The terrestrial microsnail genus Aulacospira Möllendorff, 1890 (Eupulmonata, Stylommatophora, Hypselostomatidae) in Thailand with key to Thai species

Abstract Thai terrestrial microsnails in the genus Aulacospira Möllendorff, 1890 are revised based on the collection of the Zoological Research Collection, Burapha University, Chonburi Province, Thailand and recently collected material. Three new species are described: Aulacospira nutadhirai sp.nov. from Southern Thailand, and Aulacospira tekavongaesp.nov. and Aulacospira vanwalleghemisp. nov. from Eastern Thailand. The radula and genital system are described, and a key to Thai species is presented.


Materials and methods
Types and voucher specimens of previously described species were deposited in the reference collection of the Zoology Laboratory, Faculty of Science, Burapha University. The new species were collected from limestone hills in eastern Thailand. Collecting sites and their distribution shown in Figure 1. Shells were digitally photographed using a Cannon MP-E. Shell terminology (e.g., whorl number, apertural teeth, etc.) follows Panha and Burch (2005). Shell measurements (in mm) were taken by using a digital vernier caliper (Mitutoyo, Japan). Taxonomic identification of specimens was based mainly on Panha and Burch (2005), Dumrongrojwattana andPanha (2005, 2006), and Dumrongrojwattana (2008). Dichotomous key construction was based on shell morphology. The radula was exacted by boiling the dead snail in 1.0% NaOH for 1-2 minutes in a small test tube. The contents of the test tube were transfered into a small petri dish and radula removed under an Olympus SZ51 stereomicroscope. The radula was washed in three changes of distilled water, 3 minutes per rinse, and then dehydrated in an ethyl alcohol series of 10%, 30%, 50% and 70% v/v for 5 minutes in each concentration. The radula was then air-dried on a stub and scanned using an LEO 1450 VP scanning electron microscope at the Microscopic Center, Faculty of Science, Burapha University, Chonburi Province. Adult snails were also dissected to examine the genital system.
Remarks. Páll-Gergely et al. (2019) suggested that Thai and Philippine Aulacospira may not be closely related due to their unusual distribution pattern and suggested that the similar shell shape of these snails may be due to convergence but more data are needed to support this hypothesis. However, we continue to use Aulacospira for Thai species following the description of this genus by Pilsbry (1916Pilsbry ( -1918.
Remarks. The specific epithet "depressus" must be corrected to "depressa" to agree in gender with Aulacospira (musculine).
Radula. Central tooth small, unicuspid, triangular. Laterals irregularly bicuspid and consisting of a large internal cusp near and adjacent to a smaller, shorter outer cusp. Four laterals on each side of central tooth; first tooth largest, other teeth sequentially smaller. Marginals also irregularly, unequally bicuspid, with internal cusp larger than outer cusp. Marginal teeth 7 or 8 on each side of central tooth (Fig. 3A).

Aulacospira pluangtong
Radula. As in A. depressa (Fig. 4B). Genital system. Atrium shorter than vagina. Penis longer than epiphallus, with anterior portion a slender tube. Epiphallus connected to distal end of penis. Epiphallus glossy white, longer than vas deferens, with its anterior portion slender and cylindrical, its central portion slender and more bulging than posterior portion. Epiphallic flagellum absent. Epiphallic retractor caecum rounded and bulbous, attached to posterior portion of epiphallus. Vas deferens very long, slender, entering epiphallus apically. Vagina and free oviduct cylindrical, with vagina shorter than free oviduct. Gametolytic sac very long and cylindrical, with anterior portion connecting vagina and free oviduct and posterior portion with curved knob. Uterus long and cylindrical, with very thin prostate gland adhering to it. Hermaphroditic duct loosely convolute. Albumen gland large and yellowish. Dart apparatus absent (Fig. 4C, D).
Distribution. This species is only known from the limestone hills in Botong District, Chonburi Province, eastern Thailand (Fig. 1). Diagnosis. Shell minute, helicoid. Protoconch smooth; body whorl stout, with a short projecting downward tuba; peristome not expanded; aperture lacking teeth.

