Large urchin wedged tight in narrow crevice.
Depth 4-5m on scuba.
Almost an iconic Southern Oz rocky reef urchin, I feel.
This is a relatively common species in terms of being unmistakable and easily spotted from afar due size and striking appearance but I never see more than a few individuals on any one dive, if any.
On night dives, the crevice occupied by an urchin of this taxon will often conceal either Sawtooth Pipefish or less often Heraldia nocturna, and possibly both in some cases.