Contributions to the taxonomy and ecology of the Chironomus plumosus sibling species aggregate (Diptera: Chironomidae): the brackish water populations of Tvärminne area, Finland

Based on pupal exuviae, two sympatric pupal forms of Chironomus plumosus auctt. are present in the museum materials collected in 1952–1962 from the brackish water near the Tvärminne Biological Station at the northern Baltic Sea. The predominating undescribed type of the pupal exuviae is called here the “Balticmarine species” (possible C. plumosus sensu Linnaeus; direct observations by Linnaeus of Tipula plumosa from freshwater are not on record). Its pupal exuviae and the associated female and male from the Tvärminne population are described. Attempts to find larvae of the genus Chironomus in the sea area of Tvärminne for the renewed and more complete studies failed during the 1980s and 1990s. Only two larvae of the undescribed species of the karyological Chironomus plumosus group were captured. The possible reasons for the supposedly changed environmental conditions are discussed.