5 NEAT things about the Caribbean/Tropical Atlantic Cushion Star Oreaster reticulatus

Image from STRI's O. reticulatus page

Today, I thought I would treat all of you with some info about one of the most strikingly colored of Atlantic echinoderms.. the so-called "Cushion Star" of the Caribbean aka Oreaster reticulatus.

The species name "reticulatus" refers to the net-like pattern on the body surface whereas "Oreas- refers to "mountain"... So breaking it down, the latin name means "Reticulated Mountain Star."

O. reticulatus is a pretty iconic animal for this region. It is so, distinguished that it even occurs on the 1 cent coin on the Common Wealth of the Bahamas!!                       
These have been made into CUFFLINKS!
                         
and postage stamps!

The genus Oreaster only in the tropical Atlantic, on both the east and west side and is known only to occur in shallow water.  Oreaster reticulatus tends to be thought of as being primarily a west Atlantic species.

The east Atlantic/African species of Oreaster is called Oreaster clavatus and varies in color and spination...

Image borrowed from this excellent French site for identifying marine fauna "Sous les Mers"

I would comment that although they are known from shallow water doesn't mean they are really a good intertidal species, so its preferred to leave them as-is where they live underwater. Propping them up on sandy beaches with their arms propped up like a tentpole in the sand is pretty much a death warrant for this or any starfish....

Moving on! Adults do vary somewhat in color (note also juveniles below)... Some lighter
                    
Some darker...
                    
Most times, these are 5 rayed, but occasionally you get the odd one with 4 or 6..
                    
But enough with the intro!!  Here we go!

5. Oreaster reticulatus are omnivorous feeders but eat a lot of algae and encrusting food. Often, they feed in feeding "fronts"
So, one of the seemingly constant assumptions (I would say misconceptions) that are often made of sea stars is that they ALL adhere to the feeding modes of shallow-water asteriids, such as Asterias.. i.e., the old trope of "all starfish feed on mussels or clams" I have written at length about the diversity of feeding modes in sea stars. You can see more of that here.  and here..

O. reticulatus feeds primarily on microalgae and/or on other kinds of encrusting food. Work by Scheibling (1980 in Marine Ecology Progress Series 2: 321-327) shows them feeding on a seagrass bed where they obtain nutrients from a likely combination of organisms on the seagrass, the seagrass, and organic materials in the sediment, etc.  but what's interesting? is HOW they do this...
                   
When Oreaster reticulatus feed, they do so in a FEEDING FRONT!! Kind of like an army across the sand bed...

The pic below hails from the paper cited. The authors describe this feeding front:

A feeding front of the sea star Oreaster reticulatus off St. Croix, U.S. Virgin Islands. The front is moving from left to right. Feeding mounds (fm) of darker sediment surrounded by lighter halos can be seen behind the front on the highly turbated sand bottom. In advance of the front, the sediment appears darker because of a microalgal film which has developed in the absence of sea star grazing in the previous weeks. Average sea star diameter is 0.26 m

This from Jean-Sébastien Lauzon-Guay, Robert E. Scheibling, and Myriam A. Barbeau. 2008. Formation and propagation of feeding fronts in benthic marine invertebrates: a modeling approach. Ecology 89:3150–3162.

So, you may see this just sitting there on the sea bottom by themselves. But "on their own" in the wild?? These guys form organized feeding groups. Think about it too, they feed on algae and possibly clear the sediment. Maybe their effect is similar to that of some sea cucumbers? 

Also worth noting?  Food varies with location. Some feed on algae, but others feed on sponges. In some places, up to 61% of the species were feeding on MANY different sponge species (see Wulff 1995 in Marine Biology 123: 313-325)

Even MORE interesting? Feeding by O. reticulatus is so specific that they can actually tell apart different species of sponges that humans cannot recognize!  (see Wulff 2006 in Biol. Bulletin 211: 83-94)


3. Juveniles are a different color/appearance than the adults.
Oreaster reticulatus are members of the family Oreasteridae.  As adults, these are big, massive very heavily armored individuals.   But when smaller, most have a VERY different looking juvenile form.

This, for example, is a photo of the many growth forms that the Indo-Pacific Cushion star, Culctia novaeguineae undergoes as it gets bigger.

The same is true for Oreaster reticulatus, which undergoes size AND color transformations as it increases in size.... This probably varies even MORE depending on where the animal lives, and what its food might be...

