Helix perversus Linnaeus, 1758 by subsequent designation of E. von Martens in Albers (1860).

Vietnam: Dextral, lectotype of “Amphidromus ingens”, SMF 7565/1 (Fig. 3A); 2D + 2S, paralectotypes of “Amphidromus ingens”, SMF 7566/4 (Fig. 3B). Vietnam: Dextral, holotype of “Amphidromus naggsi”, RMNH.5003908 (Fig. 3C).

Figure 3. 

Shells of Amphidromus ingens Möllendorff, 1900 A lectotype of “Amphidromus ingens” (SMF 7565) B paralectotype of “Amphidromus ingens” (SMF 7566) C holotype of “Amphidromus naggsi” (RMNH.5003908) D, E specimens from M’drak, Dak Lak, Vietnam (NMNS-8764-082, NMNS-8764-084) F specimen from Ea M’doal, M’drak, Dak Lak, Vietnam (NMNS-8764-087) G specimen from Krong A, M’drak, Dak Lak, Vietnam (NMNS-8764-088) H, I specimens from Ea Sup, Dak Lak, Vietnam (NMNS-8764-093, NMNS-8764-101). Credit: J. Goud, RMNH (C).

Vietnam: 4D + 1S specimens, M’drak District, Dak Lak Province, NMNS-8764-082–NMNS-8764-086 (Fig. 3D, E); 1D specimen, Ea M’doal ward, M’drak District, Dak Lak Province, NMNS-8764-087 (Fig. 3F); 4D + 1S specimens, Krong A ward, M’drak District, Dak Lak Province, NMNS-8764-088–NMNS-8764-092 (Fig. 3G); 7D + 5S specimens, Ea Sup District, Dak Lak Province, NMNS-8764-093–NMNS-8764-104 (Fig. 3H, I).

Shell large conical and chirally dimorphic (sinistral and dextral coiling). Shell surface with coarse growth lines; last whorl with subsutural depression area and more or less prominent keel on periphery. Genitalia with appendix.

Amphidromus ingens is unique among all reported Vietnamese species (Schileyko 2011) in having a last whorl with subsutural depression area and more or less prominent keel on periphery. Amphidromus bozhii is similar in most of the shell form and sculpture, but the shell sculpture of A. bozhii has a very weak spiral depression area and sometimes with or without keel, and the shell colour is generally rose-pink to dark colour, with last whorl stained with dark brown colour below periphery and ~ 1/2 of upper periphery. On the other hand, A. ingens has a monochrome (whitish, yellowish, tinted pink) shell, often stained with dark brown to blackish below periphery. Amphidromus ingens is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. ingensoides sp. nov. in COI (10.2%) and A. bozhii in 16S (2.76%) (Table 2).

Shell large (height 62.3–74.6 mm, width 38.5–42.5 mm), chirally dimorphic, solid, and ovate conical shape. Spire long conical to elongate conical, apex acute without black spot on tip. Whorls 5–7 convex; suture wide and depressed; last whorl rounded to slightly angulated. Periostracum brownish to thin corneous; varix usually absent. Shell surface generally with irregular and coarse growth lines; below sutural with broad subsutural depression area, and with blunt or low to prominent keel on periphery. Shell colour highly variable: monochrome (whitish, yellowish, tinted pink) to stained with dark brown to blackish below periphery. Parietal callus thickened and white, dilated at umbilical area. Aperture broadly ovate; inner side of outer wall with white, yellow or dark brown to blackish colour. Peristome thickened, expanded, and reflexed but not attached to last whorl; lip whitish. Columella white, straight, or little twisted. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, slightly curved, with wide notch and dull cusp; ectocone large with truncated to slightly curved cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth (Fig. 4A).

Figure 4. 

SEM images of the radula of Amphidromus spp A Amphidromus ingens Möllendorff, 1900 from Ea Sup, Dak Lak, Vietnam (NMNS-8764-100) B Amphidromus asperoides sp. nov. from Ea Tu, Buon Ma Thuat city, Dak Lak, Vietnam (NMNS-8764-001) C Amphidromus bozhii Wang, 2019 from Tuy Hoa, Phu Yen, Vietnam (NMNS-8764-016). Central teeth are marked in yellow. The left and right images show the outer and inner sections of each radula, respectively.

Genital organs. Atrium relatively short. Penis slender, conical, and short ~ 1/3 of vaginal length. Penial retractor muscle thickened and inserting on epiphallus close to penis. Epiphallus long, slender tube, slightly narrower than penis. Flagellum short ~ 1/2 of epiphallus and terminating in slightly enlarged folded coil. Appendix short, slender tube, approximately as long as epiphallus, and ~ 2× longer than flagellum. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 5A). Internal wall of penis corrugated, exhibiting series of thickened and swollen longitudinal penial pilasters forming fringe around penial wall, and with nearly smooth to weak folds around base of penial verge. Penial verge short conical with nearly smooth surface, and with opening on the tip (Fig. 5B).

Figure 5. 

Genitalia of Amphidromus spp A–C Amphidromus ingens Möllendorff, 1900 from Ea Sup, Dak Lak, Vietnam (NMNS-8764-100), showing A general view of genitalia B interior structures of penis C interior structures of vagina chamber and gametolytic duct D–F Amphidromus asperoides sp. nov. from Ea Tu, Buon Ma Thuat city, Dak Lak, Vietnam (NMNS-8764-001), showing D general view of genitalia E interior structures of penis F interior structures of vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster

Vagina slender, long cylindrical, and ~ 3× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to slender tube terminally and connected to gametolytic sac (missing during dissecting). Free oviduct short; oviduct compact and enlarged to form lobule alveoli (Fig. 5A). Internal wall of vagina possessing corrugated ridges near genital orifice; ridges becoming thinner and smooth surfaced longitudinal vaginal pilasters, swollen with irregularly shaped and deep crenelations close to free oviduct opening. Spermatophore (in part) dark brown stuck inside gametolytic duct (Fig. 5C).

Living specimens generally with pale brown to yellowish body covered with reticulated skin. Foot broad and long with uniform pale brownish to yellowish colour to posterior tail. Dorsal side of anterior body usually with stripe of darkly reticulated skin; head area at base and just behind upper tentacle with orange patch. Upper tentacles drumstick shaped, orange to paler and with dark eyespots on tentacular tips; lower tentacles short and pale orange in colour (Fig. 6A–C).

Figure 6. 

Living Amphidromus spp A–C Amphidromus ingens Möllendorff, 1900 from Dak Lak, Vietnam D Amphidromus placostylus Möllendorff, 1900 from Hoai An, An Lao, Binh Dinh, Vietnam E, F Amphidromus ingensoides sp. nov. from Hon Ba, Khanh Son, Khanh Hoa, Vietnam G Amphidromus asperoides sp. nov. from Ea Tu, Buon Ma Thuat city, Dak Lak, Vietnam H, I Amphidromus buelowi Fruhstorfer, 1905 from Lang-Biang plateau, Lac Duong, Lam Dong, Vietnam J Amphidromus thachi Huber, 2015 from Krong Bong, Dak Lak, Vietnam.

There was a total of 12 COI haplotypes (Fig. 7A) and nine 16S haplotypes (Fig. 7B) of A. ingens in this study, and the highest numbers of mutational steps in the COI and 16S minimum spanning networks are 13 and three, respectively.

Figure 7. 

Mitochondrial haplotype minimum spanning networks of Amphidromus ingens Möllendorff, 1900 A COI and B 16S rRNA. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

The distribution range of the species covers Dak Lak and Lam Dong provinces, Vietnam.

Thach and Huber (2014) introduced A. naggsi, which is described to differ from A. ingens in its wrinkled outer surface, the presence of 2–3 broad spiral channels on the body whorl, the more prominent sculpture on the penultimate whorl, and a more elongate aperture. However, upon examining the type specimens of both A. ingens and A. naggsi, these diagnostic characters were also present in the lectotype and paralectotypes of A. ingens, and the holotype of A. naggsi agrees well with all the type specimens of A. ingens in terms of shell shape, shell surface sculpture, peristome, and apertural shape. Thus, A. naggsi is regarded herein as a junior subjective synonym of A. ingens.

The shell colour generally varies from whitish (typical) to yellowish to rose-pink colour (Fig. 3). In our examined specimens, many are stained with dark brown colour below periphery and some are stained nearly entirely on the last and penultimate whorl. The shell sculpture generally has two depression areas, one upper periphery and one below suture, and the conspicuous keel to weak keel is generally present on periphery.

Shell large conical and dextral. Shell colour with dark triangular blotches connected with dark zigzag radial streaks. Aperture ovate and rounded anteriorly, columella straight. Genitalia with appendix.

The new species differs from the similar species A. buelowi in being exclusively dextral, having a straight columella, and lacking an apertural notch and umbilical hump. In contrast, A. buelowi is chirally dimorphic, and possesses a distinct twisted columella plait, a prominent umbilical hump encircled columellar area, and an apertural notch projecting anteriorly. In addition, on the soft body of living snail, A. asperoides sp. nov. has a uniform brownish yellow to pale brown of the entire body, while A. buelowi exhibits a reddish orange body. This new species is also recognised as a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. placostylus in COI (9.83%) and A. ingens in 16S (3.02%) (Table 2).

The specific epithet asperoides is from asper, and the suffix ‘–oideus’, meaning ‘like or resembling’. This name refers to the resemblance in shell morphology of the new species to the nominal species A. asper, which is now treated as a junior synonym of A. buelowi.

Holotype. Vietnam: dextral, shell height 61.7 mm, shell width 34.9 mm, with 7 whorls, 15 July 2016, coll. A. N. Pham (NMNS-8764-001, Fig. 8A). Paratypes. Vietnam: 2D specimens, same collecting data as holotype (NMNS-8764-001–NMNS-8764-003, Fig. 8B); 1D specimen, same collecting data as holotype (NHMUK 20230613, Fig. 8C).

Figure 8. 

