Fossilized viscera in primitive echinoderms.

Fossilized visceral organs in ancient echinoderms have anatomical features that were not inferred from the anatomy of extant relatives. The unique visceral anatomy of extinct echinoderms demonstrates the need to integrate paleontological and neontological analyses in order to fully evaluate this and other morphologically complex phyla. Comparative analysis of the visceral anatomy of extinct and extant echinoderms necessitates regrouping these animals into three new subphyla. Similar analyses for other metazoan groups could yield equally significant results.