Another Living Jewel

My last post showed a jewel-like case made by a single-celled amoeba. This one shows the remarkable case made by a marine worm.  We found this little tapered tube, about 5 cm. long, on the sandy beach at Warkworth in Northumberland this afternoon. It was made by a worm called Pectinaria koreni and when the animal inside is alive only the last few millimetres of the narrow end of the tube protrudes above the sand. The worm lives head-down in the sand, drawing in a current of water through the narrow end of the tube.

You can see the dark zone at the narrow end here - that's the bit that normally protrudes above the sand. The tube is made up of hundreds of sand grains and minute shell fragments, selected for smoothness inside and outside the tube and ....

.... neatly fitted together with a degree of precision that a stonemason would envy....

 

.... and although the tube is only one sand grain thick it's remarkably strong. That's because....

... the worm secretes a form of cement that glues the grains together, like mortar in a wall ......

.... as you can see here at higher magnification.

A pair would make rather fine ear-rings, provided the wearer didn't have any qualms about wearing jewellery made by a worm rather than by a jeweller.

You can see a picture of the worm here.

A Living Jewel

This exquisite object, nature's equivalent of a Fabergé egg but only about one tenth of a millimetre long, is a testate rhizopod - a species of amoeba that lives inside a balloon-shaped shell. Testate rhizopods either secrete their shells or they cement minute sand grains together to create one. When you think about it, that's a remarkable feat of construction for one of the lowest forms of life that, superficially, is little more than a slithering blob of cytoplasm. You can see some more examples here. Testate rhizopds that assemble a shell from sand grains are often assigned to the genus Difflugia and scores of 'species' have been described, based on the components and construction of their shell, although it's not clear to what extent these are really distinct 'species'. You can download a guide to identification and where to find them here. I found this specimen when I was screening a sample of water from amongst the waterweeds on the edge of a pond in Durham. I have to admit that the image above has involved a bit of optical trickery because......... 

... this is what I saw when I first examined the organism under normal bright field microscopy, revealing the translucent quartz grains that formed its case. Switching to dark field microscopy....

... where the image is formed from light diffracted by the translucent grains showed them in a new light. But it was only when I switched to polarised light microscopy, which reveals the interference colours formed by the birefringent grains, that the ultimate beauty of this tiny organism's case was revealed.

Jewellery on a microscopic scale...

Cyclops with Hitch-hikers

This little crustacean, about a millimetre long, is Cyclops, with a single red eye-spot in the centre of its head - a minute freshwater counterpart of the monocular monster of Greek mythology. My garden pond is swarming with them at present, even though the ice has barely thawed. If you take a close look at the top end of the tail, near the body, you can just make out clusters of short-stalked objects attached to the animal's exoskeleton. At higher magnification these turn out to be....

.......... Vorticellids - single celled protists with beating cilia around their mouth, creating a whirlpool current that sucks in foot particles. You can see a movie of Vorticella in action here. At even higher magnification..........

..you can see their cilia and the contractile vacuoles that they use to expel waste (double-click for a larger image). Vorticellids attach themselves to all sorts of small pond animals, hitching a ride.

As Jonathan Swift (1677-1745)  noted,

So, naturalists observe, a flea

Has smaller fleas that on him prey;

And these have smaller still to bite ’em;

And so proceed ad infinitum.

Knapweed nemesis...

This little barrel-shaped grub is the larval stage of a picture-winged fly Urophora jaceana, which spends the winter hidden deep inside the seed head of a knapweed plant. Late last summer the adult female fly would have....

...laid its eggs in a knapweed flower like this and since then the larvae have been feeding on the developing seeds inside. The larvae induce the formation of a hard, woody gall inside the seedhead so if you.....

... gently squeeze a seed head like this one you'll find some that are squashy and some that have a hard lump inside, which is the Urophora gall. If you carefully cut the gall open ...

.. the larvae are revealed in their chamber inside. Here, a fully-fed larva is on the right and one that has developed into a pupa is on the left.

By this stage most of the seeds (on the right here) have usually been eaten but sometimes you'll find a few survivors.

This pupa will hatch out early this summer, just in time to lay eggs in a new crop of knapweed flower buds.