Shells of Amphidromus spp A–C Amphidromus asperoides sp. nov. from Ea Tu, Buon Ma Thuat city, Dak Lak, Vietnam A holotype (NMNS-8764-001) B, C paratypes (NMNS-8764-002 and NHMUK 20230613) D–F Amphidromus bozhii Wang, 2019 D, E specimens from Phu Hoa, Phu Yen, Vietnam (NMNS-8764-009, NMNS-8764-013) F specimen from Tuy Hoa, Phu Yen Vietnam (NMNS-8764-014) G–J Amphidromus ingensoides sp. nov G holotype from Cu’Mta, Mdrak, Dak Lak, Vietnam (NMNS-8764-106) H paratype from Cu’Mta, Mdrak, Dak Lak, Vietnam (NHMUK 20230614) I, J paratypes from Hon Ba, Khanh Son, Khanh Hoa, Vietnam (NMNS-8764-107, NMNS-8764-106).

Vietnam: Ea Tu village, Buon Ma Thuat city, Dak Lak Province, 12°42'24.4"N, 108°07'25.3"E.

Vietnam: 20D specimens, Krong Pak, Dak Lak Province, NMNS-8764-192–NMNS-8764-211, 6 Oct. 2022, coll. V. V. Hoang.

Shell large (height 54.6–61.7 mm, width 31.3–34.9 mm), dextral, solid, and ovate conical shape. Spire long conical with white or pale colour; apex acute without black spot on tip. Whorls 6–7 convex; suture wide and depressed; last whorl ovate. Periostracum thin corneous; varices generally present. Shell surface generally with coarse growth lines. Shell ground colour pale pink, decorated with dark triangular blotches connected with dark zigzag radial streaks. Parietal callus thickened, slightly opaque, white and much thinner in central area. Aperture ovate; without (or very weak) anterior notch and umbilical hump; inner side of outer wall whitish colour; peristome thickened, expanded, and reflexed but not attached to last whorl; lip whitish. Columella white, straight, or weakly twisted. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, with shallow notch and blunt cusp; ectocone large with curved cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth (Fig. 4B).

Genital organs. Atrium relatively short. Penis slender, conical, and short ~ 1/4 of vaginal length. Penial retractor muscle thickened, long and inserting on epiphallus near penis. Epiphallus very long ~ 2× longer than vagina, and slender tube. Flagellum short, extending from epiphallus and terminating in slightly enlarged tube. Appendix short and slender tube, 4×longer than flagellum and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 5D). Internal wall of penis corrugated, exhibiting series of thickened and swollen longitudinal penial pilasters forming fringe around penial wall, and with nearly smooth to weak folds around base of penial verge. Penial verge short conical with nearly smooth surface, and with opening on the tip (Fig. 5E).

Vagina long, slender, cylindrical, and ~ 2× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to slender tube terminally and connected to gametolytic sac (missing during dissection). Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 5D). Internal wall of vagina possessing corrugated ridges near genital orifice; ridges becoming thinner and smooth surfaced longitudinal vaginal pilasters, swollen with irregularly shaped shallow crenelations close to free oviduct opening (Fig. 5F).

Living specimens with soft body morphology generally similar to A. ingens. Animals with uniform brownish yellow to pale brown of the entire body including foot, upper and lower tentacles (Fig. 6G).

This species is known from Dak Lak Province, Vietnam.

This new species had been previously identified as A. asper in Thach (2017). However, based on the difference in shell size and apertural characteristics to the holotype of A. asper, those specimens featured in Thach (2017) should be regarded as A. asperoides sp. nov. See also under the remarks of A. buelowi.

Vietnam: 10D specimens, Phu Hoa District, Phu Yen Province, NMNS-8764-004–NMNS-8764-013 (Fig. 8D, E); 8S specimens, Tuy Hoa District, Phu Yen Province, NMNS-8764-014–NMNS-8764-021 (Fig. 8F).

Shell large conical and chirally dimorphic. Shell surface with coarse growth lines; last whorl nearly absent of spiral depression area and keel. Genitalia with appendix.

This species is similar to A. ingens in most of the shell form and sculpture. The distinguishing characters are the shell colour which is generally rose-pink to dark colour. The last whorl is stained with dark brown colour below periphery and ~ 1/2 of upper periphery. The shell sculpture has a very weak spiral depression area and sometimes with or without keel. This species looks like an intermediate form between A. ingens and A. placostylus. Amphidromus bozhii is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. placostylus in COI (9.61%) and A. ingens in 16S (2.76%) (Table 2).

Shell large (height 69.1–82.9 mm, width 38.3–42.0 mm), chirally dimorphic, solid, and ovate conical shape. Spire elongate conical with pale colour; apex acute without black spot on tip. Whorls 5–7 convex; suture wide and depressed; last whorl ovate. Periostracum brownish to thin corneous. Shell surface generally with irregular and coarse growth lines; very weak to nearly absent of spiral depression area and keel. Shell colour generally rose-pink to stained with dark brown colour below and ~ 1/2 of upper periphery. Parietal callus thickened, white, and dilated at umbilical area. Aperture broadly ovate; inner side of outer wall with yellow or pale brown colour; peristome thickened, expanded, and reflexed but not attached to last whorl; lip whitish. Columella white, straight, or little twisted. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and short-spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, with wide notch and slightly curved and dull cusp; ectocone large with truncated to blunt cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth. Outermost teeth with small and curved cusp on endocone and ectocone; mesocone large, with curved cusps (Fig. 4C).

Genital organs. Atrium very short. Penis slender, conical, and short ~ 1/2 of vaginal length. Penial retractor muscle thickened and inserting on epiphallus close to penis. Epiphallus long and slender tube. Flagellum short, extending from epiphallus and terminating in slightly enlarged tube. Appendix short, slender tube, approximately as long as flagellum, and ~ 1/3 of epiphallus length. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 9A). Internal wall of penis corrugated, exhibiting series of swollen longitudinal penial pilasters forming fringe around penial wall, and with nearly smooth to weak folds around base of penial verge. Penial verge conical with nearly smooth surface (Fig. 9B).

Figure 9. 

Genitalia of Amphidromus spp A–C Amphidromus bozhii Wang, 2019 from Tuy Hoa, Phu Yen, Vietnam (NMNS-8764-016), showing A general view of genitalia B interior structures of penis C Interior structures of vagina chamber D, E Amphidromus placostylus Möllendorff, 1900 from Dak Po, Gia Lai, Vietnam (NMNS-8764-217), showing D general view of genitalia E interior structures of penis and vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster

Vagina slender, long cylindrical, ~ 2× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to slender tube terminally and connected to gametolytic sac (missing during dissection). Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 9A). Internal wall of vagina possesses strong corrugated ridges near genital orifice, ridges become weaker corrugated vaginal pilasters, and swollen with irregularly shaped deep crenelations close to free oviduct opening (Fig. 9C).

There were seven COI haplotypes of A. bozhii in this study, and the highest number of mutational steps in the COI minimum spanning network is ten (Fig. 10).

Figure 10. 

Mitochondrial COI haplotype minimum spanning networks of Amphidromus bozhii Wang, 2019. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

This species is found in Phu Yen Province, Vietnam.

Vietnam: Dextral, lectotype of “Amphidromus placostylus”, SMF 7593 (Fig. 11A); dextral, holotype of “Amphidromus johnstanisici”, MNHN-IM-2000-33218 (Fig. 11B).

Vietnam: 4D + 1S specimens, Dak Po District, Gia Lai Province, NMNS-8764-213–NMNS-8764-217 (Fig. 11C, D); 3D + 1S specimens, Kbang, Gia Lai Province, NMNS-8764-218–NMNS-8764-221 (Fig. 11E, F); 4D + 6S specimens, Hoai An, An Lao, Binh Dinh Province, NMNS-8764-222–NMNS-8764-231 (Fig. 11G–I); 1D specimen, Binh Dinh Province, NMNS-8764-232; 7D + 14S specimens, Hoai An district, Binh Dinh Province, NMNS-8764-233–NMNS-8764-253.

Figure 11. 

Shells of Amphidromus placostylus Möllendorff, 1900 A lectotype of “Amphidromus placostylus” (SMF 7593) B holotype of “Amphidromus johnstanisici” (MNHN-IM-2000-33218) C, D specimens from Dak Po, Gia Lai, Vietnam (NMNS-8764-213, NMNS-8764-215) E, F specimens from Kbang, Gia Lai, Vietnam (NMNS-8764-219, NMNS-8764-221) G–I specimens from Hoai An, An Lao, Binh Dinh, Vietnam (NMNS-8764-222, NMNS-8764-227, NMNS-8764-231). Credit: M Caballer, MNHN (B).

Shell large and chirally dimorphic. Periostracum thick corneous with greenish brown radial streaks. Shell surface generally smooth. Genitalia with appendix.

Amphidromus placostylus is similar to A. schomburgki (Pfeiffer, 1860) in having greenish to greenish brown radial streaks on periostracum, but A. placostylus has a larger shell (height up to nearly 80 mm) with a whitish apertural lip, and A. schomburgki exhibits a relatively smaller shell (height up to 58 mm) with a purplish apertural lip. Amphidromus placostylus is also similar to A. cambojiensis (Reeve, 1860) in having a relatively large shell and ovate to elongate conical shape, but A. placostylus possesses a thick greenish periostracum, uniform whitish shell ground colour, and whitish to dark brown inner side of outer wall. In comparison, A. cambojiensis possesses a thin corneous periostracum, with irregular brown to dark brown radial streaks on the shell ground colour, and a bright purplish pink or violet colour on the inner side of outer wall. Amphidromus placostylus is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. bozhii in COI (9.61%) and A. ingens in 16S (4.23%) (Table 2).

