Starfish
Serpent Stars, Sea Cucumbers, Sea Apples, and Sea Urchins
(Echinoderms)
These strange animals are a superb additions to the reef aquarium. The term echinoderm is a scientific name, echino means spiny, and derm refers to skin. These are the spiny skinned animals. Some like the sea urchins have true spines, others like most starfish have thorny or bumpy plates and peach fuzz sized tiny spines and pinchers. All have tube feet that are like tiny suction cups used for locomotion. The following ones are all reef safe tank inhabitants and clean up detritus and uneaten food, others eat algae. Still others keep the top surface of the sand stirred and aerated as they dig through the sand for food.
Pink Hawaiian Sea Cucumber. (Holothuria Sp)
Nice coloration. It’s a filter feeder & scavenger.
Pink and yellow with yellow tentacles like tree branches. About 4 inches.
Sand Sifting Stars / Burrowing Starfish
These 4 inch gray sea stars or starfish clean and aerate the sand bed as they burrow through it feeding on detritus (aquarium dirt). Aeration of the sand bed allows bacteria in it’s top layers to receive more oxygen and thus these bacteria can work better to break down nitrites.
Variegated Sea Urchin or Green Sea Urchin (Lytechinus variegatus)
These urchins are not brightly colored, but they do come in a variety of colors. Purple, olive green, and white are common. They have a habit of holding onto fragments of seashells, seaweed, and gravel thus concealing themselves from predatory fish. Do not house them with plants as they will eat many saltwater aquarium plants.
Long spine sea urchins (Diadema antillarum,)
Long Spine Sea Urchins are quite large, in the wild they appear to be about a foot across, and their is not much that is more intimidating than seeing those long venomous spines pointing at you. I have never been stuck, however, caution must be taken because if you are stuck with these needle sharp spines a trip to the emergency room will be needed so the broken spines can be removed from inside your flesh. In conclusion if you buy a long spine Diadema urchin online be cautious.
With that said the are remarkable in a very large reef tank where they can find exposed live rock and rock ledges to reside among.
Sea Apple (Pseudocolochirus) 
Attaches to the glass or live rock and uses it’s branching tentacle’s to capture plankton or other small particles of food.
Blue Starfish (Linka Laevigata)
Vibrant blue and very attractive starfish. Perfect for reef tanks.
Orange Starfish Orange Sea Star and Red Formia Starfish.
(Formia Sp)
Common Brittle Star (Ophiomastix or Ophiocoma )
Black with delicate and very spiny but harmless arms, sometimes other colors. Great scavengers.They like to hide but will emerge when they smell food.
Green Serpent Star (Ophiarachna incrassata) 
Olive green coloration.
For more invertebrate choices see:
Starfish
Lobsters and Shrimp
Crabs
Snails
Clams
Giant Clams
Sponges
Saltwater Aquarium Plants
Clean up Crew Packages
Or Click Here For General Information On Invertebrates.