Let's Learn About Multi-armed OPHIUROIDS!

I've often talked of my love of multi-armed sea stars. BUT brittle stars can have more than five rays (arms) also!!

So wait, there are ophiuroids (brittle stars, basket stars, etc.) that have MORE than 5 rays?? 
Yes.
Most sea stars (close relatives to ophiuroids) have 5 rays, but a significant number of them have more than five rays and there are some entire groups of sea stars (e.g., the Brisingida) which are characterized by having multiple arms (six to 20ish). When sea stars have more than 5 rays there tend to be about 7 to 15 of them. But some, such as the Antarctic Labidiaster can have up to 50.

What one sees in most  starfish species is that multi-armed sea stars tend to be large, highly mobile and predatory. This tropical, shallow water Luidia maculata for example demonstrates all of those qualities.

In contrast, Multi-armed ophiuroids have different patterns than what sea stars demonstrate. Ophiuroids tend to be either six to seven rayed or 10 or more. Generally none with intermediate arm numbers (i.e., 8 to 9) and no species are known with more than 12 rays.

Certainly no 20-50 rayed beasts like the sea star Labidiaster. And as we'll see, there's no apparent ecological association with having more than 5 arms in ophiuroids.

The multi-armed condiiton occurs  in many, many different groups of asteroids throughout evolutionary time (here) and has evolved multiple times throughout the group. This is also the case for brittle stars...
(My thanks to Dr. Sabine Stohr for assistance with names!)

Diversity in Multi-armed Ophiuroids
Most brittle stars have 5 rays. Having more, implies that the extra arms are somehow adaptive or suggest that the added investment to develop one further body part is somehow consistent with the life mode of the animal. Most ophiuroids appear to have a much more invested skeleton compared to asteroids, so it would seem that adding more arms is much more of an investment in development,


Low numbered multi-rayed brittle star species, those with about six to eight arms are not uncommon and seem to show a fairly diverse range of habitats. But the ones with more than 10 rays are more seldom seen.

This one for example is Ophiothela danae. 6 rays. These occur in tropical-shallow water habitats and live with their arms wrapped around the stalks of sea fans and sea whips.  Does the sixth arm help facilitate this lifestyle??

This species appears to be successful. It occurs widely in the tropics and has "invaded" the tropical Atlantic from the Pacific. 

Here is Ophiactis savignyi, a brittle star that reproduces both sexually and asexually (i.e. it divides in half) brittle star which occurs globally all around the world (read more here). Perhaps its sixth arm is part of the asexual condition? Or maybe its cryptic life style?

Here is Ophionotus hexactis. Six arms. Adaptive? Predatory? Highly Mobile? An animal I'm not sure much is known about it.

But on the OTHER hand, here are some Antarctic brittle stars, such as Ophiacantha vivipara which have SEVEN arms. Its a brooding species (i.e., the adults raise babies on their bodies). Not sure how this benefits the animal. Maybe in feeding?  Aids in parental care somehow? Or maybe its just an incidental feature?

From Antarctic ophiuroid blog https://brittlestars.wordpress.com/2010/01/27/some-peculiarities-of-the-antarctic-ophiuroids/

There are a few more species of ophiuroids that show six to seven arms than I've shown here. But for various reasons (i.e,  I either didn't have pictures of them, space, etc) I haven't included them. Several species of serpent stars in the genus Asteromorpha for example can demonstrate six or seven arms.

Species with more than 10 arms

Ophiacantha enneactis & O. decaactis. The genus Ophiacantha, is kind of unusual because it includes several species which possess more than 5 arms (see O. vivipara above).

Two of them, O. enneactis (illustration-top) and O. decaactis (below) have been collected from the Aleutian Islands in deep-water. O. enneactis is from 549-881 m. And O. decaactis is from comparable depths.

These are similar species and both are pretty small. What they do down there in the deeps with all their arms is "poorly understood." (i.e. we don't know). Perhaps suspension feeding? Predation?

