BRITTLE STARS! COLOR EXPLOSION!

A big heads up thanks to Wild Singapore who took these lovely images!

This week is busy for travel, etc.. So what do you get? yes! Its time for BRITTLE STAR COLOR EXPLOSION!

Let's start out with some Arthur Anker goodness! 

Ophiothrix from Arthur Anker! 

A brilliant Ophiothrix savignyi by Alexander Semenov

Ophiothrix spp. below Fantastic images below by Michael Zeigler via Flickr...

Another brilliant Ophiothrix. 

Image by Mark Rosenstein

From Wild Singapore (and Rita Tan)! The commensal brittle star Ophiomaza cacaotica! More on the biology here. 

It lives commensally on ANOTHER echinoderm! Feather stars!

Various shots of Ophiothela danae, a small brittle star that lives wrapped around gorgonian branches..

An outstanding ophiothricid in pink and blue...

Image by Budak

This one from Wild Singapore looks the same

Ophiothricid on a sponge..

Image by Steve Williams

Arm spines!

Image by Mike Toy

Brittle Star Domination! When Ophiuroids Carpet the Murky Deep!

Image by MatYts

Brittle stars are THE most diverse of living echinoderms.

There are well OVER 2135 species known and many more discovered every day.  However, its not enough to know that there are many KINDS of brittle stars, but another important fact is that they are also some of the most ABUNDANT echinoderms.

They live everywhere..small cryptical hiding things. Under rocks, in crevices, on other animals, under other animals, buried in sediment, even hiding among OTHER brittle stars!

Here, for example are brittle stars with their arms emerging from the holdfast (i.e. the anchor) on kelp!

Image by Mr. Lobos

So, sometimes, it strikes one as kind of unusual when all of a sudden you see them literally CARPETING the seafloor!

Image by Jylnott

What's going on with these?? When we see this many of some OTHER echinoderm, we often wonder if there is some ecological problem.. For example, with sea urchins, we have a situation where we see "urchin barrens"   and really.. you can't help but wonder what's going on here...

Image by Anne Crawley

In this case, the removal of predators has unleashed a huge torrent of sea urchins which devour everything in their path!  Hence the name "barren" because there is naught else but urchin!

When one sees brittle stars en masse, one cannot then, be a little concerned...

Image by shawn_broes

BUT fear not!  As it turns out, these massive aggregations of brittle stars are NATURAL. So while the effect appears the same, perhaps "barren" is not quite as appropriate or even accurate!

What's going on? 
So, I'll discuss two kinds of situations where brittle stars literally CARPET the sea bottom.

In a cold-temperate water genus of brittle stars, called Ophiothrix which you can find in Europe, and in the cold-temperate waters of both the Pacific and Atlantic coasts of North America, they frequently occur in very dense, very abundant numbers!

How dense?  One paper by G.F. Warner found that the mean population of O. fragilis in the British Islands was found to cover 23% of the ground in some areas, with a mean population density of 1330 indivdiuals per square meter!! 

For example, here's a couple of nice shots of dense Ophiothrix fragiis beds them from Scotland (and thus the North Atlantic!)

Image by MatYts

Image by hsacdirk

This one is a pic of a different, Pacific species but it is a tighter shot and it gives you an idea of how the animals are positioned and what they look like individually.. Note that their arms are ALL extended up into the water!

Image by echo&dust

Spines are ALL over these things.. but they aren't necessarily for defense!

Image by hsacdirk

Here is a nice video of Ophiothrix in Santa Barbara, where they completely carpet the bottom.  

Another video of Ophiothrix from Anacapa Island, Channel Islands

And another species occurring in Monterey.. perhaps members of the Amphiuridae..

In either case, arms are extended into the water current where their spines capture organic food particles being carried along by the water....Spines are used in conjunction with tube feet for filter feeding!  WATCH those tube feet go!  An example of the original science of this can be found here.

So, they're feeding. Fine.  WHY ARE THERE SO DANG MANY OF THEM???

Image by Kristy Moore

HOW did they get there???  Did they all migrate there?  Or did they all just kinda... START there and never went anywhere else?

YES! This paper by Raphael Morgan and Michel Jangoux showed that larvae were encouraged to undergo metamorphosis into adults by the presence of OTHER adults.

So, in theory, one or others settle down because they are taking advantage of a desirible water/current/food flow. And then another and then another..

And before ya' know it the larvae in the water sense that other adults are around and THEY settle out and more and MORE...

Imge by MatYts

...and BOOM there goes the neighborhood!  Even if you're a voracious Crossaster papposus "rose star" you can only eat and go through so many brittle stars...

Image by MatYts

If you're an urchin or a starfish trying to make an earnest living, you've got to push all the pesky things out of the way! 

Filter Feeders can also be found in the deeps! Remember Brittle Star city?? Go here to see a nice write up of this massive colony of Ophiacantha living on a near-Antarctic seamount! 


But What about in the Deep-Sea???
I said TWO kinds of brittle star carpets! so here ya' go...    Ophiuroids are crazy abundant in the deep-sea as well.. comprising a HUGE amount of the biomass living on the bottoms!

Image by Scripps Oceanography

Here's a dramatic image by my Japanese colleagues at JAMSTEC from the Shinkai 2000 submersible of Ophiura sarsi carpeting the bottom...

yikes.

The story is in many ways similar to those at shallow water depth.. juveniles sense the presence of other adults and settle.. but arms are not upheld in the water as readily... What could they be doing down there?

Many have indicated that they are possibly detritivores. Feeding on dead stuff and other organic material as it falls to the deep-sea bottom... as seen here (and fighting amongst each other for food!)


