The Armoured Brigade

Every time I lift the lid of our compost bins to dump another load of kitchen waste a horde of woodlice scurry away in all directions, so I thought I’d catch one and take a closer look under the microscope. It turned out to be the common shiny woodlouse Oniscus asellus. Woodlice are terrestrial crustaceans – relatives of crabs, prawns and lobsters but more closely related to marine isopod (meaning that all the legs are the same length) crustaceans like the one portrayed at http://beyondthehumaneye.blogspot.com/search/label/isopods

Michael Chinery notes in The Natural History of the Garden (Collins 1977) that woodlice have acquired at least 65 local names, including sow-bugs, tiggy-hogs, sink-lice, slaters and coffin-cutters.

Woodlouse senses are centred around the jointed antennae and simple eyes that have only about 25 individual ocelli – probably enough to detect light and shade and largish moving objects, but probably incapable of forming images with a very high degree or resolution.

The tail segment of a woodlouse is called the telson, flanked by two appendages called uropods , and its shape is often an important species identification feature.

All woodlice have only six pairs of legs in their infancy (when they’re known as mancas) and the full complement of seven pairs, visible here, only appears after their first moult, a day after they’re released from the brood pouch of their mother who carries them around. From below you can see the mouth at the head end, between the antennae .

Woodlice are omnivores but will eat other small animals if they can catch them, so have two pairs of jaws – crushers at the front and lethal-looking pointed ones behind.

The armour is an obvious adaptation to surviving terrestrial predators like spiders but the woodlouse’s main problem is keeping moist, because it obtains oxygen by diffusion over these lung plates at the tail end. Generations of schoolchildren have conducted simple experiments offering woodlice a choice of moist or dry environments but the outcome is never in doubt – in a dry environment a woodlouse will suffocate, for lack of dissolved and diffused oxygen.

Swallowtail Scales

Like most long-established university biology departments, Durham University School of Biological and Biomedical Sciences has substantial collections of specimens that have been donated over the years, including a large number of butterflies ........... which offer an opportunity to explore one the the microscopist’s favourite natural objects – butterfly wing scales. These are the wing scales of a swallowtail Papilio macheon which in this old pinned specimen can't match the vibrancy of colour in the living insect portrayed below, but they are still exquisite objects. If you look closely you can see that they vary in shape as well as colour ... notice how the edges of the red ones are more indented than the blue ones. The metallic colours in butterfly scales are the result of optical effects rather than pigments and are produced by ultra-fine grooves in the scales, where light penetrates to different depths and the reflected light waves interact to produce the electric blue interference colours.

Hydra

A while back I posted some pictures of Hydra viridis (see http://beyondthehumaneye.blogspot.com/search/label/Hydra) showing its remarkable ability to change shape. The pond that I regularly use for collecting small freshwater protists and invertebrates is currently teeming with these tentacled hunters, so I took the opportunity to shoot this short video sequence of this elastic animal in motion.

The Magic of Mushrooms

These are the radiating gills of the toadstool known as weeping widow Lacrymaria velutina. For more about this toadstool, visit http://cabinetofcuriosities-greenfingers.blogspot.com/2009/10/weeping-widow.html

The surface layer of the gills, known as the hymenium, produces thousands of spores, and for these to be successfully released into the airstream the gills must always be vertically aligned, so they are very sensitive to the force of gravity and quickly realign themselves if the stipe of the toadstool bends away from the vertical and tilts the cap.

Here, at a microscope magnification of x40 you can see the spores lining the surface of the gills....

...and here, at a magnification of x100 you can see that each is shaped like a small brownish-black lemon..

The spores are formed in groups of 4 on a cell called a basidium, attached to it by short stalks, seen here at a magnification of x400 under the microscope....

... and these appear to be two basidia where the spores are beginning to form. When they're mature and drop off they'll fall vertically down the gaps between those parallel, perfectly vertical gills and will be wafted away in the airstream

If you cut off a toadstool cap, turn it gill side down on a piece of paper of contrasting colour to the spores and leave it in a warm room where there are no draughts for a couple of hours, the falling spores will produce a beautiful spore print.....

