Shells? Who needs shells?

Exams all done now, so back to the fun of blogging about awesome animals!

So far, the molluscs we have looked at have had some sort of shell, but not all molluscs have taken the shelled path.

Today, and in the next post, we are going to meet some which prefer to be without shells, and are, in my opinion, some of the most beautiful molluscs around: So, without further ado, let me introduce you to todays topic: the nudibranch (from the Latin nudus meaning naked, and the Greek brankhia meaning gills, so literally, “naked gills”)

Berghia coerulescens, a species of nudibranch. Image from wikipedia

This group of animals has a whole lot of awesomeness going on, some of which we will cover today, and then it will spill over into the next post too!

For today, lets take a look at the one in the video, it is called Glaucus atlanticusm and the reason it is awesome for me, is that, despite being a squishy little sea-slug like thing, around 3cm long, it eats these:

Physalia physalis (Better known as the Portuguese Man O’ War) Image from wikipedia

Now, if there is one thing we know about Portuguese Man O’ War, it is that it has a very nasty sting, due to the trailing tentacles being full of cells which can fire toxic darts into its prey (or into an unsuspecting persons leg) (See link HERE for post about Man O’ War)

So how does Glaucus cope with these stings? There is a hypothesis that it releases mucus while eating the tentacles (Yes, because it is small, and the PMOW is much larger, it nibbles its way up the tentacles), which protects its insides from the stings, which can remain active for a period of time after the Man O’ War is dead.

To make it even cooler, it takes some of these stings, and uses them in its own defense. It goes a little something like this:

Glaucus eats the tentacle with the stinging nematocysts within it.  Some of these pass through digestion, and end up in growths on the outside of the animal, called cerata. These then become part of the animals defense systems, meaning it can fire them at any attackers.

It has primitive teeth (denticles) which it uses to chomp through its prey, but also to hang onto them

So, this is a fairly cool animal so far, but, it gets even more amazing when you find out some other details about it.

This lovely little animal floats upside down, so its top side is in the water, and its underside is at the surface.  It floats because it has a bubble of air in its stomach, but this means it has no way of steering, so it floats around as the winds or currents take it

In common with many fish which are found near the surface (Sharks for example), it uses a form of camouflage which is known as countershading

Its “top” (Which is in the water) is light silvery grey, so it is difficult to spot from below, whilst its “bottom” is a deeper blue, or blue and white, which helps it blend in with the water when seen from above.

I will leave this last image of Glaucus atlanticus for you, and next post we will look at some of the other animals in this family.

Glaucus Atlanticus. Image from EOL (Encylopedia of Life)

Sunday Documentary

Yes, yes, I know it is usually the Friday documentary, but, with everything getting back into a rhythm after New Year, I thought a nice Sunday relaxing one would be ideal.

This is a BBC one from late last year, about the life cycle of stars.  I started watching it last night, aiming to fall asleep to it, but had to stay awake to the end!

Astronomy is not usually something I post about, as it is not a subject I know much about, but, this one was fascinating!

Enjoy!

Back with bivalves…

So, its the new year now, I hope everyone had a nice new year, with not too many hangovers!

Last time, way back in October, I wrote about bivalves (HERE), and wanted to pick up where we left off, so today is about their vision and movement, as promised.

I am going to focus on scallops (Pectinidae) as they have both interesting eyes, and strange movement.

Let’s start out with the eyes.  You and me have two eyes, and this is a fairly common number of eyes to have, Scallops however, seem to be quite fond of eyes, usually having between 40 and 70, but they can have up to 100!

Eyes on a giant scallop, the dark blue dots along the rim of the shell. (Image from Wikipedia)

Now, not all eyes function the same way as ours do, we have already met organisms with eyespots, which are just a bunch of light sensitive cells able to distinguish between light and shade so the organism can move away from predators, or towards the light for photosynthesis. (HERE)

The eyes of scallops are what is known as concave mirror eyes.  These are “simple” eyes, which have a reflective layer at the back of the eye, which bounces light back onto the cells which are able to process the light. As they have so many eyes, positioned along the edge of their shell, they are able to follow an object as it moves past them, rather than having to move their eye to keep it in focus.  They also have two retina in each eye, one which responds to light, and one which responds to darkness.

Scallop Eye, showing the reflecting surface at the back which bounces light to the rods. (Image from rewiring-neuroscience.com)

I have been trying to find other diagrams showing this, and have come up with a couple of sites, depending on how techy of an explanation you want:

Opthobook.com has a very simple diagram (HERE), and a little video explaining the basics of eye variation (HERE).  For the more technical diagrams and explanations, this paper by M.F.Land (1965) is interesting (HERE), as well as this illustrative paper by Colicchia et al (2009)   (HERE). One final paper on comparative morphology (similarities and differences between the parts in different organisms) from Speiser & Johnson (2008) (HERE)

So, apart from having more eyes than that teacher at school who always spotted you chatting (Not that I was ever talking during class, of course!), what else is cool about these bivalves?

