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 famili es known to form colonies were considered including the following taxa: Sph aerozoidae: Collozoum pelagicum; Collozoum serpentinum; Rhaphidozoum acufer um; Sphaerozoum punctatum; and Collosphaeridae: Collosphaera globularis-hux leyi; Acrosphaera (circumtexta?); and Siphonosphaera cyathina. Our molecula r analyses support the monophyly of the Collosphaeridae in all analyses use d, but only distance analyses support the monophyly of the Sphaerozoidae. W ithin the Sphaerozoidae, two species of Collozoum (C. serpentinum and C. pe lagicum) failed to branch together, indicating a more distant relationship than first suggested, a conclusion further supported by recent ultrastructu ral studies (see adjoining paper). Branching patterns within the Collosphae ridae indicate that Siphonosphaera diverged prior to the split between Coll osphaera and Acrosphaera, a result which challenges evidence based on data from the radiolarian fossil record. (C) 1999 Elsevier Science B.V. All righ ts reserved.