Echinoderm Tube Feet Don't Suck! They Stick!

Image taken by Barry Fackler

A few months ago, I wrote a post that summarized ongoing developments showing how the tube feet in echinoderms (best seen in sea stars and sea urchins) was primarily based on a 2-part glue/adhesive system.

Do tube feet actually use suction as has been historically thought/taught??

The whole "tube feet use suction" paradigm is a powerful one that has been observed since some of the earliest work on starfish in the 1840s. 

Its a powerful and seemingly straightforward idea. Tube feet have what appears to be a suction cup on the tip of their tube feet, and so, therefore, shouldn't it work like one??

Could this long-standing notion... BE WRONG???

Image by "ratexla"/Josefine Stenudo

The suction cup idea is pervasive and can be seen in many pop culture references.

How pervasive?  The authors of the paper I use below cite Peach the sea star from the recent movie Finding Nemo by Pixar- Peach uses the popping sounds that one associates with a rubber sucker!!

A new, recent paper from the bioadhesion labs of Patrick Flammang in Belgium, and Romana Santos and Elise Hennebert in Portugal have demonstrated several experiments that in fact, tube feet rely on adhesion (as outlined here before) and NOT on suction. This paper is OPEN ACCESS and can be found here at the Proceedings of the 7th European Echinoderm Conference! 

The paper is important to people who study echinoderms but is very straightforward and pretty easy to understand...  The authors work primarily on two species as test subjects:  

The common N. Atlantic sea star Asterias rubens

Image by Juncea

and the European urchin Paracentrotus lividus...

Photo by Marco Cortesi

Even before this recent work on adhesion in tube feet, there had been indicators, some years ago that suction was not the only force in tube feet at play. Why?

First-A study from 1985 (Thomas & Hermans) showed that echinoderms have been observed adhering to screens, meshes and grates-so how would a suction cup work if they were being applied on a porous surface with no way to create a vaccum?

Second.Tube feet leave footprints such as this one which leave behind residue suggesting a glue or adhesive was at play..

In order to test whether suction played an active role in adhesion (in other words they attempted to DISPROVE the role of suction), the authors approached the problem with some very insightful observations/ experiments.

1. Observing the tube feet directly!

The physics of your basic suction cup model is pretty straightforward. The suction cup creates a large suction cavity between the attached foot and the substrate (i.e., the ground).  

When you put a suction cup down, you press the top down and pull it up. This creates the suction cavity that attaches the suction cup to the ground..that's what you would expect.

Tube feet from Asterias (the starfish) and Paracentrotus (the urchin) were sampled immediately after it was clear they were attached, and photographed with a Scanning Electron Microscope. Histological (i.e. tissue) sections were also taken...

The top two pics (A+B) show an unattached tube foot.. But C through F? all show those attached to the bottom.

Figure  1 from Hennebert, Santos and Flammang, 2012

What they found? There was NO "suction cavity" between the tube foot edge and the substrate (i.e. the ground). The tube foot disc surface was actually flat and flush with the substrate surface. Thus, no physical evidence for suction could be observed.
The authors indicate that suction may still play a secondary role, serving in conjunction with the adhesion/glue but for the most part it doesn't look like suction is a primary influence here.

2. Measuring the Attachment Strength of the tube feet

Next, Hennebert and her coauthors measured the attachment strength of the tube feet relative to different variables. These included

A. Measuring the strength or tenacity (in terms of Force or Tenacity) of sea urchins as they hung from a glass plate at different angles.
They tested the adhesion of the tube feet on glass relative to detachment force (how hard they pulled) and pulling angle (the direction). That is they tried to pull it off and at different angles on a smooth glass surface.

fr. Fig. 3A in Hennebert et al. 2013

If this were truly suction then the tube feet would slide (i.e., no resistance) and the amount of suction would decrease. There was no (or at least no statistical) relationship between the detachment force and the pulling angle.

B. Measure strength and tenacity on a porous bottom

This one was more straightforward-if tube feet are anchored by suction, then an imperfect bottom (i.e. substrate) won't really work well as a good anchoring ground. 

The authors used a sheet of plastic with holes present in the surface.  They measured tube feet with a device that measure the force and tenacity and then recorded the footprints based on whether they completely, partially or did not cover the holes.  

Prediction:  If the tube feet use suction-the force measurements for strength and tenacity would be significantly affected. But if adhesion was at play, then the holes should make no difference.

Basically, this experiment mirrors the early observations of watching starfish or urchins moving around on a metal grate or mesh. How important can suction be if the animal can move on a non-porous surface?

