Brittlestars/Serpentstars

[ophiura]

Hi All,
Some time ago I intended to write a long thread on brittlestars, similar to my posts on seastars (linked from the archives)
Seastars
Anyway, I didn't do it

But it is better late than never...here is the Invert of the Month, the ophiuroids!

[hr]
For those of you who have known me awhile, you will likely remember that though I am trained as an invertebrate zoologist my primary focus of expertise is on the ophiuroid, or brittlestar, echinoderms.
These I studied for more years than I care to remember. However, it is the hobby that gave me an opportunity to study them alive.
The Ophiuroidea is a class in the Phylum Echinodermata (meaning "spiny skinned"). Their relatives include seastars, sea urchins, sea cucumbers and sea lilies, along with a huge number of now extinct classes. All echinoderms share some key characteristics which, in the interest of time, I won't cover here.
But let me say they are really fricken cool. They are widely studied by developmental biologists, immunologists and even mechanical engineers, intrigued by some of the properties of their connective tissue. Those interested in stem cells often study echinoderms because of their ability to regenerate lost limbs and organs - a sure sign of stem cells activity.
The class name Ophiuroidea means "serpent like," and surely you can see the origin of one of their common names. Serpentstar refers to the snake like motion of their arms. Another common name for the same animals are brittlestars, and this refers to a unique ability. Ophiuroids have the ability to autonomize, or break off parts of their body (specifically the arms) as defensive measures. They will then regenerate the part that was lost. This serves basically to confuse or distract a predator while the brittlestar escapes.
This means that "serpentstar" and "brittlestar" are two names for the same animal. A distinction is made in the hobby between these two, but it is not biologically significant. An expert in brittlestars is not likely to understand this difference. It is made on whether the spines on the arms are perpendicular or parallel to the arm, and this is not all that significant in some respects (eg it does not predict behavior or relatedness to other species).

 

[ophiura]

Brittlestars are both common hitch hikers and common additions to our tanks. Most are considered scavengers, though it is important to use another term...."opportunistic." Opportunistic refers to the fact that most brittlestars (serpentstars) are able to exploit a variety of feeding strategies. They filter feed, they deposit feed (eating the surface sediment), they scavenge larger food items....and now and then may be predatory. Predatory behavior is not unknown. It is widely reported in the large green brittlestar Ophiarachna incrassata, the most common species in the hobby. But it is less well documented in other species, where basically they may be caught with "evidence" that they didn't actually kill.
All brittlestars should be spot fed regularly or watched to at least ensure they are getting food. We often have a lot of clean up crew in our tanks. Any animal that is opportunistic should be fed. They will not typically "allow" themselves to starve if there are options.
Brittlestars, like their relatives, need very good water quality with specific attention to specific gravity, pH and alk. They may have difficulty adapting to synthetic salt mixes though not as badly as their cousins, Linckia and Fromia. They do need a good acclimation and you should watch for autonomy - breaking of the arms - which is also a sign of stress. Specific gravity should be 1.025-1.026 and all other parameters as you would find in a reef tank.
They can actually be put several to a tank, and even in relatively smaller tanks (some nano's) though not for inexperienced hobbyists where params may fluctuate.
A word on predators - there are many. Brittlestars are a key part of the diet of many reef animals. Triggers, large wrasses, puffers, etc are all predators of brittlestars. Many crabs are also a threat. Brittlestars defend themselves both with the spines on the arms, and by hiding in the rock work. Most self respecting brittlestars will hide during the day, extending only an arm or two out of the rockwork. They can spare an arm or two . At night, they may come out of the rockwork to move and feed. Don't be alarmed if you don't see your brittlestar in the open. It is normal for them to hide.
What I hope to do here is intersperse some of your images and mine, and provide what details I can. So please post your brittlestars, and information you may have, and I will add anything I can think of

I will probably cover a few other general topics while discussing some individual species.
Hopefully we can create a rather thorough list of the species commonly available in the hobby and behavioral issues.

 

[ophiura]

Ophioderma - "snake skin"
squamosissimum - refers to flattened ("squamous") granules on the disk.
This is one of the largest, flashiest brittlestars in the hobby. It is part of a large genus of brittlestars, Ophioderma, many of which are encountered in the hobby.
Ophioderma squamosissimum is a real show stopper. Quite hardy once established, it can nonetheless have some issues with acclimation. Care should be taken during introduction. This species hails from the Caribbean, where it commonly is found under massive stony corals.
This is one commonly called a serpentstar in the hobby. In the bottom most picture you can see that the arm spines are held close/parellel to the arm.
The genus name means "snake skin" and you can see that the arms have small plates that appear to be similar to snake skin.
Available here on SWF

 

[ophiura]

Ophioderma appressum is a good choice for smaller tanks. This showy brittlestar, typically called the "harlequin brittlestar" remains on the smaller side. It is typically a combination of dark green or black with a lighter shade.
This species also comes from the Caribbean.

