A green and yellow basket…” star?
Recently the NMI Unit conducted a social media poll to see which invertebrate people would most like to see moved to the front of the 3D printing queue. The choice was among a sea urchin, hermit crab, squat lobster, and basket star and the winner was….envelope, please…
So, what is a basket star?
First, a bit of context: you’re probably familiar with starfish, or, more accurately, sea stars. Sea stars are members of the phylum Echinodermata (meaning “spiny skin”).
Included in this group are also sea cucumbers, sea urchins, brittle stars, and sea lilies, etc. One of the things that makes these animals unique is that in adulthood they have pentaradial symmetry. This means that all adult sea cucumbers, brittle stars, and any other echinoderms you can think of, can be cut into five identical parts from a central axis. Instead of having blood, all echinoderms have a water circulatory system. They use this water for locomotion as well as gas exchange within their bodies.
Basket stars, belonging to the class Ophiuroidea (i.e., brittle stars), have been around for ~500 million years. Their stellar persistence through geologic time is not the only thing that makes these organisms so fascinating. When threatened, ophiuroids can voluntarily break off their appendages and regrow them later. Which is pretty cool! One Ophiuroid family (Amphiuridae) can even regenerate gut and gonad fragments lost with the arms.
Unlike sea stars (class Asteroidea), the body of a basket star is much more “bony” and flexible, without bones of course. Instead of crawling on hundreds of tube feet like sea stars, brittle stars move fairly rapidly by wriggling their arms. These agile arms are supported by an internal skeleton of calcium carbonate plates that superficially look like vertebrae, and are called vertebral ossicles.
Basket stars have five arms that extend from a central disc; each arm branches and branches and branches and branches…and so on and so on and so on in a very fractal-like way. If you hadn’t yet guessed, basket stars get their name from these long interlocking tendrils, which when weaved together resemble…well, a basket. This “basket” is mostly used for catching food. They can, and do, move the star from one place to another, but this process is very slow. Imagine coordinating all that!
Basket stars are ocean-dwellers, occurring at a wide range of depths, from very shallow to very deep. They feed by extending their arms, forming a sort of living net. Basket stars have the ability to secrete mucus at the tips of their branches, which aids in collecting plankton and other small organisms. Basket stars will roll their arms in – think continuous bicep curls – bringing trapped meals to their mouth. Since there’s not much room in that central disc, basket stars do not have an anus, rather they digest their food within their stomach, then eject any remains from their mouth when completed. YUCK!!!
Visually, basket stars are undoubtedly showstoppers, a quality that is [mostly] retained in museum specimens. Although the process of preservation often causes specimens to become tightly wrapped, giving them the appearance of a stellar Gordian knot, the remarkable complexity of these organisms remains clear.
Back to our 3D modeling endeavor. The basket star has certainly presented us with a challenge given our typical scanning method (via a Shining 3D® Einscan S)! To capture the complexity of these organisms in detail, we reached out to Allison Luger and Dr. Dominique Adriaens of Ghent University, who provided us with micro-CT scan data of basket stars on loan from the Royal Belgian Institute of Natural Sciences – an exciting cross-Museum collaborative opportunity. That scan data was then translated to a 3D model. Coming soon to the NCMNS Naturalist Center: a 3D printed Astroboa nuda (Naked Basket Star) to touch, hold, and examine in detail!
For more information, check out the following two posts from Chris Mah’s The Echinoblog (and head down the rabbit hole from there):
References for this blog include:
Thanks to Anderson Woodson for providing some of the text!
And thanks for joining us! If you would like to follow the everyday adventures of our lab, check us out on Twitter and Instagram at @BWWilliamsLab. We hope you enjoyed this awesome post as much as we did. If so, please share it with your friends and let us know in the comments! Signed, the NMI Lab.