And another one...

Okay, this might be a tricky one if you are unsure, but it could be a ton of fun!

Pick your favourite dinosaur, find out what species it was likely to eat, and what species were likely to eat it, and make a food web for its ecosystem.

Another exercise

I still feel it is best to keep away from the computer as much as I can for a while, so we might keep letting you do the fun writing for some days. (Feel free to share if you want to! That would be super-cool!!)

Today, I thought you could find the closest fossil site to where you live, and do some research into the time and environment, as well as what sort of fossils you might expect to find there. Maybe you even want to go out and look for some! 

A hint is to look in brochures for sites of geotourism, or maybe websites for Sites of Special Scientific Interest. Google!

Exercise

Because my eyes have started to hurt when I'm on the computer too much lately, I thought this time better not write a long entry. Also, maybe a break from the group descriptions could be nice. So, this time, I will just give a question, and I encourage you to write down as much as you can think of. A mind map usually helps ideas flow, so if you are stuck, maybe try that out too!

What do you think the world would have been like today, if the dinosaurs had not been extinct 65 million years ago? 

Basic groups 5: Animals II

In this post, we will cover a two more worm phyla. In subsequent entries, we will see more miscellaneous ‘lower’ invertebrates, before moving on to the ‘higher’ invertebrates, and finally to the chordates.  

Annelida, the ringworms, is a group of advanced worms (but, worms being fairly primitive, they are still relatively simple animals). They are coelomate triploblasts with bilateral symmetry (if these terms are unfamiliar, please see Part 4). The coelom (body cavity) is filled with fluid, which acts as a skeleton: as muscles work against the incompressible fluid, the body changes shape, creating movement in relation to the environment. This type of skeleton is termed a hydrostatic skeleton, and is present in several animal phyla. The specific movements vary. The video below shows how a typical annelid (and earthworm) moves forward.

Locomotion of an earthworm. By compressing the sides of the coelom (using muscles circulating across the long axis), it expands in length; by relaxing the side pressure (and contraction of muscles running long the length of the worm), the worm shortens; the front anchors into the substrate between lengthening and shortening, which makes the annelid’s net movement forward.

This is indeed a very primitive way of moving, but I personally find it fascinating in its simplicity and apparent ingenuity.

The undulating contraction series that occurs during locomotion (peristaltic movement, in formal jargon) is made possible by the segmented body. The worm is divided into multiple segments, which contain repeated sets of certain organs and muscles. The circular muscles that create the contraction wave are repeated in each segment, and so are the muscles running along the long axis, which help pulling the animal together. The excretory organs, called nephridia (which are not much like our kidneys), are also repeated, in pairs. Extensions of the semi-centralised nervous system also spread out in each segment.  The blood flow of the circulatory system (internal transport of nutrients and gases, such as oxygen and carbon dioxide) is also organised with regard to the segments, while being connected throughout the animal.

Annelids also show a greater degree of cephalisation, compared to the more primitive platyhelminths (flatworms). In the front end, there is a concentration of nerve cells, a set of five ‘hearts’ (rings that function as pumps to make the blood flow through the vessels), a pharynx and an oesophagus, and specialised gut sections: a crop (for brief storage) and a gizzard (muscular section that can grind food material before passing it on to the intestines).

The leeches (Hirudinea) are a bit of an exception: their heads are simplified and modified into a blood-sucking device we are familiar with. They can use their suckers in front and back (the hind sucker is always larger) to move on a hard substrate, or swim around in water.

Unlike the poriferans, cnidarians and platyhelminths, the annelids are too complex to regenerate with such ease, although some are capable of recovering lost parts to some extent.

An annelid (member of the group Polychaeta), perhaps less familiar than the typical, 
bristle-less earthworm (Oligochaeta). Image from http://www.mediahex.com/Polychaete

A leech. Image from http://bio1151.nicerweb.com/Locked/media/ch33/leech.html

Nematoda is another group of worms, and, like the platyhelminths, they are mostly parasitic. They are pseudocoelomate, an intermediate between the acoelomate platyhelminths and the coelomate annelids (although they belong to different evolutionary groups). The nematodes are triploblastic, with a bilateral symmetry, but they are not segmented.

