What "Evidence of Presence" do Sea Urchin tests come under?

General
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Construction I guess? Relevant observation: https://www.inaturalist.org/observations/326803592

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These would best fit under organism. Construction is for something external to the organism. Similar to mollusk shells:

https://forum.inaturalist.org/t/evidence-of-presence-a-mollusk-shell/67901

https://forum.inaturalist.org/t/what-annotation-for-mollusc-shells/54339

https://forum.inaturalist.org/t/shell-annotations-unclear/69559

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Thank you.

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Pedant* that I am, I canā€™t resist pointing out that sea urchins have an internal skeleton, so its test is more similar to a bone than a mollusc shell. Fortunately for the consistency of iNaturalist observations, ā€œboneā€ is not an option for annotating sea urchin observations. ā€œOrganismā€ is what we should call it.

  • a.k.a. ā€œannoying know-it-allā€ as one of my relatives said. I wonā€™t ask others if they think the same thing.
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Aside from the tube feet, isnā€™t the hydrostatic skeleton inside the test? Is the test considered part of the skeleton? Many mollusk also have internal shells. While weā€™re being pedantic. :)

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If you like to annotate observations, then Barbara and Thomas hit on some interesting distinctions that I had to research for myself. They probably know what Iā€™m about to say, but for anyone reading along who doesnā€™t know, and who wants to learn:

  • Barbara used the term ā€œinternal skeletonā€. What IS a skeleton? It comes from the Greek word ĻƒĪŗĪµĪ»ĪµĻ„ĻŒĻ‚ (skeletos), which just means ā€œdried upā€, as in, a dried-up mammal body (most likely a dried-up human body).
  • So a skeleton is ANY structure that supports a body. It could be an ENDO (internal) skeleton, like a sea urchin test or human bones, or it could be an EXOskeleton, like a mollusc shell or the chitinous cuticle of an arthropod.
  • What separates bone from, for example, a sea urchin test, is that vertebrate bone is living tissue that has a blood supply, is metabolically active, and can repair itself. This is in contrast to a sea urchin test or an arthropod cuticle, which is not metabolically active, and cannot repair itself. In some cases, an organism might be able to secrete more of the shell in order to repair damage, but this is different from the shell (or the cuticle) actively repairing itself.
  • This is why itā€™s good that, as Barbara said, ā€œboneā€ is not an option for annotating sea urchin tests, because even though the test is a skeleton, it is not a bone.
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I love this!

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