Meeting Abstract
The Fibulariidae is a family of miniaturized microechinoids (Clypeasteroida: Laganina) seldom achieving a body length of 20 mm. Dwarf clypeasteroids from a variety of disparate groups have been placed in this family on the basis of the superficial criterion of size. Confusion is largely due to overall morphological simplification resulting from what appears to be paedomorphosis. Extreme, paedomorphosis-driven miniaturization causes loss of terminally added characters that might otherwise inform relationships. An example of how mysteries stemming from this loss can be resolved comes from a supposed Echinocyamus, E. planissimus. This curiously flattened form seems out of place among other Echinocyamus in several respects. Using digital imaging, X-rays, microCT, and morphometrics, we examined the external and internal morphology of E. planissimus and discovered several traits suggesting that it is not only not a member of Echinocyamus, but not even a fibulariid. When compared with members of the sister family Laganidae, E. planissimus had similarly branched internal buttresses, supporting its removal from Fibulariidae and assignment either to the laganid genus Peronella, or perhaps a new genus. The resolution of such seemingly “small issues” is important because of what this means for our overall view of evolutionary pattern. With more accurate determination of the affinities of E. planissimus, we add another detailed example of convergent evolution involving miniaturization among echinoids. We also add concomitant support for theories of why this life history strategy is crucial to understanding diversification of the clypeasteroid clade. This illustrates how reassessments of phylogenetic position can culminate in enhanced understanding of the processes of evolution in marine forms.
