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 (and huge!) animal 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
- Sounds like wrestling!!
At night (this behavior was only observed using red lights), this species will sit up on its armtips and form a "pseudocrevice" , maintaining the position (shown in the top diagram) 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 CAPTURE and EAT FISH. Just let them hang naturally...and watch the wonder!