Anceyoconcha rhombostoma ( Pfeiffer, 1861 ) Nahok & Tumpeesuwan & Tumpeesuwan, 2020

Nahok, Benchawan, Tumpeesuwan, Sakboworn & Tumpeesuwan, Chanidaporn, 2020, Anceyoconcha, a replacement name for the preoccupied tree snail genus Giardia Ancey, 1907 (Pulmonata: Helicoidea: Camaenidae), Raffles Bulletin of Zoology 68, pp. 80-90 : 82-84

Anceyoconcha rhombostoma ( Pfeiffer, 1861) , new combination

( Figs. 2B , 3C, D , 4B , 6 , 7B ; Table 1)

Bulimus rhombostomus Pfeiffer, 1861: 194 .

Amphidromus rhombostomus – Morlet, 1889: 127; 1890: 121, pl. 3 fig. 6, 6a, 6b.

Buliminus rhombostomus – Dautzenberg & Fischer, 1905: 366.

Giardia rhombostoma – Schileyko, 2011: 46.

Pseudobuliminus harryleei Thach, 2017: 54 , 55, figs. 756–760.

Pseudobuliminus tuongvyae Thach, 2017: 56 , figs. 751–755.

Pseudobuliminus huberi Thach, 2017: 55 , figs. 759, 760.

Ganesella rhombostoma – Raheem et al., 2017: 11; Sutcharit et al., 2019: 61–63 , figs. 1C, 3C–I, 5E–G, 7D–F.

Ganesella rhombostomus – Sutcharit et al., 2017: 253, 257, fig. M.

Material examined. 34 empty shells, 15 live specimens (NHMSU-00022), limestone hills near Tham [= Cave] Phet Pho Thong, Khlong Hat District (13°24′52.89″N, 102°19′31.03″E), Thailand, at an elevation of about 236 m above mean sea level .

Diagnosis. Body yellowish to brown ( Fig. 2B ). Shell is brownish to light brown, conic last whorl with brownish spiral

Radula ( Fig. 6 ). Comprises 104–106 transverse rows of teeth and 57–65 teeth in each row ( Fig. 6A, B ). Dentition formula: (19–21) + (9–11) + C + (9–11) + (19–21). Central tooth symmetric unicuspid tongue-shaped ( Fig. 6C, D ). Lateral teeth similar to central tooth, but difference is oblique and cusps are wider and longer ( Fig. 6D ). Teeth on both sides begin to transform into indistinct bicuspid marginal teeth with tiny ectocone at numbers 10–12 ( Fig. 6C, E ). Marginal teeth gradually change to broad tricuspid starting at numbers 11–13 ( Fig. 6C, E ), and begin to transform into tetracuspid with two small finger-shaped ectocones from numbers 28–30 to end of teeth ( Fig. 6C, F ).

Genital system ( Fig. 7B ). Atrium (at) very short. Penis (p) relatively long and cylindrical. Penial retractor muscle (prm) short. Epiphallus (ep) short and approximately one third of penis length. Flagellum (fl) longer than epiphallus, cylindrical, with relatively small distal hook. Vas deferens (vd) long. Vagina (v) long cylindrical, almost same length as penis. Gametolytic duct (gd) extending from vagina, proximal part rather stout and gradually slender to small tube distally. Gametolytic sac (gs), swollen gland as balloon shape connected to distal end of gametolytic duct. Free oviduct (fo) short. Uterus (ut) and prostate gland (pro) long and large. Hermaphroditic duct (hd) slender. Albumin gland (ag) yellowish and dark brown distally.

Habitat. This is an arboreal species seen in both natural forests and gardens in limestone areas. The animals can be found around 1–2 m above ground surface ( Fig. 3C, D ).

Remarks. Distinct characters differentiating Anceyoconcha rhombostoma from Anceyoconcha siamensis are their body and shell colouration as well as shell, radula, and genital organ morphologies.

band on peripheral keel ( Fig. 4B ). Radula have unicuspid tongue-shaped central teeth ( Fig. 6 ). Penis has long cylindrical shape and epiphallus is shorter than penis length. Flagellum is longer than that of A. siamensis ( Table 1; Fig. 7 ).

Description. Shell ( Fig. 4B ). Sinistral, trochoid, SH 7.6–14.6 mm (11.7 ± 1.7 mm), SW 3.3–8.6 mm (7.3 ± 0.9 mm), AH 1.4–5.5 mm (3.8 ± 1.0 mm) and AW 1.9–6.0 mm (3.9 ± 0.9 mm). Whorls six. Brownish to light brown colour, transparent and lustrous, with thin brown band on suture and on peripheral keel of last whorl. Apex obtuse. Aperture large, rounded. Peristome reflexed and expanded. Umbilicus narrow, deep, half closed by peristome.

Body ( Fig. 2B ). Living snails with brown to yellowish body. Foot rather narrow and short with pale margin.

Figures

Fig. 2. Living adult snails of Anceyoconcha, new name, from Thailand. A, Anceyoconcha siamensis, new combination, from Khao Chakan, limestone hills, Khao Chakan District, Sa Kaeo Province; B, Anceyoconcha rhombostoma, new combination, from Tham Phet Pho Thong, limestone hills, Khlong Hat District, Sa Kaeo Province.

Fig. 3. Arboreal land snail of Anceyoconcha, new name, in situ, Thailand. A, B, Anceyoconcha siamensis, new combination; C, D, Anceyoconcha rhombostoma, new combination, in natural habitat (elevation approximately 1–2 m).

Fig. 4. External shell morphology of Anceyoconcha, new name, from Thailand. A, Anceyoconcha siamensis, new combination (ZRCBUU-0325);B, Anceyoconcharhombostoma, new combination (NHMSU-00022). Fig. 4A photograph courtesy of Pongrat Dumrongrojwattana.

Fig. 6. Radula morphology of Anceyoconcha rhombostoma, new combination (NHMSU-00022).A, whole radula; B, close-up view of central part of radula; C, right side of central teeth (indicated by C), lateral and marginal teeth (indicated by numbers); D, close-up view of central tooth (position indicated by C) and lateral teeth; E, close-up view of left lateral and marginal teeth; F, close-up view of marginal teeth.

Fig. 7. Genital system of Anceyoconcha, new name. A, Anceyoconcha siamensis, new combination (NHMSU-00021); B, Anceyoconcha rhombostoma, new combination (NHMSU-00022). Abbreviations: at, atrium; p, penis; prm, penial retractor muscle; ep, epiphallus; fl, flagellum; vd, vas deferens; v, vagina; gd, gametolytic duct; gs, gametolytic sac; fo, free oviduct; ut, uterus; pro, prostate gland; hd, hermaphroditic duct; ag, albumen gland.