A revision of the choanoflagellate genera Desmarella Kent, 1880 and Kentrosiga Schiller, 1953 is presented following a light and electron microscopical investigation of the type species of both genera: Desmarella moniliformis and Kentrosiga thienemanni. It is argued that differences between the type species of the two genera represents differences at the species level. The main generic character of Kentrosiga Schiller, 1953, namely, the presence of tentacle-like threads at the posterior end of the cell, is not considered to be a character even at the species level, since most choanoflagellate species illustrate this feature. On the basis of the data presented we consider the generic name Kentrosiga Schiller, 1953 is invalid as a younger synonym of Desmarella Kent, 1880. A revised list of species attributable to Desmarella Kent, 1880 is also given.