Tuesday, September 30, 2008

Xyloplax pt. 2: Conundrums & Controversies

So, in thinking about Xyloplax, I was wondering WHAT is it exactly that seems to attract people to the really oddball animals.

I touched on some of the weirdness in the first Xyloplax post..but here are a few other aspects of the "Xyloplax Phenomenon" that is common to so many weird animals in the field...

1. Rarity

People are fascinated by the rare and rarely encountered. Xyloplax has 3 species-all found from distant locales at great depth. Until the one discovered in 2004, there was a 17 year gap until it was found again!!!

So, they ain't too common...Here's the breakdown:

  • Xyloplax medusiformis. Described in 1986 based on less then a dozen specimens from New Zealand. AND found while people were looking for OTHER wood-living deep-sea critters...
  • Xyloplax turneri. Described in 1987 based on over a 100 specimens, but oddly, collected in 1980 from the tropical Atlantic!!! Collected FIRST by Dr. Ruth Turner at the MCZ and then later published as the second Xyloplax species by Frank Rowe.

2. Mystery
One of the other weird things..here is an animal that we have invested an enormous amount of energy in studying..but what do we ACTUALLY know about its biology? its ecology? What it eats in the morning? DOES it eat anything in the morning??
There have never been any REAL published observed of this animal alive or even in situ!! What does it DO with those spines? Why doesn't it have a well-developed gut?

Some useful information was inferred from the tissue analysis (reproduction, etc.) but ultimately we know little about its life habits.

is like a wonderous, wonderous piece of mystery dessert..we don't know what's IN it..but we want to taste it because it seems to be SO tantilizing on the OUTSIDE....
3. History
Okay...so this is the big one and related to the MYSTERY. How do you GET such an extreme morphology? How does EVOLUTION get you from a starfish to whatever-the heck Xyloplax is??? the problems/challenges that have followed this issue are big ones, and hence the appeal...including:
  • Homologies. What are the corresponding structures that have been modified over time? We can see forelimbs in fish and monkeys pretty easily but for echinoderms? Much more difficult. Several papers have argued and even redefined basic concepts of homology within Xyloplax.
  • Morphology is Highly Derived. All the structures are SO far beyond what we see in other echinoderms..its hard to say exactly what kind of evolutionary "signal" gets through. What is an adaptation? What is an ancestral trait?
Some notions and a brief review of some early and major ideas:

A. Non-Asteroid (i.e. Starfish) Relationships.
On one hand, there was serious consideration of Xyloplax's relationship within the Echinodermata. Is it a highly modified ophiuroid? a weird sea urchin?? a crazy modified sea cucumber?? REALLY a separate class all on its own???

One early but idea proposed that Xyloplax was possibly related to the Paleozoic Cyclocystoidea??
Cyclocystoids were a weird group of disk-shaped echinoderms that lived in the Paleozoic and look kinda like cookies with a series of plates in a solid ring around the edge. Little is known about them other than that their appearance as being "medusoid" in shape with a structural ring around the edge and a bunch of plates in the center.

Eventually the overall morphology was interpreted as dissimilar to Xyloplax..which was thought to be more closely related to asteroids...(aka starfish, sea stars) but really..the question was open for awhile.

but the Million (Sand) Dollar question over the years....???

B. Asteroid-Related Relationships
-WAS Xyloplax a separate class/lineage??
This was the original historical proposed idea from 1986. Based primarily on the radically different morphology..it was a stand-alone group. Originally, a class on par with the other "Big 5" but argued as related to asteroids.

A formidible amount of morphological data was provided: histology, morphology, sperm morphology. This perspective ultimately argued for a separation of Xyloplax based on its distinctive character suite.

With the advent of phylogenetics/cladistics-which argued for characters that are SHARED rather than characters that separate, even the paradigm of how to look at Xyloplax had changed.

...OR Was
Xyloplax ACTUALLY a starfish??? (i.e., included as a member of the Asteroidea)

Andrew Smith at the British Museum of Natural History thought so, and argued that Xyloplax was closely related to the bizarre deep-sea Caymanostellidae, which coincidentally ALSO live on deep-sea wood. But this argument, although plausible, never seemed to quite take hold....