European knapweed species were taken to North America and have since become noxious weeds there. In an attempt to control them Urophora species, which can have a major impact on the plants' reproductive capacity, were introduced too as a biological control agent. The gall fly hasn't  halted the spread of the knapweed but it has provided a nourishing food supply for North American deer mice in winter, to the extent that in Montana there has been a population explosion of well-fed deer mice. When the ground is covered in snow they climb the knapweed stalks and eat the Urophora grubs. The sudden population increase is causing some concern since they carry hantavirus, which is present in their urine and can be transmitted to humans - an unexpected consequence of a chain of events that started with Europeans carrying knapweed to the United States. It's also another example of how biological control techniques can have broader consequences than intended by those who introduced the biological control agents. Curiously, I don't think our local native field mice in Britain have yet discovered that there's a rich source of animal protein in the gall-fly infested knapweed seed heads - after the recent heavy snowfalls I couldn't find any evidence of field mice having foraged on knapweed seed heads around here. Maybe deer mice are just a bit smarter...........

Nature's Pole-vaulter

This engaging little animal is a springtail – a member of an ancient lineage of six-legged arthropods called the Collembola, that resemble insects but differ in having internal rather than external mouthparts. Springtails are everywhere and most live on detritus. This one, which was about half a millimetre long and just visible to the naked eye - and which I think belongs to a genus called Deuterosminthurus - was rambling over the surface of the soil in a flower pot in our conservatory. Lift up the lid of your compost bin and you’ll often see swarms of them scuttling around on the surface ........ and if you disturb them they leap into the air, using.......

... a specialised structure called a furcula attached to their tail and folded underneath the springtail. You can just see it in this photo, behind the set of legs closest to the camera, pointing towards the head. Springtails use their furcula much in the same way as a pole-vaulter uses their pole. It’s under permanent tension and when the animal releases it from the catch that holds it in place it flicks down instantaneously, catapaulting the animal into the air and away from danger. The tip of the furcula in this species is .....

forked – as you can see here, where it appears to be using it to scratch its mouth.

While I watched this particular animal gave itself a pedicure and rather remarkably you can see that it’s got all three legs on one side off the ground.... so why doesn’t it fall over? If your dog did that, lifting both legs on the same side, it would roll over.... but maybe if it had six-legs instead of four it wouldn't because.....

...... as you can see when the springtail tilted itself the other way and lifted all three left-hand legs off the ground, the right hand legs are acting like a tripod with feet evenly spaced at the points of a triangle.

There are numerous species of springtails that are fascinating to study, if you have a microscope. You can find a wonderful photoguide to many of the species in Britain here and you can see a wonderful movie, from David Attenborough's Life in the Undergrowth at http://www.youtube.com/watch?v=OwOL-MHcQ1w showing these pole-vaulters in action.

Some like it hot: the Firebrat Thermobia domestica

One of the pleasures of being a professional biologist is that people often bring things for me to identify that I might otherwise never see. This strange insect – a firebrat Thermobia domestica – arrived today in a jam jar. It was a little tattered – with a couple of broken tail spines and a damaged antenna, but still very much alive.

 

Firebrats are relatives of the much more familiar silverfish – primitive wingless insects belonging to an order known as the thysanura and commonly known as bristle-tails. One of their most curious features is that they’re totally covered with overlapping, iridescent scales rather like the scales on a butterfly’s wing.

Unlike silverfish, which tend to live in damp places like the space under baths and cupboards under stairs, firebrats can only survive in warm places and are very drought tolerant. They thrive at temperatures of around 37C and were once common inhabitants of crevices around bread ovens in bakeries. The name firebrat refers to the fact that crevices around hearths of open fires also suited then very well.

Thysanura, the name of the order to which bristletails belong, is derived from two Greek words meaning ‘fringed tail’ and you can see here the fringes on the central tail filament and its two flanking cerci. A large specimen is about a centimetre long, including the tail filament.

As soon as the insect was placed under the warm light of a microscope it perked up and demonstrated its ability to move like greased lightning. I’d rather like to get hold of a few more specimens, because I came across this fascinating description of their courtship in a book called The Living House by George Ordish, published back in 1960. “Firebrats have a curious courtship procedure”, he writes, ”not unlike that of the display of birds. The male dances in circles around the female and repeatedly touches her with his antennae. The actual mating is somewhat akin to that of spiders in that the male deposits a sperm bag in front of the female and then retires, while the female herself undertakes the necessary movements to absorb it, if she so desires”.

The Hidden Secrets of Ferns

Fern spores are produced in vast numbers on the understide of fern fronds during the summer months. For details of how they are catapaulted into the airstream, take a look at http://beyondthehumaneye.blogspot.com/2009/07/natures-siege-catapults.html

Each spore is less than a hundredth of a millimetre in diameter and can be carried vast distances on air currents. Ferns are often the first plants to colonise bare volcanic lava flows, carried there as spores on the wind.

