Cnidaria Part 3: Corals

Just a short introduction to corals today, I am heading off on a field trip this afternoon, so writing this just before I leave.  As it is a botany field trip, I may be blogging about plants as well as animals over the next few days.

Corals are in the same class as Sea Anemones, so Anthozoa (plant-animals), in the phylum Cnidaria.   We are all familiar with them from images such as the ones below

Tree Coral (Dendronephthya), from aqua-views.net

Pillar coral (Dendrogyra cylindricus). Image from wikipedia

When I first saw corals, I thought they were rock formations on the sea floor, and indeed, some of them are very sharp, due to the Aragonite (calcium carbonate) they are made of (calcium carbonate is commonly found as chalk, or limestone, or limescale in the kettle, and can have different hardness depending on the way the crystals in the rock form).  Later, when I heard they were living, I assumed they must be some sort of underwater plant.  The reality is stranger than I possibly imagined, and I still have problems wrapping my head around it, even though I understand how they function, I still look at them and think “That cannot be how they work”

There are two types of coral, Hermatype or stony coral, and these build reefs, and Ahermatype corals which do not build reefs. The posts on corals will mostly be about the Hermatype coral, and Ahermatype corals will be covered under their other names (Sea Pen).

Corals have been around a VERY long time, with fossils recorded in the Cambrian period (this was approx 542 to 488 million years ago), although most existing fossils of coral are from later periods, the Ordovician (488-433 million years ago), and the Devonian (468-359 million years ago).  There is some evidence for soft corals in the Pre-Cambrian period, although whether these are corals, or polyps (one of the juvenile phases in Cnidaria) is debated, see Anthozoa Fossil Record for more details

Coral Fossil, possibly a tabulate coral (From UCMP Berkeley)

Rugosa (horn coral) fossil, from UCMP Berkeley

Next post will be about how corals are formed, and cover their life-cycle, and then later posts will be about feeding, and the different types of coral within each reef, the symbiosis they have with other organisms, and their place within the oceanic ecosystem (What they do in the ocean, and how they benefit the other organisms which live there), as well as the problems facing corals today in our oceans.  (See, I said there would be a lot of posts).

Women in science…wait…what?

I know this has been done to death on the blogosphere, twitter, forums etc since the video came out, but I was away on a field trip, and only got a chance to properly look at it yesterday.  At first, I was not sure whether to bother posting about this, because my main response is to repeat “WTF” a lot, but I have been asked to blog my thoughts on it, so I will try to get something coherent down.

In case you do not know the video in question, here it is.  Bear in mind, it was commissioned by the EU, to promote science to girls.  So, someone somewhere approved this video, and thought “Yes, this will get girls interested in science”.

Ok..now do you see why I had problems even knowing where to start with discussing the problems with the video?  Well, we could start at the beginning.  It is very James Bond like, silhouetted girls distracting the serious looking man at the microscope.  Once the lights go on, the women are wearing high heels, and looking very coy.  The man looks up from the microscope, and doesn’t immediately say “No high heels in the lab, and where are your lab-coats?”  Cue montage of girly things, with a pink background, and giggling, whilst pulling an “ooops” face while balls from the structural model collapse on the floor, probably because she knocked them over while walking on the very polished lab floor in those ridiculous high heels.

Ok, I give up, I revert to my initial response of “What the fuck were they thinking, and who the fuck signed that advert off?”  But, as I have been asked to blog about this, I will try formulate that sentence a little better.

First up, when I was at school, I was in the Triple Science classes for my GCSEs (In England, you got to do either single, double or triple science at GCSE, this meant you got 1-3 science grades at 16, depending on which you chose. Single science was the bottom course, and covered very basic “This is a liquid”, double science was the one most people did, and triple science was what you took if you wanted to take a science subject at college or university, it resulted in you getting separate grades for Physics, Chemistry and Biology, and was designed to dip into A-Level science a bit.  It meant you had more hours of science classes per week, and had to choose it instead of two other subjects (handy for me, because I really did not want to take too many of the exams past Maths, English and the Sciences, so ended up filling the gaps with German, Economics and Home Economics (yes, that means I learned how to cook…although my boyfriend doubts that sometimes!))

The point being, that in my triple science class, there were 13 of us or so…of which, 4 were boys. Our physics teacher was female, and completely awesome.  She was the reason I chose physics for college (I then found out it was mostly electronics for the first year, and did not like that so much), and got us completely enthralled in our experiments for our GCSE project (predicting the size of the crater caused by dropping golf balls into sand).  Our other science teachers were male, and whilst our chemistry teacher was a bit sexist, our biology teacher was amazing, although, any teacher who let me disappear off into the woods for much of the term to write my project (studying the distribution of moss on the trunks of trees to see if there were other factors affecting growth apart from the North-South orientation) was always going to be high on my list of awesome teachers.

Whilst some of our ambitions may have been stereotypical (girls: wanting to be vets/doctors, boys: physicists), this was more due to a lack of knowledge of the possible career paths than thinking that some things were for girls, and some for boys.  I was opting to do organic chemistry, physics, and pure maths with statistics at college, without any real idea of where this could take me. I am very glad I never took this path, and that my biology teacher was right when he said I should look into environmental biology.

