Tuesday, February 22, 2011

Gorekia! A worm that lives INSIDE a Sea Urchin!

(From Fig. 1a of Schiaparelli et al., 2011)
We ALL love stuff that comes INSIDE other stuff! The Internet tells us that this is so!! For example, this website tells us that we LOVE cherry pie INSIDE a chocolate cupcake!!!
and here we have a Philly Cheese steak wrapped INSIDE a pizza!!
And so today I thought we could talk a little bit about WORMS that live INSIDE the GUTS of Sea Urchins!!

Data for this comes from a new paper published this year (2011) in Antarctic Science by Stefano Schiaparelli, Maria Alvaro and Ruth Barnich.

First, the players...

They live in Antarctica.

There's this worm. Gorekia crassicirris (family Polynoidae)
(Here's a close up of its head... The worms are small-about 2 to 4 mm long and 6 to 13 mm wide.)
(Figure 2a of Schiaprelli et al., 2011)

and as it turns out, it lives in the INTESTINE of this sea urchin, Abatus nimrodi
The authors collected the urchins from bottoms of moderate depth (90-148 meters).

Upon observing the animals alive, they began noticing this worm crawling in and out of this sea urchin's mouth!

Previously, Gorekia was reported as free-living. That is, they just live out in the open on their own. (They like sandy bottoms)

But Gorekia living in this urchin? Sometimes behavior among species varies? Or perhaps there are advantages to living for worms that have access to these sea urchin species??
Here's a diagram!
(courtesy of Echinoblog Art Department)

This presents us with a good example of a commensal relationship. That is, one in which there is essentially a benign relationship between the host and the "guest". In other words, the host isn't harmed or negatively affected.
In fact, this is considered a SPECIAL case of commensalism called inquilinism in which one organism lives WITHIN the other, usually in some part of the alimentary tract or respiratory chamber, without being parasitic or causing the host any arm.

The case of Gorekia and the two urchins shown here? Only the SECOND ever recorded and the FIRST from the Antarctic!

The authors recorded the sequence showing the behavior of the worm on its host! Read from the top left to right (a to b to c..etc.)

These show the worm basically hanging out around the mouth of the urchin, and ultimately just retreating back into the gut. The bottom part of the figure shows where they cut open the urchin to look...and to verify that indeed the worm lives INSIDE the intestine.
(Fig. 3 from Schiaparelli et al.)
Out of 14 specimens of sea urchins examined, eight of them had a worm in its gut!

Interestingly, the authors checked OTHER Antarctic sea urchins to check for infestations.

And lo and behold..it turns out ANOTHER species harbors the worms in its gut! May I present, Brachysternaster chesheri...
And what's interesting? Brachysternaster "picks up" in the range where the urchin Abatus nimrodi (above) "leaves off"!!

So, the worms find the hosts important enough that they switch out different species along their range!

Okay. So. It lives in sea urchins. So What? Why do it? Why one of these urchins?

1. Protection. So, if ya' look at a close up of one of these sea urchins, you see that the surface is covered with spines and other bumpy bosses. The protective structures not only protect the animal but apparently also "guests" living inside...
2. Food?
The authors didn't extract any gut contents from the worms, but believe it or not, OTHER species of worms have this SAME kind of relationship with other sea urchins.
And in those instances, the worms can presumably just take any of the food from the intestine that they want! (hence the moochie guest taking your food out of a well-stocked refrigerator analogy)

3. Why choose an "irregular" versus "regular" urchin to inhabit?
Location, location, location.

So, if you're a "regular" urchin...that is one of the sea urchins that you typically see with long spines and such.. there are two major anatomical differences.

1. The Aristotle's Lantern or Jaw mechanism sits over the mouth opening (and blocks access to the intestine).

2. the mouth opens on the bottom and the anus sits on the 'top'
(from the U. Michigan Animal Diversity web)

The "irregular" urchins such as the ones above? These are related to sand dollars and have special adaptations to digging through sediments!!

1. They LACK an Aristotle's Lantern. Thus, there is easy, convenient access to the intestine!

2. Instead of the intestine tracking from the mouth to anus going vertically (i.e., UP), the mouth sits at the front and the anus sits at the rear. Thus the intestine is laid out horizontally (i.e., ACROSS). So basically...you have a flat house without having to expend the energy to walk "upstairs."

