Purple sea urchin feeling around a rock with tiny tube like feet and gliding across an ocean tidepool habitat in the wild

echinoderms urchin echinoderm tide pool purple spiny species prickly organisms underwater sea water sea wildlife nature ecosystem globular seashore shell feelers animal habitat venomous creatures test rock ocean biology discovery stings anus movement marine round wild 4k feeling moving diet muskuloskeletal toxic pores science tube anatomy crawling feet tubes poop rocky