Reef Safe Critters Explained - Sea Urchins

Sea Urchins For The Reef Aquarium

Urchins can be a welcomed addition to your reef aquarium but care must be given to the type and quantity of these creatures you add to your tank. Some sea urchins will eat coralline algae when placed in an aquarium with ample supplies, which means only one or two should be placed together. We’ve included a list of some of the more popular sea urchins below with a description and photo of each so you can decide which one(s) will be right for your tank.

Pin Cushion/Tuxedo Urchin (Mespilia globules):

Pin Cushion/Tuxedo Urchins are generally small (about 2-3in in diameter) and they’re covered in short, sharp spines. They have five to ten broad-colored bands around their body which gives them a strikingly formal appearance and thus the second name “Tuxedo Urchin”. They can have black or blue bands and red, brown or black spines in any combination possible.

One of the unique characteristics of these urchins is there tendency to collect shells, coral or substrate on there bodies as they try to disguise themselves to avoid predators. This tendency sometimes gets them the additional name “Decorator Urchin” but they are all the same species.
These little guys are great for eating algae and detritus and will move about the aquarium scraping algae off glass, rocks and substrate alike. They are nocturnal creatures that do their grazing under the cover of darkness, and during the day they mostly hide in crevasses or in other dark, safe places.

These urchins have not been found to eat coralline algae and are considered safe for reef aquariums. It is important to note however that if there is insufficient alga or other organic food sources that these, and any, urchins will turn to coralline algae as their main food source.

Long Spine Urchin (Diadema antillarum):

The Long Spine Sea Urchin is an active algae eater and a very attractive addition to the reef aquarium. The long, thin spines of these urchins are perfect for deterring fish and other animals from feeding on them. It is this attribute that makes them well suited for algae control in aquariums with Trigger or Puffer Fish, which have been known to eat urchins after picking their spines off.

Like other urchins they are nocturnal, choosing to graze on algae under the cover of darkness. Their bodies are predominately black, although I’ve personally seen some that were a light brown color. One feature common to all of the Long Spine Sea Urchins is the eyespot located in the center of the body, which is usually a red or dark orange color.

Pencil Urchin (Eucidaris tribuloides):

The Pencil Urchin is one of my favorite urchins because of its thick rod-like spines that eventually get covered in coralline algae. This unique feature makes them very beautiful for a reef aquarium and thus I highly recommend this species for you mini reef.
This urchin is nocturnal as are the rest of the urchin families and will come out at dark to graze on unwanted algae.