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!


Shells and cash

The last post about Life on Earth was about Cowries, and I said that this time I would write about some of the ways they have been part of human society for a very long time.

Cowries as we saw, have very shiny, smooth shells, and this has led to them being used a currency throughout both ancient history, and modern times:

This is a species called Monetaria moneta, which looks like this:

Monetaria moneta (also called Cyprea moneta). Image from

As you may have noticed, the name of this animal sounds a lot like the word “money”, and in fact, this particular Cowry, and one or two other species, have been used historically as currency.

In China, they were used as currency from at least 1200 BC, and the Chinese Han character for money is the same character as for sea shell.

Cowrie shells from ca 900 BC, image from University of Maine

They were also used in Bengal in India as currency, and widely used throughout the Asia-Pacific region.

They were extensively used in the Maldives

Many African nations also used shells as currency, and during the slave trade era, Europeans would use cowrie shells in exchange for slaves, and there was a trade in cowrie shells between Asia and Europe for use in Africa.  Excavations of sites in the USA have uncovered cowrie shells in both the slave houses, and the houses of people who were involved in the slave trade (See further reading).

The use of shells as currency within Africa continued until the early 20th century, and in Ghana, some of their coins display cowrie shells as the image on one side.

20 Cedis coin from Ghana, image from the British Museum

Mondays post will be staying within Molluscs, but moving on to another amazing animal!

Further Reading:


Stop gap post while I am revising

As I mentioned last week, I have an exam on Wednesday, so am doing some final revision today and tomorrow, so no long posts til Wednesday.

On Wednesday I will be picking up with the story of life on earth, but until then, I wanted to share this documentary.

It is another BBC one (I have a thing for their awesome documentaries), and is on the topic of human evolution.

It is part of a series called “The Origins of Us”, and this episode is about our bones.

I hope you find it as interesting as I did.  Alice Roberts, the presenter is one of my favourite presenters of anthropology type documentaries.

Additional Sunday post

I do not usually post twice in one day, but this is far too cool to not post about:

There is a phenomena in nature known as gynandromorphy, which means that an organism displays both male and female characteristics.  This is different from hermaphroditism, which only refers to the sexual organs.

This appears to be mostly within insects, but some crustaceans have been found to have it too…This post is not about those, but these pictures of butterflies illustrate what it means (image from wikipedia):


That is interesting, I can hear you saying, but is it worth another post on a Sunday?

Well….you might not think that butterflies are cool enough for that, but, I think this is extra awesome:

Gynandromorphy in chickens. Image from

The REALLY cool thing about this is not just that it is a half male, half female chicken, but what this tells us about how chickens sexual characteristics are determined.

In humans, our male, or female characteristics are determined by our hormones when we hit puberty. There are variations within each sex, with some men being extremely hairy, others who are almost hairless, likewise with women, as well as our overall body shape.

In chickens (and possibly other birds) the sexual characteristics of the animal appears to be determined primarily by the chromosomes, instead of by hormones (so in humans, it would be XX or XY, there are variations on this, but that is a whole other post).

This image illustrates the differences between how chickens and humans develop sexual characteristics (Full link to article in references)

Differences in how mammals and chickens determine sexual characteristics. Image from Not Exactly Rocket Science

Bilateral Gynandromorphy is usually seen in insects, and is down to the way that their cells are determined during development, and I will try to explain. This is a bit complicated, but it is due to at which stage of division after fertilisation the gynandromorphy occurs.  Early on in development, between 8 and 64 cells into division (see references for info) if a chromosome (X or Y in humans) is left behind in the nucleus after division, this leads to a 50/50 bilateral gynandromorphy This is because early cell division determines the left and right sides of an organism.

Mosaic gynandromorphy occurs when a chromosome is left behind more than once during the developmental process.

The strange thing with birds appears to be that even though the gynandromorph chickens have a mix of chromosomes (Z or W in chickens) throughout their body (This was tested by tagging the chromosomes with a fluorescent molecule), one side had more female cells and one had more male cells.

Further testing showed another anomaly between birds and mammals.  In mammals, if you put an XY cell (male) into an XX environment (say, an ovary), the male cell will become a functioning part of that region, and act like the other cells around it in response to sex hormones, however, when this occurs in a bird, the cells continue their original sex designation.  So, when researchers put a lot of ZW (Female) cells into a ZZ environment, and subjected them to the hormones, the cells continued to produce female enzymes, and female structures.

As that was quite technical, I will end with some cool pictures of this, including one where the difference is not immediately obvious (all images from Dalton State College):

Butterfly bilateral gynandromorph

Bilateral Gynandromorph, slightly female on left back wing (the grey)

Moth (Malacosoma disstria) bilateral gynandromorph. The female half is the left side.


References/Further Reading









Friday Documentary

Apologies for the lack of posts this week, I am in  the middle of exams at the moment, but hope to have the 2nd post on brachiopods up at the weekend.

So, the documentary I have for you today is “How the earth made us” Episode 1: Deep Earth

I mentioned last week that I also love geology, this programme is about how the geological processes of the Earth have played a role in human civilisation throughout history.  Later episodes cover atmospheric conditions, climate, water and fire (volcanos).

For me, this series combines so many aspects of natural science that I love.  I wanted to go into Climate Science, but, Atmospheric Physics has a LOT of very scary maths in it, although I love the complexity…I have had to promise that I am not going to do stormchasing if I ever go to the USA, or at least dont tell people til after I do it!  I also have a crazy fascination with volcanos, and again, have been asked to not mention it if I am going clambering up the side of the volcano when I go travelling!

So, without further ado, Dr Iain Stewart with How the Earth made us. Enjoy!

