Hungerfordia spiroperculata 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 : 517-520

Hungerfordia spiroperculata M. Yamazaki and Ueshima sp. nov.

(Figs. 3, 4, 12M)

Materials examined. Holotype. West of Bkulsechuul island, Ulong islands (Loc. Uo7-2), Palau. Collected by R. U. and M. Y. on Jan. 27, 2010. UMUTZ-MG-B0942T. Paratypes. Ulong: Loc. Uo7-2, 4 specimens, 27/I/2010, UMUTZ-MG-B0942; ditto, 42 specimens, 25/II/2011, UMUTZ-MG-B1146; Loc. Uo8-3, 1 specimen, 25/II/2011, UMUTZ-MG-B1168; ditto, 16 specimens, 27/II/2011, UMUTZ-MG-B1223.

Diagnosis. Shell sinistral, medium-sized for Hungerfordia species, slender fusiform, with spiny projections. Shell color yellowish brown. Constriction located above the aperture, followed by an abrupt whorl swelling (= ventral protrusion), which is sharply edged along a rib in umbilical view. Tuba 3/4 whorls, with coarse granular projections on the inner surface. Axial ribs very strongly developed, strongly folded and highly protruded as spines at the periphery of whorls, rather widely spaced, absent or greatly reduced above the aperture, but developed again on the last 3/4 whorls; spiny projection of the ribs very long, slender, almost tubular, with an opened and blunt terminus, white. Interspace between the spiny ribs smooth. Apical septum present. Spiral sculpture almost absent on teleoconch whorls, but faintly developed only on outer surface of the spiny projections. Aperture squarish circular, with a canal-like depression at the baso-columellar edge. Columellar tooth weakly developed, hidden by the columellar lip in front view. Peristome double. Outer peristome expanded, obtusely angulate at the palatal side. Inner peristome narrower than the outer peristome, with a prominent baso-palatal lip, with a short columellar lip just after the columellar tooth. Interspace between the inner and outer peristomes very narrow. Operculum distinctive, unusually shaped for Hungerfordia species; outer side elevated, with a strong spiral fringe; inner side with a strong arcuate ridge.

Description. Shell (Figs. 3A–E, 12M). Shell sinistral, medium-sized for Hungerfordia species, slender fusiform, penultimate whorl widest when removing the protruded ribs and peristomes. Shell color yellowish brown, apical whorls above the apical septum always uncolored. Whorls 6–7.5, somewhat convex, obtusely angulate at the periphery of the penultimate whorl; last 1/8 whorls (including the outer and inner peristomes) weakly expanded both upward and downward, weakly ascending onto the penultimate whorl in left lateral view. Suture impressed. Constriction located above the parietal/columellar junction of the aperture, followed by an abrupt whorl swelling (= ventral protrusion), associated with abrupt disappearance or reduction of the spiny ribs, internally without palatal plica except for a low axial-crest caused by the constriction. Tuba 7/8 whorls, with coarse granular projections on the inner surface. Protoconch 1–1+1/4 whorls, almost smooth, very weakly and very finely punctated on lower whorl. Apical septum present, constructed inside at 1+1/8–1.5 whorls after the protoconch/ teleoconch boundary. Axial ribs developed on teleoconch, strongly protruded as tubular spines on most whorls; ribs on the first 1/8 whorls of teleoconch hardly developed; ribs on the following 0–1/4 whorls of the initial teleoconch low, moderately spaced, only slightly protruded, almost straight (not folded); ribs on the subsequent whorls except above the aperture (ribs on most whorls) strong, highly protruded as tubular spines, rather widely spaced (14–19 ribs in a whorl), not synchronized with those on previous whorls, strongly curled and folded at the peripheries of the whorls; upper margin of the ribs above the tubular spines (between the suture and spines) very low, never elevated nor protruded (attached to the basal wall), indistinct, hardly visible; lower margin below the spines (between the spines and the suture of the next whorl) also very low, very weakly elevated or faintly flared, but never protruded; spiny projections on the ribs almost tubular, with a blunt and opened terminus, with a narrow longitudinal slit at the adapertural side, very high (long), slender, almost straight, narrow, arising near the peripheries of the whorls (at some distance below the suture), disappearing just below the peripheries of the whorls, with the lower margin close to or slightly overlapped with the upper margin at the base, protruded rather upward on most whorls, becoming protruded downward on last 3/4 whorls, very weakly and very finely striated on the outer surface; ribs on last 1 to last 3/4 whorls above the aperture (around the constriction) abruptly weakened, completely absent or greatly reduced, variable in the degrees of the reduction, rarely with vestigial spiny projections; ribs on the last 3/4 whorls developed once more, strongly protruded as tubular spines as those on the upper whorls. Interspace between the spiny ribs almost smooth on upper whorls, with or without very weak and very fine growth lines below and above the suture in high magnification, occasionally with prominent and fine growth wrinkles below the suture on the last 3/4 whorls. Spiral sculpture hardly developed on the teleoconch, hardly visible on the whorls in low magnification, but occasionally present as very faint and very fine vestiges in high magnification, weakly but more prominently developed on the outer surface of the tubular spines, sinuous in

