Hemiplecta nemorosa, Sutcharit & Panha, 2021

Sutcharit, Chirasak & Panha, Somsak, 2021, Systematic review of the dextral Hemiplecta Albers, 1850 (Eupulmonata, Ariophantidae) from Thailand with description of a new species and list of all the Indochinese species, ZooKeys 1047, pp. 101-154 : 101

Hemiplecta nemorosa sp. nov.

Figures 8 , 9 , 10J

Etymology.

The species name is derived from the Latin word " nemoris " meaning "full of woods or shady," which refers to the type locality of this new species in the dense deciduous forest.

Type specimen.

Holotype CUMZ 5251 (height 24.6 mm, width 42.1 mm; Fig. 8A ), paratypes CUMZ 5252 (2 shells; Fig. 8B ), CUMZ 5253 (1 adult + 1 juvenile in ethanol; Fig. 8C ) all from the type locality.

Type locality.

Limestone outcrops with deciduous forest near road no. 1226, Pang Mapha Sub-district, Pang Mapha District, Mae Hongson Province, Thailand (19°34'10.2"N, 98°12'02.3"E).

Description.

Shell medium sized (height up to 15 mm, width up to 45 mm), depressed conic, thin and dextral. Whorls 5 to 6, increasing regularly, slightly convex, with very wide and shallow suture. Spire convex; apex acute; embryonic shell smooth; following whorls with thin growth lines and radial wrinkles or undulating surfaces. Periostracum thin and transparent. Shell pale brownish to yellowish. Last whorl angular with strong peripheral keel which is much reduced near aperture. Aperture not descending, widely ovate and moderately oblique; lip simple to slightly thickened in adult specimen. Columella slightly dilated; parietal callus slightly thick and translucent. Umbilicus narrowly opened, deep, and partly covered by reflected columellar lip (Fig. 8 ).

Genitalia. Atrium (at) long. Penis (p) long slender, cylindrical, and encircled by thick penial sheath (psh) extending to about half of penis length. Epiphallic caecum (ec) short, straight; penial retractor muscle (pr) thin and attached to the tip. Epiphallus (e) short, about half of penis length. Flagellum (fl) short, stout, and with thin muscle bands connected to penial sheath. Vas deferens (vd) small tube (Fig. 9A ). Internal wall of penis with sculpture over entire chamber with uniform scale-like or triangular lingulate pilasters varying in size from small to large and pilasters encircling penial verge smaller than in the middle of chamber. Penial verge (pv) small, conic, and with smooth surface (Fig. 9B ).

Vagina (v) long, cylindrical, about same length as penis; internal wall with thin and smooth longitudinal vaginal pilasters (vp). Dart apparatus (da) short and enlarged muscular cylinder; externally covered with thin longitudinal muscular bands around half of dart apparatus length. Internally with irregular wall, dart papilla (dp) conic and smooth. Gametolytic sac (gs) bulbous without distinct duct. Free oviduct (fo) long and encircled with thin blackish muscular tissue. Oviduct (ov) long and with lobules; prostate gland bound to oviduct. Albumen gland, hermaphroditic duct, and hermaphroditic gland missing from the examined specimen (Fig. 9A, B ).

Radula. Teeth arranged in wide angled U-shape. Each row containing more than 135 teeth (+58-(16-19)-1-(16-19)-75). Central tooth symmetrical tricuspid and triangular; mesocone conic shaped and with pointed cusp; ectocones short with dull cusps located at middle of tooth height. Lateral teeth asymmetrical tricuspid; endocone nearly absent; mesocone triangular with pointed cusp; ectocone with pointed cusps and located below endocone. Marginal teeth start around tooth numbers 16 to 19, elongate and obliquely bicuspid; endocone larger than ectocone and with pointed cusp; ectocone very small. Outer marginal teeth bicuspid and shorter than inner teeth (Fig. 10J ).

Distribution.

This new species is currently known only from the type locality in northern Thailand.

Remarks.

The shell morphology of this new species is similar to H. uter (Theobald, 1859) from Myanmar and Falsiplecta integripedia Schileyko & Semenyuk, 2018 from southern Vietnam. This new species, however, differs by having a shell width almost two-times larger than H. uter , but further comparison of anatomical characters is necessary to confirm their distinction. Hemiplecta nemorosa sp. nov. clearly differs from F. integripedia in having a well-developed dart apparatus, globular gametolytic sac, and long epiphallus and flagellum. In contrast, F. integripedia has no dart apparatus, a long gametolytic duct, a very short epiphallus and the vas deferens attached near the tip of the epiphallus (flagellum lacking). Hemiplecta nemorosa sp. nov. also differs from H. undosa (Blanford, 1865) by having a relatively smaller shell size, an angular last whorl with strong peripheral keel, and a narrow umbilicus. In contrast, H. undosa has a rounded to slightly shouldered last whorl, and a wide and deep umbilicus.

Figures

Figure 8. Hemiplecta nemorosa sp. nov. from Maehongsorn, Thailand A holotype CUMZ 5251 B paratypes CUMZ 5252, and C paratype CUMZ 5253 from the type locality.

Figure 9. Genitalia, mantle edge structure, and caudal region of Hemiplecta nemorosa sp. nov., paratype CUMZ 5253 from Maehongsorn, Thailand A whole genital organ and B internal wall sculpture of penis, vagina and dart chamber.

Figure 10. Representative SEM images of radula A-C Hemiplecta humphreysiana, specimen CUMZ 4573 from Singapore A central and lateral teeth B transition from lateral teeth to marginal teeth and C outermost marginal teeth D, E Hemiplecta distincta, specimen CUMZ 4560 from Chanthaburi, Thailand D central and lateral teeth and E outermost marginal teeth F, G Hemiplecta funerea, specimen CUMZ 4575 from Nan, Thailand F central and lateral teeth and G outermost marginal teeth H, I Hemiplecta esculenta, specimen CUMZ 4553 from Chiang Mai, Thailand H central and lateral teeth I transition from lateral teeth to marginal teeth J Hemiplecta nemorosa sp. nov., paratype CUMZ 5253 from Maehongsorn, Thailand. Central tooth indicated by ' C'. Numbers indicate the tooth order from lateral to marginal end.