As found, I didn't touch this urchin, BTW.
Perched atop a mildly elevated upright bit of broken pile or similar jetty junk which is heavily covered by the usual invertebrates and algae.
But the urchin is also being used for height, grazing and filter-feeding advantages by other invertebrates eg small gastropod shells.
As is said, Paradise is underwater:)
(But this marine ecosystem, admittedly partly anthropogenic being a jetty, ain't the Paradise that it was in my youth, if memory (subjective, anecdotal almost to the point of being useless) serves me well.More importantly I have a limited collection of old slide transparencies which were taken on day and night dives under this very jetty decades ago (some are from as long as 49 years ago!).I will be reviewing those asac but I already know that some are on this iNat platform eg lightning volute and a juvenile Southern Pygmy Leatherjacket that give some support to my claim that the general ecological health under this jetty has declined over the past 5 decades.