The overall total of living polycystine species is probably around 300-600, but this review includes only 164 taxa. Unfortunately, our present state of knowledge is insufficient for a significantly greater coverage. All polycystine families need detailed taxonomic work, but some are especially poorly known (e.g., Actinommidae, Pyloniidae, Litheliidae, Tholoniidae, Plagoniidae). However, the inexperienced student should not be discouraged by the fact that the available literature fails to assist in identifying very significant proportions of the shells present in any given sample. As mentioned above, most radiolarian-based ecological and paleoecological surveys restrict their scope to some 20-40 polycystines, the rest being ignored altogether. Although coverage of an ampler inventory is clearly desirable, these restricted databases allow one to draw very valuable environment-related conclusions. Furthermore, in order to circumvent identification-related problems, the use of family-level assignments has been advocated for environmental and biogeographic analyses (Kruglikova 1981, 1987).
The following section presents succinct information for the identification of the taxa recorded in the South Atlantic Ocean, as well as for several others whose presence in the area is very likely, but has not been confirmed yet.
When applicable, species names are followed [in square brackets] by some of the other most common names under which the form has been recently cited in the literature. Diagnostic information is provided as short remarks stressing the characters which help differentiate the taxon from closely related forms; they are not meant to replace detailed descriptions, but in most cases these remarks, in combination with the illustrations, should suffice for producing adequate identifications of the radiolarians treated. Keys are not adequate for this particular group due to their lack of flexibility, and because they are more prone to lead to misidentifications given the high number of rare polycystine species not included in this review. Shell size is generally of minor value for identification purposes, for which reason no detailed morphometric information is given; the dimensions specified are approximate and are furnished with the sole purpose of a general scale reference. The designation "group" denotes categories of unclear taxonomic affinities, where probably several related taxa are lumped. For each of the species treated one or more references ("Ref.") providing detailed descriptions and illustrations are included.