Shell large (height 64.6–79.5 mm, width 37.4–42.4 mm), chirally dimorphic, solid, and ovate to elongate conical shape. Spire long conical with white colour; apex acute without black spot on tip. Whorls 6–7 convex; suture wide and depressed; last whorl ovate. Periostracum thick corneous or with oblique greenish to greenish brown radial streaks; varix usually absent. Shell surface generally smooth. Shell ground colour monochrome whitish or with dark brownish streaks (without periostracum). Parietal callus thickened and white. Aperture broadly ovate and inner side of outer wall with whitish to dark brown colour; peristome thickened, expanded, and reflexed but not attached to last whorl; lip whitish. Columella white, straight, or little twisted. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and trapezoid-spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, with wide notch and truncated to slightly curved cusp; ectocone large with curved to dull cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth (Fig. 12A).

Figure 12. 

SEM images of the radula A Amphidromus placostylus Möllendorff, 1900 from Dak Po, Gia Lai, Vietnam (NMNS-8764-217) B Amphidromus buelowi Fruhstorfer, 1905 from Mount Singgalang, Sepuluh Koto, Tanah Datar Regency, West Sumatra, Indonesia (NMNS-8764-024) C Amphidromus thachi Huber, 2015 from Buon Don, Dak Lak, Vietnam (NMNS-8764-271). Central teeth are marked in yellow. The left and right images show the outer and inner sections of each radula, respectively.

Genital organs. Atrium relatively short. Penis slender, conical, and short ~ 1/2 of vaginal length. Penial retractor muscle thin, long, inserting on epiphallus close to penis. Epiphallus long, slender tube. Flagellum long, extending from epiphallus and weakly coiled at its end. Appendix short, slender tube, 2× longer than flagellum, and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 9D). Internal wall of penis corrugated, exhibiting series of weak longitudinal penial pilasters nearly entire inner penis wall. Penial verge short conical, nearly smooth surface and with opening on the tip (Fig. 9E).

Vagina slender, long cylindrical, and ~ 2× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to slender tube terminally and connected to gametolytic sac (missing during dissection). Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 9D). Internal wall of vagina possessing corrugated smooth surface ridges on nearly its entire inner wall; ridges becoming thinner vaginal pilasters in middle, and with little irregular shaped and crenelations close to free oviduct opening (Fig. 9E).

Living specimens with soft body morphology generally similar to A. ingens. Animals with dark reddish body covered with reticulated skin. Foot broad and long with uniform pale brown colour at foot margin. Head with reddish colour same as body. Upper and lower tentacles with reddish to orange in colour (Fig. 6D).

The distribution range of the species covers Bac Giang, Binh Dinh and Gia Lai provinces, Vietnam.

As the original description did not explicitly designate a type or state that the description of this species was based on a single specimen (nor could this be inferred), the designation of a holotype by Zilch (1953) in fact constitutes a lectotype designation (ICZN 1999: Art. 74.6).

This species is known only from a single worn-out lectotype, and the remaining periostracum is only traceable behind the apertural lip. Later, Thach and Huber in Thach (2017) introduced A. johnstanisici, which is described to differ from A. placostylus by the presence of prominent subsutural bands, larger aperture, more voluminous body whorl with dark brown colour, and parietal wall not bordered by a black band. However, both type materials of A. johnstanisici and A. placostylus, and all the specimens examined herein, especially ones from the type locality of A. johnstanisici, possess both subsutural bands and a black band that borders the parietal wall to some extent. These specimens and the holotype of A. johnstanisici also match well with the lectotype of A. placostylus in shell and apertural shape, and the periostracum colour. Thus, A. johnstanisici is regarded herein as a junior subjective synonym of A. placostylus. The periostracum colour can vary from greenish to greenish brown in the younger adult specimens (with thinner apertural lip), while the aged adult specimens (with thicker apertural lip) tend to have yellowish brown to eroded periostracum.

This species also exhibits a prominent population genetic structure, where specimens from the same collecting locality form its own clade (Fig. 13). The COI intraspecific distance among all A. placostylus specimens is 5.47%, which is the third highest distance of all Amphidromus species in this study. This value is higher than the optimum intra/interspecific threshold value of 4% for stylommatophoran land snails (Davison et al. 2009). In addition, the 16S intraspecific distance among all A. placostylus specimens is 3.14%, which is the second highest distance of all Amphidromus species in this study. Although each clade constitutes the specimens with the same inner shell colour (Fig. 13), all specimens still have other congruent shell morphology as stated above. We thus refrain from treating each pool of samples from the same collecting locality as a distinct taxon, before more specimens from each locality are critically examined.

Figure 13. 

Bayesian phylogeny of Amphidromus placostylus Möllendorff, 1900 based on mitochondrial COI and 16S genes. Nodal support values are given as SH-aLRT/aBayes/ultra-fast bootstrap (IQ-TREE, ML)/posterior probability (MrBayes, BI). An asterisk on each branch indicates a clade with all well-supported values (SH-aLRT ≥ 80%, aBayes ≥ 0.95, BS ≥ 95%, PP ≥ 0.95).

Shell large and chirally dimorphic. Shell surface with coarse growth lines crossed by weak spiral ridges. Genitalia with appendix.

The new species differs from the closely related A. ingens and A. bozhii in having a generally rounded last whorl, and coarse growth lines crossed with weak spiral ridges. In comparison, the two latter species having a depression area below suture and prominent blunt or keeled on periphery of the last whorl, and having only irregular growth lines on the shell surface. In addition, this new species is recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. bozhii in COI (9.99%) and A. ingens in 16S (4.19%) (Table 2).

The specific epithet ingensoides is from ingens, and the suffix –oideus, meaning ‘like or resembling’. This name refers to the resemblance in shell morphology of the new species to the nominal species A. ingens.

Holotype. Vietnam: dextral, shell height 62.1 mm, shell width 36.9 mm, with 6½ whorls, 13 Dec. 2016, coll. A. N. Pham (NMNS-8764-105, Fig. 8G). Paratypes. Vietnam: 1S specimen (NHMUK 20230614, Fig. 8H) from the type locality, 19 Sep. 2016, coll. A. N. Pham; 1D + 1S specimens, Hon Ba, Khanh Son District, Khanh Hoa Province, NMNS-8764-106, NMNS-8764-107, 31 Mar. 2017, coll. A. N. Pham (Fig. 8I, J).

Vietnam: Cu’Mta ward, Mdrak District, Dak Lak Province, 12°42'22.9"N, 108°45'13.9"E.

Shell large (height 54.3–67.0 mm, width 32.8–36.8 mm), chirally dimorphic, solid, and ovate conical shape. Spire long conical to elongate conical, apex acute without black spot on tip. Whorls 5–7 convex; suture wide and depressed; last whorl well rounded to slightly angulated. Periostracum brownish to thin corneous; varix usually absent. Shell surface generally with coarse and irregular growth lines crossed by weak spiral ridges. Shell colour variable: monochrome (whitish, yellowish, tinted pink) to stained with dark brown to blackish below periphery. Parietal callus thickened and white, dilated at umbilical area. Aperture broadly ovate; inner side of outer wall with yellow or dark brown to blackish colour. Peristome thickened, expanded and reflexed but not attached to last whorl, lip whitish. Columella white, straight, or little twisted. Umbilicus imperforate.

Genital organs. Atrium relatively short. Penis slender, conical, and short ~ 1/3 of vaginal length. Penial retractor muscle thickened, short and inserting on epiphallus close to penis. Epiphallus long, slender tube, coiled and twisted upon itself. Flagellum long, extending from epiphallus and terminating in slightly enlarged folded coil. Appendix short, slender tube, ~ 2× longer than flagellum, and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 14A). Internal wall of penis corrugated, exhibiting series of prominent and swollen longitudinal penial pilasters forming fringe around penial wall, and with strong roughly surface around base of penial verge. Penial verge short conical with weak roughly surface, and with opening at the tip (Fig. 14B).

Figure 14. 

Genitalia of Amphidromus spp A–C Amphidromus ingensoides sp. nov. from Hon Ba, Khanh Son, Khanh Hoa, Vietnam (NMNS-8764-107), showing A general view of genitalia B interior structures of penis C interior structures of vagina chamber D–F Amphidromus buelowi Fruhstorfer, 1905 from Nha Trang, Khanh Hoa, Vietnam (NMNS-8764-031), showing D general view of genitalia E interior structures of penis F interior structures of vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster

Vagina slender, long cylindrical, and ~ 3× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to slender tube terminally and connected to gametolytic sac (missing during dissection). Free oviduct short; oviduct compact and enlarged to form lobule alveoli (Fig. 14A). Internal wall of vagina possessing corrugated and deep crenelated ridges on nearly its entire vagina wall; ridges slightly smooth surface near genital orifice then becoming prominent vaginal pilasters in middle and close to free oviduct opening (Fig. 14C).

Living specimens with soft body morphology generally similar to A. ingens. Animals with pale yellowish body covered with reticulated skin, anterior body usually with dark reticulated strip dorsally. Foot broad and long, and with narrow and orange colour stripe above foot margin. Head with orange patch covering tentacles. Upper and lower tentacles orange to paler in colour (Fig. 6E, F).

This species is found in Dak Lak and Khanh Hoa provinces, Vietnam.

As a small number of specimens were dissected, this new species seems to have a vagina shorter than penis + epiphallus length, while A. ingens and A. bozhii have a vagina almost as long as penis + epiphallus. In addition, A. ingensoides sp. nov. possesses a longer appendix than the geographically closer species A. ingens from M’drak District, Dak Lak Province.

Indonesia: Sinistral, lectotype of “Amphidromus buelowi”, NHMUK 1910.12.30.98 (Fig. 15A). Vietnam: Dextral, holotype of “Amphidromus asper”, SMF 7762 (Fig. 15B). Dextral, holotype of “Amphidromus franzhuberi”, MNHN-IM-2000-31892 (Fig. 15C).

Indonesia: 2D specimens, Padang Sökeli, Singalang, RBINS I.G. 10591/1–2 (Fig. 15D); 4D specimens, Mount Singgalang, Sepuluh Koto, Tanah Datar Regency, West Sumatra, NMNS-8764-022–NMNS-8764-025 (Fig. 15E).

Figure 15. 