Perhaps surprisingly, the nematodes are actually more closely related to arthropods (insects, spiders, crustaceans, etc.) than to any worm phylum. (NB: once we have gone through the animal phyla, I will spend some time explaining how they are related, and hopefully it will create a clear picture of how the animals have evolved.) This is because they both have a hard external cuticle, a protective, multi-layered structure, composed primarily of collagen (a protein, common in connective tissues of many animals) in nematodes, and chitin (a sugar) in arthropods. The cuticle is smooth, and the nematodes have no obvious head, so there are basically no external features that characterise them – but, perhaps the lack of features itself is useful for recognising them!

A nematode. Image from http://www.flickr.com/photos/slider5/418135144/

The cuticle is rigid, and cannot grow together with the rest of the nematode, so it needs to moult – i.e. shed its cuticle and grow a new one that fits – just like arthropods; some snakes are also known to shed their skin.

This cuticle is layered in a way that makes it bendy, although inelastic, enabling the nematode to move. The nematodes only have muscles that run along the long axis, so they can only move by wriggling… *hrrmm* sorry, I should say waves of undulatory movement. A curious thing about nematodes is that they wriggle up to down, but swim on their side, so it looks like they wriggle sideways, like snakes.

Movement is possible thanks to the hydrostatic skeleton. This, coupled with the hard external cuticle, means that the nematode has high internal pressure. This has two important conesquences: first, the nematode requires a muscular pharynx in order to swallow food, because the intestines are under such pressure; second, if the cuticle breaks by accident, the nematode more or less explodes and dies. Therefore, the Nematoda does not possess any regenerative abilities, since damage basically leads to instant death.

Basic groups 4: Animals I

Now we finally got to the animals, the perhaps most interesting organisms to most of us. Animalia includes basically anything that is large and moves around, but also many organisms that are too tiny to sport with the unaided eye, and others that live attached to a substrate, usually the sea floor or a coral reef base.

In this post, we will briefly eyeball the more primitive phyla of kingdom Animalia. (If you are unfamiliar with the term phylum, and perhaps other taxonomic hierarchies, please see my old post about thetaxonomic system.) In subsequent posts, we will look at more advanced animals, leading up to the vertebrates.

I’ll start with the most primitive animal phylum: Porifera, the sponges. They are incredibly simplistic creatures, having no symmetry plan, and no true organised tissues or organs (no sensory organs, no heart, no lungs, no kidneys, no intestines, etc.). In essence, the sponges are clusters of cells, without much more organisation than having an internal empty space, or cavity; some form extending tubes.

Poriferans are sessile (i.e. living attached to a substrate; immobile) filter-feeders, so they don’t need any organs or specialised tissues to handle transport of food, waste or oxygen throughout the body (all of that occurs by diffusion – passive spread across a surface), and no sensory structures, since they filter food from the surrounding water – i.e. they are not predators that need to search for prey – and since they cannot move to escape potential dangers – i.e. there is no sense in making an effort to detect danger, if you can’t avoid it.

This might be a difficult lifestyle to imagine, and they probably strike you as incredibly boring and lame (or maybe you envy their relaxed and care-free existence?), but they can do something pretty awesome: because they are so simple, they can basically reassemble and/or regenerate (repair damaged parts) without hesitation or hindrance. What is even cooler is that if you totally disintegrate two different individual sponges into a mesh of loose cells, and mix them together, they will actually separate and reassemble as the distinct individuals they were/are!

Porifera. Image from http://rjfisherjoanides.pbworks.com/w/page/36528143/Porifera%20and%20Cnidarians%202

Cnidaria, jellyfish (Medusozoa) and sea anemones (Anthozoa, which includes corals), show a step up in complexity from the poriferans. They have true tissues, like all other higher animals; in Cnidaria, the tissues make up two layers: the external epidermis and internal gastrodermis, separated by a gelatinous goo called mesoglea. Typically, the epidermis faces outward and the gastrodermis folds inward and makes up a blind-ending gut cavity; food is filtered from water in the cavity, through the gastrodermis and into the mesoglea, where the chemical stuff happens.