Ophiacantha decaactis Belyaev & Litvinova 1976

Image from Belyaev & Litvinova 1976

Astrochlamys sol Probably the winner of ALL the multi-armed ophiuroids though is this species: Astrochlamys sol, a bizarre Antarctic form, which is a member of the Gorgonocephalidae, so its actually a modified basket star.


I thought Basket Stars already had more than five arms?? 
Basket stars are a subdivision of ophiuroids called the Euryalida. They tend to have big, thick arms with fleshy tissue covering over their skeleton. These ophiuroids extend their arms into the water column and usually have hooks or long arms to feed on food or prey as it swims by..

I've written about one particular basket star, Gorgonocephalus here.   But there are a fair number of basket stars in cold water and tropical habitats.

Note that although there seem to be many arms, there are in fact ONLY five. But they branch...

Below is the underside of Gorgonocephalus, the cold-water basket star from the Arctic/subArctic. Note that only five rays radiate away from its mouth. The  arms bifurcate or split for several iterations away from the five primary rays on the disk..

















That's what makes A. sol, so unusual. It actually has 10 to 11 arms!! Making it the ophiuroid (not technically a "brittle star") with the MOST number of arms!
Its species name "sol" refers to sun, which likely alludes to its arms radiating away from the mouth.

This species occurs in the Antarctic in fairly deep depths 300-1200 meters. It was described by the famous echinoderm taxonomist/biologist Theodor Mortensen in 1936 in his HMS Discovery monograph. We apparently don't know much about its biology aside from the fact that its a brooding species and tightly hugs its substrate...

Image by Igor Smirnov via WoRMS

On a personal note I'm always fascinated by these forms. Unusual in appearance but also kind of mysterious.  What does it do with all those arms? What is so unusual about deep-sea/cold-water/Antarctic species that they have so many arms? Is brooding related? 

What is that WEIRD THING on FACEBOOK???

So by now, everyone and their 3 best friends have seen the critter above and the video on Facebook (below) which seems to have freaked everyone the frack out. Its been circulated and seen by over 5.6 million people!!

Post by Jr Saim.

And everyone keeps on asking WHAT IS IT?? I've received this video now, what feels like a million, jillion times from people who want.. nay, DEMAND to know:  What IS IT???

Answer: A basket star. A distant relative of sea stars.

First thing: HARMLESS.  and out of its element. But we don't know much about them.

This was even given time by IFLS but not being echinoderm specialists, their answer was a bit over generalized... So, here's MORE. Its actually a pretty neat beast.

1. This is a BASKET STAR. These are specialized ophiuroids. Ophiuroids are members of the phylum Echinodermata. In other words, its related to Sea Stars, sea urchins, etc. Basket stars in particular have a highly branched system of arms which they use to feed. I've discussed the feeding biology of basket stars here.  They have hooks on those branches with which they feed on tiny bits of food.

There are actually several different groups (i.e., families) of ophiuroids which have these fleshy arms and highly branched arms.They occur widely and vary from habitat to habitat.

2. Euryale aspera?  I've consulted with one of the world's experts on basket stars and euryalinid brittle stars, my colleague Dr. Masanori Okanishi, currently at Kyoto University. Discussions with him and checking my own resources suggests that the animal above is a shallow-water tropical species, called Euryale aspera. Identification of the species is uncertain since there was only a picture and no specimen but based on my cross-check, this seems like a likely name.


3. Where and HOW does it live? Euryale aspera is a shallow water species which occurs widely across the Indo-Pacifc. This species is found throughout the Indo-Pacific, from Asia but as far west as Madagascar in the Indian Ocean.

As with other basket stars, feeding is accomplished via tiny hooks present on the MANY branching arms spread out into the water column when they feed.

Here are some videos of various Japanese basket stars which MIGHT be Euryale aspera. Its difficult to ID these from images, but these give you an idea of how they live. Arms up in the water during ideal water flow, but withdrawn when not feeding.