Aulacospira nutadhirai
Aulacospira nutadhirai sp. nov. is very similar to the eastern Thai species, A. khaopratun, but differs in its lower spire and more greatly inflated last whorl. Compared to Philippines species, Aulacospira nutadhirai sp. nov. is similar to A. porrecta but differs in the shape of the shell and in having no keel on the body whorl.
Genital system. Atrium shorter than vagina. Penis shorter than epiphallus, with anterior and central portion large, bulging and posterior portion curved. Epiphallus connected to distal end of penis. Epiphallus glossy white, longer than vas deferens, with anterior portion cylindrical, central and posterior portion cylindrical, and distal end curved. Epiphallic flagellum absent. Epiphallic retractor caecum rounded, connected to distal part of epiphallus. Vas deferens short, slender, entering epiphallus apically. Vagina and free oviduct cylindrical, with vagina large and shorter than free oviduct. Gametolytic sac long and cylindrical, with anterior portion connecting vagina and free oviduct, posterior portion swollen. Uterus long, large, with very thin prostate gland adhering to it. Hermaphroditic duct loosely convolute. Albumen gland large and yellowish. Dart apparatus absent (Fig. 4G, H).
Etymology. We name this species in honor of Mr Thammarat Nutathira or Kru Nok, a former staff member of Kampang Wittaya School, Thailand, who contributed to the study of the biodiversity and paleontology of the limestone in Satun Province.
Distribution. This species appears limited to the type locality (Fig. 1).
Aulacospira tekavongae sp. nov. is very similar to A. khaobote, but the shell is a conical and with a high spire, while that of A. khaobote shell helicoid and with a low spire.
Description. Shell minute, conical, brownish, with 4-4½ whorls. Tuba very short, projecting downward. Protoconch consisting of 1 ¼ whorls, with granulose wrinkles. Teleoconch smoothish, sculptured with uneven, oblique growth striae. Suture deep. Shell narrowly umbilicate. Spire high; first two whorls rounded, penultimate and body whorl with two distinct spiral sulci continuously to peristome. Peristome expanded; aperture round and lacking teeth (Fig. 4A).  A. depressa (Fig. 5B). Genital system. Atrium longer than vagina. Penis shorter than epiphallus, with anterior portion a short tube and bulging. Epiphallus connected to distal end of penis. Epiphallus longer than vas deferens, with anterior portion slender and cylindrical, central portion slender and more bulging than anterior and posterior portion. Epiphallic flagellum absent. Epiphallic retractor caecum rather bulging, attached to posterior portion of epiphallus. Vas deferens long, slender, entering epiphallus apically. Vagina and free oviduct cylindrical, with vagina shorter than free oviduct. Gametolytic sac long and cylindrical, with anterior and central portion bulging, posterior portion slender and curved knob. Uterus long and large, with very thin prostate gland adhering to it. Hermaphroditic duct loosely convolute. Albumen gland large and yellowish. Dart apparatus absent (Fig. 5C, D).
Etymology. We name this species in the hornor of Ms Rattanawadee Tekavong, a research collaborator, who has worked extensively on the eastern microsnail diversity.
Distribution. This species is known only from the type locality (Fig. 1).
The shell shape and periphery of the last whorl of A. vanwalleghemi sp. nov. is similar to A. pluangtong, but apertural teeth are absent. Apertural teeth are present in A. pluangtong.
Radula. As in A. depressa (Fig. 5F) Genital system. Atrium shorter than vagina. Penis shorter than epiphallus, with anterior and central portion large, bulging and posterior portion curved. Epiphallus connected to distal end of penis. Epiphallus longer than vas deferens, with anterior portion with cylindrical, central and posterior portion cylindrical, distal end curved; white glossy. Epiphallic flagellum absent. Epiphallic retractor caecum rounded, connected to distal part of epiphallus. Vas deferens short, slender, entering epiphallus apically. Vagina and free oviduct cylindrical, with vagina large and shorter than free oviduct. Gametolytic sac a very long and slender, with anterior portion bulging, connects between vagina and free oviduct, posterior portion curved. Uterus long and large, with very thin prostate gland adhering to it. Hermaphroditic duct loosely convolute. Albumen gland large and yellowish. Dart apparatus absent (Fig. 5G, H).
Etymology. We name this species in honor of Mr René Vanwalleghem, a Belgian conchologist who inspired the senior author to pursue mollusc research.
Distribution. This species appears limited to the type locality ( Fig. 1).

Key to species of Aulacospira in Thailand
This key is based on shell morphogy and is modified from Panha and Burch (2005).  (Fig. 6H)

Discussion
All species recorded here can be categorized into two groups based on shell morphology: 1) apertural teeth present and no conspicuous groove on the body whorl, and 2) the apertural teeth absent and with a conspicuous groove on the body whorl. The group with apertural teeth and without a conspicuous groove on the body whorl is composed of A. lampangensis, A. panhai, A. pluangtong, and A. smaesarnensis, while the other group without apertural teeth and with a conspicuous groove on the body whorl comprises A. depressa, A. khaobote, A. khaopratun, A. nutadhirai sp. nov., and A. tekavongae sp. nov. Aulacospira vanwalleghemi sp. nov. cannot be classified into either of these groups because both the apertural barrier and conspicuous groove are absent. The shell shape of A. panhai is distinctively different from other Thai species; its streptaxoid shell shape resembles the genus Pseudostreptaxis Mölendorff, 1890 and especially P. azpeitiae (Hidago, 1890) from the Philippines, which was described only by shell morphology (Möllendorff 1890;Páll-Gergely et al. 2019). We place A. panhai in Aulacospira, but more data, including anatomical and molecular, are needed to clarify its taxonomic placement.
The radulae of all examined species are tongue-shaped and with about 23-25 teeth per row. The radula formula is 7-8:4:1:4:7-8; there is a unicuspid central, larger bicuspid laterals, and a small, unequal bicuspid marginal. Compared with the microsnail genus Pupoides L. Pfeiffer, 1854 (Pupillidae Turton, 1831) there are 32 radula teeth per row, with the centrals trifid, laterals bifid, and marginal multicuspid. (Branson 1961) but in this study, the number of teeth per row in Aulacospira is fewer and shape of the teeth differs.
In this study, four species of the genus Aulacospira are described, based on characters of shells and genital systems. Aulacospira pluangtong was found to differ from other newly named species of the genus by its penis, vas deferens, and gametolytic sac. The penis of A. pluangtong is longer than the epiphallus and the vas deferens is a very long compared with the other new species.
Eastern Thailand and especially Chonburi and Rayong provinces seem to be a diversity hot spot for this genus and all species show high endemism ( Fig. 1; Table 1). Páll-Gergely et al. (2019) remarked on the unusual geographic distribution of Aulacospira split between the Philippines and Thailand. Further studies, including over a broader geographical area and molecular analyses, are needed to explain the biogeography of this genus.