Landouria monodon Nahok & Chanlabut & Tumpeesuwan & Tumpeesuwan 2024, sp. nov.
Creators: name: Nahok, Benchawan
name: Chanlabut, Utain
name: Tumpeesuwan, Sakboworn
name: Tumpeesuwan, Chanidaporn
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Camaenidae
Landouria
Landouria monodon

description: Landouria monodon Nahok & C. Tumpeesuwan sp. nov.
Figs 5 D – E, 6, 7, Tables 1, 2
Landouria sp. 1 — Ounchareon 2016: 27–32, fig. 4.1 A, B, table 4.3
Landouria sp. 2 — Nahok 2020: 43–44, fig. 23 B, C, table 3
Type locality.
Thailand, Kalasin Province, Mueang Kalasin District, Phu Po, 16 ° 37 ' 10.42 " N, 103 ° 37 ' 55.59 " E, Sandstone hills, alt. 241 m. 17 Jun. 2017. Benchawan Nahok and Utain Chanlabut leg.
Type material.
Holotype: • NHMSU -00059 (Fig. 5 D). 1 shell, SH = 6.4 mm, SW = 10.3 mm, AH = 3.4 mm, AW = 4.0 mm, UW = 2.9 mm. Paratypes: • NHMSU -00060, (Figs 6, 7) 12 shells, • ZCPRU -0045 7 shells, • NHMSU -000613 living specimens preserved in ethanol, • ZCPRU -0046 2 living specimens preserved in ethanol, same leg. and locality as holotype, 26 Sep. 2017.
Other material.
• NHMSU - 00062 (Fig. 5 E) 4 shells, • ZCPRU - 0047 4 shells. Thailand, Kalasin Province, Sahatsakhan District, Phu Kum Khao, 16 ° 41 ' 41.98 " N, 103 ° 31 ' 34.43 " E, Sandstone hills, alt. 267 m, 17 June 2017. Benchawan Nahok and Utain Chanlabut leg.
Diagnosis.
Shell small, depressed-conical, slightly keeled; aperture oval, oblique, with thick, reflected lip. Thick prominent lamella present on inner columellar side of aperture. Flagellum short, bend at apical portion. Penis long, large, cylindrical. Free oviduct short; vagina long, distally swollen. Basal part of gametolytic sac enlarged, swollen.
Description.
(empty shells = 28, living specimens = 5). Shell (Fig. 5 D, E) dextral, small, depressed-conical. Whorls 5 ¾ – 6 ¼; apex obtuse. Body whorl slightly keeled. Protoconch almost smooth; teleoconch with irregular wrinkles, indistinct incised spiral lines, without scaly processes. Prominent but tiny lamella present on inner columellar side of aperture. Umbilicus deep, wide. Shell dimensions of specimens from type locality (N = 20; mean values in parentheses): shell height 3.10–6.60 mm (4.68 ± 1.04 mm), shell width 5.10–10.40 mm (7.67 ± 1.24 mm), aperture height 2.10–3.50 mm (2.64 ± 0.39 mm), aperture width 2.20–4.10 mm (3.26 ± 0.55 mm), and umbilicus width 2.20–3.00 mm (2.49 ± 0.20 mm). Shell dimensions of specimens from Phu Kum Khao (N = 8): shell height 3.64–4.68 mm (4.85 ± 0.88 mm), shell width 6.43–7.67 mm (7.75 ± 1.33 mm), aperture height 2.25–2.64 mm (2.80 ± 0.35 mm), aperture width 2.71–3.26 mm (3.15 ± 0.48 mm), and umbilicus width 2.29–2.49 mm (2.60 ± 0.20 mm).
