Radiolaria Polycystina
Order and family-level diagnoses

The overall total of living polycystine species is probably around 300-600, but this review includes only 176 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., Family Actinommidae, Family Pyloniidae, Family Litheliidae, Family Tholoniidae, Family 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; Kruglikova, 1987).

This review presents in the programme's so-called Higher taxa module succinct information including illustrations, 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. Go to page Superorder Polycystina for further details.

When applicable, on the pages in the Species module on this DVD-ROM, species names are accompanied on the so-called synonym tab by some of the other most common names under which the form has been recently cited in the literature (note that this doesn't imply the alternative name being a true synonym in the nomenclatory sense). 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" (in the so-called description field of the record) 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.