In 1998, Dan Janies, a researcher at the American Museum of Natural History presented the first molecular data on Xyloplax. So, this was pretty convincing evidence that the affinities TO the Asteroidea had been only short of correct..

Xyloplax WAS placed with asteroids..and NOT ophiuroids or any of the other echinoderm groups. BUT where on the asteroid lineage did Xyloplax belong?? Molecular studies and taxon sampling were still being developed at that stage and the questions were still not QUITE answered...

Could Xyloplax be BOTH separate AND a member of the Asteroidea??
I was able to place Xyloplax within the context of fossil data on asteroids which had been unavailable in 1986 and new ideas on echinoderm homologies by Rich Mooi and Bruno David which supported an intermediate position.

My take on it was basically this:
  • Yes, Xyloplax IS part of the overall lineage of Asteroidea.
  • But. Its not part of the mainstream group of asteroids alive today.
  • Xyloplax is an early divergence away from this "mainstream" group (so in theory...it can be an asteroid but is NOT a starfish-think of it as a relict or a failed experiment from the early explosive diversification of early asteroid body plans).
So what?
From here what's left?
  • We still don't have a complete phylogeny of the Asteroidea on which to hang our inevitable, next Xyloplax data... (although I am working to remedy this issue..)
  • Will the basal split that I saw from morphology also be reflected in molecular data?
  • Will we ever find a fossil Xyloplax? There's Cenozoic deep-sea fossil wood. I've seen it.
  • Will we ever get to see one alive? Do they move? How do they eat, if they do??
  • How will development of these things change our perception of their evolution?
  • Will developmental data give us more into the homology?
There is your course!

Sunday, September 28, 2008

Xyloplax pt. 1: Echinoderm Weirdness Extreme!

This week, I thought it would be fun to discuss one of the weirdest of the weird-the beasts that we consider odd EVEN for the weirdest phylum of animals: The Echinoderms!!....What beast dares to contend for this title??? Starro??? The Star Conqueror??? (well..it would be cool if...) sadly..no!!

    • The gut was nearly gone or absent.
    • There was a ring of spines around the edge.

Thursday, September 25, 2008

The Friday Starfish Sing Along!

I've been a bit overloaded by "crisis" this and "economic" that...so today..Remember what it was like to be a kid again...
(Thanks to Kate at NIWA for sending me the link!)

and while we're at it...The classic starfish Song from Sesame Street! Can you name all the species??

Monday, September 22, 2008









Wednesday, September 17, 2008

Know your Grades of Uni!

So, I recently discovered that there was a California Sea Urchin Commission, complete with their own very interesting website.

What I didn't know was that there are actually GRADES of uni available. The CSUC describes them as such:

The Commission also adopted the following grade names and standards of quality to encourage uniformity throughout the industry, to help retail and consumer customers make better purchasing decisions, and to give assurance of product quality.

“California Gold” - bright gold, yellow or orange color; firm buttery texture; fresh salty ocean scent; and with a sweet buttery taste. Uni sections are large and complete intact pieces. This is exceptionally high-grade uni for use in top quality sushi. (formerly grade A)

“Premium California” - gold, yellow or orange color but less brilliant than California Gold; firm buttery texture; salty ocean scent; with a crisp and nutty taste. Uni sections are smaller but still primarily intact pieces. Premium uni is used for sushi, soups, salads, or combination dishes where uni is the featured item. (formerly grade B)

“Select California” - medium hues of yellow and orange or even tending to brown in color; salty ocean scent; softer creamy texture; with a more neutral nutty taste. Uni may be intact sections but can consist of broken pieces of the other grades. Frequently Select is packaged and shipped frozen. Uses include soups, sauces and dishes where the uni is mixed with other ingredients, including other seafood. (formerly grade C)

And here are Uni's Nutritional Facts!

