Amphidromus ingensoides Jirapatrasilp & Lee sp. nov.

Figs 6E, F, 8G-J, 14A-C

Diagnosis.

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

Differential diagnosis.

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).

Etymology.

The specific epithet Amphidromus ingensoides is from Amphidromus 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 .

Type material.

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).

Type locality.

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

Description.

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).

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).

Distribution.

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

Remarks.

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.