamella (Fig. 6H).
Discartemon platymorphus is closely similar to D. plussensis, but that species has a larger shell with a higher spire and lacks a sinulus. Discartemon platymorphus differs from D. epipedis sp. n. by having a lower spire, transverse ridges that diminish below the periphery, a shouldered last whorl, and apertural dentition with four lamellae. Compared with D. stenostomus, D. platymorphus has a lower spire with fine transverse ridges that disappear below the periphery, and a straight parietal lamella and one palatal lamella. Type locality. Tam Phitsadan, Prathiew, Chumphon, Thailand, 10°43'26.6"N, 99°15'23.6"E.

Discartemon afthonodontia
Diagnosis. This new species can be distinguished from D. plussensis, D. leptoglyphus and D. platymorphus in having a nearly smooth shell surface, a shouldered last whorl, and five to seven apertural lamellae. Discartemon afthonodontia sp. n. differs from D. hypocrites by having a nearly smooth shell surface and an aperture with two parietal, two palatal, one basal and two columella lamellae. The genitalia of D. afthonodontia sp. n. differ from those of D. hypocrites in lacking a penial appendix, in having the free oviduct long and slender, and in having the vas deferens passing straight through the penial sheath. They also differ from D. afthonodontia sp. n. in having conical penial papillae, long and slender penial hooks, and in having the penial wall with thick reticulated folds, and the vaginal wall with a smooth surface. Compared with D. epipedis sp. n., D. afthonodontia sp. n. has more apertural lamellae, lacks a penial appendix and has the vas deferens passing straight through the penial sheath. They also differ from D. afthonodontia sp. n. in having a penial wall with thick reticulated folds, and in having a very long and slender free oviduct.
Description. Shell. Shell depressed-heliciform, white and translucent; whorls 6, spire conical to convex with distinct suture. Shell surface glossy, smooth with transverse ridges near the peristome and varices present only on early whorls. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl shouldered, sometimes angular with strong peripheral keel, regularly expanded, and two shallow and short longitudinal furrows present. Umbilicus widely open and deep. Aperture sub-quadrangular; peristome discontinuous, thickened, expanded and reflected. Aperture dentition with one strong parietal, one palatal, one basal, one large columellar and one small supracolumellar lamella; sometimes upper parietal and upper palatal lamellae present (Fig. 7A).
Vagina (v) short, about half of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) a very long and slender tube; oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small and slender. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 13C).
Distribution. This species is known from several limestone karsts in Chumphon and Prachuap Khirikhan Provinces, southern Thailand. This is a narrow range confined to the Isthmus of Kra area, from 9° to 11° N and 99° to 100° E.
Remarks. Shell variations are detected across populations. In the Tam Khao Phlu (CUMZ 3581,3666,6214) and Khao Maeo (CUMZ 3589) populations, shells have a stronger peripheral keel, a subcircular aperture, and lack the upper parietal lamella (Fig. 7B). The specimens from Wat Tam Khao Marong (CUMZ 4219, 6014, 6211), Wat Tam Khwan Meuang (CUMZ 6015), and Suan Somdet (CUMZ 6017) exhibit a convex spire, and the upper parietal and upper palatal lamellae are sometimes absent. However, these five populations exhibit similar genitalia characters including the penial sculpture. Therefore, we consider them all conspecific.  Table 2 Type material. Holotype CUMZ 6250 (Fig. 7C). Measurement: shell height 4.6 mm, shell width 8.7 mm, and with 6 whorls. Paratypes: CUMZ 6020 (15 shells), 6215 (5 Diagnosis. Discartemon epipedis sp. n. differs from D. plussensis and D. leptoglyphus in having a higher spire, a nearly smooth shell surface, a semi-ovate aperture, and four apertural lamellae. Compared with D. flavacandida sp. n., D. epipedis sp. n. has a smaller shell, lacks longitudinal furrows, has the last whorl rounded and regularly coiled, and has four apertural lamellae. The genitalia of D. epipedis sp. n. differ from those of D. flavacandida sp. n. in having a very short and swollen penial appendix, a long and enlarged vagina, short free oviduct, low conical penial hooks, penial papillae present, and in lacking vaginal pores. Discartemon epipedis sp. n. differs from D. roebeleni in having a depressed-heliciform shell, a nearly smooth shell surface, and a semi-ovate aperture. The genitalia have a very short and swollen penial appendix, long and enlarged vagina, long and slender free oviduct, dark brown penial hooks located on conical penial papillae, and a vaginal wall with smooth surface.

