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 x50Bryozoans (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

Fatal Attraction

As the nights draw in and the lights go on earlier each evening, increasing numbers of insects are drawn to the light at windows. The local spider population seems to be aware of this, judging by the network of webs spun across our windows each morning, often capturing this little fly, known as an owl midge.

Owl midges, sometimes called moth flies, are only about 3-4mm. long so don’t make much of a meal for a spider. Their single pair of broad ‘delta’ wings, reminiscent of those of a moth and fringed with hairs, are a distinctive feature, but they seem to spend as much time running around on vegetation as in flying.

These flies, whose larvae feed on decaying vegetation in damp places, have a distinctive hump-backed profile and are covered in rosettes of hairs, especially on the thorax which, when viewed from above, is supposed to have a fanciful resemblance to an owl’s face, between partially outstretched wings.

You can find these little flies all-year-round but in spring they seem to be attracted to wild arum Arum maculatum flowers (below)

Open up the chamber at the base of the Arum inflorescence where the flies are imprisoned by this plant and you’ll often find owl midges inside.

Scarlet wild arum fruits (below), which are a conspicuous feature of hedgerows and woodland edges at this time of year, are often the work of this minute pollinator.

Mussels.....Alive, Alive O!

Mussels Mytilis edulis spend their infancy in the plankton, as swimming veliger larvae (see http://oceanexplorer.noaa.gov/explorations/02mexico/background/mussels/media/bivalve_veliger.html), but then they settle on a substrate and begin a more sedentary life. This (above, x40) is a minute juvenile mussel that anchored itself to a green seaweed frond in a rockpool on a Northumberland beach (Warkworth).


In this slightly older example the tiny shell it developed as a planktonic larva is at its base (pale brown) and since it settled it has produced the vestiges of its future shell, but it has yet to develop much pigmentation, so at this stage the shell is still transparent, creating some interesting possibilities for examining its internal structure under the microscope.... and here (above, x100) you can just make out the comb-like gills inside the pair of shells - they are the row of downward-pointing teeth running along the length of the shell, from bottom left to top right. Take a look at the two videos at the bottom of this post and you'll see how these gills work - they're lined with tiny beating hairs (cilia) that create a powerful current of water over the gills, that extract oxygen and also capture tiny food particles that are wafted into the animal's digestive tract. Somehow (and no one yet knows how) the animal can separate organic food particles from indigestible inorganic grit and debris that is expelled. Even a tiny mussel like this can process a large volume of seawater, thanks to these frantically beating rows of cilia on the gills, here shown in the videos at the bottom of this post at magnifications of x100 and x200.

This still image (above) shows a mussel at a slightly later stage (about 3mm. long), when the shell valves have become pigmented and have lost their transparency. Between the gaping shell valves you can just make out the inhalent and exhalent ports where water is wafted in and squirted out by the ciliary current.

In this side view of the same juvenile mussel (above), the original transparent shell valves of the infant mussel are visible, attached to the pigmented shell that has subsequently developed. They mark the point where the two shell vales are hinged together.

Mussels often settle at very high densities - like these, several months older than the microscopic examples depicted above, packed shoulder-to-shoulder on a rocky outcrop on the shore at Warkworth in Northumberland. Mussels attach themselves to their substrate with a protein glue that sets underwater, to form extremely strong byssus threats that prevent the animal being dislodged, even when pounded by breaking waves in the full fury of a storm. There is a lot of scientific research going on into this protein, for potential medical use – as a glue for repairing broken human bones or in dentistry (see http://www.asknature.org/strategy/4f16bf8321224ea8b146277ccdace9690). For more on the marine biology of mussels, see http://www.marlin.ac.uk/speciesfullreview.php?speciesID=3848

Sea Gooseberry videos

Prey's-eye view of a sea gooseberry. Unlike sea anemones and jellyfish, which have stinging tentacles, those of sea gooseberries are sticky

Higher magnification movie of the propulsion system - hairs (cilia) that are fused into eight rows of saw-tooth combs. Each row can be stopped and started independently, giving very precise directional control. The beating combs create flickering interference colours.

Side view of a sea gooseberry swimming

The long, trailing tentacles dangle below the animal. Swimming into a swarm of sea gooseberries, some of which are large enough to catch small fish, would be a fatal mistake for any small planktonic animal.

These are some videos of the sea gooseberries that I caught yesterday and posted at http://beyondthehumaneye.blogspot.com/2009/09/sea-gooseberries.html

and

http://cabinetofcuriosities-greenfingers.blogspot.com/

You can read more about these remarkable animals at http://www.ucmp.berkeley.edu/cnidaria/ctenophora.html

and

http://faculty.washington.edu/cemills/Ctenophores.html

Sea Gooseberries

Eight rows of beating hairs, arranged like rows of combs,

propel comb jellies in the surface plankton

The microscopic beating hairs create green, orange and blue

interference colours that shimmer across the animal's surface

At higher magnification you can see the combs of hairs, that beat in synchrony.