Shells of Amphidromus buelowi Fruhstorfer, 1905 A lectotype of “Amphidromus buelowi” (NHMUK 1910.12.30.98) B holotype of “Amphidromus asper” (SMF 7762) C holotype of “Amphidromus franzhuberi” (MNHN-IM-2000-31892) D specimen from Padang Sökeli, Singalang, Indonesia (RBINS I.G. 10591) E specimen from Mount Singgalang, Sepuluh Koto, Tanah Datar Regency, West Sumatra, Indonesia (NMNS-8764-025) F specimen from Lang-Biang, Annam, Vietnam (RBINS I.G. 10591) G specimen from Lang-Biang plateau, Lac Duong, Lam Dong, Vietnam (NMNS-8764-027) H, I specimen from Nha Trang, Khanh Hoa, Vietnam (NMNS-8764-030, NMNS-8764-031). Credit: H. Taylor, NHM (A), M. Caballer, MNHN (C), RBINS (D, F).

Vietnam: 2D specimens, Lang-Biang, Annam, RBINS I.G. 10591/3–4 (Fig. 15F); 2D specimens, Lang-Biang plateau, Lac Duong District, Lam Dong Province, NMNS-8764-026, NMNS-8764-027 (Fig. 15G); 6D + 1S specimens, Nha Trang, Khanh Hoa Province, NMNS-8764-028–NMNS-8764-034 (Fig. 15H, I).

Shell large and chirally dimorphic. Shell colour with irregularly zigzag of dark radial streaks, and dark triangular blotches. Aperture elliptical ovate with more or less prominent anterior notch and umbilical hump; twisted columella plait. Genitalia with appendix.

Amphidromus buelowi differs from the similar species A. asperoides sp. nov. in having a distinct twisted columella plait, a prominent umbilical hump encircling columellar area, and an apertural notch projecting anteriorly. In contrast, A. asperoides sp. nov. possesses a straight columella, and without apertural notch and umbilical hump. In addition, on the soft body of living snail, the entire body of A. buelowi is reddish orange, while A. asperoides sp. nov. exhibits a uniform brownish yellow to pale brown body. Amphidromus buelowi is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. ingens in COI (12.23%) and A. asperoides sp. nov. and A. ingens in 16S (4.61%) (Table 2).

Shell large (height 45.3–51.1 mm, width 26.2–26.6 mm), chirally dimorphic, solid, and ovate conical. Spire conical with white or pale colour; apex acute without black spot on tip. Whorls 6–7 little convex to smooth; suture wide and shallow; last whorl well rounded to slightly elongated and with more or less prominent umbilical hump. Periostracum thin corneous; varices generally present. Shell ground colour pale yellowish, decorated with irregular zigzag of dark radial streaks, and dark triangular blotches connected with dark streaks. Parietal callus thickened, white and much thinner in central area. Aperture elliptical ovate; with more or less anterior notch; inner side of outer wall whitish colour; peristome thickened, expanded, and reflexed but not attached to last whorl; lip whitish. Columella white, straight and with distinct twisted plait. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and slightly elongate-spatulate teeth with truncated cusp. Lateral teeth bicuspid; endocone curved with wide notch and blunt cusp; ectocone large with truncated cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth. Outermost teeth with small and curved cusp on ectocone, and endocone and mesocone with curved cusps (Fig. 12B).

Genital organs. Atrium relatively short. Penis slender, conical, and nearly as long as vagina. Penial retractor muscle inserting on epiphallus close to penis. Epiphallus long, slender tube, and almost same diameter as penis. Flagellum short, extending from epiphallus and terminating in slightly enlarged folded coil. Appendix short, thin tube, 3× longer than flagellum, and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 14D). Internal wall of penis corrugated, exhibiting series of thickened and swollen longitudinal penial pilasters forming fringe around penial wall, and with weaker folds around base of penial verge. Penial verge short conical with nearly smooth surface (Fig. 14E).

Vagina slender, long cylindrical, and ~ 2× longer than penis. Gametolytic duct enlarged cylindrical tube then abruptly tapering to long, slender tube terminally, connected to elongate gametolytic sac. Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 14D). Internal wall of vagina possessing corrugated ridges near genital orifice; ridges becoming thinner and smooth longitudinal vaginal pilasters in middle, swollen with irregularly shaped deep crenelations close to free oviduct opening (Fig. 14F).

Living specimens with soft body morphology generally similar to A. ingens. Animals with reddish orange body covered with reticulated skin. Lateral of body vary from yellowish (in younger specimen) to dark reddish orange colour (older specimens). Foot broad and long with reddish orange colour near foot sole margin. Head and dorsal of anterior body with reddish orange to dark colour. Upper tentacles pale reddish orange to brownish; lower tentacles short and paler in colour (Fig. 6H, I).

There was a total of four COI haplotypes (Fig. 16A) and three 16S haplotypes (Fig. 16B) of A. buelowi in this study, and the highest numbers of mutational steps in the COI and 16S minimum spanning networks are ten and one, respectively.

Figure 16. 

Mitochondrial haplotype minimum spanning networks of Amphidromus buelowi Fruhstorfer, 1905 A COI and B 16S rRNA. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

The species has a widely disjunct distribution: one in Mount Singgalang, West Sumatra, Indonesia, and some localities in Khanh Hoa and Lam Dong provinces, South Vietnam.

This species was originally described by Fruhstorfer (1905) from four chirally dimorphic specimens from West Sumatra. Fruhstorfer (1905) also indicated that there was a similar species collected on the way to the Lang-Bian plateau, ~ 120 km inland from the coast in southern Vietnam. He sent one specimen from this locality to O.F. von Möllendorff, who did not describe or taxonomically treat this specimen any further. Later, Haas (1934), recognising that there were some differences in shell characters to A. buelowi, described this particular specimen (now deposited in SMF) as a new species, A. asper. Thach (2016) also described a similar species, A. franzhuberi from the border of Nha Trang, Vietnam, which is described to differ from A. buelowi in having a broader shell shape, more swollen body whorls, a less excavated base, a more inflated spire, a rounded anterior end of the outer lip, and monomorphic dextrality (just from four type series). However, Thach (2016) did not compare with A. asper from the nearby area. In this study, the samples from Nha Trang exhibit dimorphic chirality (the specimen lot containing both sinistral and dextral shell coiling; Fig. 15H, I), and upon examining the type specimens of A. asper and A. franzhuberi, they agree well with the type specimen of A. buelowi in having the common diagnostic traits of a distinct twisted columella plait, a prominent umbilical hump, and a distinct apertural notch. The molecular phylogeny also revealed that all specimens from Mount Singgalang, West Sumatra, Indonesia, and Lang-Biang plateau and Nha Trang, Vietnam belong to the same clade. The mutational steps between Indonesian and Vietnamese specimens are only ten and one in the COI and 16S haplotype networks, respectively (Fig. 16). Based on the phylogenetic analyses and the common morphological diagnostics, we therefore treat A. asper and A. franzhuberi as junior subjective synonyms of A. buelowi.

Bülow (1905) introduced the monotypic subgenus Goniodromus to include A. buelowi, based on a less ovate aperture with an apertural notch projecting anteriorly. Later, Laidlaw and Solem (1961), although with doubt, listed Goniodromus as one of the three subgenera of Amphidromus, and included two more species, A. asper and A. mirandus Bavay & Dautzenberg, 1912. Another species, A. thachi, also possesses an aperture with prominent anterior notch (Fig. 17). However, these three species, A. buelowi (and its synonyms A. asper and A. franzhuberi), A. thachi, and A. mirandus did not together form a clade (Fig. 2; C-TL, unpublished data), revealing that an apertural anterior notch is not a shared derived character. Thus, the subgenus Goniodromus is regarded herein as a junior subjective synonym of the subgenus Amphidromus.

Figure 17. 

Shells of Amphidromus thachi Huber, 2015 A holotype of “Amphidromus thachi” (RBINS MT.3381) B, C specimens from fin de la route de Hon Ba (chalets de Yersin), Commune de Suoi Cat, Province de Khanh Hoa, Vietnam (MNHN- IM-214-6873) D specimen from Vinh Thanh, Binh Dinh, Vietnam (NMNS-8764-267) E Specimen from Buon Don, Dak Lak, Vietnam (NMNS-8764-271) F specimen from Da Lat, Lam Dong, Vietnam (NMNS-8764-272) G, H specimens from Lac Duong, Lam Dong, Vietnam (NMNS-8764-265, NMNS-8764-264). Credit: T. Backeljau and S. Yves, RBINS (A), B. Páll-Gergely (B, C).

Vietnam: Dextral, holotype of “Amphidromus thachi”, RBINS MT.3381 (Fig. 17A).

Vietnam: 1D + 1S specimens, fin de la route de Hon Ba (chalets de Yersin), Commune de Suoi Cat, Province de Khanh Hoa, Vietnam, MNHN- IM-214-6873 (Fig. 17B, C); 1D specimen, réserve de Hon Ba, près du chalet de Yersin, Commune de Suoi Cat, Province de Khanh Hoa, Vietnam, MNHN- IM-214-6874; 3D + 1S specimens, Vinh Thanh town, Binh Dinh Province, NMNS-8764-266–NMNS-8764-269 (Fig. 17D); 1D + 1S specimens, Buon Don District, Dak Lak Province, NMNS-8764-270, NMNS-8764-271 (Fig. 17E); 1S specimen, Da Lat city, Lam Dong Province, NMNS-8764-272 (Fig. 17F); 2D specimens, Krong Bong, Dak Lak Province, NMNS-8764-273, NMNS-8764-274; 2D specimens, Lac Duong District, Lam Dong Province, NMNS-8764-264, NMNS-8764-265 (Fig. 17G, H).

Shell medium and chirally dimorphic. Aperture obliquely elliptical with prominent anterior notch; columella bending anteriorly. Parietal callus, lip and columella whitish or with dark brown. Genitalia with appendix.

Amphidromus thachi is unique compared to all Vietnamese species reported by Schileyko (2011) in having a distinct shell shape, possessing an obliquely elliptical aperture with a prominent anterior notch, a columella bending anteriorly, and whitish or dark brown parietal callus, lip and columella. This type of shell form is similar to that of Pseudopartula Pfeiffer, 1856 (Benthem Jutting 1950). Amphidromus thachi is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. asperoides sp. nov. in both COI (12.69%) and 16S (6.22%) (Table 2).

