Sciaridae (Diptera) from forest and mire habitats from three localities in central Finland were identified. The material consisted of 609 specimens belonging to 106 species. The following species were found as new to Finland: Bradysia subbetuleti, B. submoesta, B. subscabricornis, Corynoptera fera, C. furcifera, C. saetistyla, C. subsedula, Cratyna spiculosa, Leptosciariella helvetica, Lycoriella micria, Pseudolycoriella brunnea, P. nodulosa, Scatopsciara neglecta, Trichosia glabra and Sciara sp. n. (Menzel & Salmela, in prep.) and Ctenosciara exigua sp. n. The latter is described as new to science. Bradysia subbetuleti, Leptosciariella atricha, Leptosciariella tuberculigera and Lycoriella micria are redescribed. The occurrence of some rare or poorly known species is discussed, and the importance of peatlands for sciarid biodiversity in the boreal region is emphasized.

Four Oriental species of Aerumnosa Mohrig, 1999 (Diptera: Sciaridae), a genus previously known only from Papua New Guinea, are newly described and illustrated: Aerumnosa bituberculata sp. n. (India), A. gemmifera sp. n. (Malaysia: Sabah), A. horrifica sp. n. (Brunei, Thailand) and A. impar sp. n. (Malaysia: Sabah). On the basis of the new material, the genus is redefined. A key to the known species of Aerumnosa is presented, including four new species. An updated molecular phylogenetic analysis based on four gene markers (18S, 28S, 16S and COI) shows Aerumnosa to be a member of the subfamily Cratyninae. The monophyly of Cratyninae is well supported, which clade also includes the genera Hyperlasion Schmitz, 1919, Pnyxiopalpus Vilkamaa & Hippa, 1999 and Pseudoaerumnosa Rudzinski, 2006. According to the present phylogenetic hypothesis, the monophyly of Cratyna Winnertz, 1967 s. l. needs to be revisited. The clade including Cratyna (s. str.) ambigua (Lengersdorf, 1934) appears as the sister group of Aerumnosa.

The genus Spinopygina gen. nov. (type species Camptochaeta uniceps Hippa & Vilkamaa, 1994) from western North America is described. The genus includes the following eight species: Spinopygina acerfalx sp. nov.; S. aurifera sp. nov.; S. camura sp. nov.; S. edura sp. nov.; S. peltata sp. nov.; S. plena sp. nov.; S. quadracantha sp. nov.; and S. uniceps (Hippa & Vilkamaa, 1994) comb. nov., transferred from Corynoptera Winnertz. The new species are described and Spinopygina uniceps is re-diagnosed. The species are keyed and illustrated. In the maximum-likelihood phylogenetic hypothesis based on four gene fragments (28S, 18S, 16S and COI), Spinopygina gen. nov. appears as the sister group of Claustropyga Hippa, Vilkamaa & Mohrig, 2003. In the same analysis, a remarkable, undescribed species is placed within Camptochaeta Hippa & Vilkamaa clade.

On the basis of re-evaluation of morphological characters of the Lycoriella group of genera and subgenera, generic rank is given to the two species groups belonging to Lycoriella (Hemineurina) Frey, 1942 and to Lycoriella (Coelostylina) Tuomikoski, 1960. The Lycoriella (Hemineurina) inflata group, including the type species of the subgenus, Sciara conspicua Winnertz, 1867, is treated as the genus Hemineurina stat. n. and the Lycoriella (Hemineurina) vitticollis group as the genus Trichocoelina gen. n. (type species Sciara vitticollis Holmgren, 1883). Coelostylina Tuomikoski, 1960 (type species Lycoriella (Coelostylina) freyi Tuomikoski, 1960) is a junior homonym of Coelostylina Kittl, 1894, and is renamed Stenacanthella nom. et stat. n. The genera are diagnosed and their phylogeny is discussed. Eight species are excluded from the Lycoriella group. They are transferred to the genera Bradysiopsis Tuomikoski, 1960, Camptochaeta Hippa & Vilkamaa, 1994, Merizomma Sasakawa, 2003 stat. n. and Scatopsciara Edwards, 1927 (five species) or are for the time being regarded as incertae sedis (two species) and as nomen nudum (one name). Numerous nomenclatural corrections are made also in the genera Hemineurina Frey, Stenacanthella Vilkamaa & Menzel and Trichocoelina Vilkamaa & Menzel. Altogether 42 new combinations, three changes in status and one new synonym are presented. A lectotype is designated for Hemineurina algida (Frey, 1948) and two Hemineurina species names are removed from synonymy and given full species status. The following species of Trichocoelina are newly described: Trichocoelina absidata sp. n. (Russia: Krasnodarsk region), T. aemula sp. n. (Finland, Russia: Krasnodarsk region), T. biplex sp. n. (Canada: Newfoundland and Labrador, Yukon), T. dicksoni sp. n. (Russia: Arkhangelsk oblast, Kemerovsk oblast, Krasnodarsk region), T. dispansa sp. n. (Russia: Krasnodarsk region), T. dividua sp. n. (Canada: Northwest Territories), T. hians sp. n. (Canada: Yukon), T. imitator sp. n. (Canada: Yukon), T. incrassata sp. n. (USA: Alaska), T. ithyspina sp. n. (Norway), T. jukkai sp. n. (Finland), T. magnifica sp. n. (Canada: Yukon), T. nefrens sp. n. (Russia: Krasnodarsk region), T. obesula sp. n. (Norway), T. oricillifera sp. n. (Finland, Norway), T. planilobata sp. n. (Finland), T. quintula sp. n. (Finland), T. semisphaera sp. n. (Finland, Norway), T. semusta sp. n. (Italy, USA: Alaska), and T. tecta sp. n. (Canada: Nunavut, Yukon, Russia: Krasnodarsk region, Yamalo-Nenets Autonomous Okrug, USA: Alaska). The Trichocoelina species are keyed, the 20 new species are described and illustrated, and the 9 previously known ones, transferred to the new genus, are briefly diagnosed and the taxonomically relevant literature regarding them is listed. Trichocoelina janetscheki (Lengersdorf, 1953) comb. n. and Trichocoelina brevicubitalis (Lengersdorf, 1926) comb. n. are redescribed. The genus Trichocoelina currently includes 29 species: 17 in the Palaearctic, 6 in the Nearctic and 6 in the Holarctic. All known species are northern or montane.

A checklist of the family Sciaridae (Diptera) recorded from Finland is provided. The genus Sciarosoma Chandler with a disputed family placement is also included in the list.