Aenigmatoconcha sumonthai, Tumpeesuwan & Tumpeesuwan, 2018

Tumpeesuwan, Chanidaporn & Tumpeesuwan, Sakboworn, 2018, Aenigmatoconcha sumonthai, a new helicarionid land snail from Chumphon Province, Southern Thailand (Helicarionidae: Durgellinae), Raffles Bulletin of Zoology 66, pp. 170-176 : 171-172

Aenigmatoconcha sumonthai , new species

Figs. 2–6 ; Table 1

Type material. Holotype: NHMSU-0015 ( Fig. 3 ). Shell height 8.0 mm, shell width 14.2 mm; type locality: Tham Chang Phueak limestone range, Mueang district , Chumphon province, southern Thailand, coll. Montri Sumontha, May 2015 . Paratypes: NHMSU-0016 (empty shells, genital system and radula, Figs. 4 , 5 ), ZRC.MOL.11287 (one shell), THNHM-Iv-18004 (one shell), same data as holotype .

Etymology. The species is named after the collector Montri Sumontha; the specific epithet “ sumonthai ” is from the family name “Sumontha”.

Diagnosis. The characters distinguishing Aenigmatoconcha sumonthai , new species, from A. clivicola are the colour patterns on mantle shell lobes and body, as well as morphology of radula and genital organs. Mantle shell lobes bear irregular black marbling pattern and numerous tiny white spots ( Fig. 2A ). Two black bands, each running from the base of a long tentacle (eyestalk) to mantle edge, are present ( Fig. 2A ). Central teeth of radula have a globose unicuspid cusp, with their size smaller than the 1 st lateral teeth and only the distal halves of the globose cusps emerge from the 1 st lateral teeth ( Fig. 4C ). The epiphallus is shorter than penis, and the middle part of the gametolytic sac in the new species is shorter than in A. clivicola ( Fig. 5 ).

Description. Shell ( Fig. 3 , Table 1): Dextral, flattened to depressed, with a rather wide and deep umbilicus. 6.80–8.00 mm high, 11.50–14.2 mm wide, whorls 4¼–4½, thin, glossy, slightly convex, surface with irregular low axial ridges. Last whorl not descending in front, rounded at periphery. Colour pale brown, glass-like when fresh. Aperture large, ovately lunate, moderately oblique, with a simple and fragile margin, and a short umbilical keel at the umbilical side of the aperture.

Body ( Figs. 2 , 6A ; Table 1): Living snails possess broad right and left transparent mantle shell lobes, with black marble pattern and numerous tiny white spots. Body pale brown to dark brown, with black bands behind the long tentacles. Foot dark brown, sole tripartite, caudal fossa and caudal horn well developed.

Radula ( Fig. 4 , Table 1): Rectangle, comprises 22–35 transverse v-shaped rows of teeth and 11–150 teeth in each row. All teeth unicuspid, of spatulate shape. Central teeth are at sharp angles in middle line. Half of cusp body of central teeth emerge from flanking 1 st lateral teeth.

Genital system ( Fig. 5 , Table 1): Albumen gland of moderate size, slightly swollen. Hermaphroditic duct a rather thick tube. Uterus very long, large, swollen, of dark yellow colour. Vas deferens a long and slender tube, entering apically into epiphallus. Epiphallus a short slender tube, ephiphallic flagellum absent. Ephiphallic retractor caecum shorter and thicker than distal end epiphallus. Penis longer than epiphallus, sausage-shaped. Gametolytic sac comprises three portions, including swollen gland at distal end, slender tube in the middle, and robust tube at base. Vagina yellow in colour, cylindrical, and longer than free oviduct. Free oviduct divided into three parts, distal part short, orange, middle part constricted, and proximal part swollen. Amatorial organ absent.

Remarks. Although shell morphology and radula of A. sumonthai are similar to those of A. clivicola , the shell of A. sumonthai is significantly smaller and with less number of whorls ( Table 1). The radula of A. sumonthai possesses transverse v-shaped rows of teeth, and the number of teeth in each row is not significantly different from A. clivicola , when the central teeth are excluded. Aenigmatoconcha sumonthai possesses central teeth that have only half of its small globose unicuspid cusp emerging from the 1 st lateral teeth on both sides ( Fig. 4 B–D). Genital systems are notably different, as the epiphallus of A. sumonthai is shorter than penis. The gametolytic sac comprises three parts: swollen gland at distal end, slender tube in the middle, and the base is a robust tube that is longer than the middle part.

Figures

Fig. 2. Aenigmatoconcha sumonthai, new species, in natural habitat at the type locality; photographs taken on June 2017. A, two snails with the dorsal shell surface complately covered by the mantle shell lobes; B, two snails with mantle shell lobes retracted. (Photograph courtesy of Mr. Montri Sumontha).

Fig. 3. External shell morphology; Aenigmatoconcha sumonthai new species, holotype (NHMSU-0015).

Fig. 4. Aenigmatoconcha sumonthai new species, radula of paratype (NHMSU-0016). A, whole radula; B, close up view of central part of radula; C, close up view of central, 1st and 2nd lateral teeth; D, close up view of right side of central teeth; E, close up view of right latero-marginal teeth.

Fig. 5. Aenigmatoconcha sumonthai, new species, genital system of paratype (NHMSU-0016). Abbreviations: ag = albumen gland, hd = hermaphroditic duct, ut = uterus, pro = prostate gland, vd = vas deferens, ep = epiphallus, erc = epiphallic retractor caecum, p = penis, gs = gametolytic sac, v = vagina, fo = free oviduct, at = atrium.

Fig. 6. Living snails in natural habitat at type locality; photographs taken on June 2017. A, Aenigmatoconcha sumonthai, new species, on climbing plant near limestone wall; B, Sarika sp. on limestone (photographs courtesy of Mr. Montri Sumontha).