FIGURE 3. Hungerfordia spiroperculata sp. nov. (A1–6) A topotypic paratype, Loc. Uo8-1, B1146a; (B1–5) a topotypic paratype after removal of the spiny ribs, B1146b: (B2) aperture, front view, showing the baso-palatal lip (blue arrowhead) and the columellar lip (yellow arrowhead), note that the columellar tooth (red arrowhead) is hidden by the columellar lip; (B3) basal part of the columella after removal of the palatal wall of the aperture, left lateral view, note that the columellar lip (yellow arrowhead) occurs after the end of the columellar tooth (red arrowhead); (B4) umbilical view, showing the strong ventral protrusion after the constriction, arrowheads are same as in Fig. B2; (B5) inner surface of the ventral protrusion on the last 3/4 whorls, showing the presence of granular projections inside the shell; (C) partially opened apical whorls, showing the presence of the apical septum, a topotypic paratype, B1146c; (D1–5) holotype, B1146T; (E1–2) a yellowish paratype with vestigial spiny ribs above the aperture, Loc. Uo7-2, B0942; (F1–2) outer surface, and (F3–4) inner surface of operculum, a topotypic paratype, B1146d; (G1–2) operculum, a topotypic paratype, B1146e. Scale bars, 1mm (A, B1–4, C, D, E), 0.5 mm (B5, F, G). All specimens, UMUTZ-MG.

FIGURE 4. Hungerfordia spiroperculata sp. nov. (A1) Radulae; (A2) radula with a central tooth coming off from the basal membrane; (B) buccal mass, note the very long radular ribbon which forms a large coil within the radular sac; paratype, UMUTZ-MG-B0942. Scale bars, 50 µm (A1), 20 µm (A2), 500 µm (B).

