Hungerfordia goniobasis exserta 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 : 512-514

Hungerfordia goniobasis exserta M. Yamazaki and Ueshima subsp. nov.

(Figs. 1, 12G)

Materials examined. Holotype. 0.1 km north of Ngeruleomel beach (Uo8-5), Ulong island, Palau. Collected by R. U. and M. Y. on Feb. 27, 2011. UMUTZ-MG-B1242T. Paratypes. Ulong: same data as holotype, 15 specimens, UMUTZ-MG-B1242.

Diagnosis. Shell similar to other subspecies of H. goniobasis , but differs in the following features. Inner peristome strongly protruded from the outer peristome. Interspace between the inner and outer peristomes wide. Outer peristome widely expanded, distinctly expanded from the basal keel at the baso-columellar edge. Basal keel short, weaker, located close to the columella. Distribution endemic to Ulong islands.

Description. Shell (Figs. 1A–C, 12G). Shell sinistral, small for Hungerfordia species, slender conical, penultimate whorl widest (slightly wider than the last whorl) when removing the protruded ribs. Shell color usually white, rarely reddish brown. Whorls 7–7.5, almost regularly coiled (increasing almost regularly in both width and height), rather convex; last 1/8 whorls never ascending onto the penultimate whorl in left lateral view. Suture impressed. Constriction located above the parietal/columellar junction of the aperture, associated with prominent changes of the ribbing density and height of the spiny ribs, internally without palatal plica except a low axial-crest caused by the constriction. Tuba 7/8 whorls. Apical septum absent. Protoconch 1–1+1/8 whorls, almost smooth, very weakly and very finely punctated in high magnification. Axial ribs developed on the teleoconch, oblique to the coiling axis, strongly and highly protruded as spines on most whorls; ribs undeveloped on the first 1/3–1/2 whorls of the teleoconch; ribs on the following 1/8 whorls of initial teleoconch rather low, moderately spaced, almost straight (not folded at the peripheries of the whorls); ribs on the subsequent whorls (except above the aperture) very strong, highly protruded as spines, very widely spaced (8–11 ribs in a whorl), not synchronized with those on the previous whorls, somewhat folded at the peripheries of the whorls (hardly folded on the upper whorls, but becoming strongly folded on the lower whorls), elevated by axial protrusions of shell wall along the ribs; upper margin of the ribs above the spiny projection (between the suture and the spines) low, slightly flared; spiny projections of the ribs highly protruded, weakly pointed, folded, trough-shaped, weakly curved upward, protruded slightly upward on the upper whorls, becoming gradually protruded laterally or rather downward on the last whorl, rather narrow, arising at some distance below the suture (near the peripheries of the whorls), upper margin folded over the lower margin, lower margin gradually reduced in height and extended below to the suture of the next whorl, with fine spiral sculptures on the outer surface; ribs above the aperture (ribs on the last 1 to last 3/4 whorls around the constriction) abruptly becoming moderately spaced (more closely spaced than those on the preceding and following whorls), with distinctly shorter spiny projections than those on the upper whorls, but still retaining developed spiny projections, less folded than those on the upper whorls. Interspace between the spiny ribs with characteristic growth wrinkles; growth wrinkles strongly developed below the suture on the last 3–4 whorls, coarse, shortly but distinctly protruded, somewhat lamellar, short, disappearing above the peripheries of the whorls. Spiral sculpture present on teleoconch, prominent throughout whorls, fine, extended onto the outer surface of the spiny ribs and the outer peristome, sinuous in high magnification. Base not convex, with a characteristic basal keel. Basal keel developed at the base of the last 5/8 whorls, rather sharply edged, leaving a shallow and narrow “pseudo-umbilicus” in front and oblique umbilical views, shorter and weaker than other subspecies of H. goniobasis , located very close to (developed just around) the columella in umbilical view, arising at a short distance after the constriction, connected to the outer peristome, but is not fused with the outer peristome like other subspecies of H. goniobasis , with a series of fine growth lines at the columellar side, extended beyond the inner peristome (at the columellar side) in front view. Umbilicus closed in adult. Axial protrusions of shell wall (along the ribs) strongly developed on the last 3/4 whorls. Aperture of usual size, tilted downward against the coiling axis, located below the base of the upper body whorl, slightly protruded from the previous whorl, strongly protruded from the outer peristome; columellar axis within aperture almost vertical. Columellar tooth weakly developed, low, located near the base of the columella, visible within the aperture, but never extended onto the inner peristome.

Peristome double. Outer peristome strongly developed, widely expanded beyond the inner peristome in front view, independent of the basal keel (not fused with the basal keel as other subspecies of H. goniobasis ), distinctly expanded from the basal keel at the baso-columellar edge in oblique umbilical view, abruptly expanded from the preceding whorl, with a series of fine growth lines on the inner surface, with fine spiral sculptures on the outer surface. Inner peristome squarish circular, strongly protruded from the outer peristome, weakly expanded at the basal and columellar sides, hardly expanded at the parietal and upper palatal sides; parietal margin almost straight, located below the base of the upper body whorl, slightly protruded downward from the previous whorl. Interspace between the outer and inner peristomes wide, with a series of fine riblets or growth lines.

FIGURE 1. Hungerfordia goniobasis exserta subsp. nov. (A1–9) A topotypic paratype, Loc. Uo8-5, B1242a: (A9) sculpture on the penultimate whorl; (B1–6) holotype, B1242T; (C) reddish color variant, a topotypic paratype, B1242b; (D1–2) outer surface, and (D3–4) inner surface of operculum, a topotypic paratype, B1242c. Scale bars, 1mm (A1–8, B, C), 0.5 mm (A9, D). All specimens, UMUTZ-MG.

Dimensions. Shell height 2.9–3.1 mm, diameter 1.9–2.0 mm, suture width 1.1 mm, peristome height 0.7–0.8 mm.

Operculum (Figs. 1D1–4). Operculum corneous, multispiral, circular, transparent, amber colored, thin, rather flat; outer surface smooth; inner surface with a low, arcuate ridge near the columellar margin.

Penis. Penis absent.

Radula . Not examined.

Distribution and ecology. Endemic to Palau: Ulong islands. The subspecies inhabits limestone rocks.

Remarks. H. goniobasis exserta is easily distinguished from other subspecies of H. goniobasis in the following points: the inner peristome is strongly protruded from the outer peristome, never recessed inside the outer peristome; the interspace between the inner and outer peristomes is wide, with a series of fine growth lines or riblets on its surface; the basal keel is weaker, shorter, less sharply edged, and located close to the columella; the outer peristome is distinctly expanded beyond the basal keel at the baso-columellar edge, not completely merged with the basal keel like other subspecies; the distribution of this subspecies is endemic to Ulong islands.

Etymology. The subspecific name, derived from Latin exsertus, refers to the aperture which is strongly protruded from the outer peristome.