From flat to round

Last time I said I would move on from worms today, but I thought that I should at least cover the creatures alive today that resemble those which made the fossil burrows I showed last time, and talk a bit about the links between flatworms, and the worms I will cover today, so one more post on worms (for now!)

So, without further ado (cue drum roll), let me introduce you to the subject of my post today, Nemertea (not to be confused with Nematodes, which are something completely different)

This, is a Nemertea (also known as Ribbon Worms):

Basiodiscus mexicanus. Image from UCMP Berkeley

Not all of them are this pretty, a lot of them are dull coloured, and some look like this:

Lineus longissimus, the Giant Ribbon Worm (or Bootlace Worm). Image from

The species shown above, Lineus longissimus is one of the longest creatures in the world! It is usually 5-15m long, but has been reported up to 60m long!  In contrast to its length, it is usually 5mm or so wide!

It is extremely common in the UK, and can be found wrapped around the bases of algae, or appearing to have tied itself in knots in shallow pools.

Another Lineus longissimus, this time curled up around itself. Image from MarLin (Marine Life Information Network)

This is a video of one moving around, so you can see how they move differently to the flatworms we looked at before

So, why am I showing you pictures of a slightly gross looking creature? (I cannot decide whether I find them fascinating or gross…maybe they can be both)

Well, this phylum of organisms used to be thought to be directly related to the flatworms we covered previously, but now they are thought to have arisen separately, whereas flatworms and Cnidaria are thought to have evolved from one ancestral species, with one line of descendants becoming the radial corals and jellyfish, and another heading off to become the flatworms, with the bilateral symmetry.

The latest research, looking at both genetics, and how cells develop within an organism (cell lineage) appears to show that they are not related to flatworms, but nevertheless, they have some similar features, as well as some which are more evolved, and one very unique feature.

Lets start with what they have in common, and work out from there.

They have bilateral symmetry, and a triploblast body (the three levels of cell within the body) both of which we first saw in the flatworms. (See here for the diagrams from that post)

They do not have a body cavity as such, so they are usually classified as acoelomate, but they have a special structure, which we will get to shortly, and so there is discussion about whether this is a body cavity or not.

The image below is a diagram of a Nemertea, and hopefully you can see the similarities to the cross section of the flatworms here

Nemertea cross sectional diagram. Image from North Carolina State University: Agriculture & Life Sciences

Here is a cross-section of a flatworm for easier comparison:

Acoelomate cross section. Image from University of Illinois Chicago

Nemertea also have the protonephridia that flatworm have (the flame cells which act as a simple excretory system), and they are able to reproduce both asexually, and sexually, also like the flatworms.

So, they have a few features in common, what do they have different?

Firstly, they have an exit to their digestive system (you can see this at the bottom of the picture above).  This means that solid waste does not exit through the same orifice as food goes in by.  They therefore have a complete digestive system, although still a very simple digestive system, without the liver, kidneys and other organs which we have.  Apart from the obvious yuk factor to only having one way in and out for food and waste, what is the advantage of having two ends to your digestive system?

Well, firstly, I do not think animals are bothered by the yuk factor in the way we are, but there is a very clear advantage to having both a mouth, and an anus.  The advantage is, simply, that you can eat and excrete simultaneously, which means having a complete digestive system is more efficient.

Another important development is that Nemerteans have what is known as a closed loop blood-vascular system.  In flatworms, oxygen and other nutrients are distributed by diffusion (remember how they had a digestive system spread all through their body).  Nemerteans have dedicated blood vessels to transport nutrients around their systems.

Nemertean Circulatory System. Image from North Carolina State University

Finally, I said that Nemerteans have a unique feature, and now I will see if I can explain this, because it is very weird, and very cool, and quite gross at the same time.

Nemerteans have something called an eversible proboscis. Eversible means something that can be turned inside out, and a proboscis is something which sticks out from a head, so an elephant has a proboscis, usually called its trunk.  Butterflies have a proboscis, it is the straw-like organ similar to a tongue which they stick into flowers to suck up nectar.

So, Nemerteans have a body part which is turned inside out, and comes from their head….sounds weird, but what exactly does it mean?  In the image below, the proboscis is shown inside the body, and is the dark line running the length of the body.

Diagram showing the proboscis of a Nemertea, running the length of the body. Image from

This proboscis lies within a cavity in the body, above the digestive cavity, known as the rhynchocoel.  It is because of this cavity that the discussion arises about whether Nemerteans are acoelomate or coelomate.

The proboscis itself is a hollow tube of muscle, and the image below shows it being stored in the body, and after being everted (turned inside out)

Proboscis of a Nemertean. Image from Cabrillo College

So, how does the proboscis get from the inside to the outside, and what is the point of it?

There is fluid in the cavity where the proboscis lies, and when the animal runs into prey (quite literally sometimes, as some species are not very good at finding their way around), muscles at the back of the cavity contract, and this causes an increase in pressure in the cavity, which forces the proboscis out of the body.  There is a spike on the end of the proboscis, and this is stabbed into the prey, whilst the proboscis itself coils around the prey.

The proboscis also has toxic slime (mucus) on it, and this goes into the prey.  Some of these toxins are the same as in the puffer fish (tetrodotoxin), so very effective!  The proboscis is then pulled back into the body, bringing the prey with it, this brings it towards the mouth (the opening under the head), and it is then swallowed whole.

I think the description might seem a bit confusing, so this video hopefully makes it clearer (also take a look at the length of the proboscis relative to the length of the animal).


I did say I thought they were both gross and fascinating…

Next post will be away from worms, I promise!

References and further reading:

Phylogenetic position of Nemertea derived from Phylogenomic Data -Struck & Fisse 2008:

Progress in Nemertean Biology: Development and Biology – Turbeville 2002

Information on Cell Lineage – Chisholm 2001: