Five Invertebrates that would be Terrifying if they were Bigger!

The secret of the big terrifying jaws is #1 below! 

HALLOWEEN! Every year, I like to use the season's festive theme to try and highlight some cool invertebrate diversity! Last year I did an overview of creepy worms and the year before that, I did an overview of spooky things that echinoderms (my research focus & subject of this blog's love) are known to do. 

So, note that I actually am using REAL aspects of these animal's biology that make them, creepy, terrifying, spooky, whatever. Unlike SOME places.. I won't just find some weird looking, random animal and just SAY its spooky or creepy. It actually HAS to do something worthy of the name!

This year: a theme that often comes up with invertebrates: Predators that would be terrifying if they were larger!! 

So, this is a pretty popular trope and frankly, there are ALREADY a bunch of huge, oversized marine invertebrates that freak people out. You will doubtlessly see some tweets about those beasts this week.

Here are some of my picks for invertebrate PREDATORS that to me, have earned the RIGHT to be optioned for movie rights! or other fantastic treatment!  So, nothing that is weird looking but harmless (I mean, c'mon, BASKING SHARKS? SHREWS?)

There were MANY to choose from of course and so perhaps next year I'll present more of them. But for now, here's some good ones.....

5. Arrow Worms (phylum Chaetognatha)
Imagine the oceans filled with fast-swimming, transparent worms with sharp spines for teeth on their head, and which can effectively "see" in a 360 degree field of view AND attack and devour prey several times their own size.

Bodies are transparent and with unusual "eyes" that are arrayed in 5 directions, essentially giving them a full field view (360 degrees). Fortunately, these "eyes" lack lenses and are thought primarily to be used for orienting to light and dark.
They feed with these big nasty hooks that emerge off the front of the head!!  Some are even known to do so with venoms like tetrodotoxin, the potent toxin from puffer fish.

Arrow worms have been documented as having capture prey several times their size...like fish!

Here's an interesting video that shows the spines extending from the head on a Japanese species... 

Sadly, or perhaps fortunately for us.. these are pretty small. Ranging from less than half an inch with monsters up to 4 inches! 

But what if they were HUGE????  Honestly, I think one movie from 1998, Deep Rising had these things, which swam through the water at a good clip. and the spines were KINDA chaetognath like! 

So, yes! We want MORE ARROW WORM MONSTERS PLEASE!!! 

Via Wikipedia

4. Cone Snails.  Does everyone know what cone snails are? Marine snails that use a modified tooth like a harpoon + very potent toxins to capture their highly mobile prey. Often times, vertebrates like fish..

Some of them, however, rather than using the proboscis to directly paralyze prey, will use this  highly modified "net" which is presumably, a modified feeding proboscis.. 

Yikes.. imagine what that would be like if cone snails were bigger..like bear or even elephant sized! 

3. Rhizocephalans! Barnacle Parasites that take command of your Body! 
Imagine  a fleshy parasitic network that works its way into your body, commandeering your all your bodily functions, INCLUDING your gonads, such that all you do is produce eggs to make NEW parasites.

These don't really NEED to be bigger..but merely adjusted to parasitizing MORE than crabs.

These have been written about in some detail by Rebecca Helm over at Deep Sea News. Her account is quite chilling. I recommend reading it in the dark, while you are alone with some seafood....

Or, watch this video from Casey Dunn's "Creature Cast" series which also very ably explains the life of this creepy parasitic barnacle... 

                Rhizocephala: The Extraordinary Life Cycle of a Parasitic Barnacle from Steph Y on Vimeo.

2. LEECHES! This is kind of a cheat, since I put leeches into my "Creepiest Worms" post last year.  I just thought this was kind of awesome... 

1. Labidiaster annulatus, the giant 50 armed star of the Antarctic!
This is one of my FAVORITE beasts.. which I wrote up here, early on in the blog (and on numerous other occasions).
But the short story:  Giant 1.5 foot wide starfish with 50 arms, catches krill and other prey with arms!!                  

The surface of the starfish, especially on the arms is covered by THESE.. 