While the cnidarians have a gut cavity, they do not have any internal organs: all internal transport occurs by diffusion across the mesoglea. However, they do have a simple nervous system: a network of unspecialised nerve cells, forming a so-called nerve net, which is probably useful for coordinating movement and internal signals (and, if I am not mistaken, they can detect basic environmental stimuli), although I doubt there is any central processing (i.e. thinking) going on.  

The cnidarian are radially symmetrical, meaning that if you them along any long axis, they will form two identical halves. In contrast to sponges, this means they have an up and down, but no left and right, like bilaterally symmetrical animals have (the remainder of the phyla we will consider here). This means that regenerating damaged parts requires certain sophistication, which the Cnidaria manages excellently.

However, the most obvious feature of the cnidarians might be their tentacles, which contain a unique type of stinging cell, called cnidocyte. The cnidocyte shoots out a spike, using water pressure, when stimulated. They are probably triggered by electrical signals from the nerve net. Like wasp stingers, the cnidocytes are single-use.

The cnidarian have two basic body forms: medusoid, which is typical for jellyfish, and polypoid, which is characteristic of sea anemones. However, species can shift between these forms throughout their life cycles, the mobile medusoid form being used primarily to spread out in the sea, and the cnidarian transforms into the sessile (immobile) mode when it settles.

Medusozoan cnidarians (jellyfish). Image from http://www.dramafever.com/news/yummy-jellyfish-turned-into-glow-in-the-dark-desert/

An anthozoan cnidarian (sea anemone). Image from http://hynpoikanikan.blogspot.co.uk/2011/06/sea-anemones.html

Radial versus bilateral symmetry. Image from http://ssrsbstaff.ednet.ns.ca/jcroft2/symmetry.htm

Platyhelminthes, the flatworms, are primarily disgusting parasites, a familiar example being the tapeworms, intestinal parasites that feed on our food until they are large enough to lay eggs and swirl out through our arse.

However, they represent the next step in basic animal evolution: they have three basic tissue layers, which is termed triploblastic, while the two-layered cnidarians are diploblastic. Platyhelminths have an external epidermis, an internal gastrodermis, and a mesodermis between these. In higher triploblastic animals, there is usually a space between the gastrodermis (or endodermis, as it is called in those) and the mesodermis, and this space forms the body cavity. Animals with a body cavity are termed coelomate, because the body cavity is named coelom; animals without a body cavity, i.e. the platyhelminths, are therefore acoelomate.

Moreover, the platyhelminths are bilaterally symmetrical, i.e. have a left and right side, as well as a front and back.

The mesoderm is the tissue layer that specialises into forming internal organs, muscles, and so forth, in triploblastic animals. The platyhelminths, however, only have a primitive excretory system (i.e. waste handling); there is no other internal transport system. Their gut is blind-ending, just like that of the cnidarians. In crude terms, this means they eat and defecate through the same hole.

The platyhelminths also show the beginning of head formation, or cephalisation, by the formation of a mouth and a concentration of nerve cells and sensory structures in the front.

There is one extreme exception to these general features: the cestodes, i.e. the tapeworms. These parasites are highly specialised, having lost their mouths and gut because they absorb nutrients from animal intestines through their skin. The only good their head does is hosting a sort of hook and sucker device, which they use to hold themselves attached to the intestine lining. 

The platyhelminths are capable of regenerating damaged tissue just like the cnidarians. 

A free-living (i.e. non-parasitic) platyhelminth. Image from http://kids.britannica.com/comptons/art-26318/Prostheceraeus-a-flatworm-of-the-class-Turbellaria

 

A cestode platyhelminth (tapeworm). These are too disgusting to show a real-life photograph of. Image from http://www.proprofs.com/flashcards/story.php?title=bilateriaflatworms

The next phylum will be the roundworms, Annelida, but let’s save the fun for tomorrow’s post! We will also go through a couple of more really basic phyla, before moving on to the more advanced invertebrates after that!

