Alycaeus eydouxi Venmans, 1956

Páll-Gergely, Barna, 2023, Revision of the Alycaeidae of China, Laos and Vietnam (Gastropoda: Cyclophoroidea) II: The genera Alycaeus and Pincerna, Zootaxa 5249 (2), pp. 253-276 : 254-257

Alycaeus eydouxi Venmans, 1956

( Figs 1E–H , 2B, E , 3A, B )

Cyclostoma gibbum Eydoux, 1838: 6 , pl. 117, fig 1.

Alycaeus (Alycaeus) gibbus — Kobelt, 1902: 344–345.

Alycaeus (Orthalycaeus) gibbus —Godwin-Austen, 1914 (in 1882–1920): 427, pl. 156, figs 5, 5a.

Alycaeus eydouxi Venmans, 1956: 87 , figs 6–7 (radula).

Alycaeus eydouxi — Egorov, 2013: fig. 58a; Páll-Gergely et al., 2017: 9: fig. 3A; Páll-Gergely et al., 2020: 30 figs 2A, 6A, 8.

Type material. Not investigated.

Additional material examined. VIETNAM: Annam, Touranne, leg. Fruhstorfer, coll. Möllendorff, SMF 109290 /5 ( Fig. 1E–H ); Da Nang, Marble Mountain , collected by the NHM 2008 Vietnam Expedition, collection code: V142 , 26 May 2008, NHMUK (several specimens in ethanol, Fig. 2B, E , 3A, B ) .

Diagnosis. A very large alycaeid species with dominant last whorl (shell width larger than shell height) smooth protoconch, finely reticulated R1, densely ribbed, very long R2, and a long R3 with low swelling.

Description. Shell yellowish corneous to pink or orange (some specimens are pure white, possibly albinistic specimens); wider than high, overall shell conical with a strongly bulging last whorl; protoconch consists of 1.75 whorls, superficially smooth, matte, but higher magnification (approx. 50X) reveals some very fine radial and reticulated sculpture on the last quarter whorl of protoconch, especially near the suture; R1 consists of 2.25–2.5 whorls, it is very much bulging, whorls separated with deep suture; R1 with weak, rather irregular radial ribs and somewhat weaker spiral striation resulting in a fine reticulated surface; R2 and R3 of approximately half whorl combined, they are roughly of the same length; R2 strongly inflated, with dense, lamella-like, straight and sharp ribs; tube situated deep inside suture; constriction between R2 and R3 short but deep; R3 with a hardly visible, very low swelling just anterior to the constriction; aperture rounded, outer peristome very much expanded but not (or very slightly) reflected, inner peristome slightly protruding; the boundary between inner and outer lips hardly visible; umbilicus open, shows only penultimate whorl.

Measurements (in mm). D = 10.2–12.1, H = 8.8–10.1 (NHMUK, coll. no. V87).

Operculum. Thin, corneous, concave; the inner surface with a low, blunt central nipple; outer side nearly smooth, without elevated lamina, multispiral.

Variation in specimens. There is no notable conchological variability within this species.

Differential diagnosis. See under A. goliath n. sp.

Distribution. Many specimens are labelled as being collected from “ Cochinchina ”. All samples from more exact localities were collected from the vicinity of Da Nang (= Touranne).

Habe (1965) reports the species under the name “ Dioryx gibbus (Reeve) ” from “Kao Phlong, north or Sara Buri, Central Thailand ”, without an accompanying image. This record almost certainly represents another species.

Figures

FIGURE 1. Shells of Alycaeus Baird, 1850 species.A–D: Alycaeus goliath n. sp. (holotype); E–H: Alycaeus eydouxi Venmans, 1956 (SMF 109290); I–S: Alycaeus rolfbrandti Maassen, 2006. I–L: SMF 262540 = part of the original sample, M: 25L07, N: 2019/95 (syntopic with A. goliath n. sp.); O: 7L07, P: 6L07, Q: 9L07, R: 11L07, S: 12L07. All photos: B. Páll-Gergely.

FIGURE 2. Protoconch (A–C) and R2 ribs (D–F) of Alycaeus Baird, 1850 species.A and D: Alycaeus goliath n. sp. (holotype); B and E: Alycaeus eydouxi Venmans, 1956 (Cochinchina, coll. V.W. MaAndrew, NHMUK); C and F: Alycaeus rolfbrandti Maassen, 2006 (6L07p). All photos: B. Páll-Gergely. Scales represent 1 mm.

FIGURE 3. Opercula of Alycaeus Baird, 1850 and Pincerna Preston, 1907 species. A–B: Alycaeus eydouxi Venmans, 1956 (V142, NHM); C–D: Pincerna mouhoti L. Pfeiffer, 1862 (Cuc Phuong NP, VNMN); E–G: Pincerna mouhoti, MNHN-IM-2012- 27302; H–I: Pincerna vanbuensis (Bavay & Dautzenberg, 1900) (2012/60). Scales represent 1 mm.