Jaw like structures called pedicellariae which act as "bear traps" to capture krill and other prey if they get too close to the arms. 

Thanks to Bob Ford & Taylor Steed of Frederick University for the SEM pics

These are ALREADY pretty big. About 1-2 mm. But look at those fangs!!  and the shanks on the teeth!

Can you IMAGINE if this critter was DOG or even BEAR sized on the land????  Catching everything from tiny mammals to birds!!! 

For the Next few weeks: Echinoblog Returns to PARIS!

The Hippest Post you Know! New Hippasteria species!

Research! People often speak of the rigors, hardships and even agony of their research. The long days in the field to the writing and so forth.. But what a lot of folks don't often spotlight is how damn satisfying it is (at least for me) to see something you've been doing for several YEARS come to fruition in a paper! 

Case in point is my newest starfish monograph, just published a week ago in the prestigious Zoological Journal of the Linnean Society!  You can go here to find it (sorry-paywall).

This was part of a project that began years ago in 2011 or so, as I discovered several of the specimens described below in the collections at the Muséum National d'Histoire Naturelle during one of my visits to study their starfish from far and distant lands! 

This, then combined with a project I was working on with my colleague Dave Foltz at Louisiana State University and eventually snowballed, adding on Marc Eleaume, my colleague from Paris and Kate Neill from the New Zealand Institute of Water and Atmospheric Research (NIWA). 

What's it all about?? 

You may remember a post I wrote last year about some work I did with my colleagues where we discovered that the starfish species Hippasteria phrygiana was not simply one species in the Atlantic but in fact one species that was found across THREE OCEANS! (here to see the full story)

Part of this work involved not only Hippasteria phrygiana, but testing whether or not the OTHER species of Hippasteria were the same! And what about other potentially new species?? Were those new?? 

My colleagues, especially Dave Foltz analyzed tissues sampled from samples of multiple Hippasteria species taken from all around the world. From the Atlantic to the North Pacific to New Zealand (South Pacific) to Kerguelen Island in the southern Indian Ocean! 

We sampled for genes and compared them using analysis software to get this tree, which showed us which were the mostly strongly supported species..

We ended up with 7 species, 3 of them were new to science!  Of the other 4, H. phrygiana we kinda changed (see below) and here. Hippasteria californica had some weird dynamics (see below, Hippasteria heathi was a "good" species but we found out that it had cousins which were found WAY beyond where  it was found and the final species Hippasteria lepidonotus turned out to have been "oversplit" into the genus Cryptopeltaster. That is, it turns out to be a redundant name which was likely created because of the deceptive amount of differing morphology in that species (and thus thought to be more different than it actually was).  

So, let's see some new species!!  Many Hippasteria related species are predators of deep-sea coral predators and I've described other new starfish species related to these, which you can read about here.  

1. Hippasteria muscipula

This one is the biggest and neatest of the new species I described.. A big, massive critter about 30 cm (about a foot across)! 

It was collected from various tropical Pacific localities: Hawaiian Islands, New Zealand south of New Caledonia in deep-water. 425 to 1500 meters!

What's cool about it?? The name.  The species has these very big and toothy pedicellariae (aka claw like structures on the surface, possibly used for defense)

The species was Hippasteria muscipula after the pedicellariae's resemblance to the Venus fly trap (Dionaea muscipula)!

One other cool thing we found? The specimen from New Caledonia had its stomach wrapped around a deep-sea "coral" called Metallogorgia, which is kind of an odd looking gorgonian that looks like a living wire hanger! Possibly feeding on it??  Interesting. 

2. Hippasteria tiburoni
This new species was a little tiny thing collected by the Monterey Bay Aquarium Research Institute from Pioneer Seamount in the North Pacific (southwest of San Francisco) in 2005

This species was distantly related to Hippasteria heathi, which occurs primarily in the Aleutians..

This species was named for its "collector" the now defunct Remotely Operated Vehicle Tiburon which served science and MBARI well between 1996 and 2008!

