Amphidromus placostylus Moellendorff , 1900

Jirapatrasilp, Parin, Huang, Chih-Wei, Sutcharit, Chirasak & Lee, Chi-Tse, 2024, The arboreal snail genus Amphidromus Albers, 1850 (Eupulmonata, Camaenidae) of Southeast Asia: 1. Molecular systematics of some Vietnamese species and related species from Cambodia, Indonesia, and Laos, ZooKeys 1196, pp. 15-78 : 15

Amphidromus placostylus Moellendorff, 1900

Figs 6D , 9D, E , 11 , 12A , 13

Amphidromus placostylus Möllendorff, 1900a: 132. Type locality: Phuc-son [Phuc Son Commune, Tan Yen District, Bac Giang Province, Vietnam]. Pilsbry 1900: 178. Fischer and Dautzenberg 1904: 406. Laidlaw and Solem 1961: 529, 649-650. Richardson 1985: 38. Schileyko 2011: 51. Sutcharit et al. 2021: fig. 1f.

Amphidromus Amphidromus (Amphidromus) placostylus . Zilch 1953: 138, pl. 25, fig. 41.

Amphidromus johnstanisici Thach & Huber in Thach, 2017: 41, pl. 53, figs 657-663. Type locality: Kbang District, Gia Lai Province, Central Vietnam. Thach 2021: 65. syn. nov.

Material examined.

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

Other material examined.

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 .

Diagnosis.

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

Differential diagnosis.

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 ).

Description.

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 ).

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 ).

Distribution.

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

Remarks.

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.

Figures

Figure 2. Bayesian phylogeny of Amphidromus spp. based on mitochondrial COI and 16 S 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). Species numbers correspond to those in Fig. 1 and Tables 1, 2.

Figure 6. Living Amphidromus spp A-C Amphidromus ingens Moellendorff, 1900 from Dak Lak, Vietnam D Amphidromus placostylus Moellendorff, 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.

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 Moellendorff, 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

Figure 11. Shells of Amphidromus placostylus Moellendorff, 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).

Figure 12. SEM images of the radula A Amphidromus placostylus Moellendorff, 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.

Figure 13. Bayesian phylogeny of Amphidromus placostylus Moellendorff, 1900 based on mitochondrial COI and 16 S 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).