Well..I think sometimes a video says way more than I can by rambling, so lets take a look at how these scallops move:

This movement is done by using muscles at the back of the shell to open and close it, this pushes water out of the shell, and the scallop shoots off like one of those bottle rockets you make as a kid with fizzy drinks!  They can control the direction of the jet of water, so it is not a completely random motion.

 

 

Collated information on Ash dieback

I have been asked by a few people what they can do about the Ash dieback problem in the UK, and whilst I said yesterday that there was no official guidance for the general public yet, there are some informative documents prepared by the forestry commission.

Most of these are in the original post I made (HERE), but as they are at the end of a long post, I will put them up on here again, with the new information.

The Forestry Commission has published a visual guide to symptoms: Ash Dieback Disease

The Forestry Commission has also updated its guidance, with information that this is now a quarantine pest, and gives contact details if you think you have come across a site of infection. It also outlines how it is thought that the ancient woodlands have become infected. HERE

I used this Forestry Commission PDF in my original post, it is fairly easy to read and gives an overview: Chalara Fraxinea

The Woodland Trust has updated their guidance since I last read it, with the advice that any suspected infections should be reported at once: HERE

The Government has said that 50,000 trees have already been destroyed: (BBC source HERE)

EDIT for update: There is a website which will be launching Monday at ASHTAG and there will be a smartphone app launching Monday too.  I will post details of that when it arrives.

I mentioned on my fellow blogger Argylesocks post (HERE) that my concern is that with the onset of autumn, we will not know until next year what the extent of the infection is, as the fungus is now in the leaf litter over the winter.

I hope that these are isolated cases in woodlands, but I do not understand why it took from February til late September for this to get attention, or be publicised.

For my non-UK readers, I apologise for the UK-centric posting the last few days.  I am currently writing a post relating to a US issue, so will put that up over the soon.  I will be returning to my evolution based posting next week, but will keep putting up posts of interest to current environmental issues, to go a little more in depth into those.  If you have a story from anywhere relating to environmental or ecological issues which you would like to read a bit more in depth on, you can chuck me an email at squirrellyskeptic at gmail dot com.

Bivalves…Sucking and Sieving

Today we pick back up with our journey through evolution and natural history.

Last time we met the Spider Conch and today, we meet some of its relatives, the bivalves.   As the name suggests, these animals have two shells, and the ones you probably know best are oysters and clams.  Today I will write about the various feeding methods of these animals, and then the next post will be on movement and vision.

There are bivalves which resemble a 2-shelled animal we met earlier, the brachiopod (HERE), and so can be easily confused.

The first bivalve I would like you to meet today is Pedum spondyloideum, or the blue-lipped coral oyster. I am mostly showing you this one because I think it is spectacularly beautiful

Blue lipped coral oyster. Image from wikipedia

This is a teeny tiny scallop (or Pectinidae to give it the proper family name), which lives between corals.  These are in the same order as oysters (Ostreoida), so are related to them, but are in a different family to what me and you know as oysters.

There is an important differences between these, and the other molluscs we have met so far;

General anatomy of a bivalve. Image from Merriam-Webster

I mentioned before (HERE) that molluscs have a rather cool tongue called a radula, which is essentially lots of rows of tiny teeth that they use for scraping food off of surfaces.

If you look at the diagram above, there is no label saying “radula”.  This is because bivalves do not have one!  (They also do not have a head!) The image below shows the internal structure of a clam, and will help me explain what they do instead of scraping food:

Internal anatomy of a clam, image from Encyclopedia Britannica

In the image above, you can see something labelled the “incurrent siphon” and the “excurrent siphon”. As these animals breathe (by extracting oxygen from the water), they cause small currents around their gills.  These currents contain not just water, but yummy particles of food, which get moved towards the gills.  There are cilia (those small hair-like wavey things we have bumped into a lot) on the gills, which move these currents towards tiny pores.

If you take a peek at the top diagram, there is something labelled as the “labial palps”.  These, and the gills produce mucus (like you do when you have a cold), and this covers the food particles and they fall down towards the mouth where they are eaten.  So yes, they do eat food covered in snot!  Large particles like sand fall down into the mantle, and are carried out by cilia again (those little hairs just get everywhere don’t they?). Sometimes these particles get stuck in the mantle, and become irritating, at which point they become pearls (although not the sort we use for decoration, they are formed differently).

This method of feeding is known as filter feeding, and is how most bivalves eat. There are some species however, who obtain their food using a method known as deposit feeding.

