Acinolaemus ptychochilus Thompson & Upatham, 1997

Tongkerd, Piyoros, Janjai, Teerangkul, Pholyotha, Arthit, Gojšina, Vukašin, Panha, Somsak & Sutcharit, Chirasak, 2025, The microsnail genera Clostophis and Acinolaemus (Eupulmonata, Pupilloidea, Hypselostomatidae) from central Thailand, with description of three new species, ZooKeys 1258, pp. 35-71 : 35-71

Acinolaemus ptychochilus Thompson & Upatham, 1997

Figs 8 , 9 , Table 4

Acinolaemus ptychochilus Thompson & Upatham, 1997: 225, 226, figs 7–11. Type locality: Ban Prang Ma-O, Doi Pha San Sao (Mountain), Chiang Mae [= Chiang Mai] Province, Thailand.

Acinolaemus ptychochilus — Schileyko 1998: 255, fig. 316.

Type material examined.

Holotype. Thailand • height 1.5 mm, width 1.3 mm (Fig. 8 ); Doi Pha San Sao , Ban Prang Ma-O, Chiang Mai Province; F. G. Thompson leg.; UF 113502 .

Other material.

Thailand • 4 shells (Fig. 9 ); limestone near Chai Prakan Highway Division (~ 43 km to Chieng Dao District) , Chai Prakan District, Chiang Mai Province; S. Panha leg.; CUMZ 15360 .

Diagnosis.

Shell concave-conical, peristome weakly expanded. Apertural dentitions eleven or more, long and reaching peristome edge in form of prominent knobs: three on parietal wall, palatal tubercle, four on palatal wall, one basal, and two on columellar wall.

Re-description.

Shell conical, with concave sides, colourless; spire low to high and growing regularly; last whorl expanded. Shell height 1.3–1.4 mm and shell width 1.4–1.5 mm. Apex blunt; protoconch ~ 1 ½ – 2 whorls, with narrow and fine spiral striae. Whorls ~ 4–5, rounded and convex; suture wide, well impressed, and deep. Shell surface sculptured with equidistantly spaced spiral striae, crossed with irregular radial growth lines making a rectangular reticulated sculpture throughout shell. Penultimate whorl regularly coiled; last whorl rounded. Aperture subovate; peristome thickened, slightly expanded and with weak depression on parietal side. Aperture with approx. ten or eleven dentitions and with strong knobs reaching peristome edge. Parietal wall with three lamellae: parietal lamella large, outer part low, inner part long with tall ridge and located deeper inside aperture; infraparietal lamella long and low; angular lamella long, consisting of two peaks of prominent tall ridges which are interrupted by a low wide ridge. Palatal tubercle rectangular, situated at peristome edge and continuous with upper palatal plica. Three tiny low plicae present (not reaching peristome edge) in sinulus. Palatal wall with four plicae: upper-, inter-, lower-, and infra-palatal plicae connecting peristome edge with prominent tubercles, then continuing with narrow, low ridge, and becoming a stronger fold deep inside aperture. Folding of inter- and lower-palatal plicae larger than upper- and infra-palatal plicae. Infrapalatal plica hooked (in holotype). Basal plica a low ridge and similar to infrapalatal plica. Columellar wall with three or four lamellae: columellar lamella strong, distinct, and tall ridge; supracolumellar and one or two subcolumellar lamellae present as low ridges. Umbilicus widely perforated, ~ ⅓ of shell width, rounded and deep.

Distribution.

Acinolaemus ptychochilus is known from the type locality in Chiang Dao District, Chiang Mai Province in northern Thailand ( Thompson and Upatham 1997).

Remarks.

The specimens from Chai Prakan District, which is ca 30 km north of the type locality, have only faint protoconch and teleoconch sculptures due to shell weathering. However, the original sculpture remains near the suture and around the umbilical area. These specimens differ slightly from the holotype (Fig. 8 A ) in having a slightly more depressed shell, a less expanded last whorl, infrapalatal plica that is not hooked (hooked in the type), and two subcolumellar lamellae (one in the type); however, the remaining apertural dentitions are identical to those in the holotype.

Figures

Figure 8. Acinolaemus ptychochilus from Chiang Mai Province. A. Holotype UF 113502 with enlarged aperture from three different angles; B. Inset of hooked infrapalatal plica; C. Protoconch and earlier whorl sculptures. An asterisk (*) indicates small lamella and plica situated in posterior chamber. Photo credit: B. Páll-Gergely.

Figure 9. Acinolaemus ptychochilus from Chiang Mai Province. A. Specimen CUMZ 15360 with enlarged aperture from three different angles; B. Protoconch and earlier whorl sculptures. An asterisk (*) indicates small lamella and plica situated in posterior chamber.