Eldonia ludwigi / Zacanthoides serratus

Eldonia ludwigi, is an enigmatic, disc-shaped fossil organism primarily known from the Middle Cambrian Burgess Shale of British Columbia. Its soft-bodied nature and unusual morphology, featuring a radiating pattern and a coiled gut, have made its classification challenging for paleontologists. Initially considered a holothurian (sea cucumber), later interpretations have suggested possible affinities with lophophorates or even a unique stem-group position within the deuterostomes, potentially related to echinoderms and hemichordates. The abundance of Eldonia in certain Burgess Shale layers highlights its ecological significance in the Cambrian marine environment, likely as a free-floating filter feeder, although its precise biological relationships remain a subject of ongoing scientific debate.

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Reference to Wikipedia: Eldonia