In one of my earliest posts.. I also shared the delightful world of these brittle stars as PREDATORS of moving prey! A living carpet of OPHIUROID DEATH!   You can read more on that here. 

thanks always to Steve Stancyk for the images!

Ophiuroids! I wouldn't want to mess with a bunch of them in a dark alley! They're takin' over!

Brittle Stars Have TEETH! What do they use them for?

Brittle stars are everywhere. They are the most speciose of all the living echinoderms with over 2000 species (probably MUCH more than that!).

At this moment in time, for studying brittle stars we live in a privileged time because we have several new workers who have taken to studying the various and weird lives of brittle stars!

One distinctive feature of brittle stars that researchers that study morphology have always known about are the unusual jaws present on the mouth of brittle stars. These jaws vary between individual groups of  brittle stars. Its one of the fundamental ways that brittle star taxonomists tell them apart.

These jaws are superficially similar to the ones we see in other animals in that some of them have "teeth" (called oral papillae) and other features which distinguish them.

But other than their usefulness in telling them apart, what function do these "teeth" serve?

A recent open access paper by Karin Boos, an author at the 7th European Echinoderm Conference held in 2010 (available here) addresses and discusses how the jaws might function relative to the feeding biology of two European brittle star species.

First off, Boos reviewed the feeding modes of two species with fairly distinct jaws and teeth.

One of the studied organisms, Ophiothrix fragilis is covered with many needle-like and bristling spines...
Images below by Hsacdirk


In life, they hold their arms up into the water and are almost always observed in this position in order to obtain food from water currents. Ophiothrix is a filter feeder.

They gather up food on their arms, which is then moved to the mouth via tube feet.


The other species studied was Ophiura albida which is more of a generalist. A sort of opportunistic feeder. Sometimes scavenging on dead animals but sometimes feeding on other smaller animals.

Each species has a different life mode and presumably the morphology, i.e., the teeth of each species reflects how each individual species lives.

Image by Danielguip

A brittle star from a completely different group (ie. family) and with a very different set of choppers! Here is Boos' Figure 1 which shows the two "teeth" types side by side. Ophiothrix on the left vs. Ophiura on the right.

Figure 1 from Boos 2013

1. Predator? Or generalist? type jaw/teeth in Ophiura.
Boos takes some pretty nice profile images (her Figure 2) of the papillae (=the "teeth") that allow her to infer some function.

top of pic is the oral surface, bottom is top or aboral. Fig. 2d-3

Boos argued that these teeth are in fact "predaceous (=predatory) dental equipment". Note how all of the "teeth" (=the papillae) were pointy. These, Boos argues, are used in gripping or spearing captured prey before ingestion.

It doesn't take much to take this consideration seriously. Here is some classic video from Neptune Canada showing what looks like Ophiura sp. fighting it out with another individual over some food.


and don't forget this blog about "brittlestars of death" as we saw Ophiura sarsii attacking mobile prey! (vertebrates even!)

Other related members also have jaws/teeth that sort of look like this. Maybe more of these are more predatory than we thought?

2. Ophiothrix-Sharp teeth! 

Ophiothrix (and related genera of brittle stars) occur widely in temperate AND especially in tropical waters. They can be quite striking and colorful..

Image by Arthur Anker

thanks to Wild Singapore!

Feeding in Ophiothrix is nicely shown in this video. Food caught on the spines, is moved by tube feet along the arm to the mouth, where the food ball, called a bolus is devoured.

Ophiothrix and indeed ALL members of the Ophiothricidae are well-known in the taxonomic literature for having these unusually striking types of teeth.

Here's a close up!  Usually with a very comb-like appearance... MANY papillae (ie teeth) on each "jaw"

From imaging these teeth in profile, Boos notes that the "teeth" are arrowhead shaped and pretty sharp but also pretty wide.

Boos states that this combination of "sharp" and "wide" serves to cut up and crush the bolus of food as it enters the mouth. Boos argues that the teeth would also be effective for devouring diatoms and/or grabbing parts of or complete  invertebrates in addition to big chunks of scavenged flesh.

And onwards? 
There are LOTS more brittle stars where that came from...  As I had indicated earlier, the "jaws" and "teeth" have been used heavily to classify and identify brittle stars but none were really good at understanding function...

Boos's efforts are a start. Interpretation of these structures has been surprisingly unseen in the literature. 

This for example, is an ophiacanthid from the Atlantic..

                                  

 Has a jaw similar to that of Ophiothrix....kinda.

And this euryalid ophiuroid (aka a serpent star)

Further data from observations of actual feeding and perhaps even closer observations with x-rays and measurements of brittle star biophysics may give us more insight into how brittle stars feed!

Ophiuroids (brittle stars) & other photography by Dr. Arthur Anker!

This week is busy and so I leave you with some STUNNING photography by one of my colleagues.. Dr. Arthur Anker!  He studies mostly shrimps and other crustaceans but does incredible things with a camera! If you're looking to hire a biologist who knows his decapods he gets my vote!

Artour's full photostream can be found here on Flickr!   Enjoy!

This looks like the top side of Ophiarachna

Here's the mouth and underside..

Damn... just stunning. An electric blue Ophiothrix from Australia (Great Barrier Reef)

Here's an Ophiothrix from Panama

Ophionereis? I think.. from Panama

I believe this is Ophioderma (giraffe patterned) from St. Martin

Some baby brittle stars from Moorea!

Some Non-echinoderms...

A male sea spider...

An amazing worm (Trypanosyllis sp. (Syllidae) from Moorea, French Polynesia. (ID by Leslie Harris)

A polychaete worm (Nereis cf. riisei) rolled up into a spiral

One of the most beautiful (and IMHO best named) crabs in the world-Lophozozymus incisus

A sexy yellow and purple hermit crab Pylopaguropsis lemaitrei from Moorea