 No statistical differences were found between the different groups (i.e., the tube feet that walked over a complete, partial or covered hole). 

CONCLUSION!  And so, not only has prior work (see earlier blog post) shown the huge role of adhesion/glue in the way tube feet work but now, the original historical model..i.e., tube feet use suction has been pretty effectively undermined if not disproven outright!
Its possible of course that there are further refinements to how all of this works in sea cucumbers and crinoids but starfish and sea urchins have always been the "model organism" for studying tube feet in echinoderms. 

One of the oldest and most widely known perceptions about echinoderms? Not the case. Evidence is slowly building up against it and an important lesson in science that even the most long-standing ideas can be overturned when you look at the facts with the right questions!

Time Lapse Starfish Videos!

So, between travel, being sick, yesterday's massive Inauguration Day festivities and playing catchup, this week has been crazy!

So here are some neat starfish time lapse videos to keep you informed and entertained!

The awesome video of the tropical shallow-water "chocolate chip star" Protoreaster nodosus, foraging for organic particles and other food on the sea bottom.
Stars of the Sea from Karin Brussaard on Vimeo.

The foraging behavior of the predatory Chilean/Patagonian cold/temperate water Cosmasterias lurida (Stichasteridae)


Some classic videos from the Shape of Life series showing behavioral complexity. Read this article frorm awhile back to see what's going on...
Echinoderms: Sea Star Time-lapse: Eating Dead Fish from Shape of Life on Vimeo.
Echinoderms: Sea Star Time-lapse: Don Wobber's Film from Shape of Life on Vimeo.

Here's a nice HD time lapse of a tiny aquarium asterinid starfish. Note stomach extended and the places where the algae is absent from the glass.
A day in the life of a starfish from Rate My Funeral on Vimeo.

An unusual video that shows what happens when you drop a bunch of Patiriella (bat stars) and let them run free! Starfish show up at about 1:19 (its mostly set up prior to that)


Here's a nice little vid showing Archaster typicus (different from Astropecten-you can tell between the two  by going here to see the differences)  in an aquarium burying itself into gravel


By comparison here is a species of Astropecten from Singapore doing its thing!


The giant Pacific sunflower star (Pycnopodia helianthoides) is fast enough that you can see it moving without time-lapse. What happens when you speed it up a bit? 


Hopefully next will be all caught up and I'll be back to posting more!

A Galaxy Class of Gorgonocephalus! A Basket Star Bonanza! (A Star Trek Connection?)

Image by Viktor Lyagushkin. Gorogonocephalus from the White Sea 

Basket stars are a very unusual kind of brittle star (note that they are NOT proper starfish) which have long, branching arms which they extend into the water in order to feed. Tiny little hooks on the arms are used to capture food which eventually makes its way back to the mouth.

Basket stars occur in tropical and cold-water habitats and I have written about their feeding biology here.

Here's a nice video that shows their feeding posture in the wild

and a nice time lapse video of feeding from the Seattle Aquarium

There are currently 10 species of Gorgonocephalus recognized and they seem to occur widely...(here to go to the World Ophiuroidea Database listing)

Here are some gorgeous Gorgonocephalus sp. (which occurs mainly in cold-water settings) images to kick off 2013!! Enjoy!

Some gorgeous shots of G. arcticus from the White Sea by Alexander Semenov






G. eucnemis from echeng (the "rose star" is the solasterid sea star Crossaster papposus) in Alaska.


Gorgonocephalus from Norway, 928 meters! Arms are tucked away...Image by SERPENT Project!

Several more on a ridge, using their arms to feed. Also Norway, 928 meters. Image by SERPENT Project.


More G. eucnemis from Alaska.. Images by jrixundewater

Close up of the arms..


An unusually pale, "bushy" individual from British Columbia. Image by Ed Bierman


Here's a really nice one of G. eucnemis. by "northwest diver"

Gorgonocephalus fr. Newfoundland. Image by Derek Keats

Newfoundland Image by Derek Keats

Hmmm... y'know, it never occurred to me before but Gorgonocephalus DOES bear a striking resemblance to a certain CRYSTALLINE ENTITY from the 24th Century...

5 Unusual Invertebrates that People Eat! (it takes an Invert Zoo Class to know what some of them are!)

Okay you invertebrate zoologists out there!! How many phyla can YOU recognize on the plates above???   By the end of this blog you WILL know! (and maybe, you will hate me for telling you)

Everyone seems to have a "Weirdest foods" list out there-but here at Echinoblog we offer you only the STRANGEST sampling of bizarre marine invertebrates cuisine! forget insects, snails or shrimp!

