Fine structure of the colonial radiolarian Collozoum serpentinum (Polycystinea : Spumellaria) with a reconsideration of its taxonomic status and re-establishment of the genus Collophidium (Haeckel)

Fine structural evidence shows that Collozoum serpentinum differs substantially from two previously examined species Collozoum inerme and Collozoum caudatum. The latter two have spheroidal to prolate central capsules with rounded nuclei and radially arranged lobes of cytoplasm radiating from the center of the central capsules. C. serpentinum has contorted, elongated (greater than 1 mm) cylindrical central capsules, and the intracapsular cytoplasm is highly vacuolated and suspended in a network of denser cytoplasm containing major intracellular organelles including nuclei with irregular shape, mitochondria, and Golgi bodies. This network organization of the intracapsular cytoplasm is distinctly different from the fine structure of Collozoum species examined thus far. These data, combined with molecular genetic evidence (Amaral Zettler et al,, 1999), indicate that C. serpentinum is not as closely related to other Collozoum species as was previously thought. Based on this evidence, we suggest that Haeckel's original designation of a separate genus (Collophidium) is more appropriate for colonial radiolaria with contorted, cylindrical central capsules as represented by C. serpentinum. (C) 1999 Elsevier Science B.V. All rights reserved.