Today, at university, the number of women on my courses outnumbers the men with a few exceptions.  The women on the field trip I have just returned from are as far from anyone in that video as it is possible to be whilst still being in the same species.  Yes, some of them dress up when they go out, yes, some of them know about scary things like eye lash and hair extensions, or how to do weird things with brushes and powder and all sorts of associated voodoo that is beyond me, but not a single one of them would be caught dead dressed like that in a lab, and as some of them are VERY handy with a dissection kit, I would not suggest it to any of them!

The advert seems to be pandering to the “Scientists are lab-rats” view that many people have, whereas, in reality, many branches of science never go anywhere near a lab like that.  I am tempted to say it is an advert for the beauty industry to get people interested in biochemistry, and then point them towards working in a lab for them instead of doing research, “look girls, you can help us make blusher, nail polish and eyeshadow, isn’t that cool?”

There were other adverts made which were much better, but it is this one they will be remembered for.

After that rant, I will leave you with some videos of women scientists, real ones this time, not pretend barbie doll wannabes.  No, they are not “glamourous”, but guess what? In science, you are not judged on how glamourous you look, or whether you have the latest fashion, or perfectly done hair and make-up.  The only thing that matters is, do you know what the fuck you are talking about, and more importantly, can you prove it?

 

More Sea Anemones

Yesterdays post was about sea anemones, and today is going to cover briefly how these creatures feed, and the relationships they have with other species of animal (symbiosis, from Greek sym together, and biosis living, so simply meaning things that live together…see, those scary sounding terms which put people off are fairly straight forward usually)

So, yesterday we covered the structure of the sea anemone, where the tentacles at the top of the animal direct food into the top of the pharynx (like we do with our hands), but, anemones do not have tongues, or a digestive system as advanced as ours, so how do they actually eat, and digest their food?  And, having a simple gut as mentioned yesterday, it only has one entrance/exit, so how exactly does that work, and is it as gross as it sounds?

As with us, when food enters the throat (pharynx is from the Greek for throat), the tissues within the throat expand by a wave of contractions, which work up from the base to the top, so the part of your throat at the back of your mouth expands to allow the food to enter, then the wave reverses, and the food is pushed downwards, and out of the throat into the stomach.  (Try putting your hand on your throat as you swallow to feel this).

Sea anemone feeding, or at least trying to. From BBC (very awesome pictures)

Once dinner has been digested, contractions within the tissues of the stomach (peristaltic contractions, from Greek peri and stallien meaning to wrap around), push the waste back up so they can be excreted. This type of movement of tissue is the same as we have in our small intestine, and our throat after swallowing.

Peristaltic movement (image from Wikipedia)

The diagram below shows the different stages in the feeding cycle of sea anemones, and is followed by some other pictures from the same site, mainly because they are awesome pictures, but also because they show anemones in different stages of contraction and expansion.

Feeding cycle for anemones, from asnailodessy.com

Different stages of contraction and expansion within a sea anemone, also from asnailodyssey.com

Sea Anemone releasing matter from its pharynx (White item in centre of photo). From asnailodyssey.com

So, is the feeding as gross as it seems? I do not think so, although when watching it, it can make your stomach feel a bit queasy, but this is purely because we have two exits from our stomach, and so associate exiting of material through our mouth as a sign that something is wrong.

Now, onto the symbiosis I mentioned at the start of the post.  There are several forms of symbiosis, with varying degrees of benefit to the host.  Parasitic symbiosis is the one most people are aware of, where one species lives in or on another, and is harmful to the host, examples of this in humans are malaria and tape-worms.

Mutualism is when both species gain a benefit from the symbiosis. The bacteria in our stomachs, bees and flowers are both examples of mutualism.  In sea anemones, they have mutualistic relationships with clown fish, as shown in the picture below.  The clown fish is protected from predators by the tentacles of the sea anemone, and in return, the clown fish fights off fish which would otherwise feed on parts of the anemone.  Also, the clownfish also excretes ammonia rich waste, which is used by the bacteria in the stomach of the anemone.

Clownfish on an anemone. From wikipedia

Commensalism is when one species benefits without harming the other. Anemones are often used as examples of this, and with good reason!  The picture below shows a Boxer Crab.  This animal carries anemones in its claws for protection! They are the white objects in the picture below.   If anything threatens the crab, it waves around the anemones, with the tentacles towards the attacker… if the attacker gets too close, the nematocysts will fire from the tentacles.  This relationship may be more mutualistic than commensalist, as the crab excretes nitrogen rich waste in the same way the clownfish does, and so may provide nutrients for the anemone.

Boxer crab carrying two anemones for protection. Image from MS-Starship.com

Another really good example from the anemone is of the anemone crab (a porcelain crab species), which lives in the tentacles of the anemone, and filter feeds particles passing through the tentacles.  As with the other species which have symbiosis with anemones, the crab has had to evolve an immunity to the toxins of the tentacles.

