The first urchin test I found was about twenty years ago. I have a book that calls it green sea urchin Psammechinus miliaris.
No more than 3cm wide I've never found another one since. It was so lovely I framed it with drift wood and still have it on my wall.
A few years later I found a few potato urchins Echinocardium cordatum. I just called them heart urchins not realising that there are a few species of heart urchin found in Cornwall.
So last year on Scilly when I found the live one on the right I assumed it was the same as the others. But now, having looked really closely at the tests we found this year, I know it is a purple heart urchin Spatangus purpureus. Beautifully coloured when alive with a perfectly heart shaped test. I found the one in the middle. It is not complete and quite small but it still has colour and spines and I love it. The one on the right was found by my beach combing kindred spirit http://jokehyaian.blogspot.co.uk/ A fabulous thing about 8cm in diameter.
Two other heart urchins are found in Cornwall and the Isles of Scilly. Echinocardium flavescens and Echinocardium pennatifidum but I never found these. Next year maybe.
I did find the tiny pea urchin Echinocyamus pusillus. These are from the beaches of St Martins. No more than 8mm long. Exquisite.
And the last urchin I came across on Scilly was the common or edible sea urchin Echinus esculentus (the large one they sell in baskets outside tourist shops) Coming in to Kitchen Porth at low tide from a kayaking trip I was lucky enough to find one stranded on a pile of kelp. I held it in my hands, turning it upside down to see its mouth - the Aristotle's lantern - and watched it moving in the water when I put it back under the kelp fronds. An amazing thing. Unfortunately I had no camera. We saw them later in the week as we snorkelled but still no photos. Beginning to think an underwater camera would be a fine thing to own.