ABSTRACTEight species of loricate choanoflagellates (Acanthoecidae),Acanthoecopsis spiculiferaNorris,Bicosta antennigeraMoestrup,Bicosta spiniferaThrondsen,Calliacantha multispinaManton&Oates,Calliacantha simplexManton&Oates,Crinolina apertaLeadbeater,Diaphanoeca multiannulatan. sp., andParvicorbicula socialis(Meunier) Deflandre, have been observed, by light and electron microscopy, in samples obtained from the Weddell Sea during the austral summer of 1977.Diaphanoeca multiannulatais described for the first time from these samples: the other organisms are discussed. The distribution of most species within the Weddell Sea was widespread. Habitats in which choanoflagellates were found included the water column, the edge of (or ponds on) ice floes, and the interior of ice floes. The distributional, environmental, habitat, and/or morphological range of all previously described species is expanded. Methods of variation of transverse costal diameters between genera may be potentially useful to the understanding of taxonomy and phylogeny of this family.