Dicharax semivivus Páll-Gergely & Aravind, 2025

Dicharax semivivus Páll-Gergely & Aravind sp. nov.

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Fig. 72

Diagnosis

A small species of Dicharax with smooth R1, having some widely-spaced ribs on the last whorl of R1, a combined R2+R3 length of ca 150 degrees, an R3 with a single, low, central swelling, and a moderately fringed peristome.

Etymology

The specific epithet ‘ semivivus ’ (‘half-alive, almost dead’) refers to the condition of the holotype, which was corroded, but was probably alive when found.

Type material examined

Holotype

INDIA – Mizoram • empty shell (D: 2.4 mm, H: 1.8 mm, Fig. 72); Blue Mountain, Lawngtlai district ; 22.727° N, 93.135° E; 1400 m a.s.l.; 27 Jan. 2019; N.A. Aravind leg.; Ar 45; NZSI LM1754 View Materials . GoogleMaps

Description

Shell small, off-white, semitranslucent; shell surface corroded but the holotype (single available specimen) was probably alive judging from the in situ presence of the operculum; shell outline slightly oval in dorsal view; spire elevated, conical; body whorl rounded; protoconch low, smooth, its boundary not visible due to corrosion consisting of 1.5 whorls; R1 of ca 1.75 whorls, corroded, nearly smooth, last whorl with widely-spaced, low ribs near suture and inside umbilicus, no ribs reach mid part of whorls; boundary between R1 and R2 conspicuous due to the sudden increase in rib density; R2 with ca 26 low ribs, spaces between the ribs are approximately the width of a single rib or narrower; R2+R3 ca 150 degrees; R3 slightly longer than R2; boundary between R2 and R3 clearly visible due to a deep constriction; R3 with a low central swelling, anterior and posterior slopes are declivous; aperture strongly oblique to shell axis, rounded with a shallow upper (parieto-palatal), a deep lower (basal) incision and a fringed palatal part; together with the upper and lower incisions, there are 5 incisions on the peristome; peristome thin overall, boundary between inner and outer peristomes conspicuous; inner peristome slightly protruding; outer peristome only slightly expanded, not reflected, undulated following the fringed inner peristome; umbilicus ca one fourth of shell width, nearly rounded.

OPERCULUM. The outer side is smooth, inner side could not be examined.

MEASUREMENTS. D: 2.4 mm, H: 1.8 mm.

Distribution

Known only from the Blue Mountain region.

Differential diagnosis

The most similar species is Dicharax nitidus ( Fig. 55), but it is larger, and has a longer R3, with a more posteriorly-situated swelling. Dicharax jaintiacus ( Fig. 32) is larger, has a higher spire and a narrower umbilicus, a more strongly expanded outer peristome and a more strongly fringed aperture.