NEW RECORDS OF CLAUSILIIDAE (MOLLUSCA: GASTROPODA) IN THE DEMOCRATIC PEOPLE’S REPUBLIC OF KOREA WITH NOTES ON THEIR REPRODUCTIVE STRATEGY

The knowledge of clausiliid fauna of the northern part of Korean Peninsula (Democratic People’s Republic of Korea) is still fragmentary. The field survey carried out by the Cracow Institute of Systematics and Evolution of Animals, Polish Academy of Sciences in 1971–1992 provided data on the occurrence of two species: Zaptyx stimpsoni miyanagai (Kuroda, 1936) and Tauphaedusa tau (O. Boettger, 1877) in this region. The specimens of the latter species contained embryonic shells, thus confirming its viviparity. For reproductive mode assessment we used μ-CT scanning and 3D reconstructions. kEy worDS: land snails, Phaedusinae, viviparity, Korean Peninsula, micro-CT


INTRODUCTION
Clausiliid snails of the Far East (in traditional sense) are known from Japan, eastern China, Taiwan and the southern part of the Korean Peninsula (e.g. kwon 1990, 1993, Minato 1994, norDSiEck 1997, 1998, 2005. The Phaedusinae are the main group of the Far East Clausiliidae. Much information on the subfamily's systematics, shell and genital morphology is contained in norDSiEck's papers (1998,2001,2003,2007). He also discussed the reproduction modes (oviparity or ovoviviparity) in a large number of taxa and its taxonomic significance.
Although the land snails of Korean Peninsula have been studied since the second half of the 20th century, there is little information from its northern part. MöllEnDorff (1887) published a list of 26 land snail species from Korean Peninsula, including two localities near the border of the northern part of Korea with Manchuria, but the five clausiliid species listed there (Clausilia aculus Benson 1842, C. tau O. Boettger 1877, C. gottschei Moellendorff 1887, C. clavi formis Pffeifer 1850, C. belcheri Pffeifer 1850) were found only in the southern part of the peninsula or on Korean Archipelago. He did not collect gastropods personally, but he examined materials collected by Gottsche during his trip to Korea (GottSchE 1886). Similarly, PilSbry & hiraSE (1908a), based upon the same shell collection, described several new species of land snails from Fusan (southern part of Korean Peninsula), among them one clausiliid -Euphaedusa fusaniana (as Clausilia fusaniana). The first survey of land snails of the whole Korean Peninsula was done by Kuroda (kuroDa 1908, PilSbry & hiraSE 1908b, PilSbry 1927. Kuroda explored the northern part of the peninsula and focussed on three areas: provinces Pyongan-pukdo, Pyongan-namdo and the border of Hvanghe-pukdo and Hvanghenamdo. Again, clausiliid snails were found only in the southern part of the peninsula and on the Quelpart Island. In 1939 Kuroda and Miyanaga mentioned Paganizaptyx miyanagai (Kuroda, 1936) from two localities: Sanbo and Kymgang-san Mts in the northern part of Korean peninsula. Hence, only one clausiliid species was probably recorded so far from the present territory of the Democratic People's Republic of Korea, including a record of this species in the list of land snails from DPRK (StworzEwicz 1997). To our knowledge, there are no other records of Clausiliidae from the territory of DPRK though the northern part of the peninsula was repeatedly subject to malacological field surveys (riEDEl 1967, StworzEwicz 1997. kwon (1993) listed five clausiliid taxa from the Republic of Korea: Euphaedusa aculus mokpoen sis (Pilsbry et Hirase, 1909), E. fusaniana (Pilsbry et Hirase, 1908(a)), Reinia variegata (A. Adams, 1868), Paganizaptyx miyanagai (Kuroda, 1936), and P. miya nagai ullungdoensis Kwon et Lee, 1991 Kuroda et Hukuda, 1944. The taxa in the national liSt (2015) include also E. acu lus coreana (Möllendorff, 1887), Euphaedusa gottschei (Möllendorff, 1887) and Phaedusa sieboldii (Pfeiffer, 1848).
In this paper we present the first documented data on the occurrence of clausiliids in the northern part of the Korean Peninsula (Democratic People's Republic of Korea) together with data on their reproductive mode.

MATERIAL AND METHODS
Clausiliids were collected during four out of the 22 zoological expeditions to DPRK carried out within the scientific exchange between the Cracow Institute of Systematics and Evolution of Animals, Polish Academy of Sciences and the Zoological Institute of Korean Academy of Sciences in Pyongyang in 1971-1992(Pawłowski et al. 2000. Although malacological investigations were conducted in all the provinces of the country clausiliids were found only in two sites ( Fig. 1): Kymgang-san (the Diamond Mountains) in Kangvon-do province -38°30'-38°45'N and 128°00'-128°20'E (coll. A. SzEPtycki in 1981) and Ryongak-san (= Jongak-san), mountain in the suburbs of Pyongyang, ca.13 km west of the city centre, in Pyongyang-si province -39°02'N, 125°34'E (coll. A. SzEPtycki in 1971 and1974;E. StworzEwicz in 1991). Only empty shells of one species were found in each of the localities.
To assess the reproductive mode of the collected snails, we used computer microtomography (μ-CT) which makes it possible to check the presence of embryonic shells inside the parental shell, as well as to assess the development of apertural barriers and clausilium without shell destruction. The potential of this analytical tool was previously demonstrated using fossil and extant gastropods (e.g. MarxEn et al. 2008, aShkEnazi et al. 2010, SulikowSka-DrozD et al. 2014. In this kind of analysis negative results could not be automatically classified as oviparity, while the embryos recorded inside parental shell indicated the reproduction strategy involving long embryo retention or viviparity (=ovoviviparity sensu toMPa 1979). The analyses were conducted in the X-ray Microtomography Laboratory, Department of Biomedical Computer Systems, Institute of Computer Science, University of Silesia. Scanning was performed with an XMT scanner (GE Sensing and Inspection Technologies, Phoenix|X-ray, Wunstorf, Germany) using the same setting: voltage 80 kV, current 90 µA, timing 250 ms, 1,000 projections, rotation angle 360°, and voxel size 7.5 µm.
These data were used to reconstruct 3D images of shell interior. 3D models were created in cooperation with the Custom Medical Implants Laboratory in Lodz, equipped with software Amira v.5.5.0., FEI visualization Sciences Group Ltd., USA.