Basic groups 3: Fungi

Let us look at another main group of unicellular or multicellular organisms: Fungi. This group includes the well-known mushrooms and moulds, so you can imagine that these are not edible or pleasant as a rule. Most fungi are decomposers, making their living on breaking down dead organic matter, using oxygen. They release energy in the process, and liberate some organic molecules they can use for growth, and the rest goes into the soil, available for plants to incorporate into their tissues. Fungi, together with many decomposing microorganisms, thus make up an essential component of the flow of matter through an ecosystem, by liberating matter from the dead so that the new generation can use it.

Other fungi are parasites, stealing nutrients from a host animal or plant, some with the agenda of keeping the host alive, forever parasitized upon, others that prefer to kill the host and move on to another.

Perhaps surprisingly, the fungi are closer to humans than plants in the evolutionary tree. This actually surprised me even more when we learned about their detailed biology at university last year, because they don’t seem quite like anything. The wicked thing is that many fungus groups can share cytoplasm, organelles and even nuclei between individual cells: they are basically interconnected through pores in their cell walls (made up of chitin, by the way, another large sugar, like cellulose, but different), where the cell contents can flow around as needed.

Chytridiomycota is the most primitive. The chytridiomycetes are commonly known as the water moulds. They are defined by a certain type of spores, but are otherwise quite diverse. Their spores are motile, meaning they are designed to swim around in water, in contrast to e.g. being spread by wind, which means that chytridimycetes need to grow near water (hence their common name). Some forms are unicellular, others grow as sheets or mats; however, chytridiomycetes do not form the typical filamentous (thready) hyphae present in most other fungi. Cytridiomycota includes both decomposers and parasites.

Microscope view of a chytridiomycete. Image from http://s668.photobucket.com/user/fungiblog/media/chytridio.jpg.html

Zygomycota, the pin moulds, have immobile spores, and do form hyphae, which are basically the thready bits, perhaps more easily seen on moulds, but if you take apart a mushroom, you can feel its ‘flesh’ is tightly packed threads. More specifically, the zygomycetes can be recognised by their dormant, heterokaryotic zygosporangium, which is basically a capsule for a new individual, but whose nucleus halves still have not fused properly (crazy, I know!), where they lie protected until the outside conditions are favourable. The zygosporangium looks pretty cool, though I doubt you would be able to see it unless under a microscope.

A zygomycete. Image from http://mushroomhobby.com/Gallery/Zygomycota/

 

The zygosporangium of a zygomycete. Image from http://vdshahane.hpage.co.in/gallery27137_2.html

Next are the glomeromycetes, the mycorrhizal fungi. They typically form a symbiotic relationship with plants, living in tight association with their roots (sometimes even inside them), helping the plants to take up nutrients from the soil, while the plants share some of their products of photosynthesis. This is incredibly common, and it has been estimated that 90% of all plants have mycorrhizal associations.

A glomeromycete. Image from 

http://website.nbm-mnb.ca/mycologywebpages/NaturalHistoryOfFungi/Glomeromycota.html

Ascomycetes, sac fungi, might be more familiar. They keep their spores in a sac, giving them their common name. Some sacs are open, others closed, ether to protect the spores, or to allow them to be shot out explosively by building up pressure in the camber. Lichens, which can easily be mistaken for mosses, are symbiotic associations between ascomycete fungi and some photosynthetic microorganism, either a chlorophyte (green alga) or cyanobacterium (blue-green alga).

An ascomycete. Image from http://www.clarku.edu/faculty/dhibbett/tftol/content/1introprogress.html

Finally, Basidiomycota, or ‘higher fungi’, includes the familiar mushrooms. They typically keep their spores under the cap, which protects them from above. We all know what these look like.

A basidiomycete. Image from http://renewablekinabalu.blogspot.co.uk/2013/04/mushrooms-could-be-used-to-curb.html  

Basic groups 2: Plants

Next in line, I think, should be plants and similar multicellular organisms, i.e. rhodophytes (red algae) and phaeophytes (brown algae).

These are the photosynthetic multicellular organisms. They produce organic molecules (and oxygen) from sunlight, water and carbon dioxide, in special organelles called chloroplasts, using the green pigment chlorophyll to absorb the sunlight. They also use various accessory pigments (to help with the absorption), which can give them different colours; this is why rhodophytes are mostly red, and phaeophytes have a green-brown-ish colour.

