Slugs and semi-slugs of the superfamily Helicarionoidea (Gastropoda, Stylommatophora) collected in North Vietnam during the 2023 Bulgarian Zoological Expedition, with emphasis on the genus Ostracolethe

A list of species of slugs and semi-slugs of the superfamily Helicarionoidea collected in North Vietnam in 2023 is presented. A new species of the genus <i>Ostracolethe</i> Simroth, 1901, <i>Ostracolethe penevi</i> Dedov & Vu, <b>sp. nov.</b>, is described, which was collected from a single locality in North Vietnam. The validity of <i>Ostracolethe fruhstorfferi</i> Simroth, 1901 is confirmed, and the unusual torus-toroid structure is discussed. A key for the determination of the helicarionoid genera of slugs and semi-slugs from North Vietnam is also provided.