Hippasteria tiburoni, despite its size was observed feeding on deep-sea bamboo coral!!  Ain't it an awesome little critter?? 

3. Hippasteria mcknighti
The third new species we described was found among specimens sent to us from the New Zealand Institute of Water and Atmospheric Research.  It resembles the North Pacific Hippasteria heathi but the genetic and morphological data support it as being distinct..

This species was named for Don McKnight (1936-2012), a famous echinoderm biologist who worked on echinoderms for NIWA for many years. His obituary is here. 

4. Big Taxonomic Changes! 

The rest of the paper addresses multiple taxonomic changes (i.e. names of species).  Among the most significant of these was the big discovery of how wide-ranging a species, Hippasteria phrygiana turned out to be!!   This was a species found in THREE OCEANS! 

The problem with this discovery was that historically, folks would often describe a new species if it was not previously known from that part of the world and sometimes there are widely occurring animals which do form regional subspecies. It depends.

                    

But in this case, thanks to our genetic data, we could tell that a great many described species, which were likely separated as distinct species based on minor differences are in fact, just minor variation of one wide-ranging species!

In this case nearly a dozen species, were found to be "redundant" or were applied to Hippasteria phrygiana throughout different parts of the world. 

We also looked at the other species of Hippasteria, H. californica which occurs in deeper water habitats than H. spinosa... 

Image by Dr. Steve Lonhart Via SIMON

What we had found, up this point had been pretty consistent with what had been known until we found two individuals of this species which were revealed by genetics to have been Hippasteria californica BUT in SHALLOW WATER habitats in British Columbia AND which looked like H. spinosa!

Weird.

Image by Neil McDaniel (check out his website here)

STRANGE! And a mystery that we shall have to investigate for another day....

OTHER Related Posts:
New genera and species of Hippasteria related starfish species! 

Deep-sea Corallivore Video from MBARI!

What we know about the world's most venomous sea urchin Toxopneustes fits in this blog post!

Toxopneustes! aka the "Flower Urchin" is one of four species of Toxopneustes (all of which occur throughout the tropical Pacific). One species, Toxopneustes pileolus is one of the most frequently encountered and as such, this is the name most often applied to sea urchins that have the distinct appearance (as seen above).

Toxopneustes literally means "toxic foot"undoubtedly alluding to the MANY venomous pedicellariae that compose the animal's appearance. I'll explain "pedicellariae" more below..but just so you know what I'm talking about? ALL of those yellow circles and traingles in the picture above? Those are tiny little claws and each one of them is toxic. So be careful around these guys..

Toxopneustes has all of the other stuff that you see in other sea urchins, such as spines and tube feet.

The circles and triangles below are pedicellariae. Round means the pedicellariae are "open" and the triangular ones indicate the pedicellariae are either closed or are closing.  The brown rods below that kind of look like toothpicks? Those are the spines, which are actually not themselves toxic (as far as I've read).


Toxopneustes has been known for quite a long time. The genus was described in 1841 by Louis Agassiz, so we've had some time to think about it.

This then, is the puzzle. Why do we seemingly know so little about it?? As we'll see, it has a formidable reputation as a highly venomous species and its a prominent tropical sea urchin but really, a lot of what we know essentially boils down to this....

1. Toxopneustes pileolus displays covering behavior. 
I have discussed and blogged about "covering behavior" in the past (here). Toxopneustes is a "collector" urchin, which means that it shows the curious behavior of adding rocks and other debris using tube feet and/or pedicellariae to cover over itself.

Although the reasons are not well understood, it is thought that this could serve to protect the urchins from ultraviolet rays. In some cases with other urchins, its thought that the materials serve as defense, but given the highly venomous pedicellariae on this species, I kinda doubt that's the case here.

One paper, which studied the East Pacific species, T. roseus (here) suggested that the covering response protected the animals against wave surge while they fed on coralline algae in rhodolith beds. 