To fully grasp what is unique about the red and green algae, let us first look at the more familiar green plants.

Kingdom Plantae, also called Viridiplantae, comprises all land plants and the unicellular green algae, which we covered in Part 1; so, now we will focus on the land plants, the embryophytes.

I think we all have a pretty good idea of what a land plant is, and the details, although incredibly fascinating, might just be a bit too much for this quick guide-through. All I should say is that land plants have essentially two main life stages, i.e. two main forms throughout their life cycle. So, individuals of the same species may look very different, if they are in different life stages.

Land plants can broadly be divided into vascular and non-vascular plants. Non-vascular plants lack vascular tissue, specialised structures designed to transport water and/or nutrients throughout the plant. These include mosses (bryophytes), hornworts and liverworts. In addition to lacking vascular tissue, they also lack leaves, true roots and true stems. Therefore, they are typically small, not growing higher than a decimetre or so, and cannot grow in dry places, requiring wet soils to sustain themselves.

A moss. Image from http://www.mossandstonegardens.com/blog/the-truth-about-moss-dispelling-moss-myths/

A hornwort. Image from http://www.anbg.gov.au/cpbr/program/ha/ha-liverwort-hornwort.html

A liverwort. Image from http://www.aphotoflora.com/liverwort_marchantia_polymorpha.html

Vascular plants, or tracheophytes, includes primitive vascular plants, such as lycophytes (club mosses), arthrophytes (horsetails), ferns (pteridophytes), and seed plants (spermatophytes). Lycophytes have stems and roots (I think!), but no leaves. Instead, they have microphylls: leaf-like structures, but not true leaves, because they grow directly out of the stem, without the petiole (leaf stem) in between. Arthrophytes have true leaves (macrophylls), which are needle-like (much like those of conifers), but also have a green stem that carries out photosynthesis, instead of just the leaves. These are both rather rare plants; I don’t know if I have ever seen any of them in real life. Ferns, on the other hand, are far more familiar. They can be recognised by having their spore capsules attached to the underside of their leaves, which by the way also have a very characteristic shape (though I don’t know how to describe that in words…).

A lycophyte. Image from http://www.hermonslade.org.au/projects/HSF_07_4/hsf_07_04.html

An arthrophyte. Image from http://www.online-utility.org/image/gallery.jsp?title=Equisetum+telmateia

 

A fern. Image from http://www.fanpop.com/clubs/flowers/images/28504493/title/fern-photo

Spermatohpytes represent the next step in land plant evolution: the seed-bearing plants. They are divided into the gymnosperms and angiosperms. Gymnospermophyta includes conifers and several other ancient linages (e.g. cycads, ginkgos), many of which are extinct now, or only exist as a few species. Their seeds are ‘naked’, exposed, hence the name. Angiospermophyta, the flowering plants, on the other hand, have their seeds ‘hidden’ or enclosed in something, usually a fruit.

Conifers are characterised by their cones, which are their means of reproduction, i.e. where their seeds are carried, and by their needle-like leaves. Angiosperms are identified by their flowers (hence the colloquial name ‘flowering plants’) and fruits (which contains their seeds), although these are not always easily seen, for example in grasses. But, basically, most land plants today are angiosperms, the needle-leaved ones are conifers, the second-most abundant, and then there are ferns in third place, and mosses too… The rest are quite rare.

A conifer (gymnosperm). Image from http://www.jeannerose.net/articles/Conifers_EO.html

An buch of angiosperms. Image from

 http://www.gambassa.com/public/project/4448/JillianandStephanie%27sTimeline.html

In the writing moment, I realise that this is rather scattery; the information might make little sense in the big scheme of things unless you have some background in plant biology and/or evolution. I apologise for this, and am considering writing a supplementary background entry later, maybe by the end of next week.

But now, let us jump to the red and brown algae. Both are aquatic (water-living), so they don’t need stems like land plants, as the water gives them enough buoyancy to stay upright and reach the sunlight. They differ in their accessory pigments, giving them different colours, and in other factors. Overall, many rhodophytes grow like sheets over the surface, i.e. not that tall, while phaeophytes tend to be primarily seaweed forms, with ‘roots’ (called holdfast), a ‘stalk’ (stipe) and ‘leaves’ (blades).