                     
This one is more grey/brown...

      

3. O. reticulatus "home in" on large aggregations of other O. reticulatus 

Image from Echino LifeDesks. Photo by Simon Coppard

One interesting paper by Bob Scheibling (1980-in Marine Behaviour & Physiology 7: 213-223) studied a population of O. reticulatus in the US Virgin Islands.

They performed an experiment, where a big bunch of individuals present on a large sand patch were moved off the patch to about 20 m (about 66 feet) into the surrounding seagrass bed.

As the internet is fond of saying "What happened next, WILL AMAZE YOU!" (or at least, I thought it was interesting...) the starfish then, re-oriented and then moved BACK to the patch, re-grouped with the others within 24 hours!  That is, they HOMED in on the OTHER starfish and MOVED there.

How? Probably through some kind of chemosensory cue in the water. i.e., something that those starfish leave behind that informs the others how to find them. So, yes, they can tell where they are and determine where others are as well.


2. O. reticulatus is closely related to another species in the East Pacific!
                  
One of the cool things about many of the animals which are found in the tropical Atlantic and Gulf of Mexico, is that you can often look toward the East Pacific (i.e. the other side of the Panamanian isthmus) and find ANOTHER species which often bears a close resemblance!

I wrote a story awhile back about a starfish species, Heliaster kubiniji, found as a living from in the East Pacific, but ALSO as an extinct, fossil form from Florida.

Long story short? About 10 million years ago the isthmus of Panama was not yet closed. And it was an open waterway between the "Gulf of Mexico" and the eastern Pacific (south of Baja California).

There were MANY species in this area were once connected. Some were one continuous species while others just kind of showed a close genetic connection. Then the isthmus formed about 3-5 million years ago and formed a barrier, separating these two populations.

Before we had better genetics and fossils to tell us about the precise timing, these were often assumed to be "sister" species. In other words, two sides of the same coin.. closely related by only a few million years of separation. But it is now clear to us that several of these diverged from one another much earlier than that. And are thus much more distantly related than was previously thought...


1. O. reticulatus faces "predation pressure" from tourists and studies on populations and reproductive biology do not suggest it will do well if overfished.
Yeah, sorry, this one is not quite as fun or neat as the others, but its important.  I've written about the pending threat of "overfishing" starfish species in the Indo-Pacific. This includes the widely occurring Protoreaster nodosus  as well as several other fished species (Archaster, etc.).. 

In the tropical Atlantic, O. reticulatus is regularly taken as fodder for tourist shops and so forth. The pressure on this industry has become significant and in many places the populations of this species have become locally extinct.

Based on work by Scheibling & Metaxas (see this and MANY other refs) the population of this species are relatively low, ranging from 1 to 5 individuals per 100 sq. meter and don't turn over very quickly. It is unclear how much growth goes into a large sized, adult individual, but it doesn't seem that these are very fast growers.

The species is dependent on the algae and other food found on seagrass beds, which suggests that between collection of the adults and habtiat destruction or disruption, this does not bode well for the big familiar "cushion stars" of the tropical Atlantic..
                    
So, here is a species that seemingly everyone takes for granted but if it has an ecologically important role, maybe one we haven't fully understood? and we're taking it for tourist baubles and souvenirs??

Something to think about...

....and one extra! .. I'll be honest and say I'm not sure if this is pooping...or spawning..
                   

The Things & Critters I will Miss at the Invertebrate House at the Zoo

As many of you may have noticed from the news or from my Twitter feed (@echinoblog), the National Zoo's Invertebrate House (here in Washington DC) will be closing its doors for good on Sunday, June 22nd.  So, if you're in DC on Saturday GO see it before its gone! 

The official Press release explaining the closure can be found here.   Since the closure, the Washington Post has written a very nice Requiem for the Invertebrate House.   

A very passionate and concerted effort to save the Invertebrates Exhibit was started by Terri Jacobsen. As of this writing (Friday, June 20)  it has garnered the support over over 2,281 signatures!   While this may not change the outcome on Sunday, I hope that her good efforts will result in some influence and/or demonstration that invertebrates are worthy of a full presence in ANY "zoological park"...

I dropped by to give my regards to my friends (both vertebrate and invertebrate). Everyone I spoke to was disappointed and like myself, sad to see the exhibit go. 

