Rhenopyrgus

Despite looking more like some sort of scaly tubeworm, Rhenopyrgus viviani here was actually an echinoderm, distantly related to modern starfish, brittle stars, sea urchins, crinoids, and sea cucumbers.

It was part of an extinct Paleozoic echinoderm lineage known as edrioasteroids, which lived attached to the seabed or on hard surfaces like the shells of other marine animals, using the tube feet on their five arms to catch food particles from the water around them.

Living during the Silurian, about 435 million years ago, in what is now Quebec, Canada, it stood around 3-4cm tall (1.2-1.6″), firmly anchored into the seafloor sediment by a bulbous sac-shaped base. Its long stalked body was somewhat flexible, and it was able to partially contract the top feeding region down under a “collar” of large scale-like armor plates.

Cambrian Explosion Month #13: Phylum Echinodermata – Sticking Around

It seems like echinoderms became five-way symmetric incredibly quickly following the group’s first appearances in the early Cambrian. We don’t really know why this secondary radial symmetry evolved in the group – but we do know that the common ancestors of all modern pentaradial echinoderms were suspension-feeding animals that lived attached to the sea floor.

And those ancestors were probably a group called the edrioasteroids.

Continue reading “Cambrian Explosion Month #13: Phylum Echinodermata – Sticking Around”