Metalycaeus bicarinatus Páll-Gergely & Hunyadi, 2021

Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), Zootaxa 4973 (1), pp. 1-61 : 52-53

Metalycaeus bicarinatus Páll-Gergely & Hunyadi n. sp.

Figs 39B , 40E–H

Material examined. Holotype: Thailand, Phetchaburi Province, Khao Yoi, NE side of the hill, 13°14.316’N, 99°49.493’E, 30 m a.s.l. (locality code: 2015/39), 24 Feb. 2015, A. Hunyadi leg. HNHM 104868 (D: 2.33 mm, H: 1.63 mm) . Paratype: 1 shell, same data as holotype, HA . Other Material: 4 juvenile /broken shells; same data as holotype, HA .

Etymology. This new species is named after the most remarkable conchological character, the double keel of R2.

Diagnosis. A tiny Metalycaeus species with a strongly ribbed R1, ribs narrow and elevated, short R2+R3, dense, curved R2 ribs, and an R2 with double keel, visible from lateral and ventral sides.

Differential diagnosis. Due to the peculiarly carinated R2 no other alycaeid species is similar, except for M. aries n. sp. (see above).

Description of the type series. Shell off-white, light grey, although available shells were dead collected; shell rounded in dorsal view; spire elevated, low conical; R1 body whorl rounded, R2 has distinct upper and lower keels separated by flattened zone, resulting in rectangular-shaped R2; protoconch consisting of 1.25 whorls, elevated, finely granular, last ca. quarter whorl with granules arranged into oblique striae; R1 of 1.75 whorls, with strong, narrow, elevated, equidistant ribs, areas between ribs with fine, dense spiral striae; boundary between R1 and R2 distinct because of denser R2 ribs; R2+R3 less than a quarter whorl (ca. 80˚); R2 very slightly swollen in dorsal view, and rectangular in lateral view due to upper and lower keels; R2 ribs curved toward aperture, nearly adnate, ca. 26 R2 ribs present; R2 somewhat longer than R3; R3 strongly reduced, with remnants of spiral striation and rough growth lines; R2 and R3 boundary distinct due to change in rib morphology and moderate constriction; aperture slightly oblique to shell axis; round; boundary between inner and outer peristomes barely discernible; inner peristome slightly protruding and expanded, relatively thin; outer peristome also thin, slightly expanded, not reflected; umbilicus moderately narrow, approximately one third of shell width.

Measurements. D: 2.33–2.4 mm, H: 1.63–1.87 mm.

Operculum. Unknown.

Distribution. This new species is known only from the type locality ( Fig. 5 ).

Remarks. This species is assigned to Metalycaeus even though no spiral striation has been found on the protoconch. Since all available material was dead collected, we believe that the fine shell sculpture that exists between the ribs at the end of the protoconch is probably remnants of spiral striation. Also, the protoconch of Metalycaeus aries n. sp., the conchologically most similar species is clearly spirally striated (see above).

Figures

FIGURE 5. Distribution of alycaeid species. Inverted empty triangle: Dicharax cyclostoma Páll-Gergely, n. sp., empty triangle: Chamalycaeus spiratus Páll-Gergely, n. sp., filled triangle: Metalycaeus bicarinatus Páll-Gergely & Hunyadi, n. sp., inverted filled triangles: Chamalycaeus erawan Páll-Gergely & Hunyadi n. sp., empty circles: Metalycaeus aries Páll-Gergely & Auffenberg, n. sp., filled circles: Metalycaeus heudei (Bavay & Dautzenberg, 1900) (the one in the north indicates the type locality of Alycaeus kengtungensis Godwin-Austen, 1914), square: Metalycaeus pygmachos Páll-Gergely & Hunyadi, n. sp.

FIGURE 39. Shells of Metalycaeus Pilsbry, 1900 species. A: Metalycaeus aries Páll-Gergely & Auffenberg, n. sp., holotype (UF 343786); B: Metalycaeus bicarinatus Páll-Gergely & Hunyadi, n. sp., holotype (HNHM 104868).

FIGURE 40. A–D: Metalycaeus aries Páll-Gergely &Auffenberg, n. sp., holotype (UF 343786); E–H: Metalycaeus bicarinatus Páll-Gergely & Hunyadi, n. sp., holotype (HNHM 104868).