Long-Spined Sea Urchin in Cozumel

A black ball of very long, very thin, needle-sharp spines that move when a shadow passes. Nothing else on a Cozumel reef looks like it.

Quick ID

Where You Will See It In Cozumel

Long-Spined Sea Urchin works the 3 to 82 foot band. On this island that means the sheltered west-coast reefs, and the shallow east-side entries when the sea is flat — these are the sites where the depth and the habitat line up for it.

Without a boat. It is worth looking for at Tikkila Shallow, Chankanaab Shallow and Chen Rio — all shore entries, so you dive them on your own schedule.

On an ordinary beginner boat dive. It should be within reach at Las Palmas, Molas Shallow, Palancar Gardens, Paradise and Punta Dalila. No advanced certification needed.

Deeper, and on the walls. It is also plausible on Cantarel (Eagle Ray Wall), Chun-Chacaab, Colombia Deep and Devil's Throat.

Conditions change the odds more than the site does — the current, the time of day and how much the group has already stirred up the sand. Ask your guide what they have been seeing that week.

Behaviour

Grazes algae, and in doing so keeps algae from smothering young coral. A Caribbean-wide die-off in 1983 removed more than ninety per cent of the population and is one of the main reasons Caribbean reefs shifted towards algae dominance. Recovery has been slow and uneven, and a second die-off event hit the region in 2022.

Commonly Confused With

• Rock-boring urchin — Rock-boring urchins have short thick blunt spines and sit in eroded hollows.
• West Indian sea egg — Sea eggs are white-spined with a dark body and often carry debris on top.

Diving Etiquette And Safety

Spines are brittle, barbed and mildly venomous, and break off in skin. This is the strongest reason not to steady yourself on the reef in shallow water, and to watch your knees on a shore entry.

Part of the Cozumel marine life guide · see Cozumel dive sites · plan your Cozumel dive trip

Photo: Greg Grimes, CC BY-SA 2.0, via Wikimedia Commons.