Dicharax notus (Godwin-Austen, 1914)

Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), Zootaxa 4973 (1), pp. 1-61 : 32-37

Dicharax notus (Godwin-Austen, 1914)

Figs 24–27

Alycaeus notus Godwin-Austen, 1914: 411 , plate 155, fig. 12.

Alycaeus (Dicharax) notus — Gude 1921: 262.

Material examined. Lectotype (hereby designated): Myanmar, Shan State, “ Fort Stedman , Burma, coll. Woodthorpe ”, NHMUK 1903.7 .1.3065.1 . Paralectotypes: 14 shells, same data as for lectotype, NHMUK 1903.7 .1.3065. Other Material: 1 shell ( Fig. 25B ), Myanmar, Mandalay State, Anesakhan, Dat Taw Gyaint Waterfall , 21°58.760’N, 96°23.116’E, 610 m a.s.l. (locality code: 2018/65), 18 Oct. 2018, A. Hunyadi leg., HNHM 104863 (D: 3.08 mm, H: 1.76 mm); 5 shells + 4 juvenile shells, same data as preceding, HA — Shan State; 15 shells + 6 strongly eroded shells, Myanmar, Mandalay State, Hopong, Sam Phu , Cave Ae-5 at ridge above village Ho Hwe , 20°41.103’N, 97°16.198’E (locality code: JG3 ), 02 Feb. 2019, J. Grego leg., JG ; 21 shells + 1 juvenile shell, Myanmar, Mandalay State, Hsihseng centre E ca. 4.5 km, left side of rd. + 1.7 km on unpaved rd., limestone rocks, 20°9.359’N, 97°17.883’E, 1140 m a.s.l. (locality code: 2018/39), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA ; 1 shell (photographed), Myanmar, Mandalay State, Hsihseng centre E ca. 6 km, right side of rd. + 400 m on unpaved rd., limestone hill, 20°7.983’N, 97°18.145’E, 1010 m a.s.l. (locality code: 2018/40), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HNHM 104864 ; 6 shells, same data as preceding, HA ; 14 shells, Myanmar, Mandalay State, Hsihseng centre E ca. 6 km, right side of rd. + 500 m on unpaved rd., limestone hill, 20°8.002’N, 97°18.024’E, 1000 m a.s.l. (locality code: 2018/41), 07 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA ; 1 shell + 1 juvenile shell, Taunggyi, hill over Aye Say Tee Pagoda, Dragon Cave , 20°47.489’N, 97°3.036’E, 1380 m a.s.l. (locality code: 2018/44), 08 Oct. 2018, A. Hunyadi, K. Okubo & J.U. Otani leg., HA ; 1 shell, Myanmar, Kayah State, Demoso, Demoso spring lake (locality code: JG109 ), 16 May 2019, J. Grego leg., JG ; 8 shells + 3 broken/eroded shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Bo Pha Gu Cave sink, 19°21.121’N, 97°3.759’E (locality code: JG10 ), 10 Feb. 2019, J. Grego leg. JG ; 33 shells + 13 juvenile shells, Myanmar, Kayah State, Demoso Distr., Han Li village, Lokalay Loku Gu Cave ( Myaug a San Cave ), 19°23.468’N, 97°01.372’E (locality code: JG11 ), 11 Feb. 2019, J. Grego leg., JG ; 1 shell, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li village , under bridge over Phruno River , 19°22.966’N, 97°02.153’E (locality code: JG100 ), 12 Dec. 2019, J. Grego leg., HNHM 104865 ; 7 shells + 6 juvenile /broken shells, same data as preceding, JG ; 26 shells + 4 juvenile /broken shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do, road towards Han Li Village , rocks above bridge over Phruno River , 19°23.011’N, 97°02.108’E (locality code: JG101 ), 12 Dec. 2019, J. Grego leg., JG ; 50 shells + 17 juvenile /broken shells, Myanmar, Kayah State, Hpruso Distr., Maw Thi Do Village, Entrance of Phruno River Cave , 19°22.744’N, 97°02.570’E (locality code: JG102 ), 12 Dec. 2019, J. Grego leg., JG ; 7 shells, Thailand, Chiang Rai Province, Doi Tung, 50 m before Wat Phra That Doi Tung , around the car park, 20°19.540’N, 99°49.987’E, 1350 m a.s.l. (locality code: 2015/17), 12 Feb. 2015, A. Hunyadi leg., HA ; 1 shell, Thailand, Chiang Rai Province, Doi Tung , 20°20.533’N, 99°50.350’E, 1320 m a.s.l., 08 May 1987, F.G. Thompson leg., UF 347139 .

Diagnosis. A variable Dicharax species with glossy shell, regularly ribbed R1, widely-spaced R2 ribs, blunt to somewhat narrow central swelling on R3, and strongly reflected outer peristome.

