Terrestrial Mollusca of Cuc Phuong National Park, Vietnam - Results from the 2019 VIETBIO inventory work.

Background: Cuc Phuong National Park is located along a range of limestone karst mountains in northern Vietnam and spans over an area of 222 km² mainly covered by tropical evergreen forest. While a number of works have focused on the park's rich terrestrial mollusc fauna to date, the most extensive survey so far was carried out in 1998. In the present paper with its corresponding data package, we focus on the land snails and slugs recorded in the park during the VIETBIO inventory work between 29 April and 10 May 2019. Throughout this survey, live specimens and empty shells of terrestrial molluscs were collected at 34 sampling sites via visual search and additional soil sampling. Furthermore, we summarise the current knowledge on the park's land molluscs. New information: We present new data on the terrestrial mollusc fauna of Cuc Phuong National Park, which are linked to collection material stored at the Museum für Naturkunde Berlin (dry shells, wet specimens, samples for long-term tissue preservation) and to a smaller part at the Institute of Ecology and Biological Resources, Ha Noi (dry shells). Our data package contains a Darwin Core Archive with respective collection data, and four further data sets with photos of sampling sites and live specimens. We provide soil pH values and information on the microhabitats where live specimens were collected. In addition, the paper includes photos of collection material, which were partly taken with a DORA station developed for the high-volume imaging of molluscan specimens. In total, 116 species and 1 additional subspecies of land snails and slugs from 23 families were recorded. From the (sub-)species found, we matched 70 with nominal species-group taxa, while 47 remained provisionally named, with most of the latter likely belonging to undescribed species. However, as the taxonomic identification was only based on shell morphology, external features of the soft body, and sampling locality, it should still be regarded as provisional. We collected a total of 2666 specimens, 1909 of them alive and 757 as empty shells. From all taxa recorded, ca. 26% were only found at one sampling site each and ca. 15% were represented only by a single individual, which indicates that many species are rare or unevenly distributed. Based on our survey and previous works, we compiled a comprehensive list of 159 species and 1 additional subspecies known from Cuc Phuong National Park, about one-third of them non-eupulmonates, which places the park amongst the most species-rich tropical forest regions known worldwide. A mark-recapture analysis, based on the 1998 collection and our survey, resulted in an estimate of 178 ± 7 species of shelled land molluscs present in the park. When adding further (semi-)slug species that were disregarded for this analysis, at least 184 ± 7 terrestrial mollusc species can be expected. The high overall number of species in the park probably results from a combined effect of allopatric, mosaic, and sympatric diversity.