2. Flower urchins spawn in the Spring and "undress" their covering materials to do it! 
This one is self-evident since all animals have to reproduce. And most echnoderms spawn externally. But it was only recently in a paper by Andy Chen and Keryea Soong in Zoological Studies in 2009 which showed that they showed Toxopneustes pileolus "release" all of the materials obtained via their "covering response" before they spawn.

Here is Figure 1 from Chen & Soong 2009. Showing on the left, a "covered" urchin and then on the right an urchin "uncovered" and spawning.

3. They hold the distinction of "World's most venomous" sea urchins 
     Here we have the #1 feature, this sea urchin is known for: its sting! One species in particular, T. pileolus is regarded by the 2014 Guinness Book of World Records as the "most toxic" of sea urchins (see lower left corner).

The poison is served via the pedicellariae which are all of those triangular and circular structures that you see on the surface of the urchin.. Here the pedicellariae are all agitated. How can you tell? Note that they are all triangular instead of round. That means they are closed and have been recently agitated...

Here is more of a closeup of each one. Each with a stalk connecting them to the body. They are round when open and more triangular when closed.

                   
Here's a diagram of one, showing the hard parts within all of the softer covering. Basically, each one is a claw that injects poison.
                                            

And below is a nice SEM image of a similar kind of pedicellariae from the East Pacific species. Toxopneustes roseus showing it in  more detail.

From the Echinoderms of Panama Lifedesk by Simon Coppard

4. How Toxic are they?? 

From this Japanese blog. Do not do this. It will hurt (I mean the pedicellariae. Going to the blog shouldn't hurt). 

Well, strangely enough, there are very few modern (read-quantiative) accounts of how toxic/painful/ potent Toxopneustes poison can be. However, I did locate an older account from 1935 by Dr. Tsutomu Fujiwara at the Hiroshima Zoological Laboratory in Japan who reported his experience with being stung by one (italics and paragraph break are mine) in Annotationes Zoolgicae Japonenses 15(1): 62-68 

     On June 26, 1930, while I was working on a fishing boat on the coast of Tsuta-jima in Saganoseki, I scooped up with my bare hand an individual of the sea-urchin which had been carried up by a diver with a fishing implement on the water surface from the sea-bottom about 20 fathoms in depth, and I transferred the sea-urchin into a small tank in the boat. At that time, 7 or 8 pedicellariae stubbornly attached themselves to a side of the middle finger of my right hand, detached from the stalk and remained on the skin of my finger.

     Instantly, I felt a severe pain resembling that caused by the cnidoblast of Coelenterata, and I felt as if the toxin were beginning to move rapidly to the blood vessel from the stung area towards my heart. After a while, I experienced a faint giddiness, difficulty of respiration, paralysis of the lips, tongue and eyelids, relaxation of muscles in the limbs, was hardly able to speak or control my facial expression, and felt almost as if I were going to die.  About 15 minutes afterwards, I felt that pains gradually diminish and after about an hour they disappeared completely.  But the facial paralysis like that caused by cocainization continued for about six hours. 

Other accounts have detailed stopping oyster hearts, and contraction of smooth muscle, including cardiac (heart) tissue. Some accounts of Toxopneustes have stated that swimmers have drowned following stings but I wasn't able to verify an account of this.

Is it any worse than the venom in other poisonous urchins, such as these echinothuriid "fire urchins"??? 

5. What we DIDN'T know about commensal crabs (but do now, thanks to the internet!)

That's a bit of a cheat. We DID know that commensal crabs live on Toxopneustes.  Apparently, these striped little fellows are called Zebrida adamsii. The name "Zebrida" undoubtedly hailing from the zebra-like stripes on the animals' body.

Here's one living on Toxopneustes pileolus with some eggs! 

But what is REALLY interesting is just HOW these crabs live on the urchins! Look at the video below.
They actually CLEAR off the pedicellariae and spines and live on a bare patch of the animal surrounded by all the poisonous pedicellariae and etc. 

