Gyliotrachela khmeriana Sutcharit and Panha, 2023

Sutcharit, Chirasak, Ngor, Peng Bun, Páll-Gergely, Barna, Jeratthitikul, Ekgachai, Siriwut, Warut, Srisonchai, Ruttapon, Ng, Ting Hui, Jirapatrasilp, Parin & Panha, Somsak, 2023, Notes on the hypselostomatid snails (Gastropoda: Heterobranchia) from limestone hills in Western Cambodia with a new record and a new species, Journal of Natural History 57 (25 - 28), pp. 1287-1303 : 1287-1303

Gyliotrachela khmeriana Sutcharit and Panha , sp. n.

http://www.zoobank.org/urn:lsid:zoobank.org:act:58A3E65E-0289-48D2-ABD5-

D52762D0E754

( Figures 1 , 4 ; Table 1 )

Type material

Holotype CUMZ 14206 /1 (height 3.1 mm, width 3.4 mm, and 5 whorls; Figure 4 (a, b)), paratype CUMZ 14206 /2 (1 shell; height 3.2 mm, width 3.4 mm, and 5 whorls; Figure 4 (c)).

Type locality

The limestone hills at Phnom Sampeov Mountain, Banan District, Battambang Province, Cambodia (13.026000°N, 103.101011°E) .

Etymology

The specific name ̍ khmeriana ′ refers to the most numerous ethnic groups of Cambodia; a Latin feminine adjective.

Diagnosis

Shell minute heliciform, and slightly short and straight tuba. Protoconch sculptures with shallow pits and spiral striations; teleoconch without spiral striation. Apertural dentition with six lamellae (parietal, angular, upper and lower palatals, basal, and columellar).

Description

Shell heliciform, last whorl large, straight tuba, and spire conical. Shell colour brownish, 3.1 mm in length, 3.4 mm in width, and with five whorls. Protoconch about two whorls, sculptured with roundish shallow pits, and thin spiral striations present. Teleoconch with irregularly or wrinkled arranged on strong or weak growth lines. Spire raised, whorls slightly angular, resulting in a scalariform shape of the upper whorls; suture wide and impressed. Last whorl angular and short tuba projecting anteriorly. Only wide and shallow columellar furrow present and extended to onset of tuba. Outer outline of peristome rounded, aperture triangular due to the well-developed sinulus and the angled parietocolumellar and columellar-basal junctions; peristome free with broadly expanded lip margins. Apertural dentition with six prominent lamellae: angular, parietal, upper and lower palatals, columellar (sometime very tiny), and basal. Parietal (p) lamella very tall and situated deep inside on parietal wall. Angular (a) lamella relatively small and situated anteriorly close to expanded lip. Palatal wall with tall and strong upper (upl) and lower palatal (lpl) lamellae. Basal (b) lamella small, knob shaped and located between lower palatal plica and the columellar lamella. Columella lamella strong and prominent. All apertural dentition with smooth surfaces. Umbilicus wide and deep.

Distribution

Gyliotrachela khmeriana sp. nov. is known only from the type locality ( Figure 1 ). The snails were found on a limestone wall outside the cave, occurring sympatrically also perhaps syntopically with G. torticollis and Georissa sp. However, G. khmeriana sp. nov. was found in lower abundances than the others, and only two specimens were collected.

Differential diagnosis

This new species differs from all other known hypselostomatids from Cambodia in having slightly angular whorl, short and straight tuba, strong angular lamella, last whorl angular, protoconch with rounded pits, and spiral striations. In contrast, H. cambodjense has an elevated spire and a shouldered last whorl, is without angular lamella, and has an infraparietal plica; A. informis Vermeulen et al., 2007 from Vietnam possesses a rounded last whorl, spiral striations on teleoconch, and adnate peristome, is without angular lamella, and has upper palatal and basal lamellae that are sometimes absent ( Benthem Jutting 1962; Vermeulen et al. 2007). This new species also differs from H. rupestre Benthem Jutting, 1962 and H. dilatatum Benthem Jutting, 1962 from Vietnam, both of which possess a rounded last whorl, elongate conical spire, interpalatal and infrapalatal plicae, and a robust supracolumella, and are without angular lamella ( Benthem Jutting 1962).

In addition, two congeners, G. tarutao ( Panha and Burch, 2002) and G. khaochakan Panha and Burch in Burch et al. (2003) from Thailand, also differ from this new species. In comparison, G. tarutao has a very short tuba, elongated conical spire, umbilical furrow extended to an expanded lip, and infraparietal and subcolumellar plicae present, while G. khaochakan possesses an elongated conical spire, spiral striations present on the entirety of the shell, the last whorl shouldered, and an infrapalatal plica present ( Panha and Burch 2002; Burch et al. 2003).

Remarks

The type locality, Phnom Sampeau, is located about 13 km west of Battambang town on road no. 57 leading to Pailin Province. The mountain is of karstic limestone with limestone forest and is surrounded by villages, plantation areas and paddy fields. Conspicuous human disturbance includes the presence of a temple with complex tourist attractions, such as a bat cave and a memorial commemorating the grisly history of the caves during the previous civil war, and small-scale limestone quarries around the foot of the hills.

The difference between the genera Gyliotrachela and Paraboysidia Pilsbry, 1917 [= Bensonella Pilsbry and Vanatta, 1900 ; see Páll-Gergely and White (2023)] lies in the detached aperture in the former and the adnate aperture in the latter. However, as Pilsbry (1917) already suspected, there is a nearly perfect morphological continuum between the two extremes, and Gyliotrachela khmeriana sp. nov. can also be considered an intermediate character state. This new species is similar to some Paraboysidia species from the Malaysian Peninsula, mostly in terms of the arrangement of the apertural barriers. The most similar species is probably Paraboysidia serpa Benthem Jutting, 1950 , which also has a keel on its body whorl. However, the new species has a more strongly detached aperture, and more keeled upper whorls.

Figures

Figure 1. Distribution map of all hypselostomatids known from Cambodia. The small black dots indicate the approximate type locality for 1. Acinolaemus carcharodon, 2. Acinolaemus pyramidalis, 3. Acinolaemus rectus, 4. Anauchen chaunosalpinx, 5. Anauchen depressus, 6. Aulacospira conica, 7. Aulacospira furtiva, 8. Gyliotrachela khmeriana sp. nov., 9. Gyliotrachela torticollis, 10. Hypselostoma benetuitum, 11. Hypselostoma cambodjense, 12. Hypselostoma discobasis, and 13. Hypselostoma srakeoensis. The approximate location of limestone areas in Cambodia (Sisophon-Battambang, Stung Treng, and Kampot areas) is modified from Mouret (2004). Asterisks (*) indicate new localities recorded in this study.

Figure 4. Gyliotrachela khmeriana sp. nov. (a, b) Holotype CUMZ 14206/1 from Phnom Sampov, Battambang, (a) shell with apertural dentition arrangement, and (b) protoconch sculpture. (c) Paratype CUMZ 14206/2 from the type locality with apertural dentition (very reduced basal lamella). Abbreviations: a = angular lamella, b = basal lamella, c = columellar lamella, lpl = lower palatal lamella, p = parietal lamella, upl = upper palatal lamella.