RESULTS AND DISCUSSION
Clausiliids collected in the Democratic People's Republic of Korea were identified as Zaptyx stimpso ni miyanagai (Kuroda, 1936) and Tauphaedusa tau (O. Boettger, 1877).
The first species was previously placed in Hemiphaedusa (Hemizaptyx) Pilsbry, 1905(norDSiEck 2007), or in Paganizaptyx Azuma, 1982(lEE 2014. However, the latter genus is currently provisionally treated as a junior synonym of Zaptyx (sensu lato) (Motochin et al. 2017) "due to the poorly resolved phylogenetic status" and we follow this view. Zaptyx stimpsoni (A. Adams 1868) is a variable species with several subspecies described (norDSiEck 2007) and should be regarded as a complex of species (r. uEShiMa, personal communication). From South Korea the subspecies Zaptyx stimpsoni miyanagai (Kuroda, 1936) was reported (kwon 1990).
In Kymgang-san, two shells of Z. stimpsoni miyan agai were collected from a moss-covered oak trunk. The dimensions of the individuals (one shell with broken apex and a hole on the back of the body whorl) are: shell height 11.3-11.72 mm, shell width 2.86-3.1 mm, number of whorls 7.5, aperture height: 2.41 mm, aperture width: 1.96 mm. The upper and spiral lamellae are connected, the subcollumellar lamella does not reach the aperture margin. The principal palatal fold is long and well developed, the lunella is attached to the upper palatal fold and together they form the letter tau (τ). The μ-CT examination revealed no embryos inside the shells (Figs  2-6). Although it is not the direct evidence of oviparity, the narrow shape of clausilium and the steeply ascending lower lamella suggest this mode of reproduction (see norDSiEck 2003).
Among the localities of Z. stimpsoni miyanagai in the Republic of Korea kwon (1990) lists also "Oekŭmgang", situated on the southernmost fringe of the Kymgang-san Mts., which extends up to the border of South Korea. The new locality of Z. stimp soni miyanagai on the other side of the border (in DPRK) is the northernmost record from the Korean Peninsula. The next nearest locality of this species is known from Mt. Soyo in Gyeonggi-do (type locality), situated ca. 200 km to the south-west of the Kymgang-san (rED Data book 2012: 56-57). The remaining known sites are Sambang and Ullŭng Island (kwon 1990).
The second species, Tauphaedusa tau, (previously Tauphaedusa was treated as subgenus of Euphaedusa (norDSiEck 2007)) was found in Ryongak-san, in 1971Ryongak-san, in , 1974Ryongak-san, in and 1991. The southern slope of Ryongak Mountain is covered mainly with dry oak forest with pines, and shells (13 specimens) were collected on the ground around trunks of the old trees, among dry leaves and stones.
Three individuals were examined by μ-CT; two of them contained single embryos (shell of 2-2.5 whorls) (Figs 7-13). Thus the viviparous reproduction of this snails is unquestionable, as in the previ-ously examined populations of Tauphaedusa tau from Honshu (SulikowSka-DrozD et al. 2018). The apertural barriers in these shells include a broad clausilium plate and the lower lamella spirally ascending, the superior and spiral lamella connected, the inner end of the lower lamella situated close to the inner end of the spiral lamella, the plica principalis long, the upper palatal fold connected to the lunella, forming a reversed Greek letter τ, however the lunulla in some shells is very weak. The structure of apertural barriers of our individuals differ significantly from that of E. fusaniana which features a significant gap between the superior and spiral lamella. Taupheadusa tau is widespread in Japan and also introduced to the main-land China (Minato 1994, norDSiEck 2001. The phylogenetic relationships between T. tau and similar species T. gottschei described from Mokpo city situated in the south-western part of the Korean peninsula (MöllEnDorff 1887) and also found in Reisui, ca. 150 km east of Mokpo (kuroDa & MiyanaGa 1943) remain to be investigated in the future taxonomic revision of the genus.
Both Zaptyx stimpsoni miyanagai and Tauphaedusa tau seem to be very rare in North Korea. Despite the careful search in most of the provinces of DPRK, only a few empty shells were found. Z. stimpsoni miyanagai is regarded as an endemic Korean subspecies, and is placed in the rED Data book (2012).
Figs 2-6. Zaptyx stimpsoni miyanagai (Kuroda, 1936) from Kymgang-san (the Diamond Mountains) in Kangvon-do province, North Korea: 2-3 -frontal and side view of the shell, 4-6μ-CT based reconstruction of shell: position of clausilium (4), clausilium (5), position of upper and spiral lamella (6). Scale bar (Fig. 2) 1 mm Our study contributes to the knowledge of the land snail fauna of the North Korea. We report the localities of two clausiliid species close to the northern limits of their distribution in the continental Asia. Acquiring μ-CT images of shells allowed to identify the reproductive mode of collected snails.