Some of the edible (?) metazoans below are usually only noticed by marine biologists, zoologists and the well-studied biologist!

What better application of knowing the strangest of marine invertebrate phyla can there be than to recognize it on your plate? Its scientific name disguised by colorful cultural argot  or perhaps in a different language?

1. SEA SQUIRTS! (Halocynthia sp. possibly H. roretzi). The Korean name for sea squirts as food is: meongge (although there are several more)
Sea squirts are a kind of tunicate, which are in turn members of the phylum Chordata (the group humans and other vertebrates belong to) and when alive they look like this:

As it turns out, sea squirts are eaten all over the world, including Japan (called hoya and maboya) and Korea (meongge, and in a stew called agujim). They also eat sea squirts in France, Italy, Greece, and Chile .
Images of sea squirts eaten in Korea. Image by scbrianchan

image by scbrianchan

A video showing preparation. Sea squirts are filter feeders and processing water through their body is a primary function. Thus, drainage seems to be an important feature...

when cooked and prepared it looks like this

image by seoxcookie

or this..

Image by toughkidcst

sometimes served with oysters...

Image by Food Fetishist

UPDATE February, 2014. I've actually tried hoya in Tokyo! The raw stuff! Its got a very...sour, almost soapy taste. Not for everyone.. but I'm told that its an acquired taste. Folks who grew up with it, LOVE it...

 

2. ECHIURAN WORMS! aka "fat inkeeper worm" aka "penis fish" aka gaebul (genus Urechis)
Most people have never heard of this phylum of worms. Commonly known as "spoon worms"

One of the best studied examples is Urechis caupo, occurring on the North pacific coast -living in muddy burrows which serve as homes for many other commensals, including tiny shrimps and fishes.

Image by Peter_r

But in Korea, a related species, Urechis unicintus is collected and eaten!

Apparently it is cut up into segments and served while twitching....

In other cuisines, it is cooked and stir fired..

the picture above? gaebul and mongae aka Echiuran and Sea squirt!!

and uh yeah, there's a belief that eating these imbues men with more virility. That seems unlikely....

3. INARTICULATE BRACHIOPOD  (Lingula sp.)
Brachiopods are one of the oldest animals observed in the geological record, going as far back as 500 million years. In some cases-they appear relatively unchanged appearing very much as they do as fossils.

and now we eat them.

This gives you an idea of what they look like alive..living in a muddy habitat

Image by Changhua Coast Conservation Action

There are two shells that fit over the animal on the top and bottom. Bivalves and other clams are fundamentally different in that their shells are oriented on the body left-right. 

In one group, known as the "inarticulate" brachiopods, there is a big fleshy structure called the "peduncle" which emerges from the shell

Biologist Richard Fortey noted that they tasted like "straw' (quote is here).

Here is an image of brachiopods as sold in a food market in Makassar.

Image by Arthur Anker

Here is another from a Thai market.

Image by Peter Roopnarine

In Indonesia this dish is called Probolinggo TEBALAN. The blog linked here suggests that Lingula  tastes "sweet and spicy" whereas others I've seen suggest that it is served with a tasty curry.

Huh. Brachiopod curry. NOT something I was expecting to write today!

4. STALKED BARNACLES! Barnacles. Those well-known shelled crustaceans that live on docks and use their "legs" to filter feed out of the water like this:

These of course are what's known as "goose" or "goose-necked" barnacles because of the long, prominent stalk attached to the body sitting on top.

Yes. People eat them! I've seen them in Paris and Belgium.

Imge by RobertoGrego

In some places, barnacles are quite expensive...

Image by erikamussen

Other "unstalked" barnacles are also eaten! 

Image by charclam

In the Azores and Portugal, these are called cracas!  Basically, these are boiled "acorn" barnacles. 

Image by Bellyglad

5. SEA STARS! (family Asteriidae- species: Asterias amurensis)
So, first let me distinguish between the "starfish for show" pictures that one sees around like this versus apparently real accounts of people who eat the gonads of starfish as seen in the video below..

Image by Robin G. Ewsing

Honestly, eating sea stars baffles me. And I  recommend against it (as here) and here but obviously, people really eat these.  On the plus side, Asterias amurensis (the species shown below) is a problematic invasive in Australia (as I wrote here)

so maybe there is a silver lining to this?