Monday, September 15, 2008

Why Sea Urchin sushi (uni) tastes SO frakking good!

If you've ever enjoyed the fine diversity of Japanese cuisine, and are a serious sushi connaisseur (as I am) you have probably experienced the singular love of uni-a type of sushi made from the gonads (which produces the roe) of a sea urchin. To be sure, uni is not something everyone "gets" the first time they try sushi.
But, for people who enjoy uni, they REALLY enjoy it. Its a compulsion to order it when they visit the sushi bar!! But why???

Uni has a "euphoria-causing chemical" ingredient (albeit in very small quantities) similar to what you find in cannabis! Yes, pot, marijuana, etc. Specifically, a chemical neurotransmitter called an anandamide,also known as arachidonoylethanolamide or AEA
What are anandamides doing there in the first place?? These are actually naturally occuring chemicals in sea urchin gonads, which are thought to be important in the reproductive system, among other physiological/enzymatic processes associated with sea urchin fertility.
Interestingly, (according to Wired)-some scientists have hybridized the euphoria-causing anandamides from sea urchins in conjunction with the psychoactive chemicals from marijuana in order to better study the endocannabinoid system, which is partly responsible for pleasure and pain signals.

So far, anandamides have been studied in the N. Pacific purple sea urchin, Strongylocentrotus purpuratus and the European sea urchin Paracentrotus lividus.
I've not tried uni from other species (the two other species,S. franciscanus and S. droebachiensis I believe are made into uni). Several species are fished in Australia. One wonders if the amount of anandamide and the perception of taste (and the "high"), varies per species..

That being said can sea urchins handle the fishing stress?
Incidentally, according to one of the papers I foundthe chemical in S. purpuratus can reduce the fertilization capacity of sperm cells. This study was via direct application-not via ingestion, but if you are trying to be fertile, it probably doesn't hurt to lay off the uni, if you're having it every night! (plus uni is quite rich..so you probably can have too much of a good thing!!).

Thursday, September 11, 2008

Holothurian Video Friday!!

The Famous Defense Response of a tropical holothurian

Reddish Holothurian (don't know what it is-but a gorgeous animal) and a bit of Pentaceraster cumingi

"Sea Apple" (Pseudocolochirus violaceus?) Feeding

Click here for an excellent video of this species feeding....

And here is just a long-ass synaptid sea cucumber

Have a Great Weekend!

Tuesday, September 9, 2008

Ye Olde Haeckelian Phylogeny-Brisingids Rule!

So, the other day, was looking through one of my favorite older monographs "On Some Remarkable Forms of Animal Life...Researches on the Structure and Affinity of the Genus Brisinga" by George Ossian Sars, Professor of Zoology at the University of Christiania and came upon this cool older idea of Echinoderm Phylogeny: The phylogeny recounts some very early and....unusual...ideas about metazoan relationships originally developed by Ernst Haeckel and modified by Sars. The monograph was published in 1875. Darwin's ideas on evolution had only been around since 1859.

This particular monograph emphasized brisingids, which look sorta like a cross between a "normal" looking starfish and a brittle star: but what was NEAT and weird about Sars take on this animal's history? The fundamentals of this phylogenetic idea was that the Echinodermata were formed by "Colony Forming Vermes" which was another way of saying "Let's take 5 of these" and turn them into something kinda like this: But Sars hypothesized that brisingids were essentially a separate and independent "step" between these "colony forming vermes" and starfish and other echinoderms...essentially a missing link to ALL echinoderm diversification!! And that seems kinda reasonable..when you look at it... I could easily see how this could be "spun" this into the ancestor of crinoids, ophiuroids, and asteroids+echinoids+holothuroids!
Image of: Psolus chitinoides
The general gist of the phylogeny from there is that echinoderms were given towards greater "concrescense" or centralization...So from independent worms coalescing to bigger, lumpier things. So holothurians or sea cucumbers would be chief evidence of "concrescence"..especially with something like the armored and essentially sessile Psolus, which was seemingly even LESS pentameral than other cucumbers.