Anceyoconcha elongata, 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 : 561-565

Anceyoconcha elongata , new species

Figs. 3C–E , 5 ; Tables 1–3

Giardia siamensis – Srihata et al., 2010: 364–365, 367, fig. 2. Phu No, Kalasin.

Pseudobuliminus siamensis – Jumlong et al., 2013: 72–76, fig. 2. Phanom Sawai Forest Park, Surin.

Anceyoconcha sp.5 – Nahok, 2020: 77–78, figs. 25H, 41, 46–47, 50, 53, tables 3, 5, 7–10. Phanom Sawai Forest Park, Surin.

Anceyoconcha sp.6 – Nahok, 2020: 79–80, figs. 25I, 42, 46–47, 50, 53, tables 3, 5, 7–10. Phu No, Kalasin.

Anceyoconcha sp.7 – Nahok, 2020: 81–82, figs. 25J, 43, 46–47, 50, 53, tables 3, 5, 7–10. Phu Po, Kalasin.

Material examined. Holotype: NHMSU 00039 ; Phu Po (sandstone hill), Mueang District, Kalasin Province, Thailand (16°37′10.42″N, 103°37′55.59″E); alt. 241 m; 17 June 2017; SH = 21.8 mm, SW = 7.8 mm, AH = 6.5 mm, AW = 4.1 mm ( Fig. 3C ) . Paratypes: 55 shells, 6 living specimens preserved in ethanol (NHMSU-00040), same data as for holotype. 1 shell ( NHMSU 00041 ), 1 living specimen preserved in ethanol (NHMSU-00042), Phu No (sandstone hill), Tha Khantho District, Kalasin Province, Thailand (16°51′42.33″N, 103°14′45.20″E); alt. 264 m, 27 September 2017 ( Fig. 3D ) ; 18 shells ( NHMSU 00045 ), 1 living specimen preserved in ethanol (NHMSU-00046), Phanom Sawai Forest Park (basalt hill), Mueang District, Surin Province, Thailand (14°45′34.88″N, 103°21′56.62″E), alt. 206 m, 14 October 2017 ( Fig. 3E ) ; 1 shell ( NHMSU 00047 ), Khao Sala , Buachet District, Surin Province, Thailand (14°25′44.87″N, 103°56′3.34″E), alt. 312 m, 14 October 2017 .

Diagnosis. Shell elongate conic. Flagellum equal to or longer than epiphallus.

Etymology. Specific epithet derived from Latin word ‘elongatus’, meaning prolonged and referring to the elongate shell of the new species.

Description. Shell ( Fig. 3C–E ; Table 3): elongate conic, whorls 7¾, shell height 21.6–28.1 mm, shell width 7.6–9.7 mm, aperture height 6.1–7.8 mm, and aperture width 4.1–7.6 mm. Pale grey to light brown or white to light yellow, transparent, and lustrous. Apex obtuse. Embryonic shell smooth. Last whorl large, evenly rounded, polished. Peripheral keel and peripheral band absent. Aperture halfmoon-shaped to sub-ovate. Peristome expanded, parietal callus transparent. Umbilicus narrowly opened.

Genital system (n = 5, comprising three specimens from Phu Po, one specimen from Phu No, one specimen from Phanom Sawai) ( Fig. 5A–D ): atrium short. Penis long cylindrical shape. Penial retractor muscle present, swollen at base. Epiphallus is equal to or half of penis length. Flagellum is equal to or slightly longer than epiphallus length, cylindrical, and slender hook-shaped or sickle-shaped at distal end. Vas deferens long. Vagina length is equal to or slightly longer than penis length. Gametolytic duct swollen and thickened at base, and gradually slender to small tube distally. Gametolytic sac small, swollen, balloon-shaped gland at distal end of gametolytic duct. Free oviduct very short. Uterus and prostate gland very long. Inner wall of penis rather smooth ( Fig. 5E ). Proximal part of epiphallus (ep1) inner wall with five corrugated longitudinal pilasters ( Fig. 5E ); distal part of epiphallus (ep2) inner wall with smooth longitudinal pilaster ( Fig. 5F ). Inner wall of flagellum with two longitudinal pilasters, one very thin and smooth, and the other robust and smooth ( Fig. 5G ). Inner wall of vagina with six slightly undulating longitudinal pilasters ( Fig. 5H ).

