Radiolaria Phaeodaria
Morphology and classification system

The classification of phaeodarian families presented here was put in place by Haeckel (1879). See page Superorder Phaeodaria and further (orders, families and genera). It has been used by subsequent students of the group, and some new families have been added. The morphology of each family is so distinctive that there has been essentially no controversy as to their taxonomic identity. Haeckel also proposed a classification of families into orders, which is presented here, although it is perhaps in need of revision. It is based on skeletal morphology, and further analysis of the cytological relationships might provide a basis for a more natural order-level classification. The generic classification proposed by Haeckel (1887) has been followed generally in subsequent works, but occasional revisions have been suggested, and inconsistent usage (particularly among the challengerids) persists into modern times.

Remarkable intraspecific variations have been described for this group. Reshetnjak (1966) noticed that, for example, in Aulosphaera bisternaria and Sagenoarium chuni the shape of the meshwork can be either spherical, oval, spindle-shaped or pyriform. Spherical and pear-shaped Castanidium variabile occur regularly. Tuscarantha braueri’s pyramidal shell can be either 3 or 4-sided. Tuscaretta tubulosa can be pear-shaped, egg-shaped or ovoid. Intraspecific variability is not circumscribed to shape, but also affects other morphologic traits. In Tuscaretta tubulosa, for example, the number of oral radial spines can vary from 2 to 5. In some cases this variability is probably associated with ecological settings: in some Tuscaroridae, for example, the number of radial spines increases with decreasing water-temperature (Reshetnjak, 1966).