Which kind of urchin will the worm like?

The "irregular" urchin! Its perfect polychaete worm housing!

Another reason why things inside other things is NEATO!

Sunday, February 13, 2011

New genera and species of Antarctic Starfish! Stories behind the species!

What is this crazy thing?

So, just last week my NEW monograph on the goniasterid starfishes of Antarctica was published in the journal Zootaxa (Mah 2011, 2759:1-48)!

What does "monograph" refer to? Basically, its a scientific catalog to all of the starfishes in the family Goniasteridae found in the Antarctic and adjacent waters.

On the outside, the paper is pretty formal, very technical, and pretty dry, but this is by necessity. It is a scientific paper afterall, and it needs to have a professional feel to it. Its written primarily for my colleagues and my colleagues to come...

If I've done a good job, this is a paper that scientists will be able to refer to for decades (if not longer) to come.

Some of the species I've referred to were described in the 19th Century!! And yes..I had to refer to those paper in order to further write about them.. (this is not unusual in our field though..)

Below, I'd like to give a little "behind the scenes" action on various cool highlights of the paper! Especially since you may have seen parts of the story from before....

1. Where did the Specimens Come from? Okay, in one sense, you know the starfish came from Antarctica (as I mentioned it above), but how did they come into my care, handling and publication?

Remember this blog post with the US Antarctic Research Program back in 2008?
A whole buncha starfish specimens had just been returned to the museum from our colleagues in New Zealand.

Each one of those barrels above? FILLED to the brim with Antarctic starfishes!!

Bear in mind, that some of this material was collected almost 40 years ago! It found its way into various hands for study...and then stored and then off to study again! Until, finally the material has come back to the museum.
I was tasked with not only identifying and helping to sort them..but to research and PUBLISH on them as well.

There's a certain logistical hump to get over at first, as the specimens get sorted out, cataloged and so forth. But after all is said and done..you eventually come down to a few you don't recognize. And others that represent significant new discoveries compared to what's known!

and THAT is what leads to publication.

This paper then, is the kinda-sorta "final chapter" of what happened in my earlier blog! ("parenthesis" because often times naming new species is often the BEGINNING of a story...)

So what's in it?

The paper presents an overview of 19 species and 10 genera. Some of those species are pretty rarely seen. Here's a few of them...

2. Meet some New Species!! (and a new genus!)

So, there were three new species that I described in the paper! ONE of them was so unusual that I actually had to describe a new GENUS to put in!!

For comparison with what you may be more familiar with, the genus for humans is Homo (which means "man"), vs. the full species which would be Homo sapiens. (which means "wise man").

Let me introduce you to Eratosaster jenae!
Its primary distinction for being new? Its got all of those cool spines on the body surface.

Plus, its overall body shape and the many plates that make up the surface area arranged in a substantially different way from any other known genus of goniasterid starfish.

Hence, it gets a new genus AND species.
The genus, which is a noun, breaks down to Eratos, which is Greek for "lovely" and -aster for "star", so the Lovely Star. Its a dang pretty animal. And so that's what I called it.
and the species? (or more precisely speaking-the specific epithet) "jenae"? Refers to my colleague Dr. Jen Hammock, who administered the US Antarctic Research Program.
As seen above, Jen is providing scale for a giant starfish that I've used in my blog before..

How did I end up making her the namesake for my new species (full name is Eratosaster jenae which translates roughly to Jen's Lovely Star).

Scientists who name species, can assign names after individuals they feel have made an important contribution to their research, or sometimes to society-sometimes colleagues or celebrities. It varies.

Dr. Hammock oversaw the USARP through a lot. she provided supervision for interns, visiting scientists, cataloged specimens, managed the USARP (now folded into the USNM database (here to see) and many other things. So, I was happy to name something after her. :-)

The 2nd new species: Chitonaster trangae!

It belongs to the genus Chitonaster which was described by Walter Percy Sladen as part of the original H.M.S. Challenger expedition results in 1899!!

The name is Greek for "tunic" which probably alludes to the fact that there's kind of a thin layer of pulpy skin over the surface, which is in turn covered by spines or granules.

