Hypselostoma srakeoensis ( Panha and Burch, 2004 )

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

Hypselostoma srakeoensis ( Panha and Burch, 2004)

( Figures 1 , 2 ; Table 1 )

Anauchen srakeoensis Panha and Burch in Panha et al. 2004: 62, 63, fig. 4. Type locality: Plubpluengtong limestone hills, Srakeo Province. Panha and Burch 2005: 52, 53, fig. 48.

Material examined

Holotype CUMZ Ver44037 from Plubpluengtong limestone hills, Srakeo Province (13.448781°N, 102.217914°E); paratypes CUMZ Ver 44038 (9 shells; Figure 2 (a)). THAILAND: CUMZ 14201 (77 shells) from Wat Tham Khao Chan, Phra Phloeng , Khao Chakan District , Sa Kaeo Province (13.578111°N, 102.091972°E). CAMBODIA: CUMZ 14202 (35 shells; Figure 2 (b, c)) from Prasat Phnom Korngva (Thammaban Khiri Temple), Serei Saophoan (Sisophon), Banteay Meanchey Province (13.633056°N, 102.943472°E). CUMZ 14203 (2 shells) from Kirirom Phnombak Temple , Serei Saophoan (Sisophon), Banteay Meanchey Province (13.592056°N, 102.933333°E).

Diagnosis

Shell depressed heliciform, and long and descending tuba. Protoconch sculptured with only shallow pits. Spiral striations absent. Apertural dentition with four major lamellae (parietal, upper and lower palatals, and columellar), and numerous plicae. All lamellae and plicae spinose.

Description

Shell depressed heliciform, last whorl enlarged with descending tuba, and spire elevated conical. Shell colour brownish, 3.2–3.4 mm in length, 3.1–3.2 mm in width, and with 4–4½ whorls. Protoconch about two whorls and sculptured with roundish and shallow pits. Teleoconch sculptured with malleations or wrinkles arranged on strong or weak growth lines. Spire raised, whorl rounded and evenly sloped, and impressed suture. Last whorl shouldered, flattened periphery, and long tuba projecting downward. Two wide and shallow furrows present: one on upper periphery and one surrounding umbilicus and extended to expanded lip. Aperture irregularly circular; peristome free with broadly expanded lip margins. Apertural dentition with four prominent lamellae including parietal, upper and lower palatals, and columellar. Parietal (p) lamella very tall, with lower portion anteriorly, and situated anteriorly located to peristome. Palatal wall with strong upper (upl) and lower palatal (lpl) lamellae, two small suprapalatal plicae, one small and one tiny interpalatal plicae, and five tiny infrapalatal plicae. Columella area with strong columellar (c) lamella, two tiny subcolumellar plicae, and two small supracolumellar plicae. All apertural dentition (lamellae and plicae) with small spines along approximately central line of lamellae. Umbilicus very wide and showing nearly all preceding whorls.

Distribution

Currently, this species is known from Srakeo Province, Thailand ( Panha and Burch 2005), and the limestone outcrops in Serei Saophoan District, Banteay Meanchey Province, Cambodia ( Figure 1 ).

Differential diagnosis

This species differs from all known congeners from southern Cambodia in having a depressed heliciform shell, enlarged and truncated last whorl, and long and descending tuba. In contrast, H. benetuitum , H. cambodjense and H. discobasis have turret heliciform shells, a shouldered last whorl, and a short and straight tuba. From a conchological point of view, A. chaunosalpinx Vermeulen et al., 2019 possesses a long tuba with an irregular parietal lamella but was classified in Anauchen ( Vermeulen et al. 2019b) . Hypselostoma srakeoensis differs by having a more descending tuba, without spiral striation and a shouldered last whorl, and is without hook-shaped lamellae. In comparison, A. chaunosalpinx tends to have a turret spire, slightly descending tuba, spiral striations, angular last whorl, and a hook shape of the upper and lower palatal lamellae.

Remarks

This species was originally placed under the genus Anauchen Pilsbry, 1917 (type species = Boysidia gereti Bavay and Dautzenberg, 1904 , junior synonym of Hypselostoma rochebruni Mabille, 1887 , see Páll-Gergely (2023); Figure 5 (a)), which is characterised by having adnate tuba and without angular lamella ( Pilsbry 1917; Schileyko 1998; Panha and Burch 2005). However, this species tends to have a long and descending tuba, and parietal lamella with lower portion anteriorly that may indicate that it is a composite of angular and parietal lamellae, while the last whorl bears upper periphery and umbilical furrows. Therefore, in the meantime, we formally reclassify this species into the genus Hypselostoma , which is a more appropriate genus than Anauchen .

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 2. Hypselostoma srakeoensis. (a) Paratype CUMZ Ver44038 with apertural dentition. (b, c) specimen CUMZ 14202 from Serei Saophoan, Banteay Meanchey, (b) shell and apertural dentition, and (c) protoconch sculpture. Abbreviations: c = columellar lamella, lpl = lower palatal lamella, p = parietal lamella, upl = upper palatal lamella.

Figure 5. Comparative shell (tuba) and apertural dentition among the three genera based on the respective type species. (a) Anauchen Pilsbry, 1917 (syntype MNHN-IM-2000-35,161 of Boysidia gereti; Bavay and Dautzenberg, 1904). (b) Gyliotrachela Tomlin, 1930 (lectotype SMF 4587/1 of Hypselostoma hungerfordianum Möllendorff, 1891). (c) Hypselostoma Benson, 1856 (syntype NHMUK 1954.6.2.568 of Tanystoma tubiferum Benson, 1856; after Preece et al. 2022: fig. 70d). Abbreviations: a = angular lamella, p = parietal lamella.