...like this

Golden Algae

Forty years ago, when I was a university student, life – more specifically, cataloguing life – was relatively simple. Living organisms fell into one of five kingdoms: bacteria, plants, animals, fungi ................and protists, which were a rag-bag of mostly small organisms that no one knew enough about to be able to fit them into any of the other four categories. The science of classifying living organisms and understanding their evolutionary relationships has moved on, thanks to our ability to look at species’ relationships by comparing their DNA sequences.......which has made classifying life more intriguing and much more complicated. Those rag-bag protists are now subdivided by biologists into several kingdoms, one sub-division of which contains this lovely little organism, less than a millimetre long and called Dinobryon, which is known as a golden alga (or Chrysophyte). There are now thought to be about a thousand different Chrysophyte species, mostly single-celled, but this is one of the more complex types. They all have a golden yellow pigment called xanthophyll, which you can just about detect in the top photo of Dinobryon. This organism, which is common around pond and lake edges, consists of individual cells, each with a couple of lashing flagellae (which you can just about make out poking out of the uppermost 'vase' in the bottom photo), with each cell encased in a glassy vase and attached to a branching stem. The top photo is taken with polarised light, which generates the lurid interference colours, while the bottom one is taken with interference contrast microscopy, which gives better resolution of the individual cells in their ‘vases’.

Last of the Summer Whines

Ever had the experience where you get into bed, turn the light out, lay awake for a few minutes then pick up a high-pitched whining in the room – which can only be a mosquito? There’s no alternative but to get up and catch it, because there’s no possibility of going back to sleep in the knowledge that you might become a victim of one of these dipteran Draculas. So having caught it, I thought I’d have a quick look at it under the microscope – and it turned out to be an object of great beauty (double-click images for a better view).

The first thing that strikes you about a mosquito under the microscope is its wonderful eyes, sparkling with a kaleidoscope of iridescent colours, that provide wrap-around vision that’s even more complete than in dragonflies (seen above from above and below from below).

Then there are the antennae. This is a female (and therefore a blood-feeder – the males feed on plant juices), identifiable by those radio aerial-like antennae, which are bushier in males. Mosquitoes find their prey by vision, heat sensing, carbon dioxide sensing and scent, so if you are alive and breathing they’ll find you, even with the light out.

Then, of course, there’s that stiletto-like proboscis........

Seen here (above) in victim’s-eye view

With the lights going on earlier every night, more mosquitoes find their way into houses at this time of year – until the first frosts kill them off. I guess it’s one of the perils of having a garden pond that they can breed in, although water in a forgotten bucket in the corner of a yard will suit them just as well.

I’m not certain of the identify of this species but I think it’s Culex pipiens which according to Keith Snow’s Mosquitoes (Richmond Publishing Naturalists’ Handbooks No. 14) ‘feeds almost exclusively on birds’. So, maybe if I sleep with the budgie in the bedroom I’ll be OK..... although he adds, reassuringly, that adults hatching at this time of year feed exclusively on plant juices and enter buildings only to hibernate. That’s alright then. The budgie can relax.

Travelling light

This strange object, magnified one hundred times under the microscope, is a single seed of a common spotted orchid Dactylorhiza fuchsii. The lower photo shows a couple of the orchid’s seed capsules, with the dust-like seed laying on the paper below.

Unlike seeds of oak and horse chestnut, which send their seeds out into the world with a large food store surrounding the embryo, orchids have a much more minimalist approach to equipping their embryos for future survival. The orchid embryo – inside the darker object in the centre of the seed in the top photo – has no food store and is housed in a fragile papery coat, just one cell thick. The whole seed is no larger than a speck of dust and is so light that it can be swept up by air currents and wafted long distances – orchid seed could easily be blown across the English Channel, for example. So, unlike heavy seeds with a large food that are unlikey to disperse very far from the parent plant, orchid seeds are great travellers heading for random destinations and this accounts for their tendency to suddenly appear in unlikely places – lawns, roadside verges, industrial spoil tips, to name but a few. A large orchid flower spike will produce tens of thousands of these minute seeds, but only a tiny fraction will ever achieve the next critical step in the life cycle – landing on soil that contains the essential mycorrhizal fungus that will link up with the germinating seed and provide the embryo with the nutrients that it lacks until the seedling is large enough to produce leaves and survive on its own. After that the orchid's roots returns the favour by supplying its partner fungus with nutrients for the rest of the orchid's life. Early growth of the orchid seedling is slow and its leaves passes unnoticed - until it's large enough to produce a spectacular flower spike........and to read about the next step in the life cycle - pollination of the flowers - take a look at  http://cabinetofcuriosities-greenfingers.blogspot.com/search/label/orchids

The Most Numerous Multicellular Animals on Earth

Looking like a writhing python – but less than a millimetre long – this nematode worm came from water that I squeezed out of a patch of wet moss. It was photographed using polarised light, which generates the interference colours you can see here; the bottom image is nearer to the true appearance – most small nematodes are transparent.