Discartemon epipedis
Description. Shell. Shell depressed-heliciform, white and translucent; whorls 6, spire only slightly convex with distinct suture. Shell surface glossy, nearly smooth with few transverse ridges near peristome; varices present. Embryonic shell large, about 2½ whorls. with a smooth surface; following whorls regularly coiled. Last whorl shouldered or rarely rounded, regularly expanded; umbilicus widely open and deep. Aperture semi-ovate; peristome discontinuous, thickened, expanded and reflected. Apertural dentition with a strong parietal lamella and one palatal, one basal and one columellar lamella (Fig. 7C).
Genital organs. Atrium (at) very short. Proximal penis (p) very short penial appendix (pa) swollen in middle, and distal penis slender. Penial sheath (ps) thin, extending about two-thirds of penis length; penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 14A). Vas deferens (vd) passes through about one-seventh of penial sheath length before entering into penis distally (Fig. 14B). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.
Vagina (v) long, enlarged, about half of penis length. Gametolytic duct (gd) expanded at base and tapering to long and tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) a long and narrow tube; oviduct (ov) enlarged and folded; prostate gland inconspicuous and bound to oviduct. Talon (ta) small, short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about three times longer than the length from talon to branching point of seminal vesicle (Fig. 14A).
Vaginal wall with smooth surface of strong recticulate vaginal folds (Fig. 17I). Etymology. The specific epithet "epipedis" is derived from the Greek "epipedos" meaning "flat" It refers to the flattened-or depressed-heliciform shell.
Distribution. This species is known only from the type locality. Remarks. Apparently rare and only extensive searching yielded living animals.  Diagnosis. This new species is distinguished from D. plussensis, D. leptoglyphus, D. platymorphus, D. roebeleni and D. collingei by having a larger shell with a smooth shell surface, a shouldered and slightly axially deflected last whorl, two longitudinal furrows and seven apertural lamellae. Its genitalia are distinctive in having a long but thick penial appendix.
Embryonic shell large, about 2½ whorls and with smooth surface; following whorls regularly coiled. Last whorl shouldered, slightly axially deflected, regularly expanded, and two short longitudinal furrows present. Umbilicus widely open and deep. Aperture semiovate; peristome discontinuous, expanded and reflected. Apertural dentition with strong parietal and small upper parietal lamellae separated at right angle, one small upper palatal, one palatal, one basal, one columellar, and one small supracolumellar lamella (Fig. 7E).
Genitalia organs: Atrium (at) long and slender. Penis (p) long; proximal penis slender; middle part enlarged with a long but thick penial appendix (pa) about half of penis length; distal penis long and slender (Fig. 14C). Penial sheath (ps) thin, extending about half of penis length; penial sheath retractor muscle (psr) very thin, originating at atrium and inserting distally on penial sheath. Vas deferens (vd) passes through about one-fifth of penial sheath length before entering into penis distally (Fig. 14D). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.
Vagina (v) very short, about one-fourth of penis length. Gametolytic duct (gd) a long narrow tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) very long, slender, proximal with equivalent diameter with vagina, and tapering to smaller tube distally. Oviduct (ov) folded and prostate gland inconspicuous. Talon (ta) small, and very short. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about one and half times longer than the length from talon to branching point of seminal vesicle (Fig. 14C).

Species and locality and CUMZ nos
Remarks. Discartemon roebeleni can be distinguished from D. collingei by its rounded, regularly coiled last whorl and wider umbilicus. It differs from D. stenostomus in the higher spire with transverse ridges that diminish below the periphery, a sub-quadrangular aperture, and in having a basal lamella. (Sykes, 1902) http://species-id.net/wiki/Discartemon_collingei Figs 8H, 23
Discartemon collingei is similar to D. lemyrei, but the latter species has a larger shell with a higher spire, a shell surface with transverse ridges, the last whorl rounded and more inflated, a narrower umbilicus, and only one parietal lamella. Remarks. Shell globose-heliciform, semi-transparent, spire only slightly convex and with a distinct suture. Shell surface glossy with thin transverse ridges at suture; following whorls regularly coiled. Last whorl rounded and regularly expanded; umbilicus widely open and deep. Aperture triangular; peristome thickened, expanded and reflected. Apertural dentition with one sinuous parietal, one palatal, one columellar and one supracolumellar lamella (Fig. 9A).