A rhodophyte. Image from http://www.jonolavsakvarium.com/blog/200711/blog200711.html

A phaeophyte. Image from http://en.wikipedia.org/wiki/Brown_algae

I’m sorry for this post, I feel the quality is so low I am hesitating of whether to publish this or not; I am frankly too demotivated to improve it or start over. I think in order to break this evil circle, I shall publish it and seek to come back with a supplementary post later, when I feel more energised. I don’t know what came over me today, but I’m sure it will pass! I promise the next one will be more enthusiastic!

Basic groups 1: The unicells

In light of yesterday’s post, I thought why not just write a few posts briefly describing the main groups of organisms that I am familiar with? So, the first one is about the unicells.

This is not where you end up if you fail university. Unicells is just an (informal) shortening of unicellular organisms, living things that only consist of a single cell that is capable of surviving on its own. This includes bacteria, archea and protists. 

On a very large scale, all life forms are divided into three domains: Bacteria, Archaea and Eukaryota. Bacteria and achaea are both prokaryotic, meaning they have no nucleus, which is the core of a eukaryotic cell. We humans, all animals, plants and fungi, belong to the Eukaryota, together with the protists, which are unicellular eukaryotes, i.e. single-celled organisms that have a nucleus.

Bacteria and archaea are virtually indistinguishable to anyone who doesn’t know them in detail. They are defined based on complex genetics, biochemistry and structure. But they are both everywhere, in enormous quantities. There are many times more bacteria and archaea in a handful of soil than there are humans on this entire planet. Archaea also tend to be extremophiles, i.e. organisms that thrive in extreme environments, such as near-boiling temperature, extremely acidic or saline water. This can be highly advantageous, as there is little competition for space and nutrients in such unfriendly environments.

Prokaryotes, i.e. bacteria and archaea, have no nucleus, which is where all DNA is kept in eukaryotes; their DNA is instead floating around freely inside the cell, in circles. Prokaryotes also basically have no organelles, which are the ‘organs’ of eukaryote cells, such as the mitochondria (where energy is ‘produced’) and the lysosome (where ‘dead’ parts are broken down). This means that prokaryotes are generally more simple organisms than eukaryotes. Finally, eukaryotes are typically ten times larger than bacteria and archaea.

Now to the unicellular eukaryotes, previously classified as Protista, alongside Animalia, Plantae and Fungi (animals, plants and fungi, respectively). However, the eukaryote classification has changed since, and is now rather complicated, even at a basic level. But I will try to guide you through as best as I can. Hopefully, you’ll come across odder cells than you ever heard of!

There are five big groups of eukaryotes: Unikonta, Archaeplastida, Rhizaria, Excavata, and Chromalveolata. I don’t know these very well, but based on notes from last year’s module on unicellular organisms, there are some cool things to say about each.

Unikonta includes animals and fungi (yes, fungi are mong the closest relatives of animals, insane isn’t it!), which are multicellular. The main unicellular unikonts are the amoebozoans, slimy-looking goos with a very flexible cell membrane that can reshape very easily, and even extend as pseudopodia (singular: pseudopod), false limbs, to move around or grab and engulf food or prey. Yes, some amoebozoans are predators, which feed on bacteria and/or other protists.

Amoebozoa. Image from:
http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/amoeba.html

Archaeplastida includes land plants (multicellular), red algae (mostly multicellular), and green algae. Land plants (Embryophyta) and green algae (Chlorophyta) together form the group Plantae, which is all plants. However, since we are discussing unicellular organisms here, let us consider the green algae alone. Chlorophytes have a rigid cell wall outside their cell membrane, made out of cellulose a type of large sugar molecule, and, most importantly, are capable of photosynthesis, the familiar set of chemical reactions that produce organic molecules out of sunlight, water and carbon dioxide, with oxygen as a byproduct (oxygen is actually a waste gas for plants, much like a fart, seriously!).

Chlorophyta (green algae). Image from http://www.chdiagnostic.com/H_Photo%20Gallery.htm

Rhodophytes, red algae, are primarily multicellular, so I might discuss them with plants in a later post.

