Brittlestars: Well-Armed, Laid-Back and Full of Tricks  

If you think of brittlestars as just a variation on the familiar, pointy starfish, think again. They’re made quite differently, they act differently and they live quite a different lifestyle. 

It’s all in the long, whip-like arms.

Two or more brittlestars snooze away inside a vase sponge at Roatan, Honduras. Come nightfall they’ll be outside, hauling in zooplankton.

BRITTLESTARS ARE MORE THAN JUST TRADITIONAL STARFISHES WITH LONG, SINUOUS ARMS AND LAID-BACK ATTITUDES. Actually, there are many differences between brittlestars and star-shaped starfishes, both in body design and behavior.

In contrast to sea stars, brittlestars have flexible, jointed arms and can move gracefully and speedily along the sea floor. They can tuck themselves into nooks and crannies to hide out from predators. Rather than pursuing diets of mollusks and other squishy animals, they sweep the seafloor for detritus and the ocean currents for plankton.

Although you sometimes see them during the day, lying around nonchalantly tucked into vase sponges pretty much in plain sight, they’re basically nocturnal animals that don’t go into action until the sun goes down.




Their name comes from the fact that their arms are easily broken off. And, in fact, they are perfectly capable of breaking those arms off themselves as a distraction while escaping predators – and then growing new ones.

And, when they have those arms, they make wily use of them. Brittlestars are the only echinoderms who can use one of their five arms as a “rudder” and “row” with the other four, like oarsmen in a racing shell.

dark red-spined brittlestar
Out for a night’s work, a dark red-spined brittlestar (Ophiothrix purpurea) (probably), shares a sponge with a sleeping toby pufferfish in the southern Philippines.


Brittlestars are in Phylum Echinodermata (“spiny skinned”) with starfishes but in a different class (Ophiuroidea, from the Greek for “serpent tail-like,” reflecting those long, whip-like arms, rather than Asteroidea, “star-shaped”). They’re the major occupants of Ophiuroidea, Clade Ophiurida. The only other members of the class are the less-common – and much less seen – basketstars, Clade Euryalida.

They both share the basic echinoderm design of identical body sections arranged with five-way radial symmetry, most obvious in a starfish’s (usually) five arms arranged around a central disc-shaped body (It should be noted that some species of brittlestars actually have six or more arms).

Most basically, brittlestars differ significantly in the design and function of those arms, their dining habits and their general behaviors.

Ophiothrix angulata
Most likely angular brittlestars (Ophiothrix angulata), this bunch struts their stuff at night on sponges in Bonaire.


Among all echinoderms, brittlestars show up with the most species – more than 2,000 identified worldwide. Scientists suspect that the true total may be as high as 3,000. They’re found in every habitat, tropical and arctic, shallow and deep. You won’t see most of them in person, however. It’s estimated that some 1,200 of those 2,000 species are found in waters more than 660 ft/200 m deep.

In some locations, they’re especially plentiful. Actually, they pile up. Several years ago, millions of them were found packed together on the seafloor off Antarctica.

In terms of distribution, it’s believed that more than 800 species are denizens of the Indo-Pacific basin – both shallow and deep. Identified species in the Caribbean are closer to 100. Arctic seas count some 75.

With so many species and so wide a range, diversity rules. Measuring by their central disc size, brittlestars can range less than an inch across to several inches in diameter. The length of a brittlestar’s arms are generally two to three times the diameter of its disc. But in some species, the arms can be as much as 20 times as long.

Many are solid colors like brown or red or at least reddish. But some show up with arms adorned with red and white bands, or white and other vivid colors. Some, particularly among Indo-Pacific species, are a fantastic sight to see.


As with starfishes, a brittlestar’s central disc-shaped body packs in digestive and other essential organs. These include a large stomach, a ring-shaped central nerve that manages movements in the arms and the locus of a water vascular system that makes the arms work.

