Hungerfordia irregularis M. Yamazaki and Ueshima

Yamazaki, Midori, Yamazaki, Kazunori, Rundell, J. & Ueshima, Rei, 2015, Systematic review of diplommatinid land snails (Caenogastropoda, Diplommatinidae) endemic to the Palau Islands. (3) Description of eight new species and two new subspecies of Hungerfordia, Zootaxa 4057 (4), pp. 511-538 : 530-532

Hungerfordia irregularis M. Yamazaki and Ueshima sp. nov.

(Figs. 9, 12F)

Material examined. Holotype. A limestone outcrop, 1.5 km west of Oikull (Loc. BA7-1), Airai State, Babeldaob island, Palau. Collected by R. U. and M. Y. on Feb. 1, 2010. UMUTZ-B1093T. Paratypes. Babeldaob: same data as the holotype, 15 specimens, UMUTZ-B1093.

Diagnosis. Shell sinistral, small for Hungerfordia species, slender conical. Shell color white or reddish brown. Axial ribs on most whorls strongly developed, shortly protruded and somewhat lamellar, irregularly spaced, with or without some riblets at the interspace; interstitial riblets frequently developed between the ribs, also irregularly spaced, variable in the degrees of height and strength; ribs above the aperture always closely spaced, low. Spiral sculpture present throughout teleoconch whorls. Base convex, with a weak circum-columellar fold. Columellar tooth moderately developed. Outer peristome weakly develped at the dorsal margin of the thickened lip or not. Thickened lip developed, rather wide.

Description. Shell (Figs. 9A–D, 12F). Shell sinistral, thick, small for Hungerfordia species, slender conical, penultimate whorl widest when excluding the thickened lip; sides almost straight or slightly concave on the upper conical whorls, weakly convex on the last 2 whorls. Shell color white or reddish brown. Whorls 6.5–7, convex; last 3/4 whorls without dorsal groove, without dorsal fold; last 1/8 whorls (including the thickened lip) expanded upward, ascending onto the penultimate whorl in left lateral view. Suture impressed. Constriction located above the parietal/columellar junction of the aperture, associated with abrupt changes of the ribbing pattern, internally without palatal plica except a low and axial crest caused by the constriction, without parietal tooth. Tuba 7/8 whorls. Protoconch 1–1.25 whorls, almost smooth, weakly and finely punctated on the lower whorls. Apical septum absent. Axial ribs developed on teleoconch, distinct throughout whorls, almost straight (never folded at the peripheries of the whorls), oblique to the coiling axis; ribs on the first 1/4 whorls of the teleoconch absent; ribs on the following 1/3–1/4 whorls of initial teleoconch weak, closely spaced, very low; ribs on subsequent whorls (ribs on most whorls except above the aperture) strongly developed, distinctly (but shortly) protruded, somewhat lamellar, irregularly spaced, with or without some riblets at the interspace; interstitial riblets frequently developed between the ribs, also irregularly spaced, always somewhat lower (less protruded) than the ribs, variable in the degrees of height and strength (variable from highly protruded like the ribs to very weak and almost reduced to FIGURE 9. Hungerfordia irregularis sp. nov. (A1–7) A topotypic paratype, Loc. BA7-1, B1093a: (A7) sculptures on the penultimate and the higher 2 whorls, showing the irregularly spaced axial ribs and riblets, note that the interstitial riblets are variable in the degrees of development; (B1–5) holotype, B1093T; (C, D) topotypic paratypes, B0476b–c; (E1–2) outer surface, and (E3–4) inner surface of operculum, a topotypic paratype, B1093. Scale bars, 1mm (A–D), 0.5 mm (E). All specimens, UMUTZ-MG.

growth lines), occasionally undeveloped between some ribs; ribs above the aperture (ribs on the last 1 to last 3/4 whorls around the constriction) abruptly becoming closely spaced and low, never protruded. Spiral sculpture present on teleoconch, fine, prominent throughout whorls, sinuous in high magnification. Base rather convex, with a circum-columellar fold; circum-columellar fold weakly developed around the columella on the last 3/4 whorls, with a series of fine and short growth wrinkles in umbilical view. Umbilicus closed in adult. Aperture not protruded, tilted downward against the coiling axis in left lateral view; columellar axis within the aperture almost vertical. Columellar tooth moderately developed, emerging at the aperture, but never extended onto the inner peristome. Peristome single or double. Outer peristome weakly developed at the dorsal margin of the thickened lip or not. Inner peristome subcircular or squarish circular, moderately expanded, but less expanded at the upper palatal (=angular) side; parietal margin located below the middle level of the upper body whorl. Thickened lip developed behind the aperture, wide, expanded beyond the inner peristome at the upper palatal and columellar sides in front view, white, lacking of periostracum, with a series of fine growth lines on the outer surface, gradually narrowed toward the aperture in umbilical view; dorsal margin distinct, abruptly expanded from the preceding whorl; uppermost margin (=suture) ascending onto the penultimate whorl in left lateral view; base extended almost horizontally toward the aperture in left lateral view; palatal margin weakly protruded beyond the penultimate whorl in apical view.

Dimensions. Shell height 2.8–3.2 mm, shell diameter 1.7–2.0 mm, suture width 1.4–1.6 mm, peristome height 0.9–1.1 mm.

Operculum (Figs. 9E1–4). Operculum corneous, multispiral, circular, semi-transparent, amber-colored, thin, flat; outer surface smooth; inner surface with a low, thin, arcuate ridge near the columellar margin.

Penis. Penis absent.

Radula . Not examined.

Distribution and ecology. Endemic to Palau: Known only from a limestone outcrop near Oikull, Babeldaob island. The species inhabits limestone rocks.

Remarks. H. irregularis is distinguished from other low-ribbed Hungerfordia species by having irregularly spaced ribs and riblets, the slender shell shape, and the absence of dorsal fold and groove on the last 3/4 whorls.

Etymology. The specific name, derived from Latin irregularis , refers to the irregularly spaced ribs and riblets.