Description. Shell yellowish, corneous, occasionally with some reddish/pinkish colouration on initial whorls, sometimes semi-translucent; shell outline rounded in dorsal view, spire rather low, only slightly elevated, but somewhat variable, body whorl rounded; protoconch low, glossy, 1.25–1.5 whorls; R1 approximately 1.75 whorls, sculpture variable, first 1–1.25 whorl with weak growth lines or finely ribbed, gradually becoming widely-spaced, rather prominent ribs; boundary between R1 and R2 not conspicuous but discernible because R2 ribs denser than R1; R2 ribs curved toward aperture, ca. 20–22 R2 ribs present; R2 ribs relatively widely spaced or densely arranged; R2+R3 ca. quarter whorl or more (90–110˚); R2 and R3 of comparable lengths, or R2 slightly shorter; R3 beginning smooth, glossy, anterior portion (between swelling and peristome) smooth or with few ribs similar to end of R1; boundary between R2 and R3 conspicuous due to sculptural change and rather deep constriction; middle of R3 with prominent, variably shaped swelling, high convex or low rounded; aperture strongly oblique to shell axis, rounded; boundary between inner and outer peristomes barely discernible, inner peristome not protruding; outer peristome strongly thickened and reflected in all directions, even to parietal shell wall; umbilicus relatively wide, slightly less than a third of shell width.

A cross-sectional view of R2 was examined in one specimen ( Fig. 27 ): anterior crust forms significantly elevated, sometimes hollow rib, with anterior and posterior projections of comparable sizes resulting in a T-shaped cross-section; anterior crust folds over much weaker posterior crust; posterior crust thick; cross-sectional view of microtunnel is nearly round;

Measurements. D: 2.98–4.61 mm, H: 1.62–2.56 mm.

Operculum. The outer surface of the opercula of two live-collected specimens could be examined: it has a closely-coiled lamina, similar to that of Dicharax species known from Vietnam (Páll-Gergely et al. 2017), although the lamina is seemingly deciduous since only remnants were visible.

Differential diagnosis. Dicharax (?) bifrons ( Theobald, 1870) (examined material: Shan States, NHMUK 1888.12.4.956–958, 3 syntypes, Fig. 20A ) is rather dome-shaped, possesses two swellings on R3, and its outer peristome is not much reflected. Dicharax (?) woodthorpei (Godwin-Austen, 1914) (examined material: Fort Stedman, Burma, coll. Woodthorpe, NHMUK 1903.7.1.3064, 22 syntypes in two vials, Fig. 20B ) is also somewhat similar to this species in terms of general shell and aperture shape, but it has a higher spire, a less convex swelling on R2, and R2 bears no elevated ribs, but has light and dark alternating colour stripes. Dicharax politus (W.T. Blanford, 1865) (examined material: Phungdo, Arakan, coll. Blanford, NHMUK 1906.4.4.178, 3 probable syntypes, Fig. 20C ) is similar to this species in terms of general shell shape and sculpture, but differs in having a less thickened peristome, less expanded outer peristome, denser R2 ribbing, and glossier R1. See also under Dicharax omissus .

Distribution. Dicharax notus is known from the Mandalay, Shan, and Kayah states of Myanmar, and from Chiang Rai Province, Thailand ( Fig. 28 ).

Remarks. This is a variable species in terms of shell size, R1 sculpture, density of R2 ribs, and the narrow width of the R3 swelling. See Table 2 .

The Japanese Metalycaeus vinctus ( Pilsbry, 1902) and M. minatoi Páll-Gergely, 2017 are probably sister species to each other with ribbed and smooth R2s, respectively ( Páll-Gergely & Asami 2017). Dicharax notus and D. woodthorpei may present a similar situation, because they are very similar in shell shape and have geographically adjacent distributions, differing mostly in the fine morphology of the R2 ribs, indicating that the character may be the subject of rapid evolutionary changes.

Figures

FIGURE 20. Shells of Dicharax Kobelt & Möllendorff, 1900 species. A: Dicharax (?) bifrons (Theobald, 1870), syntype (NHMUK 1888.12.4.956-958); B: Dicharax (?) woodthorpei (Godwin-Austen, 1914), syntype (NHMUK 1903.7.1.3064); C: Dicharax politus (W.T. Blanford, 1865), probable syntype (NHMUK 1906.4.4.178).

FIGURE 24. Dicharax notus (Godwin-Austen, 1914), A: site 2018/40 (coll. HA); B: site JG100 (coll. JG).

FIGURE 25. Dicharax notus (Godwin-Austen, 1914). A: lectotype (NHMUK 1903.7.1.3065.1); B: site 2018/65 (HNHM 104863).

FIGURE 26. Dicharax notus (Godwin-Austen, 1914). A: UF 347139; B: site JG11 (operculum); C: site 2018/41 (operculum in situ).

FIGURE 27. Dicharax notus (Godwin-Austen, 1914). A: SEM image of the cross-section of R2; B: schematic drawing of the same image. Abbreviations: a—anterior crust; p—posterior crust; t—microtunnel.

FIGURE 28. Distribution of Dicharax omissus (Godwin-Austen, 1914) (circles) and Dicharax notus (Godwin-Austen, 1914) (triangles). Sample codes correspond with those in the list of examined material and Tables 2 and 3.