Sunday, November 16, 2008

Underwater death star

And it's green! It's a giant brittle star with a frightening way of catching and eating fish. Who knew that a humble brittle star could catch a smarter and faster fish?

Thanks to The Echinoblog for this revelation of the brittle star of death from the Phillipines, Ophiarachna incrassata, described as a "crepuscular and nocturnal predator "...

Diagram credit, James Morin of UCLA from the 1988 International Echinoderms Conference (Burke et al. pp. 401-407.)

Quoting from Echinoblog:

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.
Oh my!

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