Genital system (N = 3) (Fig. 6). Atrium short. Penis cylindrical, longer than flagellum, internally with four corrugated, longitudinal pilasters, distally giving rise to densely interlocked longitudinal rows to verge. Verge small, short (Fig. 6 B). Penial retractor muscle present. Proximal part of epiphallus (ep 1) shorter than half of penis length. Distal part of epiphallus (ep 2) very short. Flagellum approximately as long as proximal part of epiphallus, regularly short-cylindrical, slightly bent at the tip, internally with four smooth, longitudinal pilasters (Fig. 6 C). Vas deferens a thin cylindrical tube, apically entering epiphallus. Vagina long, distally swollen, internally with thick, undulating, transverse pilasters (Fig. 6 D). Free oviduct shorter than vagina. Gametolytic sac swollen at base, short cylindrical tube, and with swollen spherical sac at distal end. Prostate gland long; uterus swollen.
Radula (N = 3). Comprises 136–140 transverse rows with 63–71 teeth per row (Fig. 7 B); radular formula: (19–21) + (12–14) + 1 + (12–14) + (19–21). Central tooth usually symmetric, small, tricuspid, triangular. Lateral teeth short, bicuspid, with tiny ectocone and gradually changing into tricuspid marginal teeth; endocone small; mesocone large, long, with curved margins; ectocone triangular, with 2–4 tiny cusps (Fig. 7 C).
Etymology.
Specific epithet “ monodon ” is derived from the Greek words, “ monos ”, one or single, and “ odous ”, tooth, and refers to the single prominent lamella on the inner columellar side of aperture.
Habitat.
This new species lives on sandstone hills under leaf litter, in rock crevices, hollow trees, etc. at bases of hills in dry, dipterocarp forest.
Distribution.
Landouria monodon sp. nov. is currently known from separate sandstone hills, at Phu Po and Phu Kum Khao, Kalasin Province, northeastern, Thailand (Fig. 1).
Remarks.
Landouria monodon sp. nov. differs from other Thai species of Landouria by its tiny but prominent columellar lamella on the inner side of the aperture (Fig. 5 D, E). Its genital system and radula are quite similar to L. diplogramma from Nakhon Ratchasima, northeastern Thailand, but the new species differs in having its penis not divided into two short portions and its vagina thicker (Fig. 6). The radular central tooth is triangular but differs by its smaller size (Fig. 7). Conchologically, L. monodon sp. nov. closely resembles Helix ptychostyla L. Pfeiffer, 1862, whose types specimen are in MNHN (MNHN - IM- 2000-1974; Fig. 5 C). (https://www.gbif.org/occurrence/1019688902). Still, the two species differ by many characters: (1) parietal callus prominent in H. ptychostyla, but faint or absent in L. monodon sp. nov.; (2) last whorl and lip descending in front in L. monodon sp. nov.; (3) growth lines prominent in H. ptychostyla, but faint in L. monodon sp. nov.; (4) umbilical keel absent in H. ptychostyla, but prominent in L. monodon sp. nov.
Moreover, the type material of H. ptychostyla L. Pfeiffer, 1862 likely comes from the Henri Mouhot expedition to Thailand and Laos, which included Bangkok, Wat Phra Phutthachai Saraburi, Korat, Chaiapume, Leute, Kenne Tao, Paklaie, and Thadua (see Inkhavilay et al. 2019: fig. 1), which is over 150 km away from the type locality of L. monodon sp. nov.
Recently, Schileyko (2011) proposed that Helix ptychostyla was preoccupied by von Martens (1860) and indicated that H. goniochila L. Pfeiffer, 1862 (Figs 5 A, B) is a synonym of H. ptychostyla von Martens, 1860. He used Thaitropis ptychostyla (von Martens, 1860) as the available name for this taxon, whereas T. ptychostyloides was proposed as nomen novum for Helix ptychostyla L. Pfeiffer, 1862 (Table 2).
description: Published as part of Nahok, Benchawan, Chanlabut, Utain, Tumpeesuwan, Sakboworn & Tumpeesuwan, Chanidaporn, 2024, Two new species of Landouria Godwin-Austen, 1918 (Gastropoda, Camaenidae) from Thailand, with a key to Thai species, pp. 347-362 in ZooKeys 1208 on pages 347-362, DOI: 10.3897/zookeys.1208.117056