Shell medium (height 25.0–30.0 mm, width 17.0–18.5 mm), chirally dimorphic, thin to slightly thickened, and conical. Spire short conical with white or pale colouration; apex acute without black spot on tip. Whorls 6–7 little convex to smooth; suture wide and shallow; last whorl well rounded to slightly elongated and with less prominent umbilical hump. Periostracum thin corneous; varices absent. Shell colour uniform whitish to pale cream; subsutural band opaque white. Parietal callus thickened, whitish and translucent or dark to dark brown. Aperture elliptical to obliquely elliptical with prominent anterior notch; inner side of outer wall whitish; peristome thickened, slightly expanded not reflected; lip whitish or with dark to dark brown. Columella whitish or dark, shortly straight then bending anteriorly. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and spatulate with truncated cusp. Lateral teeth bicuspid; endocone slightly smaller than ectocone, curved, with wide notch and dull cusp; ectocone large with curved to dull cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth. Outermost teeth with small and curved cusp on ectocone; endocone and mesocone with curved cusps (Fig. 12C).

Genital organs. Atrium relatively short. Penis slender, conical, and short, ~ 1/2 of vaginal length. Penial retractor muscle thickened and inserting on epiphallus close to penis. Epiphallus long, slender tube, almost same diameter as penis. Flagellum short, extending from epiphallus and terminating in weakly coiled. Appendix short, slender tube, similar length with flagellum, and ~ 1/2 of epiphallus length. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 18A, B). Internal wall of penis corrugated, exhibiting series of thickened and smooth surfaced longitudinal penial pilasters forming fringe around penial wall, and with nearly smooth wall around base of penial verge. Penial verge short conical with smooth surface (Fig. 18C).

Figure 18. 

Genitalia of Amphidromus spp A–D Amphidromus thachi Huber, 2015 A general view of genitalia of specimen from Krong Bong, Dak Lak, Vietnam (NMNS-8764-274) B–D specimen from Buon Don, Dak Lak, Vietnam (NMNS-8764-271), showing B general view of genitalia C interior structures of penis D interior structures of vagina chamber E–G Amphidromus metabletus Möllendorff, 1900 from Nha Trang, Khanh Hoa, Vietnam (NMNS-8764-130), showing E general view of genitalia F interior structures of penis G interior structures of vagina chamber. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster.

Vagina slender, cylindrical, and ~ 2× longer than penis. Gametolytic organ relatively short than other congeners: gametolytic duct shorter to slightly longer than vagina, cylindrical tube, then tapering to short, slender tube terminally; gametolytic sac globular shape. Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 18A, B). Internal wall of vagina possessing smooth longitudinal ridges near genital orifice; ridges becoming stronger and corrugated vaginal pilasters with swollen, irregular shaped and deep crenelations (Fig. 18D).

Living specimens with soft body morphology generally similar to A. ingens. Animals with whitish to creamy body covered with reticulated skin. Foot broad and long with uniform whitish to creamy colouration to posterior tail. Head with whitish or sometimes with yellowish colour. Upper tentacles drumstick-shaped, greyish to brownish, with dark eyespots on tentacular tips; lower tentacles short and greyish in colour (Fig. 6J).

There was a total of six COI haplotypes (Fig. 19A) and five 16S haplotypes (Fig. 19B) of A. thachi in this study, and the highest numbers of mutational steps in the COI and 16S minimum spanning networks are 26 and eight, respectively.

Figure 19. 

Mitochondrial haplotype minimum spanning networks of Amphidromus thachi Huber, 2015 A COI and B 16S rRNA. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

The distribution range of this species covers Binh Dinh, Dak Lak, Khanh Hoa, and Lam Dong provinces, Vietnam.

This species was originally described by Huber (2015) from outskirts of Nha Trang, Vietnam. Later, Thach (2018) described another subspecies from Lac Duong, Lam Dong, Vietnam as A. thachi krisi, which was different from the nominotypical subspecies in having a totally white lip. Based on this study, the specimens having a totally white lip from Lac Duong, Lam Dong constitutes a distinct clade from the remaining specimens with totally or partially dark lip, and the mutational steps between these two morphs with different lip colours are 26 and eight in the COI and 16S haplotype networks, respectively (Fig. 19). More specimens from wider distribution range will be needed to assess the taxonomic status of these A. thachi subspecies.

Two dissected specimens were found to have different lengths of the gametolytic duct. The specimen XM2 from Krong Bong, Dak Lak, Vietnam has a shorter gametolytic duct (Fig. 18A) than the specimen VCD2 from Buon Don, Dak Lak, Vietnam (Fig. 18B).

Vietnam: Dextral, lectotype of “Amphidromus metabletus”, SMF 7583/1 (Fig. 20A); 1S paralectotype of “Amphidromus metabletus”, SMF 122346/1 (Fig. 20B); 2D + 1S paralectotypes of “Amphidromus metabletus”, SMF 122347/3 (Fig. 20C); 2D + 1S paralectotypes of “Amphidromus metabletus”, SMF 7647/3 (Fig. 20D); 1D + 1S paralectotypes of “Amphidromus metabletus”, SMF 82371/2 (Fig. 20E); 1S, paralectotype of “Amphidromus metabletus”, ANSP 81428 (Fig. 20F). Sinistral, lectotype of “Amphidromus metabletus insularis”, SMF 7585/1 (Fig. 20G). Dextral, lectotype of “Amphidromus metabletus pachychilus ” forma tritaeniata, SMF 7587/1 (Fig. 20H); 1D, paralectotype of “Amphidromus metabletus pachychilus ” forma flava, SMF 7588/1 (Fig. 20I); 1D, paralectotype of “Amphidromus metabletus pachychilus ” forma alba, SMF 122348/1 (Fig. 20J); 1S, paralectotype of “Amphidromus metabletus pachychilus ” forma trizona, SMF 122350/1 (Fig. 20K); 1S, paralectotype of “Amphidromus metabletus pachychilus ” forma interrupta, SMF 122352/1 (Fig. 20L); 1D, paralectotype of “Amphidromus metabletus pachychilus ” forma confluens, SMF 122354/1 (Fig. 21A); 1S, paralectotype of “Amphidromus metabletus pachychilus ” forma fusca, SMF 122356/1 (Fig. 21B).

Figure 20. 

Shells of Amphidromus metabletus Möllendorff, 1900 A lectotype of “Amphidromus metabletus” (SMF 7583) B–F paralectotypes of “Amphidromus metabletus” B SMF 122346 C SMF 122347 D SMF 7647 E SMF 82371 F ANSP 81428 G lectotype of “Amphidromus metabletus insularis” (SMF 7585) H lectotype of “Amphidromus metabletus pachychilus ” forma tritaeniata (SMF 7587) I paralectotype of “Amphidromus metabletus pachychilus ” forma flava (SMF 7588) J paralectotype of “Amphidromus metabletus pachychilus ” forma alba (SMF 122348) K paralectotype of “Amphidromus metabletus pachychilus ” forma trizona (SMF 122350) L paralectotype of “Amphidromus metabletus pachychilus ” forma interrupta (SMF 122352). Credit: ANSP (F).

Figure 21. 

Shells of Amphidromus metabletus Möllendorff, 1900 A paralectotype of “Amphidromus metabletus pachychilus ” forma confluens (SMF 122354) B paralectotype of “Amphidromus metabletus pachychilus ” forma fusca (SMF 122356) C–F specimens from Nha Trang, Khanh Hoa, Vietnam (NMNS-8764-123, NMNS-8764-125, NMNS-8764-127, NMNS-8764-129) G–L specimens from Ninh Hoa, Khanh Hoa, Vietnam (NMNS-8764-136, NMNS-8764-143, NMNS-8764-144, NMNS-8764-146, NMNS-8764-147, NMNS-8764-149).

Vietnam: 4D + 4S specimens, Nha Trang city, Khanh Hoa Province, NMNS-8764-123–NMNS-8764-130 (Fig. 21C–F); 15D + 4S specimens, Ninh Hoa, Khanh Hoa Province, NMNS-8764-131–NMNS-8764-149 (Fig. 21G–L).

Shell medium to large, elongate conical, and chirally dimorphic. Spire elongate conical; aperture ovate. Genitalia with appendix.

The monochromic form of the chirally dimorphic A. metabletus is similar to A. cochinchinensis (Pfeiffer, 1857) in having a monochrome whitish yellow shell, but A. cochinchinensis is distinct in having a very little expanded lip, elongate last whorl, and elliptical aperture (Sutcharit et al. 2015). The banded form is similar to the chirally dimorphic Aegistohadra dautzenbergi (Fulton, 1899), but A. metabletus has a shell ground colour varying from whitish, yellowish, to reddish brown, and the shell is without an umbilical hump, while Ae. dautzenbergi has a ground colour varying from whitish to yellowish and tinted pink, and the shell sometimes possesses an umbilical hump. Aegistohadra dautzenbergi also has a thinner shell, a more ovate last whorl with an expanded lip that is not thickened or reflected, a thin parietal callus and a straight columella, whereas A. metabletus has a thicker shell, a rounder last whorl with an expanded and usually reflected lip, a thick parietal callus and a curved columella. Moreover, the genitalia of A. metabletus lack a dart complex, while it is present in all Aegistohadra species (Jirapatrasilp et al. 2022). Amphidromus metabletus is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. ingens in COI (15.91%) and A. thachi in 16S (10.68%) (Table 2).

Shell medium to large (height 36.5–46.5 mm, width 20.9–27.2 mm), chirally dimorphic, elongate conical, rather thick and glossy. Spire elongate conical to ovate conical; apex acute, without black spot on tip, and earlier whorls whitish to tinted pink. Whorls 6–7 convex to smooth; suture wide and shallow; last whorl well rounded. Periostracum thin corneous; varix usually absent. Shell ground colour varying from whitish, yellowish to reddish brown; banding pattern variable from non-banded (monochrome colour) to narrow to wide multiple reddish brown spiral bands on whitish or yellowish ground colour. Parietal callus slightly thickened, whitish or transparent. Aperture ovate; peristome expanded and not reflected; lip whitish. Columella straight, thick or thin. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and short spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, with wide notch and blunt cusp; ectocone large with blunt cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth (Fig. 22A).