Porcelain Crab in the tentacles of an anemone. They filter feed on particles passing through the current in the tentacles. Image from MS-Starship

I find it fascinating trying to work out reasons for how these relationships evolved, and why they arose.  For a crab or fish to begin living on what is an aggressive toxic animal means that the benefit of the protection gained must outweigh the danger of being accidentally eaten, or stung by the host.  In the case of the boxer crab, I think that originally, anemones may have settled onto a crabs claws, and then over time, the crab began to utilise the anemones in the local area.  In the case of clownfish, or porcelain crabs, which came first, the immunity, or the behaviour, is something which keeps me busy for hours when I start thinking about it.  I am sure there are evolutionary biologists out there who know the answer, but, I prefer for now to try and work it out for myself, maybe over time I will study more ethology (the study of animal behaviour), and be able to better understand it for myself.  Presently, I think that it was a mix of immunity and behaviour.  Some ancestral fish would have had a slight immunity, which made it able to utilise the anemone for a short period of time, and over time, this was selected for because of the protection gained from the behaviour….being able to hop into an anemone when a predator came past, even for a few moments, is an advantage, and if while there, food is available, that is a double advantage.

Next time will be starting out on corals…I have no idea at the moment how many posts that will be, as the topic is huge, and amazingly interesting!

Cnidaria Part 2: Sea Anemones

So, it has been a while, but the craziness of exams has died down now, so, back to posting!

Last time was an overview of Cnidaria, and this post will be about the members of this phylum (group) which are sessile (stationary).

The animals we will cover are in the class Anthozoa, which is from the Greek Anthos (flower), and zoa (animals).  Before I got into biology, I, like many people, thought of corals, or sea anemones as a type of plant, and so it is easy to see where the class name comes from.

Within this class, I find corals particularly interesting, and so will cover those over several posts in the days to come, but this post is about Sea Anemones, and I hope I can show you that they are also extremely cool!

In common with other Cnidaria, Sea Anemones contain cells known as cnidocytes, which are cells that produce nematocysts,which are a bit like miniature harpoons, which fire threads containing toxins, this is what gives jellyfish their sting, however, in Sea Anemones, the threads are unable to penetrate human skin, so the result is merely a tickling sensation. The video  linked below shows the mechanism of these cells firing (it states jellyfish, but it is the same for all Cnidarians.

 

Sea Anemone, Image from  image from
http://deepbluehome.blogspot.dk/2011/09/sea-anemones.html
 Check out the site for more awesome pictures!

Ok, so, you can see how they look a bit plant-like, especially in this image below:

Another sea anemone, this one definitely looks more plant-like. Image from valdosta.edu

So, how do these animals work,where do they live, and what do they eat?

Well, they are immobile in their adult form, and they attach themselves to rocks, shells, or pretty much anything they can grab a hold of.  They do not have the medusa stage that was mentioned in part 1 of Cnidaria, but instead, the fertilized eggs develop into larvae, as shown below

Sea Anemone larvae, from Sciencephoto.com

The larva shown above has a mouth (the brown section in the centre), and so is likely a planktonic larval form, which means that it feeds on plankton whilst drifting through the ocean.  There are larva from sea anemones which feed on the yolk from the egg whilst developing, and these are known as lecithotrophic larva (from the greek for yolk lecitho and trophic meaning food or feeding). These differences in how the larva feed have an effect on how far they can travel before they mature.  If they are planktonic larva, they can travel further, as food is always available, whereas lecithotrophic larva are limited in how far they can travel by how much yolk is available from the egg sac.

These larva may spend weeks travelling through the ocean whilst they develop into juvenile anemones.  This form has no tentacles, and instead has cilia (fine hairs) around it, which may be used for movement, or for extracting plankton from the water for feeding.  Once the juvenile anemone settles onto a suitable surface, it develops into the adult form.

Although I said earlier that these are non-moving animals once settled, some species do in fact have the ability to move a small distance by using the muscles within their foot (pedal disc) to detach themselves from the rock which they are attached to, and “walk” a short distance to a more suitable location.

Now, how do the adults actually look?

Sea anemone structure. Image from University of Hawaii

Don’t worry about all the scary sounding words in there, they are actually quite straight forwards (Us sciencey types like to use long Latin or Greek sounding words for things to make it look complicated!).  If we start at the top, the oral disc is simply a flat bit at the top of the anemone, which has the tentacles attached to it.  This leads into the pharynx, which is the top end of the stomach cavity.  As these animals have a simple digestive system, they use the pharynx for both taking in nutrients in the form of food, and for excreting waste products (yes, technically, they poop out of their mouth).

The perforations at the top are for allowing water to circulate better through the pharynx, allowing for easier transport both in and out.  On the blown up section to the top right, the pharynx is the hole in the centre of the cut-away section, and the siphonoglyph labelled at the right of it is a groove covered in fine hairs, this aids the movement of water into the pharynx.

Nearer the base, is the gonad.  Sea Anemones are hermaphrodites (having both male and female organs), so they produce sperm and eggs, which are then fertilised by other anemones.

The video below shows sea anemones feeding, which I find completely fascinating, and utterly gross at the same time!

Next post will be about the  feeding mechanisms and symbiosis some animals have formed with anemones!