Available here on SWF

 

[ophiura]

The genus Ophioderma is commonly represented in Florida and the Caribbean, so many species can be found in the trade in addition to the above.
Here are a few additional pics.
Ophioderma cinereum
Ophioderma brevispinum

 

[ophiura]

Believe it or not, but a close relative of Ophioderma (above) is the "green death" Ophiarachna incrassata. These two genera are in the same family.
No other brittlestar species in the hobby is so popular yet has such a bad reputation.
This is probably the single most common brittlestar in the hobby. It gets huge, is often less "shy" than other species, and is green. These make for an interesting specimen. It is certainly one that catches the attention of people, especially those who don't notice many other things in a tank.
This species is a KNOWN PREDATOR IN THE WILD. There is no doubt it has caught things in captivity - shrimp, small fish like gobies, firefish and blennies in particular. Large fish likely died in some other way, but as active scavengers, the green will find it.
They capture prey by arching up on their legs. As fish look for places to sleep for the night, they swim into the trap. The brittlestar draws their arms closed and entraps the fish.
Shown below is a rather famous image of a green eating a cleaner shrimp. Please note that this is how the animal will look after eating a fish or shrimp, so if your brittlestar doesn't look like this...it probably didn't eat whatever you are missing!
This is rather fascinating behavior, considering brittlestars do not have what we would consider a "brain."
That being said, many people (including myself) keep these with no signs of predatory behavior. However, I keep mine very very well fed.
Also shown is a yellow morph of Ophiarachna, that I came across several years ago.
Available here on SWF

 

[ophiura]

A word on regeneration...
One major characteristic of echinoderms is the ability to regenerate parts (sometimes large parts) of their bodies.
Brittlestars are no exception.
If you find a brittlestar with signs of the arms regrowing, there is no cause for alarm. If yours loses and arm, it is not a great concern, unless it continues. This usually indicates a problem with water quality. Regeneration of arms can take months to complete.
Two images below show a series of regeneration of two specimens I have. One is an Ophioderma that was left in a bag in an LFS overnight. This is probably a pH burn or similar. Within a week or so, the wound was healed. The other (spiny one) is Ophiomastix. It is unclear what caused this but it is likely a feeding injury where something big or sharp just poked through.

 

[scottallert]

great info
thanks for sharing

 

[ophiura]

The large tropical genus Ophiocoma is well represented in the hobby. The species are no where near as vibrantly colored as the Ophiodermatid brittlestars, but these guys are still great additions and scavengers.
Most species in the hobby are from the Caribbean.
Ophiocoma echinata and Ophiocoma wendtii are two similar species. They can be distinguished by the arm spines, in particular the uppermost arm spine.
In O. echinata, the spine is swollen and blunt and in O. wendtii it is long and thin.
In my tank, O. echinata lives under a small piece of rock work where it has excavated a "burrow" of sorts. In runs a constant supply of sand grains in a conveyor system, probably looking for food particles in between.
O. wendtii is one of the more "famous" species available. If seen during the day, the animal is quite dark. Scientists noted that the brittlestar actually becomes lighter at night, which went against typical camouflage behavior.
Upon investigation, it was revealed that this species, and many other brittlestar have optically perfect microlenses in their arms. The dark color effectively serves as "sunglasses" during the day, and the pigment is redirected at night - the sunglasses come off.
It is unclear how the animal processes this information (again, they do not have a brain) but you may notice that it is very sensitive to light and shadow at night.
These two images are of Ophiocoma echinata. The top is a more typical coloration. Note the short rounded upper arm spine.

 

[ophiura]

Typically, the "black brittlestar" in this hobby is Ophiocoma wendtii, though now and then it may be another species of Ophiocoma.
Available here on SWF

The following images are of Ophiocoma wendtii, including several from the original publication of the findings of microlenses.
The first image is the animal in the wild. The red tube feet are often not as obvious as this.
The second are "day" and "night" colorations.
The microlens images are scanning electron micrographs of the dorsal (opposite the mouth) arm plates.

 

[ophiura]

A close relative of the Ophiocomids above, Ophiomastix is an occasional import in the hobby. The most commonly seen species is Ophiomastix annulosa.
This is one of my real favorites. In my tank, it is most typically a filter feeder, and hangs out in an upper corner near a powerhead.
The genus is from the Indo-Pacific. It is a relatively large species of brittlestar that is named for the annulations on spines and various plates.
Now and then people have reported getting one of these brittlestars, and a bonus one! Indeed, this animal can have "brood parasites" living in the bursal slits (used in respiration and reproduction). This can be the same species or another related species (eg often an Ophiocoma). Somehow a juvenile settled and was able to crawl onto a large individual, using it for protection. It is called a brood parasite though it is not considered particularly parasitic...."babysitting" is perhaps more appropriate!