Questions!? 
How far/how long do they hitch a ride?
Do they feed on the tissue from the tube feet and pedicellariae?
Are those "bare patches" long term? Or are they only from acute attacks? (those crabs seem to be pretty comfortable there!)
Are the crabs as well camoflaged as they seem?
Interestingly, note also that the pedicellariae are all open and seemingly comfortable. Does that mean they are pretty cool with the crabs living on them that way?  What do the urchins get out of it?
IS Toxopneustes REALLY the world's most venomous sea urchin???

Someone go find out and tell em' the Echinoblog sent ya! (unless you get stung-then uh.. it wasn't)

Wow! Urasterias Vs. Amphipods! BONUS Echinoblog!

Last night I found this..

A video that shows the Arctic asteriid starfish Urasterias linckii just PLOWING into a field of creepy caprellid amphipods!  This looks like it might be feeding or possibly the opposite-defending itself?. Are the pedicellariae "batteries" on the side being used? Do these species typically interact?  Many mysteries!

As a caveat-this video could have been staged, obivously some time lapse was used, not sure. but it IS pretty cool and is I think the first time I have EVER seen Urasterias alive in a video! So, enjoy!

here's some better pics of the animal itself I found on Flickr

Photo by Alexander Semenov

And a close up of the MANY pedicellariae. They are quite abundant and pretty frakking HUGE!

Photo by Alexander Semenov

If you want to why/how the pedicellariae might be used in feeding click first on this intro post  and then there's this earlier post about asteroids feeding on moving prey! (and on Labidiaster-the king of starfish predators on moving prey!)

I've spoken recently of how the diving community and the many, many legions of marine photographers have captured SO much on the Internet-often without realizing what they've done! And here is another GREAT example! 

The Panoply of Pedicellariae Post!

Wonderful image by Judt on Flickr

Pedicellariae! 

No term excites a starfish biologist (well, me anyway..) more than trying to figure out what pedicellariae do!

But wait, you've never heard of the word? What are they?  I'm glad you asked! 

Pedicellariae (singular pedicellaria) is a blanket term that is used to describe a panoply of tiny claw, clamp, wrench or beak shaped structures that are present on the external surface of starfish and sea urchins. 

Pedicellariae absent in sea cucumbers, ophiuroids, and crinoids but seem to have developed as very different structures in sea urchins vs. starfish. 

As a generality though, they are used by the animal to interact with the environment. They can grab or protect-but the exact use of pedicellariae in some groups seems... mysterious. I'll treat pedicellariae in sea urchins another day but today, let's go through some examples of what some pedicellariae are known to function as. 

In some cases function is known and other times not...There are many different kinds of pedicellariae-but here are some of the best known (and easiest to see..)

1. "Forceps-like" (also called forcipulate) Pedicellariae

These are pedicellariae that are composed of three pieces with two really pronounced wrench-shaped "jaws" that usually have teeth or some kind of nasty looking shank on each piece.

In a lot of forcipulate species, such as this Antarctic Labidiaster annulatus (which I wrote about before here)  they use the pedicellariae to aid in capturing krill!  

                                

And in fact there are at least one or two other instances of forcipulate starfish species that use pedicellariae to capture prey.. Go here to see the write up on how some starfish can capture active prey.

  But in Labidiaster, these pedicellariae are HUGE! And NASTY lookin'... The ones in this species are quite large. The one in the picture below is easily a whole MILLIMETER or two across!  (trust me that's big for pedicellariae!)

Here's a Scanning Electron Micrograph picture to give you a clearer idea of what they look like and with all of the glorious details! 

SEM pic from Dearborn et al., 1991

The pic of the pedicellariae above the SEM was taken from the arm below for scale.. Note the whitish fuzzy stuff on the surface of the arm? Those are the pedicellariae.

                                      

And here's the specimen the arm is from for reference... (a living example is above)

Forceps-like Pedicellariae are formidible and numerous.  Below are some close up pictures of these  tiny structures on two well-known species on the North American Pacific coast: the giant sunflower star (Pycnopodia helianthoides) and the ochre star (Pisaster ochraceus).

Pedicellariae are typically present around the spines in retractable rosettes or pompons, numbering in the THOUSANDS! These could be extended or retracted like gun batteries if the animal felt threatened.