4. What does the name mean? So, as you may have noticed from one of my earlier posts, one of the better known genera of basket stars is called Gorgonocephalus. "Cephalus" means head while "Gorgon" refers to the head of Medusa and her sisters: The Gorgons of ancient Greek Myth. One of Medusa's sisters is named EURYALE. She was identical to Medusa in appearance with snakes for hair and transformed men into stone with her gaze. Thus, the genus of this other "basket star" follows the theme of a "medusa's head" type appearance. The species name "aspera" is Latin and a references a descriptor for "rough" which likely alludes to the spines and other tiny accessories on the body surface.

Euryale aspera was described in 1816 by the famous zoologist Jean Baptiste Lamarck himself!

5. What about OTHER BASKET STARS???
The term "basket stars" informally refers to several groups of ophiuroids within the order Euryalida, which all have thick, fleshy arms. Some are more serpentine (i.e. serpent stars) whereas others are branching and appear to form a "basket" (i.e., basket stars). But they are often similar in appearance leading once again to some "blurred lines" where common names are applied. There are about 177 species in five families.

Members of the Euryalida occur widely throughout the ocean depths. Many are shallow water, occurring in both cold and tropical habitats whereas others occur in the deep, deep sea (> 1000 m). Many of them occur at depths in between. But you can encounter basket stars at SCUBA depths on reefs or other shallow habitats, which is where the "creature" above was apparently collected from.

A "serpent star" (Asteroporpa annulata from the tropical Atlantic)

A "basket star"


And by the way, these have been caught on deck and seen before... 


The original video indicates that the one collected was returned to the ocean. These don't take exposure very well.. but perhaps more adverse to the animal was its ability to re-establish a perch to resume feeding. But, frankly our knowledge of their biology is very poor. We don't know much about them.

Treasures of Paris 2013: Brittle Stars @Le_Museum!

PARIS! I'm here continuing my research at the world famous and awesome Museum national d'Histoire naturelle! (Twitter: @Le_museum) in Paris, France!

Many of my new species were found in these collections. I enjoy my visits to Paris, one of the most delightful cities in the world, and of course, the opportunity to collaborate with my echinoderm colleagues (whom I've profiled in prior posts!)

My work involves sorting through hundreds of asteroid specimens collected from the most exotic places in the world.. New Caledonia, Madagascar, the Solomon Islands...

I never pass up an opportunity to share these awesome collections (many are likely undescribed!). In the past, I've shown exotic sea urchins  and crinoids (stalked and unstalked)!

This time around I thought I would share another group with exotic members from distant locales: The brittle stars and serpent stars (aka the Ophiuroidea)!

As I've mentioned in prior posts, ophiuroids (aka brittle stars) are tiny and often cryptic, so we often fail to appreciate their beauty without a little close up attention!  They can be striking and beautiful....

So here's an assortment...

From New Caledonia, 480 meter depth: Amphiophiura bakeri!  The central disk is pretty much a solid ball... The actual animal is small, only about two inches across..

Here's a nice shot of Amphiophiura liberata from Fiji, 488-500 m. Yes, those five primary plates kinda got nipples on 'em. 

One of my favorites..identified as Ophiomusium, possibly O. scalare (thanks to Rafael).. But its from New Caledonia (about 300 m depth)

Here we have Ophionotus hexactis from the Kerguelen Islands (subAntarctic region). Yes. A SIX rayed brittle star. Not too many of those...

SPINY! 

Some species of euryalid ophiuroids (aka serpent stars) live on deep-sea coral (gorgonian) hosts. These were collected while still tightly wrapped around the branches...

and here's a huge brittle star (Ophiothrix longipeda) in a handsome glass-wood display case!

Why?  Because this was one of the original specimens prepared by the great French naturalist Jean-Baptiste Lamarck!