A new spider species of the genus Pholcus Walckenaer, 1805, Pholcus osaek sp. nov., in the family Pholcidae C.L. Koch, 1850, is described from Korea. This new species belongs to phungiformes-group in the genus. It can be distinguished from its congeners by the shape and structure of genital organs of both males and females. It is found on and between rock walls in mountainous mixed forests. Additionally, the taxonomic status of Pholcus uksuensis Kim & Ye, 2014 is revalidated, re-diagnosed, and redescribed based on specimens collected from the type locality. Considering differences mentioned in the diagnosis through revalidation, P. uksuensis is regarded as a distinct species. Therefore, it should be removed from the synonymy of P. woongil Huber, 2011.

Two spider species of the genus Pholcus Walckenaer, 1805, Pholcus muju sp. nov. and Pholcus yeongheung sp. nov. in the family Pholcidae C. L. Koch, 1850 are newly described from Korea. These two new species belonging to phungiformes-group in the genus can be distinguished from their congeners by the shape and structure of genital organs of both males and females. They are found on rock walls in mountainous mixed forests. This work provides diagnoses, detailed descriptions, and taxonomic photographs for these new species.

The present study describes Philodromus rufus Walckenaer, 1826 with detailed descriptions, taxonomic photographs, distribution map, and proposition of a new synonym. Due to morphological similarity between P. pseudoexilis Paik, 1979 and P. rufus, taxonomic identity of P. pseudoexilis has been doubtful to date. A detailed bibliographic study of types of P. pseudoexilis between P. rufus and examination of specimens from the type locality of P. pseudoexilis with specimens of P. rufus collected across the country showed that P. rufus has all diagnostic characters found in types of P. pseudoexilis. Therefore, P. pseudoexilis Paik, 1979 should be regarded as a new synonym of Philodromus rufus Walckenaer, 1826.

A poorly known spider, Pholcus kwangkyosanensis Kim & Park, 2009 is redescribed with diagnosis, detailed descriptions, and taxonomic photographs of diagnostic characters. P. kwangkyosanensis is similar in appearance to P. kwanaksanensis Namkung & Kim, 1990, in terms of the shape of the genital organ and body, but it can be easily distinguished from the latter by the shape of the cheliceral apophysis, uncus, and procursus in males, as well as the shape of the epigynum and pore plates in females. The specimens of this spider were collected at the type locality (Mt. Gwanggyosan, Suwon), specifically under the bridge on a local stream in an agricultural landscape surrounded by rice fields, upland fields, or horticultural greenhouses.

Three species belonging to two families of minute-sized spiders, viz, Theridiosoma fulvum (Araneae: Theridiosomatidae), Microdipoena ogatai and Microdipoena shenyang (Araneae: Mysmenidae), were discovered for the first time in Korea. Previously T. fulvum and M. ogatai were known to distribute only in Japan, M. shenyang only in China. All former records of Microdipoena jobi from Korea are misidentifications of M. shenyang. Detailed descriptions and photographs of three species are provided.

The present study describes Philodromus paiki sp. nov., which was previously misidentified as P. fuscomarginatus (De Geer, 1778), P. poecilus (Thorell, 1872), and P. spinitarsis Simon, 1895 in Korea, as a new species with diagnosis, detailed descriptions, and taxonomic photographs. Additionally, P. spinitarsis is also described to correct previous misidentifications of Korean records of the species.

Currently 41 valid species of the Pholcus phungiformes-group (Araneae: Pholcidae) have been known from Korea. In this study, four new species of this species-group were discovered from Gangwon-do and eastern Chungcheongbuk-do. These new species have common characteristics with Pholcus socheunensis, such as broad and membranous prolateral process and strongly curved pseudoappendix in male palp. The female of Pholcus montanus in the original description is the misidentification of a new species. Brief diagnosis, photographs and a distribution map of the new species and P. socheunensis with discussion on their sympatric distribution are provided.

A male Spheropistha melanosoma Yaginuma, 1957 from Korea in the family Theridiidae Sundevall, 1833 is described with measurements and morphological photos of the diagnostic characteristics. This species was collected with a sweep net around arable lands in a mountainous mixed forest during the investigation of spider fauna on Ulleungdo Island in 2019.

Two species of the genus Oxytate L. Koch, 1878 have been recorded in Korea to date. The spider fauna was surveyed in the mountainous terrain of Mt. Hallasan National Park in 2019. A female of Oxytate lobia sp. nov. was collected with a sweep net between shrubs in mixed forests during a seasonal spider survey and is described with measurements, morphological illustrations, and a diagnosis. The new species can be easily distinguished from similar species within the genus by the long copulatory duct conjugated with a spermatheca, a pair of triangular pits at the bottom, and no ditches.

Two linyphiid spiders, Saitonia kawaguchikonis Saito & Ono, 2001 and Asthenargus niphonius Saito & Ono, 2001 were confirmed from Korea for the first time. Males of S. kawaguchikonis and a female of A. niphonius were collected with pitfall traps in a leaf litter of mixed forests in three National Parks (Hallyeohaesang National Park, Mt. Naejangsan, and Mt. Sobaeksan) during the seasonal surveys for the spider fauna in mountainous terrain from 2018 to 2020. These two species were formerly known from China and Japan, or only from Japan, respectively. The present study describes these two species with measurements, morphological illustrations, and a distribution map. This report adds the genus Asthenargus Simon & Fage, 1922 from Korea to the Korean spider fauna for the first time.

Arcuphantes catillus n. sp., a new species of the genus Arcuphantes Chamberlin and Ivie, 1943 is described from Korea. The present species is distinguishable from its known similar congeners by a conspicuous proximal process and a blunt lateral process of the paracymbium, feathery tipped lamellar extension of the pseudolamella, and bowl-like posterior part of radix. The present new species was collected from the leaf litter layer of mixed forest on a hillock around rice fields with a pitfall trap.

Haplodrassus nojimai Kamura, 2007 of Gnaphosidae, which is only known in Japan was newly described in Korea with measurements and morphological illustrations. A female was collected from the levee of rice fields using a pitfall trap. The female epigynum has thick and remarkable transverse wrinkles and is densely covered with long blackish-gray hairs. The anterior hood was slightly rounded and the lateral margins were relatively short. The median septum was V-shaped with a broad base on the median part, and a pair of spermathecae was visible. The male is still unknown.