Figure 22. 

SEM images of the radula A Amphidromus metabletus Möllendorff, 1900 from Nha Trang, Khanh Hoa, Vietnam (NMNS-8764-130) B Amphidromus madelineae Thach, 2020 from Duy Xuyen, Quang Nam, Vietnam (NMNS-8764-110) C Amphidromus costifer Smith, 1893 from Ea Sup, Dak Lak, Vietnam (NMNS-8764-048). Central teeth are marked in yellow. The left and right images show the outer and inner sections of each radula, respectively.

Genital organs. Atrium relatively short. Penis slender, and short ~ ¼ of vaginal length. Penial retractor muscle thin, long and inserting on epiphallus close to penis. Epiphallus long, slender tube, and almost same diameter as penis. Flagellum short, extending from epiphallus and terminating in slightly enlarged folded coil. Appendix long, slender tube, ~ 3× longer than flagellum, and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 18E). Internal wall of penis corrugated, exhibiting series of swollen and smooth surfaced longitudinal penial pilasters forming fringe around entire penial wall. Penial verge very short conical with smooth surface (Fig. 18F).

Vagina slender, long cylindrical, and ~ 4× longer than penis. Gametolytic duct very long cylindrical tube then abruptly tapering to slender tube terminally and connected to globular gametolytic sac. Free oviduct short; oviduct compact, forming lobule alveoli (Fig. 18E). Internal wall of vagina possessing corrugated ridges with wide crenelations on its entire vagina wall; ridges becoming stronger corrugated close to free oviduct opening (Fig. 18G).

There were 12 COI haplotypes (Fig. 23A) and six 16S haplotypes (Fig. 23B) of A. metabletus in this study, and the highest numbers of mutational steps in the COI and 16S minimum spanning networks are seven and two, respectively.

Figure 23. 

Mitochondrial haplotype minimum spanning networks of Amphidromus metabletus Möllendorff, 1900 A COI and B 16S rRNA. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

This species is found in Khanh Hoa Province, Vietnam.

One species that was described earlier, A. cochinchinensis was originally described from “Cochin China”, the old geographic usage which is now interpreted as southern Vietnam, and this species was known only from the type materials (Sutcharit et al. 2015). This species is similar to A. metabletus, which is described from the same vicinity. The further inclusion of A. cochinchinensis-like specimens from southern Vietnam into the phylogenetic analyses will help clarify the taxonomic statuses of these two species.

Möllendorff (1901) introduced several subspecies and shell forms. However, these forms could not be differentiated by mtDNA (COI and 16S rRNA) and some shell morphs with different colours and patterns belong to the same mtDNA haplotype (Fig. 23).

Laos: Sinistral, lectotype of “Amphidromus haematostoma var. viridis”, SMF 7559/1 (Fig. 24A); sinistral, lectotype of “Amphidromus haematostoma var. varians”, SMF 7561/1 (Fig. 24B); sinistral, holotype of “Amphidromus attapeuensis”, NHMUK 20170278 (Fig. 24C).

Figure 24. 

Shells of Amphidromus spp A–G Amphidromus haematostoma Möllendorff, 1898 A Lectotype of “Amphidromus haematostoma var. viridis” (SMF 7559) B lectotype of “Amphidromus haematostoma var. varians” (SMF 7561) C holotype of “Amphidromus attapeuensis” (NHMUK 20170278) D specimen from Samphanh, Phongsali, Laos (NMNS-8764-056) E, F specimens from Ba Chien, Pakse, Champasak, Laos (NMNS-8764-064, NMNS-8764-076) G specimen from Kbang, Gia Lai, Vietnam (NMNS-8764-080) H–M Amphidromus madelineae Thach, 2020 H holotype of “Amphidromus madelineae” (MNHN-IM-2000-35566) I, J Specimens from Duy Xuyen, Quang Nam, Vietnam (NMNS-8764-112, NMNS-8764-108) K–M specimens from Za Hung, Dong Giang, Quang Nam, Vietnam (NMNS-8764-114, NMNS-8764-118, NMNS-8764-122).

Laos: 5S specimens, Xe Pian village, Paksong District, Champasak Province, CUMZ 10217 (Inkhavilay et al. 2019: fig. 44a); two lots in W.J.M. Maassen Collection (8S specimens and 14S specimens), Boloven Plateau, Paksong District, Champasak; 4S specimens, Samphanh District, Phongsali Province, NMNS-8764-053–NMNS-8764-056 (Fig. 24D); 20S specimens, Ba Chien, Pakse District, Champasak Province, NMNS-8764-057–NMNS-8764-076 (Fig. 24E, F).

Vietnam: 5S specimens, Kbang District, Gia Lai Province, NMNS-8764-077NMNS-8764-081 (Fig. 24G).

Shell medium and sinistral. Parietal callus, lip and columella with bright to dark rose-pink. Varix sometimes present. Genitalia without appendix.

Amphidromus haematostoma differs from the similar sinistral species A. madelineae in having a whitish apex, slightly thickened parietal callus with pale to dark rose-pink colouration, while A. madelineae has tinted pink ~ 1–2 whorls from apex, and thin transparent parietal callus. This species also differs from the similar A. roseolabiatus in that the latter has a chirally dimorphic shell, a whitish apex and the genitalia with a very long appendix. The molecular phylogeny in this study reveals that A. haematostoma is a distinct clade from its sister A. madelineae (Fig. 2). The COI and 16S p-distances between A. haematostoma and A. madelineae are 13.93% and 6.04%, respectively (Table 2).

Shell medium (height 23.8–35.4 mm, width 13.3–21.0 mm), sinistral, ovate conical, rather thin and glossy. Spire elongate conical; apex acute, without black spot on tip, and earlier whorls whitish. Whorls 6–7 convex to smooth; suture wide and depressed; last whorl well rounded. Periostracum thick corneous or with green to greenish yellow colour; varix occasionally present. Shell ground colour white or yellowish colour (without periostracum); dark yellow subsutural band and a band at around umbilicus usually present (rarely indistinguishable). Parietal callus thickened with bright to dark rose-pink colour. Aperture broadly ovate and inner side of outer wall whitish; peristome little thickened, expanded, and weakly reflexed but not attached to last whorl; lip bright to dark rose-pink colour and with little darker colour at the edge. Columella bright to dark rose-pink colour, straight, or little twisted. Umbilicus imperforate.

Genital organs. Atrium relatively short. Penis slender, conical, and short ~ 1/3 of vaginal length. Penial retractor muscle thickened, long and inserting on epiphallus close to penis. Epiphallus stout tube and approximately as long as vagina. Flagellum short, extending from epiphallus and terminating in curved tip; appendix absent. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 25A). Internal wall of penis corrugated, exhibiting prominent series of thickened and swollen longitudinal penial pilasters forming fringe around penial wall, and with fine and weak folds around base of penial verge. Penial verge very short, with smooth surface, and opening at the tip (Fig. 25B).

Figure 25. 

Genitalia of Amphidromus spp A, B Amphidromus haematostoma Möllendorff, 1898 from Ba Chien, Pakse, Champasak, Laos (NMNS-8764-061), showing A general view of genitalia B interior structures of penis and vagina chamber C, D Amphidromus madelineae Thach, 2020 from Duy Xuyen, Quang Nam, Vietnam (NMNS-8764-110), showing C general view of genitalia D interior structures of penis and vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster.

Vagina slender, long cylindrical, and ~ 2× longer than penis. Gametolytic duct cylindrical tube then gradually tapering to slender tube terminally and connected to gametolytic sac (missing during dissection). Free oviduct short; oviduct compact, forming lobule alveoli (Fig. 25A). Internal wall of vagina possessing corrugated ridges near genital orifice; ridges becoming smooth longitudinal vaginal pilasters in middle, swollen with irregularly shaped deep crenelations close to free oviduct opening (Fig. 25B).

This species has a wide distribution range covering Attapeu, Champasak, and Phongsali provinces, Laos, and Gia Lai Province, Vietnam.

A degree of shell colour variation occurs in the specimens from Pakse, Champasak, Laos (Fig. 24E, F) in having yellowish to golden-yellow periostracum, indistinct subsutural band and a dark rose-pink apertural lip. In addition, the type specimens and recently collected specimens from Kbang, Gia Lai, Vietnam (Fig. 24B, C, G) tend to have broad brownish radial bands on the earlier spire whorls.

This species also exhibits a prominent population genetic structure, where some clades constitute only the specimens from the same collecting locality (Fig. 26). The COI intraspecific distance among all A. haematostoma specimens is 10.03%, which is the highest distance of all Amphidromus species in this study. This value is higher than twice the optimum intra/interspecific threshold value of 4% for stylommatophoran land snails (Davison et al. 2009). However, as all specimens have congruent morphology as stated above, we refrain from treating each pool of samples from the same collecting locality as a distinct taxon, before more specimens from each locality are critically examined.

Figure 26. 

Bayesian phylogeny of Amphidromus haematostoma Möllendorff, 1898 and Amphidromus madelineae Thach, 2020 based on mitochondrial COI and 16S genes. Nodal support values are given as SH-aLRT/aBayes/ultra-fast bootstrap (IQ-TREE, ML)/posterior probability (MrBayes, BI). An asterisk on each branch indicates a clade with all well-supported values (SH-aLRT ≥ 80%, aBayes ≥ 0.95, BS ≥ 95%, PP ≥ 0.95).

Vietnam: Sinistral, holotype of “Amphidromus madelineae”, MNHN-IM-2000-35566 (Fig. 24H).

