Today..the SECRET LIVES of FEATHER STARS! (HINT: wait for the twist at the end!)
In many ways, feather stars (aka crinoids-owing to their membership in the Class Crinoidea) are among the most mysterious of echinoderms. We know them as fairly stationary flower-like animals that feed passively as water currents flow by them...
They don't really pursue prey and they seem pretty quiet and keep to themselves, even for echinoderms.
Are they even animals? Even starfish and sea urchins kind of move around and do stuff. What sort of stuff do crinoids do??
Some can maybe capture bigger prey...
and some stalked crinoids are in a game of cat and mouse with predatory sea urchins! (usually as the mouse!)
A recent conference and exchange with researcher Greg Rouse at Scripps Institute of Oceanography reminded me of the SECRET, SECRET lives of feather stars (=unstalked crinoids or just "crinoids" from here on in...) [note-SECRET details herein are from Haig & Rouse 2008)
First, some basics. You got your adults and they produce your eggs and sperm. You get your gametes together and pow! You got them together to form a doliolaria larvae!!
So what happens after that?? Pictured here is a series of what happens!!! The doliolaria settles and begins to TRANSFORM!!! Into this sort of weird transition before it becomes a weird protolarvae called a cystidean larvae!!
Here, we have ACTUAL photos of an Australian crinoid-Aporometra wilsoni showing various transitionary larval stages:
Then...VOILA you have a CYSTIDEAN larvae!!
But WAIT!! The cystidean larvae doesn't look at all like the weird feathery thing we started with....
It looks more like this: a STALKED crinoid!!!
"Unstalked" crinoids are those which are basically a skeletal cup with a bunch of arms, sometimes with little "legs" called cirri. The great majority of crinoids alive today...especially in tropical shallow-water or in many cold-water settings are unstalked or "comatulid" crinoids.
Keep that in mind...and let's get back to the story...
But THEN, the as the larvae grows, the TOP cup part??? It starts to form little cirri/legs and as it gets bigger and bigger...the cystidean starts to look more like a little tiny stalked crinoid.
Once the feeding arms and etc. have become fully formed..it reaches what's called the pentacrinoid stage.
The top, cup segment of the pentacrinoid stage develops until this happens:
The little cup matures and BOOM!! It separates from the stalk!! and the "cup" is what we see as the adult stage of the "unstalked" crinoids!!
We see the ancestry of these animals in their life cycle!!The thing with crinoids? the lessons are subtle but VERY rewarding!
(special thanks to Jodie Haig & Greg Rouse for the images!)