A Molecular Approach to Questions in the Phylogeny of Planktonic Sarcodines.
1997
Angela, Linda | Zettler, Amaral
The relationships of the Acantharea and the Polycystinea (order Spumellarida) to other protists were investigated using phylogenetic analyses of small-subunit ribosomal RNA (SSU rRNA) genes. These two classes are included in the superclass Actinopoda based on specialized pseudopodia called axopodi& SSU rRNA-based phylogenies do not support the common ancestry of the Acantharea and the Polycystinea, implying that the superclass Actinopoda is artificial and should be discarded. All analyses supported the monophyly of the Acantharea and the separate monophyly of the Polycystinea. The origin of the sequences was confirmed by in situ hybridizations. The SSU rRNA-based method was also useful in fine-scaled comparisons. Sequence comparisons for the solitary spumellarian Thalassicolla nucleata from the Sargasso Sea and the Pacific Ocean indicate there may be different species which are morphologically identical or that there may be allelic variation in a given individual. Analyses between the solitary T. nucleata and seven colonial spumellaria indicate that the colonial spumellaria may not be monophyletic. The results from examination of branching patterns within three of the four orders of the Acantharea placed the symphyacanthid Haliommatidium sp. branching among the Arracanthida, indicating that the Symphyacanthida are not monophyletic as defined by morphology-based systematics.
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