Vietnam: 5S specimens, Duy Xuyen District, Quang Nam Province, NMNS-8764-108–NMNS-8764-112 (Fig. 24I, J); 10S specimens, Za Hung, Dong Giang District, Quang Nam Province, NMNS-8764-113–NMNS-8764-122 (Fig. 24K–M).

Shell small to medium, sinistral; apex tinted pink to purplish pink. Parietal callus transparent; lip whitish to purplish pink; columella and inner side of outer wall around columella purplish pink. Genitalia without appendix.

Amphidromus madelineae differs from the similar sinistral species A. haematostoma in having tinted-pink colour ~ 1–2 whorls from apex, and thin and transparent parietal callus, while A. haematostoma has a whitish apex, slightly thickened parietal callus with pale to dark rose-pink colour. This species also differs from the similar A. roseolabiatus in that the latter has a chirally dimorphic shell, a whitish apex and the genitalia with a very long appendix. The molecular phylogeny in this study reveals that A. madelineae is a distinct clade from its sister A. haematostoma (Figs 2, 26). The COI and 16S p-distances between A. madelineae and A. haematostoma are 13.93% and 6.04%, respectively (Table 2).

Shell small to medium (height 27.7–38.0 mm, width 16.2–20.2 mm), sinistral, elongate to ovate conical, rather thin and glossy. Spire conical; apex acute, tinted pink to purplish pink and without black spot on tip. Whorls 5–6 nearly smooth; suture wide and shallow; last whorl rounded to nearly globose. Periostracum usually deciduous to yellowish green radial streaks, more conspicuous on last whorl and faded in earlier whorls. Last whorl with thin, dark green subsutural band, sometimes with irregular greenish spiral blotched bands below periphery; varix sometimes present. Parietal callus thin and transparent. Aperture ovate to elongate; peristome little thickened and expanded; lip generally whitish to purplish pink; inner side of outer wall whitish around columella with purplish pink colour. Columella straight, thickened and pale to dark purplish pink. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and spatulate with truncated cusp. Lateral teeth bicuspid; endocone small, slightly elongate, with wide and deep notch, and dull cusp; ectocone large with slightly blunt to dull cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth. Outermost teeth with small and multicuspid (Fig. 22B).

Genital organs. Atrium relatively short. Penis stout, cylindrical, and short, ~ 1/2 as long as vagina. Penial retractor muscle thickened, short and inserting on epiphallus close to penis. Epiphallus stout tube and approximately as long as vagina. Flagellum short, extending from epiphallus and terminating in slightly curved tip; appendix absent. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 25C). Internal wall of penis corrugated, exhibiting prominent series of thickened and smooth surfaced longitudinal penial pilasters forming fringe around penial wall. Penial verge very short and with smooth surface (Fig. 25D).

Vagina long cylindrical, and ~ 2× longer than penis. Gametolytic duct long cylindrical tube then gradually tapering to slender tube terminally and connected to bulbus gametolytic sac. Free oviduct short; oviduct compact, forming lobule alveoli (Fig. 25C). Internal wall of vagina possessing slightly corrugated ridges near genital orifice; ridges becoming roughly irregular vaginal pilasters in middle and close to free oviduct opening (Fig. 25D).

This species is found in Quang Nam Province, Vietnam.

Specimens from Za Hung, Dong Giang, Quang Nam, Vietnam (Fig. 24L, M) are superficially similar to A. haematostoma in having greenish shell colour and a purplish pink lip.

Vietnam: Dextral, lectotype of “Amphidromus costifer”, NHMUK 1893.2.26.4 (Fig. 27A); dextral, holotype of “Amphidromus costifer gemmalimae”, MNHN-IM-2000-35550 (Fig. 27B); dextral, holotype of “Amphidromus nguyenkhoai”, MNHN-IM-2000-35569 (Fig. 27C).

Vietnam: 10D specimens, Tay Son District, Binh Dinh Province, NMNS-8764-035–NMNS-8764-044 (Fig. 27D, E); 6D specimens, Ea Sup District, Dak Lak Province, NMNS-8764-045–NMNS-8764-050 (Fig. 27F, G); 2D specimens, An Lao District, Binh Dinh Province, NMNS-8764-051, NMNS-8764-052 (Fig. 27H, I).

Figure 27. 

Shells of Amphidromus costifer Smith, 1893 A lectotype of “Amphidromus costifer” (NHMUK 1893.2.26.4) B holotype of “Amphidromus costifer gemmalimae” (MNHN-IM-2000-35550) C holotype of “Amphidromus nguyenkhoai” (MNHN-IM-2000-35569) D, E specimens from Tay Son, Binh Dinh, Vietnam (NMNS-8764-035, NMNS-8764-040) F, G specimens from Ea Sup, Dak Lak, Vietnam (NMNS-8764-047, NMNS-8764-048) H, I specimens from An Lao, Binh Dinh, Vietnam (NMNS-8764-051, NMNS-8764-052). Credit: H. Taylor, NHM (A), P. Bourguignon, MNHN (B), A. Lardeur (C).

Shell large, dextral, and spire ovate conical. Shell surface with prominent irregular growth lines or prominent crests of expanded lip. Aperture broadly ovate or truncate. Genitalia with appendix.

Amphidromus costifer is unique among all reported Vietnamese species (Schileyko 2011) in having a large, dextral shell with an ovate conical spire, and the shell surface with prominent irregular growth lines or prominent crests of expanded lip. Amphidromus costifer is also recognised by a distinct clade in the molecular phylogeny (Fig. 2), with the closest p-distance to A. metabletus in COI (16.63%) and A. buelowi in 16S (13.44%) (Table 2).

Shell large (height 48.9–59.7 mm, width 27.3–34.8 mm), dextral, solid, and ovate conical shape. Spire ovate conical; apex acute without black spot on tip. Whorls 5–7 little convex; suture wide and shallow; last whorl large, rounded to slightly ovate. Periostracum brownish to thin corneous; strong varix usually absent. Shell surface: spire generally with prominent irregular growth lines or with weak radial streak; last whorl with strong irregular growth lines, coarse or with prominent radial ridges, and usually prominent crest of expanded lip present. Shell colour highly variable: spire generally uniform whitish to yellowish (pale yellowish subsutural band detectable); last whorl has no pattern but usually stained with dark to dark brown blotches, smear or radial streaks. Parietal callus thickened and white, and broadly dilated at umbilical area. Aperture broadly ovate or truncate (sometimes irregular); inner side of outer wall generally whitish to yellowish. Peristome thickened, expanded, and slightly reflexed; lip whitish. Columella white and straight. Umbilicus imperforate.

Radula. Teeth arranged in anteriorly pointed V-shaped rows. Central tooth monocuspid and spatulate with truncated cusp. Lateral teeth bicuspid; endocone slightly curved with wide notch and curved cusp; ectocone large with truncated to blunt cusp. Lateral teeth gradually transformed to asymmetric tricuspid marginal teeth. Outermost teeth with tiny ectocone; endocone and mesocone large with curved cusps (Fig. 22C).

Genital organs. Atrium relatively short. Penis enlarged, conical, and nearly 1/2 as long as vagina. Penial retractor muscle thickened and inserting on epiphallus close to penis. Epiphallus long and slender tube. Flagellum short, extending from epiphallus, approximately as long as penis, and terminating in slightly enlarged coil. Appendix short, slender tube, 3×longer than flagellum and approximately as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 28A). Internal wall of penis corrugated, exhibiting series of thickened longitudinal penial pilasters forming fringe around penial wall, and with smooth wall around base of penial verge. Penial verge short conical with thin longitudinal ridges surface, and with opening at the tip (Fig. 28B).

Figure 28. 

Genitalia of Amphidromus spp A–C Amphidromus costifer Smith, 1893 from Ea Sup, Dak Lak, Vietnam (NMNS-8764-048), showing A general view of genitalia B interior structures of penis C interior structures of vagina chamber D, E Amphidromus pankowskianus Thach, 2020 from Khammouan Province, Laos, near Minh Hoa District, Quang Binh Province, Vietnam (NMNS-8764-152), showing D general view of genitalia E interior structures of penis and vagina chamber. Red dots indicate the shape of the missing gametolytic sac. Green arrows indicate the genital openings. Abbreviations: ap, appendix; e, epiphallus; fl, flagellum; fo, free oviduct; gd, gametolytic duct; gs, gametolytic sac; ov, oviduct; p, penis; pp, penial pilaster; pr, penial retractor muscle; pv, penial verge; v, vagina; vd, vas deferens; vp, vaginal pilaster.

Vagina slender, long cylindrical, and ~ 2× longer than penis. Gametolytic duct cylindrical tube, extremely enlarged then abruptly tapering to slender tube terminally and connected to enlarged elliptical gametolytic sac. Free oviduct short; oviduct compact, enlarged to form lobule alveoli (Fig. 28A). Internal wall of vagina possessing corrugated ridges near genital orifice; ridges becoming swollen and smooth longitudinal vaginal pilasters in middle, and irregular shaped and deep crenelations close to free oviduct opening (Fig. 28C).

There was a total of seven 16S haplotypes (Fig. 29) of A. costifer in this study, and the highest numbers of mutational steps in the 16S minimum spanning networks are 18.

Figure 29. 

Mitochondrial 16S haplotype minimum spanning networks of Amphidromus costifer Smith, 1893. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

The distribution range of the species covers Binh Dinh, Dak Lak, and Gia Lai provinces, Vietnam.

As Smith (1893) did not explicitly designate a type, and stated that a total of seven specimens were examined, the indication of the holotype in Sutcharit et al. (2015) is thus incorrect. Therefore, the syntype of “Amphidromus costifer” NHMUK 1893.2.26.4 is hereby designated as the lectotype.

Our recent specimens with a monochrome whitish shell identical to the holotype of A. nguyenkhoai were found to belong to the same clade as the typical A. costifer, with 14–18 mutational steps to the other specimens in the 16S haplotype network (Fig. 29). In addition, upon examining the type specimens of A. costifer and A. nguyenkhoai, except for the shell colour, the holotype of A. nguyenkhoai agrees well with the lectotype of A. costifer in terms of shell shape, shell surface, peristome, and apertural shape. Thus, A. nguyenkhoai is regarded herein as a junior subjective synonym of A. costifer.

