Lochhead, John H. London, United Kingdom.
McLaughlin, Patsy A. Formerly, Shannon Point Marine Center, Western Washington University, Anacortes, Washington.
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A group of tiny marine crustaceans (body length 2.0–4.0 mm or 0.08–0.16 in.), discovered in 1954. Initially, cephalocarids were thought to be a living representation of what the primordial crustacean looked like. In recent years, that view has changed, with the Branchiopoda currently postulated to represent the most primitive of extant major crustacean taxa. In the classification of J. W. Martin and G. E. Davis (2001), the Branchiopoda are basal, whereas the Cephalocarida are positioned between the Remipedia and Maxillopoda, suggesting a more advanced evolutionary position for the class. Nonetheless, in their discussion of “most primitive,” Martin and Davis acknowledge that the question is still unresolved. At present, the Cephalocarida comprise ten species, assigned to five genera in one family. They have been found in flocculent surface deposits of mud or silty sand, from the intertidal zone down to depths of 5000 ft (1500 m), on the shores of all continents except Europe. Population densities up to an average of 16 individuals/ft2 (177/m2) have been recorded. See also: Brachiopoda; Crustacea
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