Rhizaria includes mainly the foraminiferans and radiolarians, typically enclosed in secreted shells, called tests. Foraminiferans have porous (hole-y) tests with multiple chambers, and thin pseudopodia radiating out from the holes, used to grab food particles from the surroundings. Radiolarians also have pseudopodia sticking out from their single-chambered test, but they are used to engulf other microorganisms, like those of the amoebozoans. The foraminiferan test is typically made up of calcite, while the radiolarians make them out of silica.

Froaminifera. Image from

 http://www.mnhn.fr/mnhn/geo/Collection_Marine/themes_recherche/PageForaminiferes_eng.htm

Foraminifera with extended pseudopodia. Epic image from

 http://news.softpedia.com/newsImage/The-Waterproof-Glue-of-the-Future-2.jpg/

Radiolarian. Image from http://livelikedirt.blogspot.co.uk/2012/04/microfossils-i-alveolates-foraminifera.html

Excavata are characterised by lacking a cell wall, unlike most single-celled organisms (bacteria and I’m pretty sure archaea also have cell walls). The group includes diplomonads, which are dikaryotic, i.e. have two nuclei (plural of nucleus), parabasalids, with shrunk mitochondria, and euglenozoans, which posses a curious crystal rod inside their flagella (organelle used for swimming around) of unknown function.

Diplomonad. Image from http://faculty.uca.edu/johnc/heterotinvert.htm

Parabasalid. Image from

 http://www.visualphotos.com/image/1x374517/trichomonas_vaginalis_scanning_electron_micrograph

Euglenozoan. Image from http://protist.i.hosei.ac.jp/pdb/images/mastigophora/euglena/limnophila/limnophila_1a.html

Chromalveolata includes brown algae (Phaeophyta, mainly multicellular), ciliates, apicomplexans, diatoms and dinoflagellates. Brown algae, basically seaweed, are primarily multicellular, so they will be discussed in a later post. Ciliates are dikaryotic, like the diplomonads, except their two nuclei are of different sizes; they also use cilia (the things that look a bit like hair, on many unicellular organisms) diligently to move and feed. Apicomplexans are nasty animal parasites, with an apical complex of organelles specially designed for penetrating into the host. Plasmodium, the pathogen behind malaria, is an apicomplexan.

Diatoms have cell walls made of silica, full of pores, and divided into two halves, one always slightly smaller than the other. Diatoms are photosynthetic, and together produce about 20% of all oxygen every year. Plants are not the only organisms that can photosynthesise. Another important group of photosynthetic organisms are the cyanobacteria (which are bacteria), also known as the blue-green algae.

Dinoflagellates are as cool as they sound. They are among the most bizarre-looking cells, with heavily modified cell walls to look like alien space ships or I don’t know what. The cell wall is divided in two, just like for the diatoms, and contains armour plates made out of cellulose. The two flagella that stick out of the grooves in this armour is a main defining feature of the dinoflagellates. Some dinoflagellates are photosynthetic, many of which live in symbiosis with corals, giving them their magnificent colours, and others are predatory. One dinoflagellate that has blown the minds of experts is Pfiesteria piscicida, the ‘cell from hell’, which has about 24 different life stages and is highly toxic to fish, and humans. I can imagine the nickname came both from the toxicity and the hell the experts must have gone through trying to classify it!

Ciliate. Image from 

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/wimsmall/cilidr.html

Artist’s interpretation of an apicomplexan. 

Image from http://www.deviantart.com/art/Subphylum-Apicomplexa-181570076

Diatom shells. Image from http://www.calacademy.org/science_now/archive/academy_research/sarah_spaulding.php

Dinoflagellate. Image from http://www.studiovandam.com/rational-noctiluca.html

That is what I had to say this time, except one last note: remember that unicellular organisms require water to live in, even those in soils, etc., they need water as a medium to move around, and also as a medium where their chemical reactions can occur.

I misstakedly forgot that many fungi are unicellular, such as yeasts, so they should have been adressed here as well. However, they will now be part of Part 3, on fungi.

What's that animal over there?

From Trust me, I'm a "Biologist" Facebook page.