Pedicellariae are smaller in other forcipulate asteroids but can be quite effective.

During the days of my halcyon youth when I worked as a docent at touch tidepools at Steinhart Aquarium and Monterey Bay Aquarium, people with hairy arms had to exercise some care not to completely apply the surface of the ochre star (Pisaster) lest  you wanted all of the thousands of little claws to tear off all your arm hair!

Here's a nice close up of Pycnopodia helianthoides-note the many, tiny white bits around each large white spine. The finger-like translucent structures are called papulae (aka the gills).

Image by Judt

Here's a pic of the whole animal for comparison. Pycnopodia are soft to the touch but get quite large-reaching up to 2.5 to 3 feet across!

Image by Yawnthensnore

Here's an image of the pedicellariae on Pisaster ochraceus. Pedicellariae are the tiny little beak-shaped structures that are around each spine on the surface of the animal. Those big white things are spines-

Image by Alan Davis Photo

Here's a pic pulled farther back to give you some scale as to where pedicellariae are found..

Image by Alan Davis Photo

There are often several types of pedicellariae on each species. In addition to the ones above Pisaster ochraceus also has these really distinctive ones that look like claws rather than beaks!

Image from Fisher, 1930, Fig. 8a

There are a few species of forcipulate asteroids that display how pedicellariae are used-probably for feeding and maybe defense.

But let's look at a few other weird shaped ones...

2. Bivalve Pedicellariae

Starfish in the Goniasteridae and the related Oreasteridae have a different type of pedicellariae. These are flattened and more "lip-like" and can be VERY abundant on the surface of some species.

This is one tropical oreasterid called Anthenea for example..

And if we want to take those bivalve pedicellariae to extremes.. here's a genus and species of deep-sea goniasterid I described a few years back from New Caledonia..called Akelbaster 

And there's some pretty neat triads of bivalve pedicellariae on this beast.. the goniasterid Eknomiaster beccae! This was another species I described awhile back.. 

Some bivalve pedicellariae are not only large but also a bit taller such that they actually seem like large clamps!

Some awesome pics of Hippasteria phrygiana by Katie Gale! 

And here is a closeup showing several tinier bivalve pedicellariae on the surface of a tropical oreasterid fron Singapore:  Anthenea aspera. The pedicellariae are the tiny little white clamp-shaped structures..

    Image by Wildsingapore!

Very neat looking-but again the question: WHAT DO THEY DO?? 

Do they use them to protect themselves from small, annoying crustacean predators? Do they aid in feeding? Some weird biophysics thing we've not figured out yet???

3. Cholocariform or "Other"? 

And then, every so often you get an especially weird and large pedicellariae such as the one you see in the deep-sea Antarctic Chitonaster felli...

The pedicellariae are these five huge pincer-shaped structures that are present on the surface of each interradius. 

Each one seems to be made up of two clamp-like components...

But again the question?? What are they used for? Why so big in this species but so small in its sister species?  How would the animal use these as a defense?  What other function might they be used for?

Scientists have been observing pedicellariae for literally 100s of years (they were originally described as animals! if you can believe it!) but a good understanding of these structures has been elusive! Its weird stuff like this which makes echinoderms such a joy to study...

Brisingids pt1! Weird Deep-Sea Halloween Starfishyness!

(Novodinia antillensis from Ocean Explorer)

As a summer student at the Hopkins Marine Station/Monterey Bay Aquarium Research Institute program back in the late 90s I was still deciding what I wanted to do with my life.

I was thinking that I would go into Entomology unless my summer student internship thingie worked out.

It did.

I fell hard for starfish. and naturally I went directly to the strangest of a strange group of animals living in a strange world. Starfish were odd and alien enough...but to see the REALLY bizarre ones?? Amzing.

I fell in love working with these animals and the first time I ever saw a living one was a HUGE day!!
I eventually went on to "cut my teeth" on brisingids, doing my Masters in Marine Biology at San Francisco State University and the California Academy of Sciences.