This is thought to be the original form of feeding for bivalves.  Instead of the gills assisting in filtering food, they are used purely for breathing, whilst the labial palp has tubes attached to it which stick out to grab food from the sand or mud.  Food which is caught in currents moving towards the gills is also grabbed and eaten.

Still other species use symbiosis with small organisms (a lot like the corals do) whereby these organisms carry out photosynthesis and the bivalve gets most of its nutrition that way, while doing a small amount of filter feeding.  The most well known example of this is the giant clam, which is a huge animal, up to 1.2m or so long.

Giant clam, image from wikipedia

These animals are so huge that they are not able to move, so they sit on the sea floor, often in places like the Great Barrier Reef:

Giant clam on the Great Barrier Reef. Image from National Geographic

The bacteria, and dinoflagellates which I wrote about HERE obtain food by photosynthesis, like plants do, and then the Giant Clam feeds on the by-products produced, as shown in this video:

One final point about bivalve feeding.  Because they filter feed, they also perform a role in cleaning water, which benefits other organisms in their ecosystem, and mussels can be used as an indicator of how polluted a body of water is.  This is because as they feed, heavy metals and other pollutants are filtered, and build up within their bodies as they are unable to process them (like us with mercury etc).  So, if you measure the levels of these pollutants in mussels and other bivalves, it gives you an idea of how polluted the area is.

This video shows oysters and how they can function as filterers of water:

As mentioned in the video, populations of bivalves are decreasing in some areas, and this means they are less able to filter the water, which in turn has an impact on the other animals and plants in the ecosystem.

Friday Documentary

This weeks documentary is following up on a post I made earlier, where I showed some Bathymetry images HERE

This one is from Discovery Channel, and is called “Drain the Ocean”, and shows some very nice images of what the seafloor looks like, and some of the amazing creatures down there.  It also helps illustrate why I think we should investigate the ocean before we go into space.

Stalks, eyes and feet

Last time I wrote about life on Earth, we covered Cowries, and how they were used as currency.  We are staying within the molluscs still, as there are a couple more organisms I want to show you, to illustrate the different solutions that have been found to the same problems, namely feeding, and getting around.

Today, we are going to meet the cutely named Lambis lambis, or one of the Spider Conch molluscs, we may also meet some of its relatives.

Everyone knows what a conch shell looks like, it is the famous “Listen to the ocean in this” shell, and the ones you may have seen probably look like this:

A shell of Lobatas gigas, the Queen Conch. Image from wikipedia

This is the shell of Lambis lambis:

Lambis lambis shell. Image from gastropods.com

I have already covered how shells are formed, by secretions from the mantle, the fleshy part of the mollusc, so that is not what I am writing about today, although I am sure I will write a post about how the different shell shapes arise at some point!

The shell above has spikes all around it, and one long spike at the bottom.  The long spike at the bottom is where we will start today, because it is actually functional, it is called the Anterior siphon canal, and it provides support for an appendage called a siphon, which is an extension of the mantle.  This structure draws water into the cavity within the animal, and passes water over the gills, assisting in getting oxygen from the water, but also acting as a “nose” (Otherwise known as a chemoreceptor) to help the animal find food.

Lambis lambis is a herbivore, but this does not mean it is not guided towards food by what we would know as smells.

Here is what the external (outside the mantle cavity) body parts of Lambis lambis looks like:

Morphology of Lambis lambis. Image from University of Queensland

There are several features of this mollusc (and all conchs), which I want to elaborate a bit on, as I think they are fairly cool.

Firstly, the radula (the toothy tongue thing we met HERE), which is usually contained within the cavity, is actually on the end of the part labelled “proboscis”, so it has a stalk with its mouth on the end, and the radula too.

Here is a video of one chomping away happily on some algae, note the eyes which are also out on stalks, these are checking out the area for predators while it is eating, and if one is spotted, it pulls itself back inside its shell.  I personally like the eye stalks, as they look a little bit like cartoon alien eyes.

All true conchs are herbivores, (that is, ones which are members of the Strombidae family).  Other animals are known as conchs too, and not all these are herbivores, for example the crown conch (Melongena corona) feeds on oysters and clams by using its proboscis to pry open a bit of their shell and eat them from inside their shell.

The other very obvious structure in the morphology picture is the foot, and the part labelled “operculum”.  This is used to dig into the sediment to..well..propel the animal, or turn it over if it gets upside down.  I think this is easier to see than to explain, so here are two videos showing this in action:

Finally, here is a video showing this funky creature moving along a flat surface:

It is not just us humans who like these shells…hermit crabs also use them as mobile homes, as these two videos show:

I hope I have shown you some things so next time you see one of these pretty shells, you also think about the very cool animal which lives inside it.