The essential role of "Minor" phyla in molecular studies of animal evolution

Abstract

Molecular studies have revealed many new hypotheses of metazoan evolution in recent years. Previously, using morphological methods, it was difficult to relate "minor" animal groups representing microscopic metazoans to larger, more well known groups such as arthropods, molluscs, and annelids. Molecular studies suggest that acanthocephalans evolved from rotifers, that priapulids share common ancestry with all other molting animals (Ecdysozoa), and that flatworms, gnathostomulids and rotifers form a sister group to the remaining non-molting protostomes (Lophotrochozoa), together forming Spiralia. The lophophorate phyla (phoronids, brachiopods and bryozoans) appear as protostomes, allied with annelids and molluscs rather than with deuterostomes. These findings present a very different view of metazoan evolution, and clearly show that small and simple animals do not necessarily represent ancestral or primitive taxa.