Wednesday, August 10, 2016

HYMENASTER Deep-Sea Slime Stars from the Atlantic and Pacific!

From 2001. Hymenaster pentagonalis from the Hawaiian Islands region. Image by H. Reiswig
Probably one of my FAVORITE deep-sea starfish, other than brisingids has to be these enigmatic and bizarre deep-sea "slime stars"! aka the genus HYMENASTER in the family Pterasteridae!  I've talked about these briefly in a prior account of shallow water slime stars in the genus Pteraster here. 

My first exposure to LIVING Hymenaster was back in 2001 when I was working with Craig Young on an expedition to study glass sponges in the Hawaiian Islands (see pic above)

I got an opportunity to collect a bunch of deep-sea asteroids at that time and saw my FIRST deep-sea slime star!!

and a few minutes after, I discovered for the first time that, just like their shallow-water cousins, Hymenaster could emit mucus just as effectively!!  In other words SLIME!
Image by H. Reiswig.
Hymenaster is a WEIRD animal. The entire surface has evolved into a strange soft covering, This varies in different species. In some the body is membranous and kind of leathery, others, sometimes soft and in others, almost completely gelatinous. In those latter gelatinous species, almost the entire body, save for the tube foot grooves, mouth frame and various other structures are nearly all soft and squishy. Very little in the way of "hard parts"

The name Hymenaster translates from the Greek into "Hymen" and "aster" or "Membrane Star" which as we shall see is pretty fitting.

The body is almost transparent. You can see the five radiating tube foot grooves plus the mouth and some spines and etc. in the surface areas which you can sort of see through.
 Hymenaster sp. from Maro Crater (Hawaiian Islands)
Hymenaster's translucent body draws an analogous comparison with many deep-sea sea cucumbers such as this one observed at 4800 m in the Hawaiian Islands... So perhaps there is an adaptive advantage to having this gelatinous body wall?

Hymenaster occurs all throughout the world: Atlantic, Pacific, Arctic, Indian and Antarctic (i.e. the Southern) Ocean. The genus includes approximately 60 species.

Hymenaster lives primarily in very DEEP water (1000-8400) with some species occurring in the DEEPEST of ocean depths, setting records for starfish deep-sea occurrence (here). The deepest known Hymenaster was recorded from 8,400 meter depths aka the ULTRA abyssal!!  But some, such as the shallow Hymenaster pellucidus take advantage of the cold water in the Arctic and can occur in as shallow as 128 meters.

The problem with many of these deep-sea pictures is that the diagnostic characters used to ID them are from characters that are either on the underside, along the tube foot grooves or actually INSIDE the body. Color, shape and surface texture all seem to it can be difficult to "nail down" which species is which..

Unfortunately, these animals don't hold up well after collection. Here's one after the delicate touch of a robot submersible. Think about what what a delicate animal like this looks like AFTER a trawl net has dragged it for about an hour on the sea bottom!
It depends on the species of course, some of the tougher species are pretty tough. This one looks like its in pretty good shape. Still weird but the features are all there...

One of the most complicated aspects of studying these animals is "matching up" the examined, often damaged specimens from above with the living animals. And lately there have been a LOT of images of living animals!

There is nearly NOTHING known about the biology of these animals. What do they eat? What is the slime used for? What is the gelatin-like body an adaptation for?  Where do the species live? Are they separated by depth? How have they evolved?

ALL of the observations below have screengrabs via the Okeanos Explorer program!!

The deep Pacific is a VAST area. Images below are mostly from North Pacific observations..undoubtedly there remain many MORE species further south.  

A Pink One from the southern region of "Bank 9" in the Hawaiian Islands region

here was an ENORMOUS one from the Hawaiian Okeanos that was HUGE about 20 cm across!

This one nicely illustrates the osculum, which is that big center hole on the surface which is how water enters the cavity surrounding the body surface thus bringing water/gases to the papulae (i.e. the gills) within..
 It gave us a nice show with its opening and closing osculum!

This is what I previously identified for HURL as H. pentagonalis..but it doesn't seem to match the orange one at the top of the post above in terms of color or texture. So, possibly something else.

From East Necker Seamount in the Hawaiian Islands region. A different color from H. pentagonalis.

and yet ANOTHER Hymenaster species (I think??)  from Salmon Bank in the Hawaiian region. White with flyffy surface texture!

A recent image of Hymenaster sp. from McDonnell Guyot in the Wake Island region. Same genus but the surface texture is VERY different..

