Tuesday, November 11, 2008

Giant Green Brittle Stars of DEATH!! When they ATTACK--AGAIN!!

With all of the vicious ophiuroid feeding going on, I am recently reminded by a neat paper written by James Morin at UCLA from the 1988 International Echinoderms Conference. about Ophiarachna incrassata, what he describes as "crepuscular and nocturnal predator "...

Ophiarachna occurs in the Philippines and in tropical Pacific waters and is frequently seen in the pet trade (for examples..see videos below). Its a handsome naimal that looks like this:

His paper describes an AWESOME feeding method!! Something that he calls "The Body Spiral Behavior"...and you KNOW its good when its
  1. Echinodermish
  2. Sounds like wrestling!!
This next part is pretty awesome.

At night (this behavior was only observed using night-vision), this species will sit up on its armtips and form a "pseudocrevice" , maintaining the top position for many minutes without moving. Apparently, he found many individuals found in this posture during the night.
From here, it gets interesting.

Short version: Fish get too close..and then... Ophiarchna will RAPIDLY wrap its body into aspiral (as above) ..forming the "body spiral". This action apparently takes less than a SECOND.

The fish is trapped by the elongate spines on the arms creating "bars" to a "prison" formed by the helically arranged arms.

The brittle star holds the position for several minutes, gradually lowering the disk toward the bottom and moves its arms outward.

Prey captured was digested head first as it was swallowed WHOLE by the ophiuroid.

Interestingly, Ophiarachna takes advantage of several of these fish's natural nocturnal behavior to find hiding spaces. And although they feed on a variety of items (e.g., algae, etc.) this behavior was observed to be quite successful.
And thanks to Youtube...here's some video footage of this beast doing something VERY close to the behavior described, but I'll betcha most people don't actually know that these critters can EAT FISH. Just let them hang naturally...and watch the wonder!

6 comments:

Cephalopodcast said...

Had occasion to witness this on many occasions when I worked at a fish store. The green brittle stars are often sold as "reef safe," meaning they are fine for hard and soft corals but they sure do a good job of cleaning up the Pseudochromids. If customers came in complaining of errant mantis shrimp in their live rock, it would sometimes turn out they had one of these lovely creatures in their tank instead. Of course, sometimes they had both. :P

Ivan said...

Amazing. When my friend mentioned this, I was skeptical at first.

But won't the struggling prey damage the arms? Or is this particular species not so 'brittle'?

ChrisM said...

Well..one should always be skeptical, but its sometimes things are just as amazing as they seem.

The arms on these beasts are quite tough (armor plated with big arm spines) and smaller fish are not likely to pose much of a threat. In one sense, the term "brittle star" does not always apply...

j@son said...

Just witnessed my green brittlestar do this with my lawnmower blenny! I couldn't believe it. Luckily I caught it in time to rescue him!

Gregory M Leach said...

I've literally just put a small specimen in my tank, and watched with baited breath, waiting to dive- in and intervene if it bothered any of my shrimps, as they can do..
...then my pistol jumped out and 'snapped' a leg off the starfish. Hmmm.

Rob Knight said...

I did have a fairly large arrowhead crab for a while.. It went through a molt and got ambushed! It's a shame as Im now over-run with bristle worms!