The subspecies A. costifer gemmalimae was described as distinct from the nominotypical subspecies in having a stouter shell shape, smoother, not well-defined and not strongly calloused parietal wall, axial ribs with regular strength, a regularly convex outer rib, a completely closed umbilicus, and a columella not widening laterally (Thach 2020a). However, these characters fall within the intraspecific variations shown in A. costifer clade. Thus, A. costifer gemmalimae is also regarded herein as a junior subjective synonym of A. costifer.

Additional shell variations, which occur in the monochrome whitish specimens from An Lao, Binh Dinh, Vietnam (Fig. 27C, H, I), are the occurrence of strongly thickened parietal callus, a thickened, multi-layered and broadly expanded apertural lip, and the shell surface much coarser with irregular growth lines and malleated pits.

The COI intraspecific distance among all A. costifer specimens is 7.84%, which is the second highest distance of all Amphidromus species in this study. This value is higher than the optimum intra/interspecific threshold value of 4% for stylommatophoran land snails (Davison et al. 2009). In addition, the 16S intraspecific distance among all A. costifer specimens is 3.39%, which is the highest distance of all Amphidromus species in this study, and the 16S haplotype network also exhibits a prominent population genetic structure (Fig. 29). However, as all specimens have congruent morphology as stated above, we refrain from treating each pool of samples from the same collecting locality as a distinct taxon, before more specimens from each locality are critically examined.

Thailand: Sinistral, lectotype of “Amphidromus roseolabiatus”, NHMUK 19601462 (Fig. 30A); 1S, paralectotype of “Amphidromus roseolabiatus”, NHMUK 19601463 (Fig. 30B).

Vietnam: Sinistral, holotype of “Amphidromus phuonglinhae”, MNHN-IM-2000-33200 (Fig. 30C).

Cambodia: 4D + 6S specimens, Kampong Siem District, Kampong Cham Province, NMNS-8764-254–NMNS-8764-263 (Fig. 30D–F).

Figure 30. 

Shells of Amphidromus spp A–F Amphidromus roseolabiatus Fulton, 1896 A lectotype of “Amphidromus roseolabiatus” (NHMUK 19601462) B paralectotype of “Amphidromus roseolabiatus” (NHMUK 19601463) C holotype of “Amphidromus phuonglinhae” (MNHN-IM-2000-33200) D–F specimens from Kampong Siem, Kampong Cham, Cambodia (NMNS-8764-254, NMNS-8764-258, NMNS-8764-260) G–L Amphidromus pankowskianus Thach, 2020 G holotype (NHMUK 20200213) H–J specimens from Lak Sao, Khamkeut, Bolikhamsai, Laos (NMNS-8764-154, NMNS-8764-170, NMNS-8764-192) K, L specimens from Khammouan Province, Laos, near Minh Hoa District, Quang Binh Province, Vietnam (NMNS-8764-150, NMNS-8764-151). Credit: M. Caballer (C), K. Webb (G).

Shell medium and chirally dimorphic. Parietal callus transparent; lip and columella purplish pink. Genitalia with appendix.

This species is very closely similar to A. pankowskianus in terms of shell morphology and colour pattern. However, this species lacks a dark radial band behind the reflected lip which is also visible in the inner side of the shell, and a dark spiral band below periphery, both of which are present in A. pankowskianus. Amphidromus roseolabiatus differs from the similar species A. madelineae and A. haematostoma in having a chirally dimorphic shell, and genitalia with a very long appendix, while both A. madelineae and A. haematostoma are exclusively sinistral, and the genitalia lacks an appendix. Amphidromus roseolabiatus also differs from both A. smithi Fulton, 1896 and A. ventrosulus Möllendorff, 1900 from Vietnam (Zilch 1953; Sutcharit et al. 2015) in having a chirally dimorphic shell, a purplish pink lip and fine green streaks. In contrast, A. smithi has a sinistral shell, a dark red to brownish lip with dark spot on the apex, and A. ventrosulus has a sinistral shell, uniform green colour, elongate spire and more depressed suture. The molecular phylogeny in this study reveals that A. roseolabiatus is a distinct clade from its sister A. pankowskianus (Fig. 2). The COI and 16S p-distances between A. roseolabiatus and A. pankowskianus are 13.02% and 6.14%, respectively (Table 2).

Shell medium (height 33.1–38.6 mm, width 19.2–21.6 mm), chirally dimorphic, elongate to ovate conical, rather thin and glossy. Spire conical; apex acute, light brown and without black spot on tip. Whorls 6–7 nearly smooth; suture wide and depressed; last whorl rounded. Periostracum usually deciduous to yellowish green radial streaks, more conspicuous on last whorl and faded in earlier whorls. Last whorl with thin, whitish subsutural band; with or without reddish brown spiral band on periphery but usually not reaching apertural lip; varix absent. Parietal callus thin and transparent. Aperture ovate to elongate; peristome expanded and not reflected; lip usually purplish pink. Columella straight, thickened, purplish pink. Umbilicus narrowly opened.

There was one COI haplotype of A. roseolabiatus in this study (Fig. 31).

Figure 31. 

Mitochondrial COI haplotype minimum spanning networks of Amphidromus roseolabiatus Fulton, 1896 and Amphidromus pankowskianus Thach, 2020. The size of each circle corresponds to the frequency of that haplotype, also shown as the number in that circle. The bars on the branches indicate the number of mutational steps between haplotypes. Specimen codes correspond to those in Table 1.

This species is found in Khammouan Province, Laos, Kampong Cham Province, Cambodia, and Quang Binh Province, Vietnam. The distribution of this species in Bolikhamxay, Laos according to Inkhavilay et al. (2017) is dubious (see below).

Inkhavilay et al. (2017) also included the white-lipped morph from Bolikhamxay, Laos in A. roseolabiatus. However, in this study we only incorporated the typical purplish pink-lipped morph in the phylogenetic analyses. Therefore, the identification of the white-lipped morph from Bolikhamxay, Laos as A. roseolabiatus or another distinct species remains to be further investigated.

Vietnam: Holotype, NHMUK 20200213 (Fig. 30G).

Laos: 2D + 1S specimens, Khammouan Province, near Minh Hoa District, Quang Binh Province, Vietnam, NMNS-8764-150–NMNS-8764-152 (Fig. 30K, L); 23D + 17S specimens, Lak Sao, Khamkeut District, Bolikhamsai Province, NMNS-8764-153–NMNS-8764-191, NMNS-8764-212 (Fig. 30H–J).

Shell medium and chirally dimorphic. Last whorl without or with narrow to spiral band on periphery. Parietal callus transparent; lip and columella pale purplish pink; dark radial band on palatal wall. Genitalia with appendix.

This species is very closely similar to A. roseolabiatus in terms of shell morphology and colour pattern. However, this species is distinct in having a dark radial band behind the reflected lip which is also visible in the inner side of the shell and sometimes with a dark spiral band below periphery. In addition, this species also differs from A. haematostoma and A. madelineae in having a chirally dimorphic shell, with dark radial bands behind the expanded lip, and the genitalia with a long flagellum. The molecular phylogeny in this study reveals that A. pankowskianus constitutes its own distinct clade which is sister to A. roseolabiatus (Fig. 2). The COI and 16S p-distances between A. pankowskianus and A. roseolabiatus are 13.02% and 6.14%, respectively (Table 2).

Shell medium (height 30.8–39.9 mm, width 17.2–19.2 mm), chirally dimorphic, elongate to ovate conical, rather thin and glossy. Spire conical; apex acute, light brown and without black spot on tip. Whorls 6–7 nearly smooth; suture wide and depressed; last whorl rounded. Periostracum usually deciduous to yellowish green radial streaks, more conspicuous on last whorl and faded in earlier whorls. Last whorl without or with narrow to wide brownish spiral band on periphery; varix absent. Parietal callus thin and transparent. Aperture ovate; peristome expanded and not reflected; lip pale purplish pink. Outer palatal wall with dark radial band just next to expanded lip (also visible on inner wall) and brownish radial band encircled umbilicus present (sometimes absent). Umbilicus narrowly opened.

Genital organs. Atrium relatively short. Penis enlarged, conical, and almost as long as vagina. Penial retractor muscle thin and inserting on epiphallus close to penis. Epiphallus thin and long slender tube, and approximately as long as penis. Flagellum short, extending from epiphallus, ~ 1/2 of penis length, and terminating in slightly enlarged coil. Appendix short, slender tube, nearly as long as epiphallus. Vas deferens slender tube passing from free oviduct and terminating at epiphallus-flagellum junction (Fig. 28D). Internal wall of penis corrugated, exhibiting series of weak longitudinal penial pilasters forming fringe around penial wall, and with smooth wall around base of penial verge. Penial verge very short conical with opening at the tip (Fig. 28E).

Vagina slender, cylindrical, and approximately as long as penis. Gametolytic duct cylindrical tube, similar diameter as vagina then tapering to slender tube terminally and connected to enlarged elliptical gametolytic sac (missing during dissection). Free oviduct short; oviduct forming lobule alveoli (Fig. 28D). Internal wall of vagina possessing smooth ridges near genital orifice; ridges becoming swollen and corrugated longitudinal vaginal pilasters in middle, and with deep crenelations close to free oviduct opening (Fig. 28E).

There was a total of five COI haplotypes of A. pankowskianus in this study, and the highest number of mutational steps in the COI minimum spanning network is two (Fig. 31).

This species is found in Bolikhamsai and Khammouan provinces, Laos, and Khanh Hoa Province, Vietnam.

Empty shells from Phong Nha National Park, Quang Binh Province, Vietnam, identified as ‘A. roseolabiatus’ in Inkhavilay et al (2017: CUMZ 7053; 2D+3S shells) possess a transparent parietal callus with a dark radial band on the palatal wall just next to the lip. This specimen lot could probably be assigned to A. pankowskianus instead. Future molecular evidence is needed to shed light on the systematic status of this population.