Light microscopic and EM investigations of lorica-dwelling choanoflagellates (Acanthoecaceae) were carried out on water samples from the Isefjord, collected Jan. and Feb. 1975. Seven species are reported from the area. These include two new species, CRINOLINA isefiordensis gen. nov. et sp. nov., and Parvicorbicula circularis sp. nov. Pleurasiga reynoldsii is new to the Danish flora, and P. orculaeformis (recorded with some reservation as to specific identity) is a new record from North Atlantic waters. A morphological description is given of the spherical colonies of Diaphanoeca pedicellata which predominated in the Jan. plankton samples. The arctic species D. aperta is transferred to Crinolina: C. aperta (Leadbeater) comb. nov.