Bursae, sac-like cavities located at the base of each arm contain the genitals and are where the essential gas exchange for oxygen takes place. Bursae are unique to brittlestars and basketstars. A brittlestar’s underside features a mouth surrounded by five jaws (together resembling a star) and a madreporite, a dot-shaped opening that draws in water to operate the vascular system.

Ophiolepsis superba
The pentagon design on its central disc, and of course, the bands on its arms, mark this guy as a banded brittlestar (Ophiolepsis superba), spotted near Reunion Island in the Indian Ocean.


Like all echinoderms, brittlestars are supported under their skin by calcium carbonate plates called ossicles. The plates in their arms are fitted together with ball-and-socket joints that let them move with finesse and flexibility. On the other hand, that flexibility is geared to sideways movements. Stressed upwards or downwards, they’ll break off (Remember: brittlestars.”)

Brittlestar arms are lined with delicate spines and, on the underside, tiny tube feet. But these tube feet lack the suckers that are key to locomotion in starfishes. Sensitive to odors and coated with mucus, they’re used to detect and capture food.


Depending on their species, brittlestars largely live on diets of detritus – organic matter they can scrounge up from the seafloor, on zooplankton those mucus-equipped arms can take from the passing currents, and, sometimes, on small crustaceans, mollusks and fishes they may capture by wrapping arms around them.

Once caught up, the harvest is swept down the tube feet into the animal’s mouth and digested in the 10 pouches in its stomach. They don’t have a separate anus so waste exits through the mouth.

brittlestar arms
Sometimes during the day, a glimpse of arms is all you get.


These tube feet aren’t made for walking but, still, a process of wiggling their arms is key to brittlestars’ speedy ambulation. And they do it uniquely for echinoderms – more-or-less like oarsmen in a racing shell.

A brittlestar moves by using one of its five arms as a sort of rudder, pointing the way forward. The other four, two each on each side, act as coordinated levers in a sort of rowing motion that propels the animal forward.

If it wants to change course, no need to turn. A different arm assumes the role of pointer and the brittlestar begins rowing in that direction. No other radially symmetrical animal has been observed doing this.


Brittlestars’ arms play a role in defensive movements, as well. Faced with imminent threat in the face of a predator, its nerve network stimulates the disintegration of tissue at the base of one arm, detaching and dropping it.  Distracting the predator by this act of self-amputation, it makes its getaway. Not clear on whether it rows its way to safety with only four arms to work with.

Fortunately, it brittlestars have the power of self-amputation they also have the ability to regenerate it. Once the wound heals, the arm most likely will grow back in a period of weeks to months.

Ophioderma rubicunda
A passel of ruby brittlestars (Ophioderma rubicunda) in a spawning group at Flower Gardens in the Gulf of Mexico.


Although a small number of species are hermaphrodites, overwhelmingly brittlestars come in male and female sexes. Many brittlestars produce more brittlestars by broadcast spawning – launching their gametes into the currents.

In some species, this results in free-swimming larvae that after a period settle on the substrate and morph into growing brittlestars. With close spawning, some brood the larvae in their bursal sacs, releasing live little brittlestars once they have developed.

In some species, like those in the six-armed Family Ophiactidae, regeneration provides a reproductive twist with a process called “fissiparity.” The disc simply divides in half and both halves regrow the missing section of disc and the missing arms. Temporarily, this results in creatures with three normal arms and three shortened arms.



PRINCIPAL SOURCES: Marine Biology, Peter Castro, Michael Huber; Marine Life, Caribbean, Bahamas, Florida, Marty Snyderman & Clay Wiseman; Coral Reef Animals of the Indo-Pacific, Terrence Gosliner, David Behrens, Gary Williams; Reef Creature Identification, Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Reef Creature Identification, Tropical Pacific, Paul Humann, Ned DeLoach; Brittle Stars of the Sea,; Brittle Star, Science Encylopedia; Introduction to the Ophiuroidea, University of California Museum of Paleontology; Arctic Wildlife: Get to Know Brittle Stars, Ocean Conservancy; Brittle star,