Episode 23: Meet the Echinoderms! Adventures with Ancient Sea Stars!

This episode was a blast to produce for a vertebrate scientist. I learned a ton about the echinoderms, the group of invertebrate animals to which sea stars, brittle stars, sea cucumbers, sea urchins, and crinoids belong. Be prepared for more adventures with invertebrate animals in the future.

Engineering Echinoderms with Elizabeth Clark!

Yale University Ph.D. student Elizabeth Clark, holding examples of modern-day echinoderms. The animal on the left is a sea star (Asteroidea), while the animal on the right is a brittle star (Ophiuroidea).
Yale University Ph.D. student Elizabeth Clark, holding examples of modern-day echinoderms. The animal on the left is a sea star (Asteroidea), while the animal on the right is a brittle star (Ophiuroidea).

This episode would not have happened with Elizabeth Clark, graduate student in the Geology Department at Yale University and my gateway to echinoderms. As a part of the lab of Derek Briggs, Liz has studied a wide range of topics on echinoderm paleontology and biology. You can check out the original scientific paper on her Ordovician asteroid in Biology Letters and the Yale News story about the discovery. The original specimen of Protasterina flexuosa featured in the study is pictured below. It actually lived alongside the Flexicalymene trilobites featured in our previous invertebrate episode. You can see their fossils (and hundreds of thousands of others) at the Cincinnati Museum Center in Cincinnati, Ohio.

The ventral side of Protasterina flexuosa. From left to right: 1) a three-dimensional model of CT scan data, 2) the model with the water vascular system inside, 3) the water vascular system in 3D.

Scurrying with Sea Stars, Crawling with Crinoids, and Battling with Brittle Stars!

I had a lot of fun watching echinoderms locomote while making this podcast. I really cannot believe the diversity of movement styles they adopted throughout their history. A lot of this system is built on the water vascular system and associated tube feet, but many species explore different methods for motion. Check ‘em out below!

  • Sea star (Asteroidea) stranded on a beach, but working its arms and tube feet like crazy to reach the shoreline.

  • Brittle stars (Ophiuroidea) walking around the seafloor AND battling over a shrimp dinner!

  • A sea urchin (Echinoidea) walks across the glass surface of an aquarium, exposing its tube feet.

  • This video features many sea cucumbers, scurrying around and vacuuming up the sea floor in search of dinner. It also features an unusual symbiosis, in which a fish lives inside of the sea cucumber’s anus.

  • A bizarre type of sea cucumbers, sea pigs have very large tube feet that let them walk like insects!

  • Clearly not using tube feet here! Sea cucumbers can also propel themselves by flexing and extending their whole bodies to swim!

  • Crinoids, the plant-like echinoderms that anchor themselves to the sea floor, don’t seem like good candidates for moving around…

  • …but they can move like any other echinoderm when they want, using their arms to walk…

  • …and others flex their feather-like arms to swim!

  • Echinoderm armies! Sea stars, brittle stars, sand dollars, and urchins battle it out and shape the reefs and landscapes.

Further Reading:

  • Liz Clark’s paper on the Protasterina specimen:
    • Clark, E. G., Bhullar, B.-A. S., Darroch, S. A. & Briggs, D. E. Water vascular system architecture in an Ordovician ophiuroid. Biology Letters 13, 20170635 (2017).
  • Fossil Focus is a recurring article produced by the Palaeontological Association. Some of its past articles have featured families of echinoderms:
  • Echinoblog covers all aspects of modern-day echinoderm research and zoology. Lots of cool images of modern-day species.
  • Scripps Institute of Oceanography also covers the details of the fossil record of echinoderms, back to their origin over 540 million years ago. Just like Liz said, there are a LOT more fossil echinoderm species than living ones. Consider this site an introduction to the topic.

Licensed material used in the episode and associated images:

Filed under: Biology, Locomotion, Palaeozoic, Paleontology, anatomy, brittle star, crinoid, echinoderm, echinoderms, invertebrates, sea cucumber, sea star

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