Nematodes – commonly known as roundworms – are ubiquitous and there are thought to be about half a million species, which may well be a conservative estimate. Some live freely in the soil or in fresh or salt water, some are predators, many are parasites of animals and plants and several species cause serious damage to the roots of crop plants.

One microscopically-small species, called Phasmarhabditis hermaphrodita is a parasite of slugs and is commercially available in garden centres for killing these garden pests. Another species, a parasite of sperm whales, grows to a length of 9 metres. A square metre of fertile soil will contain several million nematodes. A single rotting apple was once found to contain 90,000 individuals.

One nematode species, called Caenorhabditis elegans, is used by biologists for investigating the way in which a complex animal develops from a single fertilised egg. Its transparency allows biologists to follow and map the fate of every cell in its body during its development. Amazingly, consignments of this species that were part of an experiment in space were recovered alive in the wreckage of the space shuttle Columbia, which disintegrated during re-entry into Earth’s atmosphere in 2003 (see http://news.bbc.co.uk/1/hi/sci/tech/2992123.stm)

Nudibranch Video

Here's a short video of Eubranchus, the nudibranch featured in the Seaweed Microcosm post, below. Note the tiny swimming crustacean that puts in a brief appearance, about 9 seconds in from the start.

For more on British species of nudibranch, visit http://www.seaslug.org.uk/nudibranchs/
where you can read all about them and access pictures of all the British species

For pictures of their exotic, gaudy tropical cousins, see
http://ngm.nationalgeographic.com/2008/06/nudibranchs/doubilet-photography

A Seaweed Microcosm...

If you want to explore exotic marine life in shallow seas you could jet off to a warm climate and scuba dive over a coral reef.......or you could just nip along to your nearest stretch of coastline (in our case Whitburn, near the mouth of the River Wear at Sunderland), collect a few small pieces of red seaweed and some seawater, take it home and examine it under the microscope. This (below) is the piece of seaweed in question, floating in a rockpool........

...and these (below) are just a few of the animals that I found living in it.....

First to break cover were these little crustaceans called isopods (which literally means 'equal legs' - all their legs are the same length - woodlice are terrestrial isopods). These are highly active little detritus feeders, breathing through gills at their tail end, and belong to a genus called Idotea.

...and they were swiftly followed by this little amphipod (meaning legs of two distinct lengths, long ones at the front, shorter at the back) which emerged from the waving weed fronds. Note the exquisite eyes of these little shrimp-like animals, known as gammarids...(more of those eyes in a future blog).....

Whereas isopods tend to be flattened dorsiventrally (i.e. top-to-bottom), amphipods tend to be flatted laterally (side-to-side).

It soon became apparent that the thicker parts of the seaweed were covered with colonies of another phylum of animals called bryozoans (literally 'moss-animals'). These live colonially, interconnected, in little calcareous compartments. In the case of this species, each individual's shell was performated with holes, like an exquisite microscopic ceramic vase. The magnification used here is roughly x50

Bryozoans (I haven't identified this species for certain yet, but I think it's Electra pilosa) feed by waving a tentacled arm called a lophophore, that looks a little like an old-fashioned wire egg whisk. You can see extended lophophores (rather indistinctly, I'm afraid) in the following couple of photos...........

The third phylum of animal to put in an appearance under the microscope (so far we've had crustaceans and bryozoans) was this exquite little sea slug, known as a nudibranch, which belongs to a genus called Eubranchus. Fully extended, this was about 3mm. long - a juvenile, that will probably grow to five or six times this size. Nudibranches are carnivores and it may well have been feeding on the lophophores of some of those bryozoans, although they typically feed on hydroid colonies (more about them in a future post). The back of this nudibranch is covered with strange, skittle shaped objects that wobble from side-to-side as it glides through the water. They're called cerata and are for gas exchange (nudibranch means 'naked gills' and that, in effect, is what these are). Remarkably, some species of nudibranch that feed on hydroids that are armed with stinging nematocysts (for more on nematocysts, see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/09/flower-animal.html) can incorporate the nematocysts of their prey into the body wall of their own cerata, to protect themselves. Nudibranches detect their prey using incredibly sensitive organs called rhinophores, which are the top pair of tentacles at the head end. The pictures below are all of the same animal, but the lighting varies.

So there you have it.........a whole community of weird and wonderful microscopic animals living in a single frond of red seaweed in a rockpool. I spent a couple of very enjoyable hours photographing these but I've not doubt that I could have spent another day, extracting more microscopic marine life, before I exhausted the possibilities of this microcosm. There's a short video of the nudibranch on a separate post, above this one.

You can find out more about all of these animals at http://www.marlin.ac.uk/species.php