Meeting Abstract

67.8  Saturday, Jan. 5  Consensus and confusion in molluscan phylogeny SIGWART, JD*; SCHROEDL, M; Queen's Univerity Belfast; Zoologische Staatssammlung Munich

Molluscs are the second largest and morphologically most disparate animal phylum, they are ubiquitous, and have a formidable fossil record. Monophyly of the eight Recent molluscan classes is undisputed, but relationships between these groups and patterns of early molluscan radiation have remained elusive. Molecular, fossil and anatomical data show apparently contradictory evidence for branching patterns within Mollusca. The traditional reductionist model of the ‘hypothetical molluscan ancestor’ has hampered the resolution of molluscan topology; some hypotheses rejected as artifacts (e.g. Serialia) continue to find additional support and cannot be dismissed conclusively. Derived conditions in major body plan modifications, such as shell-loss, have occurred repeatedly in most groups. Rather than interesting sidelines, these anomalies, and evidence for rampant reversals, apparently represent the true norm of molluscan evolution. Based on new molecular clock results—the first to include multiple exemplars of all 8 classes—diversification of molluscs started immediately in the early Cambrian and was far more rapid and more complex than previously appreciated. Extensive evolutionary plasticity by heterochronic shifts in development and multiple convergent adaptations, as demonstrated in extant molluscs, were already within the evolutionary potential of their Cambrian forebears, and continue today.