high magnification. Base rather convex, with a prominent circum-columellar fold; circum-columellar fold developed around the columella on the last 5/8 whorls, becoming stronger and more prominently ridged toward the aperture in umbilical view. Ventral protrusion strongly developed, occurring at a short distance after the constriction, caused by an axial protrusion of shell wall along a spiny rib, which firstly reappears after the constriction, hidden by spiny projection of the rib in fresh specimens, sharply edged along the rib in umbilical view (visible after removal of the spiny projection of the rib), highly projected toward the ventral side. Axial protrusion of shell wall along the ribs on last 3/4 whorls very weakly developed after the ventral protrusion, hidden by the tubular spines (only visible after removal of the tubular spines); abapertural side very narrow; adapertural side convex, much wider than the abapertural one in umbilical view. Umbilicus closed in adult. Aperture hardly tilted against the coiling axis in left lateral view, not protruded, located at base of the previous whorl (hardly expanded onto the upper body whorl in front view), characteristically shaped with a canal-like depression at the basocolumellar edge, which is caused by development of a baso-palatal lip and a columellar lip; columellar axis within aperture almost vertical. Columellar tooth weakly developed, recessed inside the aperture, rather sharply edged just before the aperture, hidden by a columellar lip in front view, never extended onto the inner peristome, penetrated inward about 3/4 whorls. Peristome double. Outer peristome developed, shortly expanded beyond the inner peristome at the palatal side in front view, obtusely angulate at the palatal side, weakly protruded at the upper palatal side in left lateral view, rather gradually expanded from the preceding whorl. Inner peristome weakly expanded, squarish circular with rounded palatal and baso-columellar edges, characteristically shaped by a basopalatal lip and a columellar lip, leaving a canal-like depression at the baso-columellar edge between these lips, somewhat narrower than the outer peristome, hardly or slightly protruded from the outer peristome; parietal margin located at the base of the upper body whorl (located far below the middle level of the upper body whorl); basopalatal lip strongly developed inside the inner peristome, a narrow ridge extended along and inside the palatal and basal margin of the inner peristome, weakly but prominently protruded forward in umbilical view, becoming stronger toward the base, abruptly truncated at the base at a short distance before the columella; columellar lip weakly developed at the columellar side of the inner peristome (near the base), a weak and axial ridge developed near the base of the columella, short, low, seemingly a columellar tooth in front view, but a distinct structure developed after the end of the columellar tooth, shortly protruded forward in umbilical view. Interspace between the inner and outer peristome very narrow or almost without space at the palatal and basal sides; columellar side shortly erected, weakly grooved on its outer side.

Dimensions. Shell height 4.5–5.1 mm, diameter 3.2–4.1 mm, suture width 1.8–2.1 mm, peristome height 1.3– 1.5 mm.

Operculum (Figs. 3F1–4, G1–2). Operculum corneous, multispiral, circular, not flat, semi-transparent, amber colored, unusually shaped for Hungerfordia species; outer side smooth and flat only at the central part, elevated at the marginal part, with a wide and thin spiral fringe; inner side with a strong arcuate ridge neat the columellar margin; arcuate ridge highly protruded, thick, C-letter shaped.

Penis. Penis absent.

Radula (Figs. 4A1–2, B). Radula of specialized type of taenioglossate; ribbon very long, forming a large coil within the radular sac. Central tooth very large, with a very wide, large, and blunt central cusp, with 1–2 pair(s) of vestigial lateral cups, basal plate longitudinally elongated and strongly constricted at the base. Lateral teeth also large, with a large, very wide and blunt major cusp, with a vestigial inner cusp, without outer cusp, basal plate obliquely elongated. Inner marginal teeth shorter than the lateral teeth, elongated, with a large major cusp, with two small and slender inner cusps, with a small outer cup. Outer marginal teeth shorter than the inner marginal, with a large, wide and blunt major cusp, with two small and slender inner cusps, without outer cusp.

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

Remarks. H. spiroperculata is readily distinguished from other spiny Hungerfordia species by the following features: the development of a strong baso-palatal lip inside the inner peristome; the presence of a short columellar lip just after the columellar tooth; the development of a strong ventral protrusion after the constriction; the presence of granular projections inside the tuba; the spiny projections of the ribs being tubular and slender; the slender shell with rather closely spaced spiny ribs. H. echinata tubulispina Yamazaki & Ueshima, 2013 is most similar to the species in having tubular projections of the ribs (Figs. 12M, N), but is distinguishable by the features mentioned above. H. spiroperculata is also unique among the genus in having a peculiar operculum (Figs. 3F1–4, G1–2): the operculum is not flat, with a strongly protruded spiral fringe on the outer surface, with a strongly developed arcuate ridge on the inner side. These unusual opercular features are rather similar to those of the other Palauan diplommatinid genus, Palaina (Eupalaina) , but differs from the latter in that the operculum is not deeply concave nor thickened ( Yamazaki et al., 2013). Despite such superficial similarities to Palaina in the operculum, the characteristic features of the shell, the radulae, and the absence of penis in the species consistently support the taxonomic placement in Hungerfordia . Occurrence of such an exceptional type of operculum within Hungerfordia shows that operculum morphology is not necessarily conserved within the genus.

Etymology. The specific name, derived from the Latin spiro + operculatus, refers to the characteristic operculum with a strong spiral fringe.