Feeding with their feet

I’m excited to share some photos and video of crinoids (also known as feather stars).  These intriguing animals are echinoderms (related to sea stars and sea urchins).  However, we don’t get to see crinoids often along the California coast because they are restricted to deeper water.  When Kate brought back some of her offshore oceanographic equipment from Cordell Bank, she found a few of these feather stars (Florometra serratissima) attached to her gear.   

 

All echinoderms share the unique feature of tube feet — hydraulically powered structures that are usually arranged in rows along the arms.   Most echinoderms (like sea stars, sea urchins, and sea cucumbers) use their tube feet both to attach to rocky surfaces and to crawl along the bottom.  For example, here's a close-up of the tube feet of a Sunflower Star (Pycnopodia helianthoides):

 

However, it is believed that the tube feet of ancient echinoderms were not used for locomotion, but rather were used to capture suspended food from the water.  The tube feet of crinoids have retained this ancestral function of suspending feeding.   

Crinoids hold their long, feathery arms aloft in the water.  Their arms have many fine branches (called pinnules).  A groove runs down the middle of each branch, and the tube feet are arranged in sets of three along the groove.   

 

The primary tube feet are long and are used to capture food particles from the water (see next photo).  They are covered with mucus and fine projections (papillae) to help snare food.  The primary tube feet can also bend over rapidly to flick particles into the food groove.

 

The shorter (secondary and tertiary) tube feet help transfer captured particles from the primary tube feet into the food groove.  Once particles are in the food groove, they are transported by cilia down the groove to the mouth, which lies at the base of the arms.  The extended arms, branches, and tube feet of the crinoid all face upward into the water, creating a cone-like structure with a lot of surface area for capturing food.     

In the video below, you will see two feather stars perched on a rock, followed by close-ups of their tube feet.  As you watch the video of these crinoids feeding, think about how different their tube feet are from those of more familiar echinoderms like a sea star.  For example, notice how the crinoid’s primary tube feet are long, slender, and papillate, and extend up into the water.  In contrast, a sea star’s relatively smooth, muscular tube feet end in suckers and face downward for crawling on the bottom.  Crinoids are so different in their appearance and behavior that they somehow seem more like prehistoric fossils than living animals!

crinoids_sanford from Jackie Sones on Vimeo.

P.S. Many thanks to Kate for sharing these amazing animals with us.   

 

Far offshore and deep below

Mystery image #1:

 

And here's another — mystery image #2:

 

Ready for the answers?

The first image is a segment of the skeleton of a bamboo coral.  This piece is in the collection at the Bodega Marine Lab.  It was collected decades ago from ~500 fathoms off of Bodega Bay.  

The second is a single arm of a crinoid, also known as a feather star.

I'm sharing these images with the hope that it encourages you to tune in to live footage of ROV exploration at Bodega Canyon this week.  You can watch and listen to scientists documenting corals, crinoids, brittle stars, sea spiders, sponges, octopus, and other unusual deep-sea marine life thousands of feet below the surface.  This is a wonderful opportunity to learn about a variety of animals that most people never get to see!

In 2008, during a clean-up of abandoned fishing gear near Cordell Bank, a few animals were brought back to the marine lab.

I took a few quick photos of the beautiful crinoids clinging to the old, tangled ropes.  Crinoids are a class of echinoderms (related to sea stars, sea urchins, and sea cucumbers).  There are about 600 species of crinoids in the world.  Some crinoid species hold on to the substrate with finger-like cirri (see the cluster of short appendages near the center of the image below).

 

Most crinoids are known for their long feather-like arms.  The side branches of the arms are called pinnules.  Crinoids are suspension-feeders.  They hold their arms upward (like an upside-down umbrella) and capture food particles drifting down from above.  

A long groove runs along the center of the each arm and is lined with clusters of tube feet and modified ossicles (calcified plates) called lappets.  The tube feet and the lappets are involved in directing food particles to the central groove which then transports the particles down to the mouth at the center of the arms.

Since we took these pictures almost 10 years ago, Eric didn't have a great video camera yet.  But he did capture close-ups of the crinoid tube feet as well as the lappets flipping up and down along the food groove (we think they look like little pinball flippers!).  The footage is grainy, but I think you'll be able to appreciate this fascinating feeding behavior.  Then when you see crinoids in the live video from Bodega Canyon, you'll be able to think about how feather stars feed!

Here's Eric's short video clip:

crinoid sanford from Jackie Sones on Vimeo.

I'll end with an old illustration of a feather star holding on to a tube worm, and a reminder to check out the live deep-sea footage from Bodega Canyon!