A review of Diplommatina species in eastern Thailand with the descriptions of five new species

Abstract Background Microsnails in the genus Diplommatina Benson, 1849 from eastern Thailand are revised, based on the collection of the Zoological Research Collection, Burapha University, Chonburi Province, Thailand and on recently-collected materials. New information Five new species, Diplommatina burapha sp. n., D. chadathongae sp. n., D. chantaburiensis sp. n., D. fusiformis sp. n. and D. khwantongae sp. n., are described as new to science. The geographic distribution of these eastern species is presented.


Introduction
Terrestrial microsnails in the genus Diplommatina Benson, 1849 show some of the greatest diversity and are distributed in southern, south-eastern and eastern Asia. At present, a total of 18 Diplommatina species have been reported from Thailand. Of the 18 described species, ten (55.55%) were recorded from the south and seven (38.9%) from the north, whereas only one species, D. crispata khaochamaoensis Panha et al., 1998, was described from Khaochamao National Park, Chantaburi Province (Maassen 2001, Panha 1996, Panha and Burch 1996, Panha and Burch 2001, Panha and Burch 2005, Panha et al. 1998, Tongkerd et al. 2013). This study is focused on a survey of microsnail diversity recorded in eastern Thailand since 2005 and focused on five species of the genus Diplommatina ( D. burapha sp. n., D. chadathongae sp. n., D. fusiformis sp. n., D. khwantongae sp. n. and D. khaowongensis) as new to science, based on the external shell characters. The geographic distribution of these eastern Thai species is also presented.

Materials and methods
The specimens from the Zoological Research Collection of Burapha University (ZRCBUU) which have been collected since 2005 and recently obtained shell specimens from the field survey were studied. Shells were collected by hand searching and leaf litter sieving in several areas in eastern Thailand ( Fig. 1 and Table 1). Empty shells were cleaned with tap water and a fine hairbrush and then air-dried. Only live specimens of one species, Diplommatina khwantongae were collected. Digital photographs of shells were obtained using a Canon MP-E 65 Macro lens camera. Shell measurements (in mm), including shell height (SH), shell width (SW), aperture height (AH) and aperture width (AW), were determined using ImageJ software. Taxonomic identification and shell terminology (e.g. whorl number and shell sculpture) of the specimens were recored according to Panha et al. (1998) and Tongkerd et al. (2013). Type specimens were deposited in the collection of the Zoological Research Collection of Burapha University (ZRCBUU), Chon Buri, Thailand.

Nomenclature
We named this new species "burapha," which means "eastern." This refers to the type locality, which is located in the east and is also in honour of Burapha University, the workplace of the authors. Collecting sites. The code indicated in the map follows the list in Table 1.

Materials
Holotype: Shell minute dextral, elongated narrow, turreted with 7 ¾ round whorls that increase regularly in size and diameter until the last whorl; protoconch orange, smooth, consisting of 1 ¼ whorls, covered with minute pits; teleoconch light orange, consists of about 5 ¾ whorls that increase regularly in size and diameter until the last whorl; spires shouldered; sculpture consists of rather even and rather widely-spaced radial ribs with about 8 ribs/mm on the penultimate whorl and about 6 ribs/mm on the body whorl, the discernible spiral striae between the ribspresent; sutures deep; umbilicus closed; aperture round; peristome is thickened and expanded and doubled; columellar lamella rather bluntly rounded (Fig. 4).

Etymology
We named this new species "burapha," which means "eastern." This refers to the type locality, which is located in the east and is also in honour of Burapha University, the workplace of the authors.

Distribution
This species is known only from the type locality.

Taxon discussion
The size of the shell, shape of the shell and protoconch of D. burapha sp. n. are similar to D. doichiangdao Panha & Burch, 1998 from Doi Chiang Dao, northern Thailand and Laotian species, D. belonis Möllendorff, 1900. The spire of D. burapha sp. n. is relatively broader than that of those two species. The enlarged penultimate whorl and the body whorl of D. burapha sp. n. are relatively similar in diameter, while the last whorls of both D. doichiangdao and D. belonis are smaller in diameter than the  Shell minute dextral, cylindrical, translucent, whitish, with about 5 ¾ whorls that increase regularly in size and diameter until the last whorl; protoconch orange, smooth, consisting of 1 ½ whorls; teleoconch light orange, consisting of about 4 ¼ keeled whorls; sculpture consists of strong, rather narrowly-spaced radial ribs which are about 20 ribs/mm on the penultimate whorl and about 14 ribs/mm on the body whorl; sutures well impressed; umbilicus closed; aperture round; peristome thickened and expanded and doubled; columellar lamella well developed and directed anteriorly (Fig. 4).

Etymology
We named this new species "chadathongae" in memory of the second author's beloved mother, Ms. Wiang Chadathong.

Distribution
Only known from the type locality.