But in the meantime, as we proceed to the weekend, I thought I would offer some of the things/critters that I will miss after the closure...

1. Stomatopod! 

 2. Ant Traffic Camera! 

ANT TRAFFIC! 

3. AWESOME Marine Invertebrate Art in History! 
Nautilus! 

Japanese Crustacean Art! 

 Bronze Shell!  

Minoan Stirrup Jug with octopus motif! 

4. BIG HERMIT CRAB!

 5. Giant Pacific Octopus! 

6. Ctenophores & other Jellies!

7. The AWESOME behind the Scenes where the zoo folk work! !!! 

8. That BIG spider that they let live out in the open without any glass! 

9. Watching them feed that AWESOME Cuttlefish!

                            

10. Those AWESOME colored cerianthid sea anemones!

 11. Sunflower Stars! (Pycnopodia helianthoides)

12. And of course, the AMAZING coral reef exhibit..

My BEST to everyone at the Invertebrate House! 

                                                    

The Cousin Itt of Sea Urchins! Irregular Urchins featuring Echinocardium cordatum!

SEA URCHINS!  Everybody knows the familiar spiny balls that live in the ocean. But fewer people realize the many unusual KINDS of sea urchins.  In the past, I have written about the most highly modified sea urchins aka the sand dollars! 

As I've discussed, urchins can be loosely divided in the "regular" urchins-round spiny balls and the "irregular" urchins- the ones with a right and left side with highly modified body, spines and jaw parts which are used for moving through sediment (mud, sand, etc.).

For example the very weird, deep-sea pourtalesiid urchins  and the very odd but neat looking sea urchin Conolampas!  and sometimes even worms live in irregular urchins! 

But it occurred to me that I had never outlined how a more typical "irregular urchin" lives.. So, I thought I would illustrate with one of the most widely occurring of irregular urchins a species called Echinocardium cordatum, described in 1777 by Pennant. A member of the family Loveniidae. 

These go by the common name "heart urchins" or as I've been observing lately, the "sea potato" (not what I would call them, but there ya' go...)

Interestingly, this species occurs widely around the world. They are present in the Atlantic but also in Australia, New Zealand, the East Pacific, and South Africa across a broad depth range (0-250 m). 

Interesting side note: based on some genetic work on various populations by some of my French colleagues (here) The global occurrence of this species may actually represent SEVERAL closely related species! 

                    

At first glance, some of these urchins are just covered in spines! and its difficult to determine what end is up! Kind of like Cousin Itt from the Addams Family! 

                                           
So, I thought I would compare with some specimens without the spines.... The genus name Echinocardium means "Spiny heart" and cordatum which also means "heart shaped", so the whole "heart shaped" thing seems to be a theme...

Here's the skeleton (called the test) of one without the spines. (individual alive with spines is the white one shown above) so, yeah, they have a heart shaped skeleton. This is the top surface..

                                                    

The skeletons on these urchins has evolved for living in sediment (i.e., sand, mud, etc.). This pic below shows the UNDERSIDE of the animal.. and that weird-shaped hole??  That's the mouth (called a peristome).

Note all of those knobs on the surface? Those are where the spines are connected to the surface of the skeleton. 

Basically, all these spines function to help shovel and move sediment INTO the mouth and serve to help the animal move through the sediment, etc. 

Here's a video of one that's been turned upside down. Its nice because it shows pretty closely all of the various spine types on the underside. Some are more spoon or spade shaped. And all of them are pretty agile..  Another nice shot of these spines is here. 
          

And of course, here is the anus (aka the periproct). Where the poop (sediment, etc.) comes out! 

How does this species live?? 

                     

According to various accounts by John Buchanan from 1966 and Dave Nichols (1959) [figure below from Nichols (1959)]  these bury themselves but run a respiratory tube foot up through the sediment.

Some great pics of Echinocardium on Flickr here. 

The folks over at the British Museum have this GREAT pic of Echinocardium (below) cleared away from sediment but with the channel clearly present! Original source with a more detailed explanation is here

This video isn't terribly exciting but it DOES give you an idea of how Echinocardium starts to bury itself into the sediment. These vary around the world in terms of how they behave when burrowing.
            
One more cool thing?  Echinocardium has a decent fossil record!  AND one of the neat things that have been found are the filled in casts of the BURROWS  of Echinocardium (or something related) that these animals lived in.. (this one from the Pliocene near Tuscany, Italy)

                   

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!