What's weird and AWESOME about brisingids? Simply put.... Everything. Some basic factoids:

• Brisingids are proper STARFISH (Cl. Asteroidea) part of the Forcipulatida-which is the same group that includes the common starfish Asterias and Pisaster. The same general kind of pedicellariae (see below) found in brisingids are also found in common intertidal starfish.
• Brisingids are deep-sea animals. Some are "shallower", occuring on the shelf (i.e., 100-700 m) but others, such as Freyella and its kin live in the "true" deep-sea-the Abyss and so forth (>1000 m!). Some of the world's deepest starfish (~5000-6000 m) are brisingids.
• They live all over the world. Antarctica, Pacific, Indian, and Atlantic. Oddly, none in the Arctic.
• Brisingids are diverse. Nominally 70 species, in 14 genera, divided into at least 2 families.
• The name "brisingid" (order Brisingida) is derived from a story in Norse mythology which is so neat that it is the subject of next week's post!!

But what is the FUNDAMENTAL thing that makes brisingids so distinctive??

Brisingids have body forms that are specially modified for suspension feeding!

This affects nearly ALL aspects of brisingid body form and ecology. But how??

While you're looking at the next couple of lines..think about the sort of body form you see in other suspension feeding echinoderms such as crinoids or even ophiuroids! Brisingids look like a weird cross between crinoids, ophiuroids and asteroids.

Body Form The endoskeleton in brisingids is closely tied to the suspension feeding lifestyle.

• Disk skeleton is fused into a ring and braced to support the arms as they are held up in the water.
• Tube feet "hold down" the animal as they raise their arms into desirible current flow. But movement is possible.
• multiple arms are found in ALL brisingids. Some might have 6 arms..but most have about 8-20 arms. This is presumably to faciliate the suspension feeding.
• Fully developed gut and stomach are missing. Possibly for secondary absorbtion of nutrients?
• Gonads are in the arms but space for internal structures is minimized.

The modifications are even so specialized that the ambulacrals in brisingids are actually uniquely shaped as vertebrae! Presumably to allow the most flexure. Note: "normal" ambulacrals look more like this: Feeding Mechanism
Perhaps the MOST distinctive aspect of brisingids is HOW they feed.

Bear in mind, that it was only in/around 1976 that we even KNEW that brisingids held their arms up in the water!! When they were first described..it was thought they just dragged their arms along the bottom!

A paper by Roland Emson (at King's College in London) and Craig Young (then at Harbor Branch, now at Oregon Institue of Marine Biology) presented a detailed study of how feeding happened. (Interestingly, I had later discovered that the Russian deep-sea biologists S. Galkin and N. Korovchinsky had documented feeding in a paper from 1984. Not as detailed as Roland and Craig's work and in Russian-but earlier nonethless..) Here's how it works:

1. Brisingids have lots of spines. Spines come off the lateral sides. They project off the tube foot furrow. They are almost everywhere! In some species-spines are even present on the surface of the body! All arranged in a familiar "cruciform" arrangement that you see over and over again in other echinoderm suspension/filter feeders. 2. Spines are covered by a "sock" of pedicellariae. Each one of those spines is covered by a sheath of tissue, like a sock. This "sock" is covered by literally THOUSANDS of Frakkin' little pedicellariae!! These are little jaw-like structures that cover the surface. Think of them like a bunch of little bear-traps.

(from Emson & Young 1994)

3. The little bear-traps (pedicellariae) densely cover ALL of these spines.

(from Emson & Young 1994)

4. The pedicellariae essentially "go off" when food hits them. So, some small shrimp, krill or other tasty bit of organic, edible goodness?? BAM! Snagged by the spine/pedicellariae!! Prey are held fast by the pedicellariae similar to velcro (to use Emson & Young's terminology). 5. Once food is captured...it is then moved via the tube feet to the mouth and devoured. According to various accounts, this is typically small amphipods, and other hapless crustaceans...(ha! take that small hapless crustaceans!)

Whew! More on brisingids next week!!