Discartemon stenostomus
The genital anatomy was described by Berry (1965). Atrium and penis short with blunt penial appendix, penial sheath extending almost entire penis length, vas deferens passing through about one-fifth of penial sheath length. Internal wall of penis corrugated with cornified ridges, penial hooks absent, but with a large hollow "stylet" presumably protrudable from the tip of the everted penis. Vagina very short, proximal gametolytic duct enlarged, distally a long slender tube. Free oviduct short; talon small, club shaped; seminal vesicle about the same length from talon to branching point of seminal vesicle. Internal wall of vaginal elaborated with parallel vaginal folds.
This species resembles D. lemyrei and D. collingei, but differs in having thin transverse ridges near the suture, a triangular aperture, and apertural dentition with a sinuous parietal lamella, one palatal, one columellar and one supracolumellar lamella. In addition, D. lemyrei has a larger shell, narrower umbilicus, and only one parietal lamella, while D. collingei has a shouldered and slightly axially reflected last whorl, and apertural dentition with a straight parietal, one palatal, one basal and one columellar lamellae. A penial stylet has not yet been found in any other Discartemon species. Material examined. Holotype ZMA 3.59.052 (Fig. 9C). Paratypes: ZMA 3.59.053 (1 shell), ZMA 3.59.054 (4 shells), and ZMA 3.59.057 (9 shells). Remarks. Shell globose-heliciform, semi-transparent, with a conical spire and distinct suture. Shell surface glossy with fine transverse ridges; following whorls regularly coiled. Last whorl rounded and regularly expanded; umbilicus widely open and deep. Aperture triangular, with sinulus; peristome thickened, expanded and reflected. Apertural dentition of only one parietal lamella (Fig. 9C).  Discartemon sangkarensis differs from D. roebeleni in having a more inflated last whorl, a triangular aperture, in having a sinulus, and the apertural dentition of only one parietal lamella. Compared with D. lemyrei and D. vandermeermohri, D. sangkarensis differs in having a sinulus. Also, D. lemyrei has a relatively larger shell and narrow umbilicus, while D. vandermeermohri has a small basal lamella. Discartemon sangkarensis differs from D. collingei in having a higher spire, the last whorl rounded, more inflated and regularly coiled, and in having a sinulus, a triangular aperture, and only one parietal lamella. Also, D. collingei is slightly axially deflected. Benthem Jutting, 1959 http://species-id.net/wiki/Discartemon_vandermeermohri Figs 9E, F, 23 Discartemon vandermeermohri Benthem Jutting, 1959: 166-168, fig. 9. Type locality:
This species differs from D. lemyrei in its smaller shell, widely open umbilicus, triangular aperture, and in having two apertural lamellae. Discartemon vandermeermohri is readily distinguished from D. roebeleni and D. collingei in its having a triangular aperture, and in lacking a basal lamella. Also, D. collingei is slightly axially deflected.  Table 3 Type material. Holotype CUMZ 6252 (Fig. 9G). Measurement: shell height 6.3 mm, shell width 9.2 mm, and with 6 whorls. Paratypes: CUMZ 4220 (27 shells  Diagnosis. Conchologically this new species superficially resembles D. roebeleni and D. megalostraka sp. n. It differs from D. roebeleni in having a higher spire, a very long penis, a penial sheath extending fourth-fifths of the penis length, a smooth atrium wall with atrial pores, and a short seminal vesicle. It differs from D. megalostraka sp. n. in having a smaller shell and apertural dentition of four lamellae, and a shorter free oviduct, vas deferens and seminal vesicle. Discartemon kotanensis sp. n. differs from D. stenostomus and D. collingei in having a higher spire, transverse ridges reaching the periphery, the last whorl rounded and regularly coiled, and apertural dentition of one straight parietal, one basal and one columellar lamella. Also, D. collingei is slightly axially deflected.
