You leave for a long weekend and come back to find a shell, two pieces of rubble and a small frag plug stuck to the top of your urchin, which is now on the other side of the tank. That is a pincushion urchin doing exactly what it does on the grass flats here, and it is worth knowing before you buy one.
Looking for one now? See the pin cushion urchin in stock, in small and large. Ours are collected by our team in the Florida Keys and conditioned in our Key West systems.
The pincushion urchin, Lytechinus variegatus, also called the variegated or green sea urchin, lives in the western Atlantic from North Carolina through southern Florida and the Caribbean to Brazil. It is part of our Florida Keys clean up crew field guide, and it is one of the heaviest algae grazers in it.
Quick facts
| Scientific name | Lytechinus variegatus |
| Size | Test (body) up to about 4 inches across |
| Diet | Hair algae, film algae, macroalgae, seagrass and coralline |
| Minimum tank | About 40 gallons, established, with algae to eat |
| Reef safe | Yes with caution. It does not eat coral, but it carries loose frags off and eats macroalgae you may want. |
| How many | One urchin of any kind per tank up to about 150 gallons |
What a pincushion urchin eats
In the wild this urchin grazes seagrass, mainly turtle grass (Thalassia), and the algae that grows on it, and its spines and tube feet catch drifting debris. In a tank it turns that appetite on hair algae, film algae and anything green on the rock. Bulk Reef Supply notes it forages day and night, so it usually needs no extra food in an established tank with plenty of algae.
The flip side is that it eats macroalgae too. If you keep chaeto in the display, or decorative red and green macros, an urchin will treat them as food. It also grazes coralline algae, so expect bare patches on rock it works hard.
The carrying habit
Pincushion urchins hold shells, rubble and bits of algae on top of their bodies with their tube feet. Researchers think the cover shades them from bright sun and ultraviolet light in shallow water. In a tank, that means a frag plug that is not glued down can end up riding around on an urchin and getting dropped somewhere else. Glue or seat every frag before you add one.
How many urchins per gallon
Our clean up crew calculator only adds an urchin for turf algae on the rock, only in an established tank of 40 gallons or more, and at one urchin up to about 150 gallons and two above that. We use the same rule for pincushions, and we count every urchin together. A pincushion and a pencil urchin in a 75-gallon tank is two urchins on one food supply, which is one too many for most tanks.
Add one, watch it for a few weeks, and offer dried seaweed once the algae is under control. A hungry pincushion will strip a tank and then starve, and BRS notes that spines starting to fall off is a sign of starvation.
Acclimation
Float the sealed bag for about 15 minutes to match temperature. Then drip tank water in slowly to match salinity, because invertebrates are sensitive to salinity swings. Never add the shipping water to your tank. Move it under water if you can.
Copper is toxic to urchins. Never add one to a tank that has had copper in it.
Lifespan and size
The test reaches about 4.3 inches across at most, with short spines, so it looks smaller than a long-spined urchin of the same weight. Color varies a lot: tests can be green, purple or dull red with white blotches. There is no reliable published lifespan for this species.
How we find them in the Florida Keys
Pincushions live in clear, shallow water on seagrass meadows, sand, rubble and rocky reef, sometimes at more than a dozen to the square yard. They are easy to spot because they are usually wearing a hat of shell and grass. We collect them by hand under our Florida certificate and condition them in our Key West systems before they ship.
Common problems and how to avoid them
- It runs out of food. A pincushion that has cleared the tank will starve unless you feed dried seaweed on a clip.
- It moves frags and rockwork. Glue frags down and make sure rock is stable.
- It eats the macroalgae you wanted. Keep macros in a refugium rather than the display.
- It gets into powerheads and overflows. Urchins climb. Cover intakes.
- Spines drop, or it stops moving. Check salinity and food first.
FAQ
Are pincushion urchins reef safe?
Mostly. They do not eat coral, but they knock over and carry loose frags, graze coralline and eat macroalgae.
Do pincushion urchins eat hair algae?
Yes. Hair algae is one of the main reasons people buy them. Fix the nutrients too, or the urchin is fighting an endless supply.
Why is my urchin carrying shells and rocks?
It is covering behavior. In the wild the cover is thought to shade the urchin from strong light. It is normal and a sign the urchin is active.
Are pincushion urchin spines dangerous?
The spines are short and much less likely to injure you than a long-spined urchin, but handle it gently and keep it under water.
How big do pincushion urchins get?
Up to about 4 inches across the body.
What do I feed a pincushion urchin when the algae is gone?
Dried seaweed or nori on a clip, a few times a week.
Buy Florida Keys pincushion urchins
Buy a pin cushion urchin (Lytechinus variegatus), collected by our team in the Florida Keys. Use the clean up crew calculator to size the rest of the crew, and see every species in the field guide.
The Underwater Gardener is a reef store in Key West, Florida. Our Florida Keys clean up crew is collected by our team under Florida certificate #AQ0254072 and conditioned in our Key West systems before it ships. Livestock ships UPS Next Day Air on Tuesdays and Wednesdays.
Corals in stock right now
Photographed in Key West, in stock today. Fill your box: up to 4 spots ship for one shipping charge. A frag takes 1 spot and a colony takes 2. Browse corals under $100 or beginner corals to fill one.
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