Alycaeus goliath Páll-Gergely, 2023

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 : 257-258

Alycaeus goliath Páll-Gergely n. sp.

( Figs 1A–D , 2A, D )

Type material. Holotype: (SH: 11.4 mm, SW: 13.9 mm), LAOS: South-Central Laos, Khammouan Province, ca. 37 km ENE of Thakhek ( Muang Khammouan), ca. 4.5 km WNW of Mahaxay, on and under rocks in dry secondary forest, under a cliff facing east, limestone, clay, black soil in limestone pockets, cave deposits, alt. 150 m, 17°25.956′N, 105°09.669′E (locality code: 3L07), leg. Abdou, A. & Muratov, I. V., 25 November 2007 ( MNHN-IM-2012-27319 , Figs 1A–E , 2A, D ) . Paratypes: Same data as for holotype, MNHN-IM-2012-27318 (3 complete shells + 8 broken shells) ; Khammouan Province, 40 km from the centre of Thakhek, Mahaxay, 2.3 km southeast from Ban Na Coc , limestone wall, 155 m a.s.l., 17°25.957′N, 105°09.669′E (locality code: 2019/95), leg. A. Hunyadi, 27 September 2019, HA/1 .

Additional material examined: Same data as for holotype, some shell fragments, MNHN-IM-2012-27318 .

Etymology. The name goliath (to be used as a noun in apposition) refers to the remarkably large size of the new species.

Diagnosis. An exceptionally large alycaeid species with dominant last whorl (shell width larger than shell height), smooth protoconch, finely reticulated R1, very long R2 having ribs that form many connections with each other by calcareous projections, long R3 with low swelling, and a protruding inner peristome.

Description. Shell exceptionally large, pinkish, conical with wide last whorl; shell wider than high; protoconch consists of ca. 2 whorls, it is nearly smooth, with only indication of extremely fine ribs on the last quarter whorl; R1 consists of ca. 3 whorls; whorls bulging; sculpture of R1 dominated by weak, dense, rather irregular radial ribs and much weaker spiral striation; R2 and R3 slightly longer than half whorl combined; R2 slightly longer than R3; R2 with sharp, dense ribs, which form many connections with each other by calcareous projections, resulting in a web-like surface continuous between tube and umbilicus; tube situated deep in suture, its surface is very rough, irregularly segmented, although internally probably continuous; constriction between R2 and R3 deep but short; blunt, low swelling on R3 situated just after constriction; aperture rounded with slight upper incision; outer peristome strongly expanded and slightly reflected, inner peristome strong, sharp, protruding, clearly separated from the outer peristome, especially in the palatal region; outer peristome attached to penultimate whorl, but inner peristome does not; peristome whitish, inner side of aperture orange in colour; umbilicus open, shows all whorls.

Operculum. Unknown.

Measurements (in mm). D = 13.8–15.2, H = 11.1–12.0 (n = 5).

Variation in specimens. There are no notable conchological differences between the examined specimens.

Differential diagnosis. Alycaeus goliath n. sp. differs from A. eydouxi by the larger size, the more protruding inner peristome, the comparatively less bulging R2, and most importantly, the R2 ribs which form connections with their neighbours, resulting in a web-like structure. Alycaeus rolfbrandti Maassen, 2006 differs from the new species by the smaller shell size and the irregularly ribbed, squamous protoconch. Although most known populations of A. rolfbrandti have keeled shells, three examined samples have a rounded edge of the body whorl. Therefore, although this is a useful shell character, this not sufficient to distinguish the two species. The Alycaeus rolfbrandti population occurring syntopically with A. goliath n. sp. has rounded body whorl ( Fig. 1N ).

Distribution. This species is known from the type locality only, where it lives together with A. rolfbrandti ( Fig. 4 ).

Remarks. This is the largest species of the family, followed by Stomacosmethis christae ( Maassen, 2006) .

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 4. Distribution of Alycaeus Baird, 1850 species in central Laos. Yellow circles: Alycaeus rolfbrandti Maassen, 2006; Red triangle: A. goliath n. sp. The map was made using Google Earth Pro.