Radula. Each row consists of 27-31 teeth with formula (13-15)-1-(13-15). The central tooth is very small and triangular with a pointed cusp. Lateral and marginal teeth are undifferentiated, unicuspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 22F).
Genital organs. Atrium (at) short. Penis (p) very long and slender. Penial sheath (ps) thin and extending about fourth-fifths of penis length, and penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 15D). Vas deferens (vd) passes a very short distance through penial sheath before entering into penis distally (Fig. 15E). Penial retractor muscle (pr) thin and very long, inserting at penis and vas deferens junction.
Vagina (v) short, about one-fifth of penis length. Gametolytic duct (gd) a long tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) short, of about same length as vagina. Oviduct (ov) slender and folded; prostate gland inconspicuous. Talon (ta) small, very short and club shaped. Hermaphroditic duct (hd) bearing long seminal vesicle (sv) about twice as long as the length from talon to branching point of seminal vesicle (Fig. 15F).
Vaginal wall generally with longitudinal vaginal folds (Fig. 20J). Etymology. The specific epithet is derived from the type locality of this new species, the Ko Tan, Ko Samui, Suratthani Province.
Distribution. This species is known from the type locality and few limestone outcrops on the southern mainland.
Remarks. Shells of this species from Samui, Suratthani were originally thought to belong to D. roebeleni. After the genital system of D. kotanensis sp. n. was examined and critically investigated, it was considered distinct enough to be a separate species.  Table 3 Type material. Holotype CUMZ 6253 (Fig. 10A). Measurement: shell height 8.0 mm, shell width 12.0 mm, and with 7 whorls. Paratypes: CUMZ 3657 (5 shells), 6031  Diagnosis. This species differs from D. lemyrei in its widely open umbilicus and apertural dentition of six lamellae. It differs from D. roebeleni in having a much larger shell, higher spire, upper palatal and supracolumellar lamellae, a very long penis, penial sheath and free oviduct, shorter seminal vesicle, and in having atrial pores. Discartemon megalostraka sp. n. can be distinguished from D. stenostomus in its larger shell, higher spire, transverse ridges, sub-quadrangular aperture, its straight parietal lamella, and in having upper palatal and basal lamellae.

Discartemon megalostraka
Description. Shell. Shell globose-heliciform, white and translucent; whorls 7-7½, spire elevated conical, with a distinct suture. Shell surface glossy with fine transverse ridges that diminish below periphery; varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl rounded and regularly expanded; umbilicus widely open and deep. Aperture sub-quadrangular; peristome discontinuous, thickened, expanded and reflected. Apertural dentition of one strong parietal, one small upper palatal, one palatal, one basal, one columellar and one small supracolumellar lamella (Fig. 10A).
Radula. Each row consists of 19-21 teeth with formula (9-10)-1-(9-10). The central tooth is small and triangular with a pointed cusp. Lateral and marginal teeth are undifferentiated and large, unicuspid and lanceolate. Latero-marginal teeth gradually reduce in size, with outermost teeth much smaller and shorter than inner teeth (Fig. 22G).
Genital organs. Atrium (at) very short. Penis (p) very long and slender. Penial sheath (ps) thin, extending about third-fourths of penis length. Penial sheath retractor muscle (psr) very thin, originating at genital orifice wall and inserting distally on penial sheath (Fig. 16A). Vas deferens (vd) passes a very short distance through penial sheath before entering into penis distally (Fig. 16B). Penial retractor muscle (pr) thin and long, inserting at penis and vas deferens junction.
Vagina (v) very short. Gametolytic duct (gd) a long and narrow tube extending as far as albumin gland; gametolytic sac (gs) ovate. Free oviduct (fo) extremely long, proximal part a straight cylindrical tube, distal part corrugated. Oviduct (ov) enlarged and folded; prostate gland inconspicuous. Talon (ta) small, very short and club shaped. Hermaphroditic duct (hd) bearing a long seminal vesicle (sv) about four times as long as the length from talon to branching point of seminal vesicle (Fig. 16C). Vaginal wall with longitudinal vaginal folds (Fig. 21F). Etymology. The specific epithet "megalostraka" is derived from the Greek "megalos" meaning "big" and "ostrako" meaning "shell".
