Sea Urchin

Urchin spines are inert, however they can get deeply embedded. At a minimum, using a topical antibiotic on the puncture spot can help. Occasionally the site can get infected, red and stay quite painful. In that case they may have to be surgically removed. Personally have a number from living in Hawaii, mine eventually worked out by themselves, did not really hurt. The urchins there are mostly 'longspine', so many centimeters long. People end up bending them, they are britile and break off.

if you can cope with it dripping candle wax on to it means the tiny bits come out when peel off the wax,,,,did this when daughter stepped on one...what was amazing was the huge number of tiny splints but they came off in the cold wax