Deviations in skeletons of radiolarians

Resumo

Deviations in the skeleton structure of radiolarians are extremely rare in the fossil record. They are known from the Devonian to Recent. This is a very ancient and periodically repeated phenomenon, which should be regarded as a regularity or “lost chance” rather than exotic or accident. Emergence of deviant “mutants” in radiolarians is probably connected with two main causes, i.e., disturbance during reproduction and mutations in particular modules. From the point of view of the morphogenesis of skeletal structures, deviancy facilitates the recognition of relatively “weak” modules–blocks in the general skeleton pattern, which are subject to structural changes. Nonheritable deviant variants have been revealed in skeletons of 61 radiolarian in all of three subphyla of the phylum Radiolaria: Polycystina, Phaeodaria, and Collodaria. Three deviant types are recognized: multiplicative, posterioric and supplemental.