Volume 29

Vietnam with its limestone ranges that are concentrated mainly in northern, north–central and southern parts, and many different limestone islands running along the coastline, has a phylogenetically-diverse land snails fauna dominated by endemic species. The genus Cyclophorus (Cyclophoridae) in Vietnam is studied. Sixty species and subspecies from various habitats of limestone areas throughout Vietnam are confirmed and recorded. New species and subspecies, Cyclophorus implicatus kanhoensis ssp. nov., from Northwestern Vietnam, and Cyclophorus tamdaoensis sp. nov., from Northern Vietnam are described and discussed. In this paper, the Cyclophorus courbeti var. leucostoma Dautzenberg et Fischer, 1905, is elevated to subspecies.

Unio mongolicus Middendorff, 1851 (Bivalvia: Unionidae) was described from Gorbitza mountain stream (in the east of Trans-Baikal Territory, Russia) and the taxonomy has changed over the past century and a half. A specimen of Middendorffinaia mongolica from the Gorbitza stream collected 160 years later is a match with the type illustration of Unio mongolicus from the type locality. Comparison of the shell morphology of the type specimen of U. mongolicus with the modern specimen collected from this location, combined with our analyses of molecular, anatomical and conchological data of M. cf. mongolica species from rivers of the Upper Amur River Basin and the far eastern Russia, revealed that these taxa all belong to a single polymorphic species. The molecular analysis of the COI gene fragment mtDNA of examined Comparatory Species assigned to Middendorffinaia Moskvicheva and Starobogatov, 1973 confirmed they are only intraspecific forms of M. mongolica. Morphological and genetic distances between M. mongolica and Nodularia douglasiae Griffith et Pidgeon, 1833 confirmed their assignment to two independent genera. Differences of morphologically similar species M. mongolica, N. douglasiae and Unio crassus Philipsson in Retzius, 1788 were separated based on conchological characteristics and anatomical features. History of the taxonomic changes for Unio mongolicus is discussed here.

For the first time, the widely spread Antarctic species Leptochiton antarcticus was found at the Emperor Seamounts in the North Pacific Ocean. In spite of a large distance between the Emperor Seamounts and Antarctica, the found specimen have very similar shell, girdle, radula and gill features to the type material. I propose that L. antarcticus spread to the North Pacific from the Antarctic via a deep-water current near the ocean floor, and perhaps it inhabits the slopes of islands and continents from the South Ocean to the Emperor Seamounts.

Two substitution names are proposed for primary homonyms introduced for land snail of the family Camaenidae in Thach [2018].