Pearsonia lamphunensis, Tumpeesuwan & Tumpeesuwan, 2015

Tumpeesuwan, Sakboworn & Tumpeesuwan, Chanidaporn, 2015, First record and description of a new species of the land snail genus Pearsonia Kobelt, 1902 (Cyclophoridae: Pterocyclinae) from Thailand, with a note on radula morphology, Raffles Bulletin of Zoology 63, pp. 287-292 : 288-291

Pearsonia lamphunensis , new species

Figs. 2–5 ; Table 1

Type material. Holotype: NHMSU-0006 ( Fig. 3 ) (shell height 9.0 mm, shell width 16.9 mm), Tham Erawan, Lamphun Province, northern Thailand, coll. Malacological Laboratory Team of Mahasarakham University , June 2014 . Paratypes: NHMSU-0007 (two shells and three specimens in ethanol; shell height 9.1–10.0 mm, shell width 15.7–17.0 mm); ZRC. MOL.5792 (one shell; shell height 9.2 mm, shell width 16.3 mm).

Etymology. The specific epithet, lamphunensis , is named after its type locality Lamphun Province of Thailand.

Diagnosis. Shell possesses backward pointing sutural tube (st) and horizontal, somewhat linguiform, peristome projection (pp). Zig-zag brown stripes present on both dorsal and ventral sides of shell.

Description. Shell: Dextral, sub-discoidal depressed, widely umbilicate, height 9.0–10.0 mm, shell width 15.7–17.0 mm, slightly thin, whorls 5¼–5½, rounded, spire a little raised. Background color pale brown, translucent, shiny, dorsal side with broad dark brown v-shaped or zig-zag stripes crossing the whorls; peripheral band broad, dark brownish; ventral side with many fine zig-zag brown stripes. Peristome double, the inner lip with sinus, at the parieto-columella angle, the outer lip expanded and forms a horizontal linguiform wing (peristome projection) near the suture. Sutural tube situated a little distance (ca. 3.6–5.3 mm.) from the peristome, in which the distal end is pointed backward ( Figs 2 B–D, 3A, C, D).

Body: Pale brown to dark brown body, foot dark brown. Black eye spot present at the base of short brown tentacles. All three living specimens available for study are female, with a vaginal groove (vg) on the right side of the head ( Fig. 2D ), which runs from the genital opening downwards to the area near the right tentacle.

Operculum: Solid, round, bi-layered; thick calcified layer form outer part of operculum, and thin corneous layer forms inner surface. The outer surface rather convex, multispiral with more than seven counter-clockwise whorls, covered with fine growth lines, nucleus normally abraded. Internal corneous layer concave and wider than calcified layer and outer surface, therefore, bending outwards at edges; opercular disc attachment site large, circular, and can be divided into 3 parts, the middle part forms horseshoe shape area, the outer part and the large circular nucleus depressed. Periphery bearing imbricated semi-circular growth line, which is concave on the left-side (Fig. 4).

indicates position of sutural tube.

Radula: Taenioglossate, the sole specimen examined has at least 84 transverse rows and each row comprises seven teeth (1-2-1-2-1), including one left marginal tooth, two left lateral teeth, one central tooth, two right lateral teeth and one right marginal tooth. Central tooth is low, stout mushroom shape, pentacuspid, central cusp very large trapezoid shape, lateral and marginal cusps, small triangle knobs. Inner and outer lateral teeth tetracuspid, the first and second cusps are small robust finger shaped, the third cusp is very large shovel-shaped and the fourth cusp is small finger shaped. Marginal tooth, tricuspid, possesses the first finger shaped cusp, the second cusp, tongue shaped and the third cusp large triangular shape ( Fig. 5 A–D, Table 2).

Remarks. The new species differs from Pearsonia tembatensis Marzaki & Clements, 2013 , by its higher spire, presence of a broader dark brown peripheral band and zigzag stripes on both dorsal and ventral sides of shell. It is easily distinguished from Pterocyclos diluvium Sutcharit & Panha in Sutcharit et al., 2014, by the backward pointing sutural tube and horizontal somewhat linguiform peristome projection. Opisthoporus pterocycloides ( Pfeiffer, 1854) is very similarly patterned, but differs from the new species by its flat spire, expanded outer peristome, forward pointing sutural tube, and absence of a peripheral band.

Shell morphology of Pearsonia lamphunensis appear superficially similar to Gude’s (1921) illustrations and descriptions of Pearsonia bhamoensis ( Theobald, 1876) from Bhamo, and Pearsonia avana ( Blanford, 1863) from Shan Hill to the east of Ava, northeast Myanmar. The shell size of Pearsonia lamphunensis is however significantly larger and the spire is higher than Pearsonia avana and Pearsonia bhamoensis (see Table 1). The peristome projection (pp) of Pearsonia lamphunensis is horizontal as in Pearsonia bhamoensis , but unlike Pearsonia avana , which is vertical. The sutural tube of both Pearsonia lamphunensis and Pearsonia bhamoensis is curved upward and backward in the suture, whereas in Pearsonia avana it is curved upward. The colour pattern of Pearsonia lamphunensis differs from these two geographically close species by the presence of dark brown zig-zag stripes on both dorsal and ventral sides of the shell, whereas stripes are only present on the dorsal side in Pearsonia avana and absent in Pearsonia bhamoensis .

Figures

Fig. 2. Pearsonia lamphunensis, new species. A, Type locality habitat in dolomitic limestone hill, Lamphun Province; B, Aestivating living snail in natural habitat. Paratype (NHMSU-0007); C, Female partially retracted with the operculum (op) showing; D, vaginal groove (vg) near right tentacle visible.

Fig. 3. Pearsonia lamphunensis, new species, dolomitic limestone hill Fig. 4. Operculum of Pearsonia lamphunensis, new species. near Tham Erawan, Lamphun Province. Holotype (NHMSU-0006). A, Paratype (NHMSU-0007). A, outer surface; B, inner surface; dorsal view; B, ventral view; C, apertural view; D, side view. Arrow C, side view; D, close up view of outer surface.

Fig. 5. Pearsonia lamphunensis, new species, radula of paratype (NHMSU-0007). A, curled position, most central teeth were covered by lateral teeth; B, close up view of left side of radula; C, uncurled position, all cuspidal features are visible; D, close up view of right side of radula (st).