Here is yet ANOTHER species from Barkley Canyon off British Columbia.. Again, very different body shape, surface texture and color..
Deep-sea Slime Star

Its also entirely POSSIBLE that SOME of these Atlantic species might actually be the SAME ones as the Pacific ones.. There are some similarities below with the ones above..

From Puerto Rico

From Atlantis II Seamount (North Atlantic)

From the Atlantic, Mytilus Seamount (via Okeanos). On top of everything else, the surface membrane is "ballooned" up... which is more mysterious behavior.

From Physalia Seamount (North Atlantic). Honestly, this one might be something else entirely. The surface texture is unusual. 

Big goopy starfish! The mysteries remain! 

Thursday, July 28, 2016

The Crown of Thorns Starfish in Macro! Acanthaster planci? or alien landscape?

Acanthaster plancii détail

Today as I was scrolling through the many years of posts I realized that I have NEVER written about the Crown of Thorns starfish, Acanthaster planci!  If you don't live in the Indo-Pacific you might not realize that this is actually one of the most heavily studied starfish in the world!  There are whole BOOKS written just about the biology and ecology of this single starfish species! 

Why? What makes this species so important?
This starfish is a voracious coral predator!  It just extends its stomach onto the fleshy tissue of a "hard coral" (i.e. scleractinian) and a little while later, only the "cleaned" skeleton of the coral remains! 
If it was a reasonable number of these animals feeding on coral, it would actually be healthy for the ecosystem. Predators control community structure and are important to ecosystem function..

The thing is though that this species, for reasons which have been studied since the 1960s, have undergone sporadic and localized HUGE population explosions! Their incredible abundance results in the wholesale LOSS of complete coral reefs! 
 Crown-of-thorns starfish

They have become especially infamous in the Great Barrier Reef and to many Australians who have become accustomed to physically destroying them on contact. They actually have developed ROBOTS to seek them out and destroy them.. 

So, unlike most starfish, they aren't very popular....

The Beauty of the Beast...

Image from Wikipedia, taken by Jon Hanson, in Thailand:
Here's the thing though. In spite of all the hate that gets laid on these animals.. I STILL think they are kind of freakin' AMAZING! 

So, today, I thought I would exploit the wonderous world of Flickr and show off some of these spectacular macro shots displaying the surreal surface of these animals...

The crown of thorns occurs across a WIDE range. From Baja California to Hawaii and Japan and then down to the east coast of Africa in the Indian Ocean. The range of colors is similarly vast! Its not entirely clear if these might represent separate species or perhaps represent some other kind of variation based on the environment. Perhaps food? growth? Difficult to say...

But genetics DOES indicate that there are multiple "cryptic species" across this animal's wide range in the Indo-Pacific..

The big thorny bits are of course, the spines.. the dark dots on the surface are the papulae  (or gills) and if you see little white or dark beak like structures, those are called pedicellariae whose function in these animals is not entirely clear... But likely some kind of "in close" defense against parasites or what have you.... 
Crown of Thorns Sea Star

Crown-of-Thorns Sea Star
Crown of thorns closeup - Okinawa
Crown-of-Thorns Sea Star (Acanthaster planci) from Aliha Giri.
Close-Up Thorns
crown-of-thorns star: Acanthaster planci
Close up picture of a Crown of Thorns Starfish (Acanthaster planci)

and the ANUS of course! That's the dark spot, probably surrounded by spines...  this shot is nice because it not only shows off the papulae (the gills) but also the pedicellariae (the red tweezer like structures)
Crown of Thorns Sea Star Center Close
Crown-of-Thorns Starfish - Kailua-Kona, Hawaii

As one finds often time in nature.. you have some big animal with lots of complex surface textures.. so are there animals to take advantage of it! Shrimps often live closely and among the spines on the animals' surface...

here are tiny shrimps.. some in the genus Periclimenes...
Sea Star Shrimp
Periclimenes soror on Acanthaster ellisii

And the ORAL surface!
Strangely enough, the top surface of Acanthaster is remarkably well known but how many people have actually seen the ORAL surface where the mouth is???

In addition to the tube feet all converging at the mouth, you also see the oral spines projecting into the mouth itself! 
Side B
and in this one, you can actually see some of the cardiac stomach below the purple spines...
upside-down crown-of-thorns
Crown of Thorns sea star (Acanthaster planci)
Crown Of Thorns Sea Star

And a video to top it all off!

At some point, there will be much, much MORE about the Crown of Thorns! 

Wednesday, July 13, 2016

Astropyga The Radial, Fiery Star Butt Urchin! Observed insights from Flickr & YouTube!

