Amphidromus costifer Smith, 1893

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

publication ID	https://dx.doi.org/10.3897/zookeys.1196.112146
publication LSID	lsid:zoobank.org:pub:7954DFBF-803A-48F5-B791-42DD09FE5D01
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scientific name	Amphidromus costifer Smith, 1893
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Treatment

Amphidromus costifer Smith, 1893 View in CoL

Figs 22C View Figure 22 , 27 View Figure 27 , 28A-C View Figure 28 , 29 View Figure 29

Amphidromus costifer Smith, 1893: 12, text fig. Type locality: dans les Montagnes boitées du Huyen de Tri-phuoc, Province Binh-dinh, An-nam [in the Huyen Mountains of Tri-phuoc, Binh-dinh Province, An-nam]. Fulton 1896: 91, pl. 7, fig. 6, 6a. Möllendorff 1898: 75. Pilsbry 1900: 176-177, pl. 59, figs 22, 23. Fischer and Dautzenberg 1904: 405. Laidlaw and Solem 1961: 590, 592, 613, fig. 40a, b. Schileyko 2011: 50. Sutcharit et al. 2015: 65, fig. 6c. Thach 2020a: pl. 46, figs 560, 561.

Amphidromus costifer gemmalimae Thach, 2020a: 55, pl. 45, figs 551-557. Type locality: Krong Nang, Dak Lak Province, Central Vietnam. Thach 2021: 58. syn. nov.

Amphidromus nguyenkhoai Thach, 2020a: 71, pl. 64, figs 776-784. Type locality: Krong Pa District, Gia Lai, Central Vietnam. Thach 2021: 71. syn. nov.

Material examined.

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

Other material examined.

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

Diagnosis.

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.

Differential diagnosis.

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 View Figure 2 ), with the closest p -distance to A. metabletus in COI (16.63%) and A. buelowi in 16S (13.44%) (Table 2 View Table 2 ).

Description.

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 View Figure 22 ).

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 View Figure 28 ). 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 View Figure 28 ).

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 View Figure 28 ). 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 View Figure 28 ).

Haplotype network.

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

Distribution.

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

Remarks.

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 View Figure 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 View Figure 27 ), 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 View Figure 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.