One of the things I love doing is finding specimens and sighting wild creatures, then hopping online to learn about them. The shell of a sea urchin is called a test. When alive/fleshed they have an internal bony structure surrounding the mouth called a lantern or Aristotle's lantern.
These two are the biggest sea urchin tests I have ever found. They were also subject to the most intensive cleaning I have ever deigned to give a beach combing find. Of course when it's as special as these two it's worth it. Neither was found fully spined and both were still occupied but definitely dead. Their remaining spines were a deep purple and based on their size, and location are most likely Purple Sea Urchins.
I did a bit of research online into preserving them with spines (one was half covered) but that would have required pure alcohol.* I have only found isopropyl alcohol in 125ml bottles at Bunnings for almost $8. It would have taken at least two bottles to cover one of these urchins. Had either been fully spined I would have considered it worth it. This process would also have preserved the animal inside as well.
Instead I gutted them, removing the lantern and scraping out of the soft innards. After much rinsing out to remove remaining crud I soaked them in a weak bleach solution to help loosen the spines. I put one aside to dry out completely. With the other I spent a couple of hours picking off any remaining external tissue and tried microwaving it to soften that up. It is quite gristley and near impossible to remove! This shrinks down into a shellac like substance when dried out, so I just let it dry out like my first one.
Photographed with a $2 coin (∅ 20.5mm) to give you an idea of size. As you can see the peristome (mouth) aperture is large. So big I could almost pop my digital camera's lens into it.
The periproct as viewed through the peristome . Yup that's the prettiest periproct I have ever seen - and the only one I have photographed I hasten to add.
A pickled sea urchin doesn't know its peristome from it's periproct!
Gah! My initial research threw me a red herring with the 70% isopropyl because I assumed what was good for preserving starfish would have been good for sea urchins as well. Right after tracking down some 40% isopropyl in a 500ml bottle @ $4.50 I hop online...Further in depth research has uncovered that it is ethanol or pure grain alcohol that is best for preserving specimens in general. Quality articles on the subject confirm this. This is what the linked to site in this post about preserving sea urchins refers to. Common as muck methylated spirits (95% ethanol) diluted with distilled water to 70-80% purity would have done the job. Professionals use an industrial methylated spirits (99.9%) but you need a licence to get it.
I am finding that 40% solution rather excellent for cleaing my laptop, mobile phone, remotes and a range of other devices. So it's not a total waste of time.