Molecular Punctuated Equilibrium in the Evolution of Rhopalura ophiocomae (Mesozoa: Orthonectida) 18S rRNA, Hairpin 17

Alternative states of the predicted structure of hairpin 17 in the small-subunit ribosomal RNA genes are described. Each of these structures is characteristic of one or several phylons of animals. For example, one of the alternatives could be found in the rRNA of most Bilateria, but not in protists, fungi, plants, or diploblastic animals. A presumable secondary structure of the 18S rRNA hairpin 17 of a lower multicellular animal, Rhopalura ophiocomae (Mesozoa: Orthonectida), was constructed. It differs drastically from the one of other lower multicellular animals, i.e., Rhombozoa, Myxozoa, and Acoela. The evolution of rRNA fragments according to the principle of punctuated equilibrium is discussed.