Taxon discussion
Diplommatina chadathongae sp. n. is another one of the Thai smallest Diplommatina species (average shell height = 1.69 ± 0.04 mm) and same size as D. krabiensis Panha & Burch, 1998 (shell height of type specimens are 1.6-1.7 mm and average shell height = 1.69 ± 0.04 mm). This new species differs from D. krabiensis by its dextral, cylindrical, narrowly-fine radial ribs, while the smallest species is sinistral, shell fusiform or ovate with widely-spaced radial ribs. This new species differs from Diplommatina miriensis Godwin-Austen, 1917 from Nepal by its shell being more slender and columellar lamella well developed.

Etymology
The species name "chantaburiensis" refers to Chantaburi, the Province of the type locality.

Distribution
Only known from the type locality.

Taxon discussion
Diplommatina chantaburiensis sp. n. is very similar to D. fusiformis sp. n. Nevertheless, D. chantaburiensis sp. n. has larger protoconch, shell more slender and no spiral striae between the radial ribs. This new species is also similar to the southern species D. hidagai Panha, 1998, but differs by its prominent protoconch, more widely-radial ribs and columellar lamella is poorly developed. Description. Shell minute dextral, fusiform, translucent, light orange, with about 6 ½ whorls that increase regularly in size and diameter until the last whorl which is slightly smaller in diameter than the penultimate whorl; protoconch orange, smooth, consisting of 1 ¼ whorls; teleoconch light orange, about 5 ¼ whorls; sculpture consists of thin, widely-spaced radial ribs with discernible spiral striae between the ribs; there are about 10 ribs/mm on the penultimate whorl and about 8 ribs/mm on the body whorl; sutures deep; umbilicus closed; aperture rounded, peristome thickened and expanded; columellar lamella relatively small (Fig. 4) .

Diagnosis
Diagnosis. Shell minute, dextral, translucent light orange, teleoconch sculpture consisting of widely-spaced axial ribs with spiral striae between the ribs; aperture rounded, columellar lamella relatively small, peristome, thickened and expanded.

Etymology
We named this new species "fusiformis" based on its fusiform shell shape.

Distribution
Only known from the type locality.

Taxon discussion
Diplommatina fusiformis sp. n. is similar to the southern species, D. hidagai Panha, 1998, but it differs by its more widely-ribbed shell, its more slender spire and its less prominent columellar lamella. Shell minute dextral, cylindrical, light orange, with about 7 whorls that increase regularly in size and diameter until the last whorl; protoconch orange, smooth, consisting of 1 ¼ whorls, covered with minute pits; teleoconch light orange, consisting of about 5 ¾ whorls; spires shouldered; sculpture consists of rather even and widelyspaced thin radial ribs with discernible spiral striae between the ribs; there are about 8 ribs/mm on the penultimate whorl and about 6 ribs/mm on the body whorl; sutures deep; umbilicus closed; aperture round; peristome thickened and expanded and doubled; columellar lamella rather bluntly rounded.

Animal.
Living animals had a greyish body, head, tentacles and foot, with an orange eye located at the base of each tentacle (Fig. 3C-E). The operculum was round and corneous. Snails were found living in leaf litter and plant debris in the limestone hills.
Due to the small population of each species, the live specimens of all species found in this study are hard to find. More observation and further study on anatomy are needed.

Etymology
We named this new species "khwantongae" in memory of Ms. Kanita Khwantong, who made the first discovery of this new species.

Distribution
This species is known only from the limestone hills in Chonburi and Rayong Provinces.

Taxon discussion
The shell shape of Diplommatina is generally fusiform or tower-shaped with mostly low and strong radial ribs, which are formed as tubular projections in some species and mostly rounded or angular periphery whorls. For example, the shell of D. hidagai is fusiform covered with low and strong radial ribs or the shell of D. nimannandhi Panha et al., 2002 has tower-shaped, radial ribs forming as semi-tubular peripheral projections. In this new species, Diplommatina khwantongae sp. n. is a very distinct species of epitoniid snail due to its cylindrical, thin radial ribs and shouldered whorls.  Table 1.

Discussion
In Thailand, a total of 18 Diplommatina species have been reported (Inkhavilay et al. 2019,Panha and Burch 2005, Tongkerd et al. 2013. From that, there is only one species, Diplommatina crispata khaochamaoensis recorded in eastern Thailand. This work increases the number of species reported in the eastern part of Thailand to five species and makes a total of 22 species of the Diplommatina in Thailand. These data imply that eastern Thailand might be a hot spot for the Diplommatina. Previous research on this microsnails' group reveals the high endemism in almost every species due to their ecology, living on the limestone hill that limits their dispersal ability (Panha and Burch 2005). In this study, the species described also show high endemism except for the Diplommatina crispata khaochamaoensis, which occurred in almost all study sites. (Fig. 5)