Creature Feature – Brittle Stars

When I was in Lauderdale by the Sea shore diving for Bugfest 2012 recently, I noticed lots of little spiky legs sticking out from hidey holes.  Hubby Rich flipped over a rock and found one hiding beneath.  I was a little shocked to see so many and couldn’t help but notice how very much they looked liked little centipede legs.  He dropped the rock when he saw it thinking it may have been a fireworm quick (which are poisonous) and a leg broke off.  The leg continued wriggling on it’s own and the rest of the brittle star crawled back in a tight corner under the rock. This got me to thinking about what the heck it was and why we were seeing so many of them.  They look very hairy or feathery but the spines are actually a bit pointy.  They are harmless to humans.  Being nocturnal creatures, you will see man underneath ledges if you look during the day.  They interesting creatures can grow up to 12 inches in diameter.  They can bury themselves and leave only an arm or two out for catching plankton.  Generally when you see them stretched all out they are catching food particles in the water.  To tell you the truth, I have never really noticed these little guys before.  From the conditions I can tell you there was an active current on most days and this one particular dive was early am.  Perhaps with all the plankton floating in the air and the darkness of the water brought of the best in the brittle star.

Is it a starfish, worm or brittle star?

Brittle stars are close relatives of sea stars.   They are both part of the echinoderm family.  They get their name due to their brittle appearance.  They can lose a leg quick and easy. I initially thought it was a spiky starfish that I was observing in LBTS.  All of the ones I saw in this habitat were black or blacking brown.  The brittle stars have a radial symmetry with a central body from which five snakelike arms protrude. These hairy spiked arms are highly flexible. Their arms are long whip like structures not at all fat like regular starfish. They can readily regenerate lost arms or arm segments unless all arms are lost.  They do this to escape predators.

They do not, like sea stars, depend on tube feet, which are mere sensory tentacles without suction. Brittle stars move fairly rapidly by wriggling their arms which are highly flexible and enable the animals to make either snake-like or rowing movements.   When they need to change direction they just switch which arm is the leader.  The brittle stars are known for attaching themselves to the seafloor or to sponges or cnidarians, such as coral. They move as if they were bilaterally symmetrical, with an arbitrary leg selected as the symmetry axis and the other four used in propulsion.  When they want to change direction, they just switch the lead arm..  Very weird to watch, almost alien like.  Imagine this creature in a sci fi flick.

They legs are attached to a central disk.   Compared to starfish, brittle stars have a much smaller central disc and no anus. The disk in the center holds all of the internal organs unlike starfish which may have some extend into arms.  The underside of the disk contains the mouth, which has five toothed jaws formed from skeletal plates.  The mouth is rimmed by 5 jaws and also serves as the anus of the creature.  Wastes are eliminated through the mouth which is situated on the underside center.

The brittle stars breathes through ten little opening at the base of each arm.  These openings are also it’s reproductive system.  It takes water in to get oxygen and it releases sperm or eggs into the ocean when reproducing.

hairy feathery legs

There are some 1,500 species of brittle stars living today, and they are largely found in deep waters more than 500 metres (1,650 feet) down.  They can be found in arctic waters up to 600 meters and even in brackish waters.  The brittle stars feast on small crustaceans, worms or scavenge from the dead remains on the bottom. They also eat detritus, coral-shed mucus, bottom detritus (detritus = organically enriched film that covers rocks).   There are many types and colors.  For the most part they are not predatory except for the green brittle star which reef tank owners I know say eat other fish.  Most of the ones I saw were in places that had pretty good currents of water moving through which makes it easier for them to catch plankton.

The brittle star has a few predators that find them tasty; starfish (crown of thorns), triggerfish, and certain types of crabs.

They are non toxic but are not used for food by man.  I am sure they would make some tasty Asian delicacy like chocolate dipped brittle star leg or deep fried brittle star in duck sauce.  How about some brittle star kabobs?

This was another fine lesson in scuba diving for me to slow down and smell the roses, or spot the brittle stars.  On this occasion diving, due to the currents we were not able to zip around looking for sharks, turtles and our other favorite friends.  I will state that the weeks diving brought many first, flying gurnard, townsend anglefish (shhh, don’t tell anyone, more to follow)

About daniellesdives

diving enthusiast
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