Radula (n = 4, comprising three specimens from Phu Po, one specimen from Phanom Sawai Forest Park) ( Fig. 5I–K ): comprises 76–80 transverse rows of teeth in specimens from Phu Po, and 100 rows in one specimen from Phanom Sawai; each row containing 51–59 teeth, (16–18) + (9–11) + 1 + (9–11) + (16–18). Central teeth symmetric unicuspid, lanceolate. Lateral teeth similar to central tooth, large, and oblique unicuspid. Teeth on both sides begin to transform into indistinct, bicuspid marginal teeth with tiny ectocone at numbers 10–12. Marginal teeth gradually change to broad tricuspid, starting at numbers 13–17, and begin to transform into tetracuspid with two cusp ectocones from numbers 18–27 to edge of radula plate.

Remarks. Anceyoconcha elongata , new species, was discovered from Phu Po and Phu No in Kalasin, and Phanom Sawai and Khao Sala in Surin. These four populations resemble each other in shell morphology, reproductive anatomy, and radula morphology, but differ slightly in size, colour, and shape of aperture ( Fig. 3C, D, F ; Table 3). The penial retractor muscle is present in specimens from Phu Po and Phanom Sawai, but is absent in the specimen from Phu No. The penis is long and cylindrical in the specimen from Phanom Sawai, notably different from those in the specimens from Phu Po, which have a proximal twist at the base, and those in specimens from Phu No, which have a thin proximal end. Anceyoconcha elongata , new species, has a similar elongate conic shell to that identified in A. chaudoensis ( Rochebrune, 1882) from Southern Cambodia (see Sutcharit et al., 2020: fig. 12E, F). However, the shell of A. elongata , new species, is bigger than that of A. chaudoensis , with shell height of the new species ranging from 21.6 to 28.1 mm, whereas shell height in A. chaudoensis ranges approximately from 16.1 to 21.4 mm. The peristome at the columella side is straight on both inner and outer sides in A. elongata , new species, but concave on the outer side in A. chaudoensis . These similarities in shell shape need further clarification, and should be supported by comparisons of genital anatomy, radula morphology, and phylogeny based on mitochondrial and nuclear DNA and genetic distances.

There exists one lot of five specimens in the Muséum national d’Histoire naturelle (MNHN) that has been attributed to the species and may possibly have been part of material provided by Harmand to Rochebrune (1882). However, these may not have been the specimens on which Rochebrune based his description, because of 1) the lack of information on the original label (compared to other species described in the same paper, which had detailed labels providing solid evidence that they are types), and 2) discrepancies between the measurement of the largest shell in the MNHN lot (21 mm) and that in the original description (24 mm in Rochebrune, 1882) (Virginie Héros, pers. comm., 2021). As the types cannot be traced, we consider Anceyoconcha chaudoensis a nomen inquirendum.

Distribution. Anceyoconcha elongata , new species, is currently known from Phu Po and Phu No in Kalasin Province, and Phanom Sawai Forest Park and Khao Sala in Surin 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. 5. Anceyoconcha elongata, new species. A, B, genital system, paratype (NHMSU-00040) from Phu Po, Kalasin. C, genital system (NHMSU-00042) from Phu No, Kalasin. D, genital system (NHMSU-00046) from Phanom Sawai, Surin. E–H, inner wall of genital system; E, penis (p) and proximal portion of epiphallus (ep1); F, distal portion of epiphallus (ep2); G, flagellum (fl); H, vagina (v). I, view of transverse rows of radula, with number of lateral and marginal teeth indicated (c = central tooth); J, left side of central tooth and lateral teeth; K, right side of marginal teeth.