Clostophis koilobasis Páll-Gergely & Vermeulen, 2020

Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander, Buczkó, Krisztina & Vermeulen, Jaap J., 2020, Clostophis Benson, 1860, is not a monotypic diplommatinid but a speciose hypselostomatid (Gastropoda: Eupulmonata), with descriptions of six new species, Raffles Bulletin of Zoology 68, pp. 350-368 : 358

Clostophis koilobasis Páll-Gergely & Vermeulen , new species

( Fig. 6 )

Type material. Holotype (SH: 1.06 mm, SW: 1.22 mm) ( NHMUK 20191126 ; original inv. number: JJV 6230 ), Vietnam, Haiphong Prov., Cat Ba Isl. , NE coast, 20°49.25′N 107°03.45′E, dry limestone scree slope with low woodland, in rock crevices, leg. J.J. Vermeulen & A.J. Whitten, 01 October 1998.

Diagnosis. A low conical shell with strongly widened body whorl, very wide umbilicus, and an elevated, distorted, short parietal lamella.

Description. Shell low triangular, wider than tall, with concave sides and strongly widened last whorl. Body whorl rounded, aperture not detached. Protoconch consisting of 1.25 whorls, with very finely raised threads arranged into hardly visible, widely-spaced spiral striae. Entire shell consisting of 4.75 whorls. Teleoconch with irregular, fine growth lines and dense (body whorl) and widely-spaced (previous whorls) spiral striation. Spiral striae ca. 22 on body whorl from lateral view (the holotype was strongly corroded, therefore the spiral striae were not counted from apertural view). Umbilicus very wide, occupies almost half of the shell width. Aperture subovate, peristome very slightly expanded, not reflected. Parietal tooth elevated, strong, but short, distorted internally (oblique to the growth axis of the body whorl).

Etymology. Combination of ‘koilos’ (= hollow in Greek) and ‘basis’ (= base in Greek), referring to the wide umbilicus as well as to the concave spire.

Differential diagnosis. Clostophis incurvus , new species, which is also known from the Halong Bay area, has a taller shell with narrower umbilicus and a strong parietal tooth. Clostophis platytrochus , new species, is somewhat similar in shell shape, but has a slightly keeled body whorl, a detached terminal part of the peristome, a strongly oblique aperture, and a strong palatal tooth. Some populations of Clostophis multiformis , new species, are similar to C. koilobasis , new species, in shell shape, but that species always has a low parietal tooth and narrower umbilicus.

Figures

Fig. 6. Clostophis koilobasis Páll-Gergely & Vermeulen, new species (NHMUK 20191126, holotype). A, apertural view; B, dorsal view; C, ventral view; D, lateral view; E–F, apertural dentition; G, protoconch sculpture; H, sculpture of the ventral side; I, sculpture of body whorl (lateral side).