Sort of like this one....
(Chitonaster cataphractus)

So, the problem with Chitonaster was that it hadn't been worked on since the late 19th/early 20th Century. NONE of the species had been compared to one another and over the last 90+ years or so, there had just been a kind of built up inertia.

The specimens were NOT matching up with all the descriptions! So, some detective work was needed.

Apparently, what had happened, was that this new species had been identified for many decades as one of the deep-sea species. No one ever really worked up the differences.

This new species? Apparently, it lives in MUCH shallower water and differs most prominently from the deep-water species in that it has papulae!

In other words, it has a lot of tiny, little fleshy pouches that that extend through the body wall that facilitate the animal's ability to "breathe".

How can you tell? Here's a dissected "top" of the animal removed. See all of the white spots? THOSE are where the "gills" extend through the top of the body surface.

This is a view from INSIDE the body top surface.
Here's one labelled... "P" is for papulae!
It turns out that this species with the papulae is one of the most COMMONLY encountered species of Chitonaster in the Southern Ocean!

AND as it turns out, its new! This new species was likely collected and handled by scientists for years before being recognized as distinct!

Who did I name this beast after? USARP research assistant Trang Nguyen who greatly contributed cataloging, processing and lending her great care to the USARP collections!
And finally, the 3rd new species..Pillsburiaster calvus!
The genus name is named for the R/V Pillsbury, which was the research vessel for the University of Miami, followed by "aster" for star..

This new species is named calvus which means "bald", which alludes to the bald spots on the marginal plates.

2. Did you know that scientific names can be made to vanish? Meet the Synonymy!!
So, most people know about the "powers" of taxonomists to name new species. But did you also know that some names can be made to "vanish"??

Its not uncommon for some evidence to show that two described species are the same thing. This means that one of those names is unnecessary and needs to be "put away", lest the multiple names lead to chaos!

There are actually a series of internationally agreed upon regulations which operates the International Code of Zoological Nomenclature, a set of rules dictating how different names are regulated.One of those rules states, that when you've discovered that a name is basically the same as another, it becomes a synonym of the name described by the first person who described the valid name.

Case in point...this beast. Originally this species was described as Pentoplia felli in 1971.
Its kind of a weird looking animal. Its genus name means "Five Weapons". Because of these weird pedicellariae on the underside...

Unfortunately, though, Pentoplia is pretty much identical with Chitonaster (see above). And thus, was this name SUNK!

Thusly, it was made a synonym of the original name described by WP Sladen in 1899! The new "combined" name? Chitonaster felli! (This assumes that no evidence in the future makes Chitonaster felli a synonym of some other species!)

3. And then, there's the RARE stuff....
Finally, let's look at some Antarctic species that are pretty rarely encountered (i.e., less than 6 species known...)

Sphaeriodiscus mirabilis
(previously known only from one specimen in the south Indian Ocean)
Cladaster analogus is a large, handsome beast known from only one or two specimens since its description in 1940 by famous Stanford marine biologist Walter K. Fisher!!
Its got some pretty cool pedicellariae (those are those lip-shaped things) and spine action going on, on the underside!!
Also..there's an identification key (to help recognize the various species) and a checklist!!!

How exciting is THAT?

Tuesday, February 8, 2011

Deep-Sea Brittle Stars Occur in Lateral Bands!!

This week's blog is based on a NEW paper (click here) by Tim O'Hara (Museum Victoria), Ashley Rowden (the New Zealand Institute of Water and Atmosphere) and Nicholas Bax from the Commonwealth Scientiifc and Industrial Research Organisation in Hobart, Australia.

This paper has been making the rounds in the popular media (here) and the blogosphere (and here)...

First, a little bit of background so that everyone can appreciate the story with the same starting point..

Faunas & What is Biogeography?
At some basic level, I think that most people realize that most organisms, including plants and animals, do not occur all around the world at equal levels.

For example- If you are an aquarium hobbyist, you've probably noticed that some fish are "cold" salt whereas others are tropical or "hot" salt. That's because the animals that live at those different temperatures are originally from different specific locations in the world.

You can often find complete "sets" of particular organisms also known as faunas (or floras for plants) specific to these regions.

