Karyology of the northern Baltic peracaridan Crustacea

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Abstract
To elucidate cytotaxonomic relationships of the species of Isopoda, Amphipoda, and Mysidacea inhabiting the northern Baltic Sea, their mitotic or meiotic chromosome configurations were investigated using orceine squash and Giemsa-stained air spread techniques. The twenty one examined species and their haploid chromosome numbers were Idotea granulosa (n = 28), I. baltica and I. chelipes (n = 29), Mesidotea entomon (n = 30), Jaera ischiosetosa (n = 15), Asellus aquaticus (n = 8), Gammarus oceanicus, G. locusta, G. salinus, G. zaddachi, and G. duebeni (n = 26–27), Calliopius laeviusculus (n = 9), Leptocheirus pilosus (n = 11), Corophium volutator (n = 14), Pontoporeia femorata (n = 14), P. affinis (n = 26), Neomysis integer (n = 34), Mysis mixta, M. relicta, and Praunus inermis (n = 52) and P. flexuosus (n = 49). The observed karyological features are in accordance with phylogenetic reconstructions based on morphology and zoogeographical histories of the species. Mysids are the connecting link with other Malacostraca and in their karyology resemble decapods with their high chromosome numbers. At lower taxonomic level, such as in Idoteidae or Gammaridae, most of the species show remarkable uniformity in their karyological features. Comparisons between geographically separated populations suggest, however, potential mechanisms which create karyological flexibility and consequent genetic variability in Crustacea inhabiting the Baltic and other northern brackish waters.