A happy July week to all of you! So, as we enter into the lull of the summer I present to you some choice Echinoblog image and video picks from various image streams that show off one the internet's most frequently photographed sea urchins! The diadematid ASTROPYGA

Common names of these urchins include "radial urchins" and "fire urchins." But many refer to echinothuriids in the genus Asthenosoma as "proper" Fire Urchins, for obvious reasons.. but mainly because they are VERY painful to get stung by..

Astropyga also appears to have a rather painful array of spines but I'm unsure if these pack quite the toxic wallop that Asthenosoma does..

Astropyga includes four known species, one in the tropical East Pacific and another in the Indo-Pacific and two in the tropical Atlantic. All are known to occur primarily from relatively shallow to mesophotic depths as we saw recently on a Bishop Museum expedition to the "Twilight Zone" (here

But even within the widely occurring Indo-Pacific species. A. radiata there appears to be quite a bit of color variation from the dark colors seen below to the lighter ones like this
Blue-spotted Sea Urchin (Astropyga radiata)

The genus name can be broken down to "Astro" meaning star and "pyga" which refers to rump or buttocks.. so the name literally translates to "Star Butt"!!.

Why? Well, you see this giant bulb on the surface? That's an extension of the intestine called the anal sac. That's where the POOP comes out! I've talked about that here.  So, basically some wry taxonomist looked at the anal sac and the pentagonal symmetry and decided "yes. The STAR ASS!"
Fire urchin
Flickr and Youtube are GREAT for picking up on natural history observations. Yes, there's always the lack of scientific rigor but sometimes divers just make simple observations. And THAT can be the start of knowledge.

All the images below are probably A. radiata from the Indo-Pacific.

Astropyga scavenging on dead fish! (Lembeh)
Based on a round up of papers I could locate, A. radiata has been reported primarily as a scavengers, feeding on algal debris and other stuff from sediments, etc. But if this image is accurate (and not posed) they occasionally much on dead fish as well. This is actually consistent with other sea urchin feeding habits, so I feel comfortable in presenting it here..
Radial Sea Urchin feeding on dead fish - Lembeh

Blue Iridescent Spots! Its been speculated that these are photoreceptors but they've not been tested and its unclear exactly what their function is.. But they immediately stick out when observed on an otherwise bright red sea urchin! 
Astropyga radiata, Red sea urchin
Fire Urchin
magnificent urchin

This speaks for itself. As with other echinoderms I've shown here (such as the sea cucumbers) just because you see white fluid being emitted its not actually clear what sexes of the species are present. The fluids likely represent BOTH sperm AND eggs. 
Sometimes this species form large aggregations, which are most likely to help facilitate their reproduction and sexy time!
Urchins unite!Magnificent Urchin family
Astropyga moves surprisingly quickly!
While I haven't actually seen one of these alive and close up, its pretty clear that even for sea urchins they are capable of a surprisingly brisk sprints! and across some unusual terrains to boot! 

That's quite a lot of coordination of spines and tube feet at play.. 

here's a bunch of them in what looks like a mating aggregation, moving en masse!

Better yet! here's Astropyga moving in TIME LAPSE!

my first underwater timelapse from prodtv on Vimeo.

Crustacean Relationships! 
Sea urchins are basically big spiny balls that seldom move and surprise! surprise! There never seems to be a shortage of OTHER, smaller animals that can take advantage of this as "habitat."

 Crab Commensals!  These don't seem to be as bad as the crabs on Asthenosoma, (the proper fire urchins) simply because these don't seem to "dig" themselves into the urchin surface. Spines on Astropyga seem long enough to provide adequate protection as-is...
Walking on fire!

and vice versa?? Probably one of the most unusual things I've seen imaged by divers since Flickr and YouTube became a thing has been this.. Crabs in the family Dorippidae that PICK UP urchins, sea anemones and carry them on their carapace in order to use them as sort of a defense as they walk along the sea bottom.
But why explain? When you can just watch...

...and of course.. POOPING!
And finally, one of the things that we LOVE to watch urchins doing? POOPING! Something that is arguably part of their namesake!  Here's the time I corrected New Scientist on their mistaken urchin pooping picture! 

Here's a whole post on echinoderm anuses for your reading pleasure! 
Here's a lovely shot entitled "Radiant Crap" by Eunice Khoo!
Radiant crap!
And of course there's pooping AND commensal crabs! TOGETHER.
Urchin crab - Zebrida adamsii - T Tebal