P is for Parasitic Snail! Enter: The Eulimidae!

From the Eulimidae EOL image gallery-Moorea Biocode

Last week, we saw some pics of big predatory snails feeding on starfish!  This week, we turn our attention to smaller snails with a more insidious means of feasting on their hapless echino-prey!

Behold the Eulimidae! A family of snails, whose primary means of nutrition is feeding on echinoderms...specifically as PARASITES! They pretty much attach themselves to every class within the living Echinodermata: urchins, crinoids, brittle stars, sea cucumbers (remember the sea pigs?) and today's subject... starfish!!

Eulimids are insanely diverse. There's over 85 genera and easily hundreds of species. With likely more being discovered as they are found on their hosts..

If you guys ever need a one-stop shop paper on the Eulimidae, you are in luck! This paper (behind a paywall) includes a summary of biology as well as an overview to all the genera.   The acknowledged world expert on these is Anders Waren,  a scientist at the Swedish Natural History Museum

Basically, eulimid snails feed by sticking their proboscis into their host and sucking the tasty, delicious juices out of them. This in itself is kind of interesting because most echinoderms use a kind of specially treated seawater (filled with body cells called coelomocytes) as a bodily fluid.

Apparently, its these cells-the coelomocytes upon which the snails feed... Note below, the extended probsocis...

This snail was described as Melanella with what appears to be its proboscis extended and gives you a general idea of how these snails operate...

Image from EOL's Eulimidae image gallery

Here is a snail in the genus Parvioris with its proboscis extended and the animal hard at work..

From the Eulimidae EOL image gallery-Moorea Biocode

From what I've been able to determine, certain snails DO tend to occur on certain hosts, but the pattern doesn't always seem to be consistent. Some specific species of snails apparently occur on different starfish hosts but some are specific to types of hosts, e.g. sea urchins or sea cucumbers.. Many of these are undersampled, and so it still remains to be seen how much host variation is observed..

1. Ectoparasites. Some eulimids are ectoparasites, that is they are attached, but only on the exterior.. Here's one hunkered down on the disk of the very gorgeous goniasterid Iconaster longimanus.

Here's another one attached to the sand star Archaster from Singapore, but several species of starfish are often hosts. Here's a short write up on their page about them..

Another well-known ectoparasite is the eulimid called Thyca crystallina...

These are famously parasites on the blue starfish Linckia laevigata where they are often found on the oral surface around the tube foot grooves..

We often see these snails well-camoflaged as the same distinctive color which identifies their host...

Some are not so well-hidden.. (and yes, sometimes Linckia laevigata is orange!)

2. Endoparasites!  On the OTHER hand..some eulimid snails, get pretty "dug in" and have literally buried themselves in their work!

They basically embed themselves in the host, attach their proboscis directly to the internal arm canals and just suck on em' all day....  This one, Parvioris fulvescens looks like its embedded itself in what looks like Ophidiaster (?)

From Femoreale Shells via EOL

Here..we have some which have embedded themselves in Neoferdina, a goniasterid... Note how they've pretty much buried themselves INTO the skeleton of the animal. The starfish are strongly calcified.. and since there's no clear damage, I wonder if  these get in as juveniles...

Here's one called Stylifer which has buried itself in the arm of the ophidiasterid Linckia multifora

3. Parasites of the Deep! 
and lest, you think that eulimids only parasitize shallow water reef species, let it be known that many deep-sea starfish are also parasitized by snails! Here is Asterophila japonicus as reported by Sasaki et al. in: Sasaki, T., Muro, K. & Komatsu, M. 2007. Anatomy and ecology of the shell-less endoparasitic gastropod, Asterophila japonica Randall and Heath, 1912 (Mollusca: Eulimidae).Zoological Science 24(7): 700-713.

This species seems to be a host in the astropectinid sea star Leptychaster,where it has burrowed UNDER the disk and lives right above the stomach!

Several of the deep-sea snail parasites are VERY unusual and some have bodies which are SO reduced that you can barely recognize them as snails..  One deep-sea snail parasite, Asterophila rathbunasteri described only in 1994! lives as a gall in the arms of the deep-sea, multi-armed asteroid which lives off the west coast of North America...

Which they were actually unable to ID to phylum until they realized, when it was spawning, that it was producing veligers (snail juveniles)!!

the HORROR!