A tentacle is trailing off to the left

Here tentacles of two sea gooseberries have become temporarily entangled

Prey's eye view of a sea gooseberry, seen from below with tentacles extended

Another view from below. Sea gooseberries spend their lives in the few centimetres below the surface of the ocean, drifting in the plankton

I collected these sea gooseberries after they were washed up by the incoming tide at Warkworth on the Northumberland coast this afternoon (see http://cabinetofcuriosities-greenfingers.blogspot.com/2009/09/sea-gooseberries.html ). Stranded on the sand, they look like minute glistening blobs of jelly, but suspended in water they’re revealed as exquisite planktonic animals, as transparent as glass. The largest is about 5mm. in diameter. These are predators, with eight rows of beating hairs that help them to hold station in the water column and long, dangling tentacles that snare their prey – other planktonic animals. When the rows of hairs - which are arranged like minute combs – beat in rhythm they create electric green, orange and blue interference colours that light up their transparent bodies. They also have one final trick – which I couldn’t photograph. When you turn the light off two minute green bioluminescent organs inside the animal glow in the dark. They probably act as lures, helping the sea gooseberry snare its prey. I've posted videos of these animals under the microscope at http://beyondthehumaneye.blogspot.com/2009/09/sea-gooseberry-videos.html

Well-Travelled Fungus

Groundsel cluster cup fungus, looking like minute tarts, on an infected groundsel leaf surface. The spores are produced in vast numbers in the centre of each cup. Each cluster cup is about as large as a full stop (period) on your monitor screen. A minute larva of a fly is crawling across the leaf surface, just to the right of the open cups, and may have been feeding on the fungal spores. In the bottom right corner (below) cluster cups are just forcing their way to the leaf surface, ready to open.

Cluster cups erupting from an infected, swollen stem. Infected stems often develop purple pigmentation and become distorted. Heavy infestations can be fatal.

 

Above: A vertical section through a cluster cup on a leaf surface, x100, showing the chains of spores that are formed in the centre of each cup.  

Below: Although apparently heathy, this plant is infected with the fungus, just visible on the surface of the bottom leaf on the left in the middle of the picture 

Take a look at the weed groundsel Senecio vulgaris stems and leaves in autumn and you’ll often find that they’re swollen and distorted, with a patches of a yellow fungus erupting from their surface. The infection is a fungus called groundsel clustercup Puccinia lagonophorae, which has an interesting history, having travelled more than half-way round the world since the mid-20th. century. Migratory people tend to take weeds, as well as their crops, with them and groundsel was accidentally taken to Australia by early settlers from Britain, where it became infected with this fungus which is native to Australia. Some clustercup-infected groundsel made the return journey and the fungus arrived in Europe in 1961, where it has been spreading ever since. More recently, within the last decade, the fungus crossed the Atlantic and has begun infecting groundsel that had been taken there by early European settlers. The Americans are not altogether sorry that the fungus has arrived, because it weakens groundsel and might offer a means of biological control of this invasive weed. In the photographs you can see the flower-like spore cups, called aecia, that produce the infective golden yellow spores. In the vertical section through one of these cups (second photo from bottom) you can see the chains of spores budding off from the fungal hyphae.

Psychedelic Citrus

Above and top: spheres of citrus oil trapped

amongst the cells in orange peel x100

Vertical section through an oil gland in orange peel.

In the intact gland oil accumulates in the central cavity

and leaks out onto the surface of the fruit via a minute pore. Polarised light. x40

The shiny flash-shaped patches in the surface of the orange peel,above the white pith, are the oil glands full of intensely fragrant oil.

Pleasure from eating comes from a combination of the taste and smell of food , and when it comes to oranges these two factors are subtly different but complementary. The distinctive taste comes from the soft acidic flesh, which only has a relatively faint aroma compared with the intensely fragrant peel. To see what I mean sniff an orange segment, then compare its scent with the rind by holding a small piece of peel under your nose, surface towards you and squeezing the peel hard. You’ll feel the citrus oils that are squirted from the flesh against your top lip and will experience a very strong citrus smell. The citrus oils are concentrated in hundreds of microscopic glands under those tiny dimples that cover the orange skin. This lunchtime I cut a thin vertical sliver through the peel of my orange and took a look at it under polarised light, which creates the psychedelic interference colours that you can see in the top three images. The central cavity of the oil gland is where the citrus oil accumulates as the fruit grows, but it leaked away when I cut the sliver of peel with a razor blade. The top two pictures show the residual citrus oil droplets that were trapped in the peel sliver, looking like those globules in 1960s lava lamps. We throw the fragrant but inedible orange peel away, but citrus oils have many commercial applications, in food flavourings and in the fragrance industry. In nature, their role is probably as a defence against insects that might otherwise burrow into the fruit. You can read more about citrus oils at http://www.aromaticplantproject.com/articles_archive/citrus_essential_oils.html