Petraeomastus gigas Chen, Dai, Wu and Ouyang, 2024

Chen, Zhong-Guang, Zhou, Yi, Dai, Yu-Ting, Wu, Xiao-Ping & Ouyang, Shan, 2024, A review of three taxonomically confused species of Petraeomastus Möllendorff, 1901 (Gastropoda: Stylommatophora: Enidae) from the Jinshajiang River Valley, with the description of a new species, Journal of Natural History 59 (1 - 4), pp. 11-28 : 23-26

Petraeomastus gigas Chen, Dai, Wu and Ouyang sp. n.

ZooBank identifier urn:lsid:zoobank.org:act:2E719AB5-2A75-4B46-BE00-45F0F1372CE4

( Figures 4 (F), 7(A), 8)

Type material

Holotype. ZMNH2409001 , Langdaquka [朗达曲卡], Batang County [巴塘县], Ganzi Tibetan Autonomous Prefecture [甘孜藏族自治州], Sichuan Province [四川省], China, 99.041°E, 29.871°N, collected by Zhong-Guang Chen, Meng-Hua Li and Jin-Sheng Mou, 17 August 2023 .

Paratypes. n = 2, NCUMB2409001–02 , other information same as holotype ; n = 10, ZMNH2409002 –11, 1 km west of Jinshajiang River Bridge [金沙江大桥以西 1 km], Mangkang County [芒康县], Changdu City [昌都市], Xizang Autonomous Region [西藏 自治区], China, 99.000°E, 29.761°NN, collected by Zhong-Guang Chen, Meng-Hua Li and Jin-Sheng Mou, 16 August 2023 .

Diagnosis

Shell large, height 30.1–40.3 mm, dextral, width 11.8–13.0 mm. Post-nuclear teleoconch reddish brown with irregular white stripes; apex region reddish brown; umbilicus slit-like. Penial caecum present, subglobular. Bursa copulatrix ovoid, with stalk, well defined. Penial and appendicular retractor short. Habitat on shrubs.

Description

Shell. ( Figure 7 (A)) n = 13. Shell cylindrical-conic to conic, with apex abruptly pointed; shell most swollen at body whorl, dextral, large, thick, solid, opaque, sub-glossy, speckled, not spirally grooved; 7.5–8.5 whorls. Whorls rather flattened, not shouldered. Protoconch smooth, polished. Post-nuclear teleoconch smooth. Growth lines distinct. Suture shallow, without narrow band beneath it. Body whorl gradually ascending towards aperture, rounded at periphery. Aperture wavy, truncate-ovate, oblique, without tooth, with angular tubercle, completely adnate to body whorl. Peristome nearly connected, with a wide channel at middle insertion; white, thickened, expanded, not reflexed. Parietal callus distinct. Columellar margin reflexed. Umbilicus slit-shaped. Shell multicoloured, post-nuclear teleoconch with reddish brown background and irregular white stripes; apex region reddish brown.

Genitalia. ( Figure 8 ) n = 5. Vas deferens short, slightly tapering distally; entering epiphallus apically with distinct demarcation. Epiphallus long; cylindrical; straight; externally smooth. Epiphallic caecum present; blunt apically; located near vas deferens entrance. Flagellum short; triangular; proximally expanded; with tip pointed. Penis with terminal entrance of epiphallus; clavate; distally tapering. Penial caecum present, subglobular. Penial appendix long; branched off from penis at some distance from atrium; divided into sections including A-1 + A-2, A-3 and A-4 + A-5. A-1 and A-2 fused. A-2 and A-3 not fused. Boundary between A-4 and A-5 indistinct. A-5 long; convoluted. Appendicular retractor and penial retractor short; biramous; attaching to penis proximally and to A-1 + A-2 of penial appendix; with penial retractor arms arising from diaphragm closed to each other. Additional retractor other than penial or appendicular absent. Muscular band connecting vagina and epiphallus absent. Atrium short; without retractor. Free oviduct longer than vagina. Vagina short; swollen; curved; unpigmented. Bursa copulatrix duct long; proximally straight. Bursa copulatrix ovoid, with stalk; without apical ligament; normal in size; with long neck; well defined. Diverticle normally present; longer than bursa copulatrix; unexpanded. Bursa copulatrix and diverticle distinguishable; forked more distally from their base.

Measurements

Holotype: shell height 40.3 mm, width 13.0 mm; aperture height 13.5 mm, width 9.9 mm. Paratypes: n = 12. shell height 30.1–39.4 mm, width 11.8–13.0 mm; aperture height 12.7–13.2 mm, width 8.7–9.4 mm.

Etymology

The specific name is the Latin ‘ gigas ’ for giant, alluding to the large size of this species compared to its congeners. It is a Latin noun in apposition.

Vernacular name

巨鸟唇螺 (Pinyin: jù niǎo chún luó).

Distribution and ecology

Petraeomastus gigas sp. n. is distributed in Mangkang County and Batang County on both banks of the Jinshajiang River ( Figure 1 (D)). It inhabits shrubs and hibernates at the base of the shrub ( Figure 4 (F)). Juveniles are not covered in mud.

Remarks

Currently, the generic diagnostic characters of Chinese Enidae are mainly based on shell morphology ( Wu 2018). Although some studies have indicated that there may be slight differences in the genitalia between genera ( Wu 2018), it is challenging to summarise these differences as a universal diagnostic character for a genus. The placement of this new species within Petraeomastus is supported by its shell morphology – shell cylindrical-conic to conic – which is very similar to that of P. heudeanus ( Figure 7 (B)), the type species of the genus. It is the largest enid species in China (height 30.1–40.3 mm vs <33.0 mm), and can be easily distinguished from all congeners by its shell size, teleoconch with reddish brown background, irregular white stripes, and slit-shaped umbilicus.

Figures

Figure 1. Distribution of four enid gastropod species reviewed or described in this study. Coloured or shadowed regions show the distributional range. (A) Petraeomastus neumayri; (B) Petraeomastus desgodinsi; (C) Petraeomastus markamensis; (D) Petraeomastus gigas sp. n.; (E–F) The location of the research region in China. ① 1 km west of Jinshajiang River Bridge, ② Chaxue Village, ③ southern Batang County, ④ Langdaquka.

Figure 4. Adjacent environment and habitat of living individuals of Petraeomastus land snails. (A&B) Environment of the Jinshajiang River Valley, left side: Batang County, right side: Mangkang County; (C) living specimens of P. neumayri; (D) living specimens of P. desgodinsi; (E) living specimens of P. markamensis; (F) living specimens of Petraeomastus gigas sp. n. and P. markamensis.

Figure 7. Petraeomastus gigas sp. n. and its similar congener, P. heudeanus. (A) Petraeomastus gigas sp. n., holotype, ZMNH2409001; (B) P. heudeanus, 24_NCU_XPWU_AN144.

Figure 8. Genital anatomy of Petraeomastus gigas sp. n. (A) aperture view; (B) back view. A-1: most proximal section of penial appendix; A-2: penial appendix section between and thicker than A-1 and A-3, usually bulb-shaped; A-3:section of the penial appendix connecting proximally A-2 and distally A-4; A-4: thinnest part of the penial appendix between A-5 and A-3; A-5: distal part of the penial appendix, more or less swollen; AR: retractor muscle of the appendicular branch; At: atrium; BC: bursa copulatrix; BCD: bursa copulatrix duct;D: diverticle of the bursa copulatrix duct; Ep: epiphallus;EpC: epiphallic caecum;Fl: flagellum; FO: free oviduct; P: penis; PC: penial caecum; PR: retractor muscle of the penial branch; Va: vagina; VD: vas deferens.