Thus, the fauna (i.e., the set or assemblage) of animals and plants you find in the cold/temperate water kelp forest (on the left) will be VERY different from those which you find in the tropical-hot water reef habitat on the right.
Scientists take this basic definition one step further. There is an active field of study known as biogeography, which seeks to determine the significance of where organisms live.

This includes the evolution/character, structure, and history of how particular groups associated with specific regions came to be distributed in those regions.
How do these regions transition into others? What dictates those distributions? These are big questions in biogeography.

Among the scientists who often work in biogeography are specialists called
taxonomists who can identify the many different types of organisms present in each specific region. And based on this, they can characterize different biogeographic areas.

So, what does this have to do with the paper again??

Brittle stars are a good model organism for understanding how life is distributed on the sea bottom because they are abundant in the deep-sea and are consistently EVERYWHERE. They live in mud, under rocks, in sponges...some brittle stars even live on EACH other!

Because brittle stars are important componenets of this region..and especially in the deep-sea, their distribution may hold clues to the biogeography, evolution and distribution of all organisms in this area which is ultimately important for marine resource planning and etc.

Enter the considerable talents of Tim O' Hara at the Museum Victoria who is one of the world's foremost experts on brittle stars!
He developed a large data set derived from 295 research expeditions, across an equator to pole sector of the Indian, Pacific and Southern oceans. This literally means identifying thousands of specimens from scientific expeditions, museums, universities and other places where brittle stars are found. The study area covers 1/8 of the globe using data from 24 museums!

Multivariate analyses (i.e., statistical) of this dataset were performed (also by O'Hara and etc.) and they found the following...

1. Brittle star faunas in different depth zones is different.

This includes:
1. A "shelf" zone, from 0-250 meters.
2. A bathyal zone from 250-2000 meters.
(data for below 2000 m apparently was too poorly sampled to yield results) This shows the depth vertically...
This figure (Fig. 1 in their paper) does a much nicer job of showing it on the map... (note the keys to different colors in the lower left hand corner).
(Figure 1 from O'Hara et al., 2011)

Brittle stars from shelf vs. those in bathyal regions are VERY different from one another-Except in the Antarctic where cold water basically forms a homogeneous environment all throughout the shelf-bathyal region.

So far so good.
This goes along with what's been known.

Historically, its been thought that the geographical faunas of brittle stars would all be clustered based on ocean basin.. In other words.. different brittle star faunas for different discrete regions in the Indian and Pacific ocean basins.
it turns out this was NOT the case...

2. Bathyal (deep-sea) brittle star faunas were observed to occur in latitudinal (i.e., "lateral") BANDS across the Indo-Pacific region!!
(Fig. 2 from O'Hara et al., 2011)

RED for Tropical species
, such as this Acanthophiothrix purpurea
(photograph by Julian Finn, Museum Victoria)

GREEN for temperate species, such as this Conocladus australis
(photograph by Julian Finn, Museum Victoria)

and blue for POLAR species...such as this Ophiosteira sp.
Although the three faunas appear very distinct, they don't show a very clear transition.

The geographical boundaries between the groups was rarely distinct.
Many of the species ranges overlap and intergrade (you can see the colors in Fig. 2 blending together in many places).

So, the boundaries were transitional and not sharply, distinct disjunctions between biogeographical regions as was historically assumed.

Unfortunately, there are no clear clues as to what may be the cause of the overall "lateral band" pattern. An evolutionary hypothesis (i.e., a phylogeny) for brittle stars is unavailable and fossil brittle stars of the appropriate age aren't really common..

The authors speculate on possible reasons in this area are distributed in this manner...
  • Water temperature?
  • Primary Productivity? (i.e., food)
  • Oceanographic reasons-current flows, etc. that might affect settlement of the larvae
As much work as this represents, this likely represents only the FIRST step towards understanding the distribution and biogeography of animals such as these in the deep-sea.

Remember also that brittle stars are the MOST diverse group within the Echinodermata, boasting over ~2159 species! How will additional discoveries of fossils?? Or new species? Or developing evolutionary histories?? affect these patterns?

Understanding distributions like this aren't just academic questions, they are also used to help management plans of the ocean for deep-sea mining of oil and gas. Possibly to help develop a network of marine protected areas.

All from the humble brittle star...