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.