All they need for germination is water and mineral salts. They swell, the brown spore case splits open and a hair-like rhizoid emerges, that anchors the spore to its substrate. Then a green photosynthetic cell emerges from the spore.

The photosynthetic cell divides longitudinally, forming the beginnings of a short chain of cells. The green blobs in the cells are chloroplasts.

The chain of cells continues to elongate until it reaches 6-7 cells long, dividing longitudinally and producing more rhizoids to anchor itself more firmly. At this stage the remains of the brown spore coat is still visible. During this stage of development the plant must be constantly wet - even a short period of drought will be fatal. I sowed these spores in September, so they've taken about four months to reach this stage, where they appear to the naked eye as a green film covering wet soil.

This is the next crucial stage in development and is about a millimetre long. The tip cell of the thread now begins to divide laterally and longitudinally, forming a flat plate of cells ....

... here you can see this two-dimensional tip division at higher magnification. The flat plate of cells that develops from this is known as the prothallus, and this is where fern sexual reproduction takes place..

These are two fully developed prothalli, each about 5mm. in diameter and only one cell thick. They are incredibly delicate and must remain permanently wet to survive. At this stage they are about six months old and male and female reproductive cells form on their surface.

These are the male antherozoids, enclosed in a structure called the antheridium. When this bursts the antherozoids are released in swarms and swim, propelled by lashing flagellae, like tiny spinning tops in the surface film of water, in search of a female egg cell inside a long-necked structure called an archegonium, which you can see here. After a successful fertilisation an embryo deveops which ultimately grows into a .......

.......new miniature fern plant. In the early stages, as seen here, it's still attached to the prothallus formed by the germinated spore but that soon withers away and the new fern grows by producing a series of ever-larger fronds. It usually takes about a year after sowing to reach this stage.

Provided you have the required patience, ferns are not difficult to grow from spores. For detailed instructions, visit http://website.lineone.net/~margaret_cole/SFG7/growing%20ferns.htm

   

For more on the fascinating world of ferns, visit http://www.nhm.ac.uk/hosted_sites/bps/

High-density Housing (for Bryozoans)

This beautifully geometric piece of natural architecture is produced by the animal commonly called the sea-mat and scientifically known as a bryozoan (which means 'moss-animal'). This particular species is Membranipora membranacea and I picked it up yesterday, in a rock-pool on the seashore at Seaburn, near Sunderland.

Membranipora forms extensive, fast-growing colonies resembling a lacy mat, that spread over the surface of kelp fronds. It's common on all coasts around Britain and has been introduced into shallow seas in other parts of the world where there is some concern that its rapid rate of growth could suppress the reproduction of some marine algae.

Each calcareous compartment, secreted by the animal inside, contains an individual animal (zooid) that extends a feeding arm called a lophophore, for filtering out plankton.

The zooids retract into a tube within their walled enclosure at the slighest hint of danger but when they're all extended they resemble a garden of transparent flowers, gently waving their arms..

Each walled enclosure has a small tower at the junction with its neighbours' walls and ......

....there are often gaps in the walls, which give the colony a degree of flexibility as the supporting kelp frond bends in the sea currents. The gaps tend to be most conspicuous in older sections of the colony.

There are at least two kinds of zooid - the flower-shaped feeding lophophores and these translucent cylindrical forms.

I'm not sure what their function is but my guess is that they provide additional surface area for oxygen uptake or maybe waste disposal.

You can find out more about bryozoans here or take a look for yourself - these are low-power micrographs (maximum magnification x50) but you can see the living zooids with a hand lens if you put a piece of the colony in a shallow dish of seawater. You can find them all year-round and fine specimens are often attached to kelps that are washed up on beaches after storms.

The Ultimate Solar Cells

These green blobs are chloroplasts - in this instance packed inside the cells of a moss leaf and magnified around 400 times - upon which our collective future depends. Using only energy from sunlight, water and carbon dioxide from the atmosphere, they produce the oxygen we breathe, control the climate by removing carbon dioxide from the atmosphere and, directly or indirectly via plants and animals, produce all the food we eat. Currently 6.3 billion of us depend on them for our survival. By 2050 9 billion of us will need their services. Maximum respect for plants, then..... and, more precisely (see Psi Wavefunction's comment), chlorophyll, in all of its manefestations, wherever it occurs