Towards a molecular phylogeny of colonial spumellarian radiolaria

Gene sequence data from the small-subunit ribosomal RNA coding region were used to explore evolutionary relationships among the colonial spumellarian radiolaria (Polycystinea). Representatives from the two spumellarian families known to form colonies were considered including the following taxa: Sphaerozoidae: Collozoum pelagicum; Collozoum serpentinum; Rhaphidozoum acuferum; Sphaerozoum punctatum; and Collosphaeridae: Collosphaera globularis-huxleyi; Acrosphaera (circumtexta?); and Siphonosphaera cyathina. Our molecular analyses support the monophyly of the Collosphaeridae in all analyses used, but only distance analyses support the monophyly of the Sphaerozoidae. Within the Sphaerozoidae, two species of Collozoum (C. serpentinum and C. pelagicum) failed to branch together, indicating a more distant relationship than first suggested, a conclusion further supported by recent ultrastructural studies (see adjoining paper). Branching patterns within the Collosphaeridae indicate that Siphonosphaera diverged prior to the split between Collosphaera and Acrosphaera, a result which challenges evidence based on data from the radiolarian fossil record. (C) 1999 Elsevier Science B.V. All rights reserved.