The plethora of different animals, plants, fungi and all other things out there are so diverse that it is inhuman to keep track of what all of them are, what makes them unique, and what makes them belong to a certain group.

As a paleontology and evolution student, knowing this stuff is important, and I personally enjoy learning about these things, so paying attention to different groups and how they are all related – their position in the big context – is instinctive.

But what about those who do not really care if a tuatara is not technically a lizard? What about those who might be interested, but don't have the education or opportunities to learn or find out for themselves?



This is not a lizard. (I'm not joking.) Technically speaking, the tuatara (Sphenodon) is not included in the taxonomic lizard group (Lacertilia). But who could blame someone for pointg at the tuatara and going "look at that lizard"? How can we go about circumvening these confusions? Image from:  http://en.wikipedia.org/wiki/File:Tuatara.jpg

Should we make awareness and understanding of how the scientists classify and organise the living organisms on this planet? Is it important enough?

My dad has always paid attention to and learned lots of native bird and plant species in Sweden, while I could not care less. Of late, I have realised the value of knowing plants, but birds are still a "meh" for me, so I could not identify more than a handful of bird species if my life depended on it! But dad can tell them from their plumage, and many even by their songs.

This puts things in perspective for me: being indifferent to knowing or not knowing bird species, I understand that many people are indifferent to the fact that dolphins and sharks are not even touching the surface of being anywhere near almost distantly related, while they look the same to the unattentive eye, and, therefore, I would not suggest forcing deep taxonomy into general education; however, starting to become interested in plants, and feeling disadvantaged because I missed opportunities to learn many, and because I have not yet found a decent free plant learning guide that is basic and to-the-point effective, I would argue that some sort of basic, comprehensive and effective learning tool for basic taxonomy should be available to whoever is just curious and wants to learn more.

Please let me know if you share my wish!

Human trace fossils

Fossils are any trace of ancient life. They can be body fossils – mineralised remains of the physical organism, such as bones, shells, teeth – or trace fossils – preserved traces of the behaiour of organisms, such as footprints, burrows, scratch marks.

Trace fossils are also known as ichnofossils, a fancier term. Ichnofossils are radically different from body fossils, not only in how they look, but how they preserve, how they are studied, and what they can tell us about past life.

I am not 100% sure of how trace fossils are preserved, since I have never really found out, but I can imagine that they are typically formed when a footprint, trackway, burrow – whatever – is overlain by a different type of sediment than it was made in. That way, the shape is preserved in the interface, or boundary, between these different sediment types. It is important that they are different types, because otherwise the actual trace would disappear in the middle. The trace fossils are exposed when one of the different layers is eroded away, so again it is important that the two sediment layers are different: one harder than the other. If the substrate where the trace was made is the one that is eroded, the trace fossil appears inverted, and the examiner needs to think backwards, or just make an inverted cast of it.

Burrows, footprints and the like are rarely well preserved, which makes them difficult to study. But, the biggest challenge of study of ichnofossils is figuring out what type of organism it belonged to. Take a footprint for example. First of all, the footprint is a reflection of the fleshy pads of the foot, so matching it with the foot bones of an animal requires quite a bit of thinking. Second, you are lucky if the footprint you have found belongs to any species whose fossils are known! Or maybe some bones are known, but not the feet? What do you do if the trace belongs to something unknown? Therefore, trace fossils are safer to match with larger groups, rather than trying to pin it down to species level. It is a shame, but cannot be helped.

Regardless, trace fossils are a valuable asset to the record of body fossils, as they are direct evidence of behaviour rather than anatomy, physiology, etc. Burrows indicate burrowing behaviour, implying an infaunal (living in the sediment) or subterranean (underground) ecology. Tracks can tell us about how the animal moved, including estimates of how fast. However, what we can learn from these traces is not very meaningful unless we can link them to any known organism, and the conclusions we draw from them must be taken with a pinch of salt.

Just as we study body fossils by comparing them with living analogues, ichnologists examine trace fossils in the light of relationships between living animals and the traces they leave. What aspects of the animals affect the traces? The answer to that question reflects what we could infer from tracks alone. Below is an example of how an ichnologist might go about studying traces of life.