Distribution. This species is known from several limestone hills in southern Thailand, particularly in the western part of the southern mainland. The animals can be found at altitudes up to 20 meters amsl.
Diagnosis. This new species is superficially similar to D. roebeleni and D. kotanensis sp. n., but the distinguishing characters are the smaller shell, lower spire, angular last whorl, very long penis and free oviduct, short seminal vesicle, and penial hooks with elongated bases. Discartemon triancus sp. n. can be distinguished from D. megalostraka sp. n. by having a smaller shell, lower spire, four apertural lamellae, a longer penis, short free oviduct, and slender penial hooks with elongated bases. Discartemon triancus sp. n. differs from D. conicus sp. n. in having a lower spire with shallow suture, transverse ridges, in lacking a sinulus, and in having four apertural lamellae.
Description. Shell. Shell globose-heliciform, white and translucent; whorls 5½-6, spire only slightly convex, with distinct suture. Shell surface glossy with transverse ridges that diminish below the periphery; varices present. Embryonic shell large, about 2½ whorls, with a smooth surface; following whorls regularly coiled. Last whorl angular, regularly expanded; umbilicus widely open and deep. Aperture subcircular; peristome discontinuous, thin and expanded. Apertural dentition of one parietal, one palatal, one small basal and one columellar lamella (Fig. 10C).
Distribution. Known only from the type locality among limestone karsts up to 100 meters amsl, surrounded by mangrove forests on the northeast Langkawi Island coastline.
Remarks. The new species is apparently rare and extensive searching yielded only three examples.

Systematics
All species of Discartemon whose genital anatomy is known have a penial sheath through which the vas deferens passes for a short distance. This is typical of many streptaxid genera included in the subfamilies Streptaxinae Gray, 1860and Gibbinae Steenberg, 1936by Schileyko (2000. In contrast a penial appendix is a much less common feature and does not occur in any of these genera as treated by Schileyko (2000), although he did not cite Berry's (1965) study of D. stenostomus.
The species of Discartemon vary in whether an appendix is present and in other respects that correspond only approximately to the subdivision of the genus into three groups based on shell morphology. The groupings are as follows. Group I: D. discusgroup have a short to long, slender penis and transparent penial hooks. The genitalia of Group II: D. plussensis-group have a short penis generally with a penial appendix, and transparent to brown penial hooks. A stout seminal vesicle may be present, and the gametolytic duct is usually enlarged and stout at the base. Group III: D. roebeleni-group have a short to very long penis, sometimes with a blunt appendix, penial hooks are transparent, short, and expanded at the base. In one case D. stenostomus, no penial hooks are present but a stylet is. The latter is the only Discartemon species whose genital anatomy was known prior to this study. Although its shell is not unusual for the genus, the species is apparently atypical in having a hollow stylet in the apex of the penis, which was not noted in other species. The function of the appendix and stylet are not known.
Genital anatomy does appear to be useful in the characterization and diagnosis of species-group taxa, however, particularly in the D. plussensis-group.

Biogeography
The distributional range of this genus is more extensive than previously known. Twenty-two of the species recorded in this study occur in the area from Isthmus of Kra to the western part of Malaysia including the Lankawi Islands. The other five species can be found in other limestone areas; Cambodia, central Vietnam, Sumatra and Sulawesi.
The genus apparently usually occurs in limestone habitats such as karst islands, isolated limestone hills and limestone mountains. Many Southeast Asian mollusks are restricted to such areas which are often threatened (Tweedie 1961;Clements et al. 2006). Furthermore many of the species here have very restricted distributions. Most are allopatric and a number appear to be endemic to single limestone hills. Others range throughout a limestone complex.
Three syntopic occurrences where one of the few common and widespread species, D. roebeleni, occurs near restricted endemics were observed in this study. These were D. nummus, D. circulus sp. n., and D. deprima sp. n. at Khao Ok Thalu, Phatthalung, Khao Pu-Khao Ya National Park, Patthalung, and Tam Phannara, Nakhon Si Thammarat respectively, all in southern Thailand.