Ordinary black Arbacia lixula sea urchins are found in great number in several places, covering rocks and stones with dozens and hundreds of dark spots.
Such a high prevalence combined with sharp spikes causes heightened danger of traumatism for swimmers, especially because the spikes are rather fragile and commonly not only break in the wound, but also crumble in the extraction attempts.

Jet-black spikes and skin of these urchins make them a complicated object for a shot, but their greenish, frequently tinted grey or lilac shells of various sizes are the most usual "trophy" from the bottom.