Mystery of Echinoderms Origins

Cambrian period = 540 million years ago Ediacaran period = Just before the Cambrian

Round, flat, disc-shaped fossil = Tribrachidium Triradial (three-point) symmetry = Tribrachidium

Symmetrically arranged parts around the center = Radial body plan Parts arranged like the petals of a flower = Radial body plan

<p>Placed in its own phylum, Trilobozoa = Tribrachidium Group with no known living descendants = Trilobozoa</p> Signup and view all the answers

<p>Shared radial body plan with modern echinoderms = Tribrachidium Triradial symmetry instead of pentaradial symmetry = Tribrachidium</p> Signup and view all the answers

<p>Their origin or how they originated</p> Signup and view all the answers

<p>Due to a lack of fossil evidence</p> Signup and view all the answers

<p>Because of its triradial symmetry matching modern echinoderms</p> Signup and view all the answers

<p>Due to its triradial symmetry differing from adult echinoderms' pentaradial symmetry</p> Signup and view all the answers

<p>It separates Tribrachidium from echinoderms with pentaradial symmetry</p> Signup and view all the answers