From a deep time perspective, modern echinoderms include only two groups: Eleutherozoa, including sea stars, brittle stars, sea cucumbers and sea urchins; and Crinoidea, including sea lilies and feather stars.
However, an additional 20-25 distinct echinoderm groups are found in Paleozoic rocks between 540 – 250 million years ago. Among these echinoderms we find the greatest variation of body plans including bilaterally symmetric, asymmetric, coiled, and discoidal forms. Understanding the evolutionary framework of these basal relationships is a major goal of the Echinoderm Tree of Life project.
This portion has three main objectives:
(I) To understand the evolutionary relationships between the diverse groups of extinct Paleozoic echinoderms,
(II) To determine how the two extant modern taxa, Eleutherozoa and Crinoidea fit into this broader picture of echinoderm evolution, and
(III) To determine the basal polarity for the echinoderm body plan.