Arctic coccolithophorids: Wigwamma arctica gen. et sp. nov. from Greenland and arctic Canada, W. annulifera sp. nov. from South Africa and S. Alaska and Calciarcus alaskensis gen. et sp. nov. from S. Alaska

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Abstract
Two new genera of coccolithophorids, one with two species, have been described and illustrated by means of electron microscopy of wild material from various sources in the northern or southern hemisphere. The main diagnostic features of the new genus Wigwamma (type species W. arctica sp. nov.) include ‘ring-shaped’ coccoliths, attached to the edges of unmineralized plates with characteristic surface patterning, and with some or all carrying superstructures composed of four (or sometimes two) rod-shaped crystallites, converging to a point distally and attached proximally to the subtending calcified scale-rim in a characteristic manner. After comparisons with the unmineralized scales of Chrysochromulina , these coccoliths are interpreted as equivalent to the bases, including the support struts, of certain spined scales comparable in a general way with those of C. pringsheimii but with the spine itself undeveloped or vestigial. Analogous changes, carried out independently and with many differences of detail implying a different prototype source, are inferred to explain the coccolith morphology of another new genus, Calciarcus , at pre­sent only known in a preliminary way in the north Pacific (near Homer, S. Alaska). The coccoliths of this organism have been investigated chemi­cally by means of the electron probe CORA. Further comparisons between Wigwamma , more especially W. annulifera sp. nov., and other coccolitho­phorids, notably Ceratolithus , Pappomonas and Papposphaera have emphasized the value of crystallographic details as taxonomic and phyletic markers, in situations where coccolith morphology as a whole is equivocal as a result of convergence. The available distributional data for all known arctic coccolithophorids are then summarized and the conclusion is drawn that collectively they may represent a highly selected community adjusted to arctic conditions and perhaps able to perennate locally but ultimately derived by immigration from the north Pacific. Other conclusions to which the arctic coccolithophorids collectively have led are summarized in a final paragraph.

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