Anceyoconcha carinata, Nahok & Tumpeesuwan & Tumpeesuwan, 2021

Nahok, Benchawan, Tumpeesuwan, Chanidaporn & Tumpeesuwan, Sakboworn, 2021, Two new species of genus Anceyoconcha S. Tumpeesuwan & C. Tumpeesuwan, in Nahok et al., 2020 (Gastropoda: Pulmonata: Camaenidae), from northeastern Thailand, Raffles Bulletin of Zoology 69, pp. 555-569 : 559-561

Anceyoconcha carinata , new species

( Figs. 3A, B , 4 ; Tables 1–3)

Anceyoconcha sp.1 – Nahok, 2020: 72–73, figs. 25C, D, 39, 46, 47, 50, 53, tables 3, 5, 7–10.

Material examined. Holotype: NHMSU-00036, Khao Plai Bat (basalt hill), Prakhon Chai District, Buri Ram Province, Thailand (14°28′55.36″N, 102°58′11.00″E), alt. 211 m, 30 May 2017, SH = 19.0 mm, SW = 7.6 mm, AH = 5.4 mm, AW = 3.3 mm ( Fig. 3A ) . Paratypes: 6 shells, 4 living specimens preserved in ethanol (NHMSU-00037), same data as for holotype. 1 shell (NHMSU-00038), Khao Angkhan (basalt hill), Chaloem Phra Kiat District, Buri Ram Province, Thailand (14°32′27.36″N, 102°50′13.60″E), alt. 251 m, 31 May 2017 ( Fig. 3B ) .

Diagnosis. Shell slightly ovate conic, last whorl with strong ridge around umbilicus ( Fig. 3A, B ). Penis and vagina shorter than flagellum. Flagellum long cylindrical, divided into two portions ( Fig. 4A, B ).

Etymology. Specific epithet ‘carinata’ derived from Latin word ‘carina’, meaning ‘keel’ and referring to the shell of this new species having a periumbilical keel.

Description. Shell ( Fig. 3A, B ; Table 3): slightly ovate conic, whorls 6½, shell height 18.5–22.0 mm, shell width 7.2–8.8 mm, aperture height 5.4–7.1 mm, and aperture width 3.3–6.1 mm. Brownish colour; semi-transparent and lustrous. Apex obtuse, acute with light colour; embryonic shell smooth. Last whorl straight, rounded; with a periumbilical keel near aperture. Peripheral keel and peripheral band absent. Aperture large, irregularly rounded or ovoid, quite oblique, with thin, reflexed margins. Peristome expanded and reflexed. Umbilicus, a minute perforation, narrow and deep.

Genital system (n = 3) ( Fig. 4A–F ): atrium short. Penis short cylindrical. Epiphallus divided into two portions, proximal part (ep1) stout and swollen, distal part (ep2) long cylindrical. Penial retractor muscle present. Flagellum approximately almost the same length as distal part of epiphallus (ep2); with proximal part twisted and distal part S-shaped. Vas deferens long. Vagina short cylindrical but longer than penis. Gametolytic duct thickened at base and gradually slender to small tube distally. Gametolytic sac small swollen gland at distal end of gametolytic duct. Free oviduct short. Uterus and prostate gland long and stout. Inner wall of penis with short, stout, and smooth longitudinal pilaster ( Fig. 4C ). Inner wall of ep1 with four corrugated longitudinal pilasters ( Fig. 4C ); inner wall of ep2 with three smooth longitudinal pilasters ( Fig. 4D ). Inner wall of flagellum with three stout and smooth longitudinal pilasters ( Fig. 4E ). Inner wall of vagina with two longitudinal pilasters ( Fig. 4F ).

Radula (n = 3) ( Fig. 4G–I ): comprises 126–128 transverse rows of teeth, each row containing 65–73 teeth, (22–24) + (10–12) + 1 + (10–12) + (22–24). Central teeth symmetric and unicuspid, narrowly rounded. Lateral teeth oblique rounded, bicuspid with indistinct or distinct blunt ectocone ( Fig. 4H ), larger than central teeth. Marginal teeth gradually changing from broadly tricuspid (13th–28th) to tetracuspid (29th–36th) with two small ectocones.

Remarks. The shell morphology of A. carinata , new species, differs from that of many other congeners in the presence of a strong keel around the umbilicus ( Fig. 3A, B ). Anceyoconcha rhombostoma also possesses the keel, but its shell is ovate trochoid, shorter than that of A. carinata , new species, and the presence of a keel on its periphery runs to an angle of the rhomboid-shaped aperture (see Sutcharit et al., 2019: fig. 3C–I; Nahok et al., 2020: fig. 4B; Sutcharit et al., 2020: fig. 12C, D). The genitalia of A. carinata , new species, possess three characters that are distinct from those of all other congeners in that the vagina and penis are shorter than the flagellum, and the flagellum is divided into two sections with a twining proximal part and S-shaped distal part ( Fig. 4A, B ).

Distribution. Anceyoconcha carinata , new species, is currently known from the basalt hill areas in Prakhon Chai and Chaloem Phra Kiat Districts, Buri Ram Province.

Figures

Fig. 3. Shell morphology of Anceyoconcha spp. in northeastern Thailand. A, B, A. carinata, new species; A, holotype (NHMSU-00036) from Khao Plai Bat, Buri Ram; B (NHMSU-00038) from Khao Angkhan, Buri Ram. C–E, A. elongata, new species; C, holotype (NHMSU-00039) from Phu Po, Kalasin; D (NHMSU-00041) from Phu No, Kalasin; E (NHMSU-00045) from Phanom Sawai Forest Park, Surin. F, A. sp.1 (NHMSU-00043) from Pha Nam Yoi, Roi Et. G, A. siamensis (ZRCBUU-0325). H, A. rhombostoma (NHMSU-00022). Fig. 3G photograph courtesy of Pongrat Dumrongrojwattana.

Fig. 4. Anceyoconcha carinata, new species. A, B, genital system, paratype (NHMSU-00037). C–F, inner wall of genital system; C, penis (p) and proximal portion of epiphallus (ep1); D, distal portion of epiphallus (ep2); E, flagellum (fl); F, vagina (v). G, view of transverse rows of radula, with number of lateral and marginal teeth indicated (c = central tooth); H, right side of central tooth and lateral teeth; I, right side of marginal teeth. J, natural habitat and living adult.