Cold marine indicators of the late Quaternary: the new dinoflagellate cystgenus Islandinium and related morphotypes

Round, brown, spiny dinoflagellate cysts characterise many modern high-lati tude assemblages. Abundance is often highest where summer sea-surface tempe ratures seldom exceed 7 degreesC and where winter sea-surface temperatures are around 0 degreesC, making this morphological group important for recons tructing cold intervals within marine Quaternary sequences. Our analysis of modern sediments from the Beaufort Sea of Arctic Canada, the Kara and Lapt ev seas of Arctic Russia, and across the Arctic Ocean, allows us to recogni se the new cyst genus Islandinium along with the extant species Islandinium minutum (Harland and Reid in Harland et al., 1980) new combination (basion ym: Multispinula? minuta), Islandinium? cezare (de Vernal et al., 1989 ex d e Vernal in Rochon et al., 1999) new status and combination (basionym: Mult ispinula? minuta var. cezare) sensu lato, and Echinidinium karaense new spe cies. Of these, the generotype Islandinium minutum is a well-known but morp hologically problematic species. We have re-examined the type material from the Beaufort Sea and studied specimens from across the Arctic, and our obs ervations clarify ambiguities in the original description of this species. The archeopyle of Islandinium minutum results from the loss of three apical plates, an unusual style among peridiniphycidean dinoflagellates. The asym metrical location of these plates around the apex is distinctive, and proba bly contributed to earlier misunderstandings of the archeopyle. Previous at tributions to Multispinula? and Algidasphaeridium? are unsustainable. Maps showing the distribution of Islandinium minutum are given for the Northern Hemisphere and show this species to be polar to north-temperate, whereas Is landinium? cezare s.l. and Echinidinium karaense appear to be more restrict ed to polar environments. Copyright (C) 2001 John Wiley & Sons, Ltd.