Thoughts about New Year's resolution

Based on the messages from the video with Tony Robbins I recommended a few days ago (also below), I think I now have a clearer idea of why I feel a need to improve my academic life. By honestly presenting how I figured out what is lacking, why it is lacking, and how I am starting to approach the problem with an embryonic plan, my hope is to inspire you to do the same in your lives, and really want to make a New Year’s resolution this year, and feel that you can and will see it through!  


This video was meant to address the difficulty all of us find in keeping our New Year’s resolution, but it really applies widely to all kinds of decisions about making a lasting improvement in your life, i.e. improvements that go beyond just one year, that become your new standards.

I don’t think I can do it much justice by trying to summarise in my words. I strongly recommend that you watch it through, even if you are not so keen on this whole New Year’s thing… especially if you are not so keen on it!

But if you are more of a reader than a listener, hopefully you will be able to follow my thoughts even if you don’t watch the video…

Argh, enough chit-chat! Let’s do this!!

… no, seriously. But I will get on with it.

The main breakthrough for me was when the message helped me finally figure out why I have had such a hard time finding motivation to do the work. I am sharing this here because I suspect I am far from alone in having those feelings.

My main source of friction is probably that I have had a change of identity from a ‘hard-worker’ to a ‘social person’. I used to be able to study all through the day, mainly because I had nothing better to do. This made me define myself as a ‘hard worker’. But, about four years ago, I started to hang out with a couple of wonderful friends, with whom I wanted to spend time with so much that I began to contradict this basic nature of getting home after school and sit down and study. Gradually, I changed priorities. (This is what I thought had happened, up until recently when I realised that this change happened without any real personal conflict, so I begin to suspect that my priorities were friends-over-work all along, but I just didn’t know it at first!)

Not implying you cannot be both hard-working and social, which would be ideal, I feel that in my case it was a one-way transition: a change of character rather than an expansion of character. I think this is how I have been limited. And I don’t think I can revert to being only a hard worker, at the expense of socialising (not without inner conflict, which we all know is destructive to the soul). Therefore, I must simply expand. I need to start to see myself as someone capable of enjoying work and fun.

For so long, I have expected the work to become more enjoyable. But half-way through my course, I know this is not going to happen. The other option is to flip some kind of switch inside that will enable me to make the work enjoyable.

A large part of me feels that something is wrong with the world when one must put in effort not to be disillusioned when working on what used to be his/her favourite subject. But another part of me is highly focused on solving problems rather than griping about how inconvenient they are, and now I need that side to take over!

So, how can I make the work more enjoyable? The texts we have to read will be the same. What can I do to make them less boring? 

Well… I don’t know yet… and I think that is something each one of us needs to find out for him-/herself.

Reflecting back, I think I usually enjoy work most when I somehow engage in it, put some energy into it. Few of the things we have been assigned so far have moved me to engagement, so maybe it is not surprising that I found them hard to enjoy. Some assignments may have required me to input effort, but I can’t think of any that motivated me to do it.

Anyway, I realise that I am spinning off the rails massively right now… and the eye soreness is coming back… I hate to interrupt posts mid-way, but I think it is the best thing to do. And I might even consider breaking this pattern of publishing every day. There is a difference between being strong and persistent and being foolishly stubborn. The pressure (I put on myself) to keep publishing, while it is not good for my health, may have compromised the quality of a number of posts so far, and although I am definitely not a perfectionist, I am a sucker for quality.

I will be back.

More thinking about New Year's resolution

Sorry to disappoint, but I am only writing to tell that I need more time to think about what I should have put today (as the title suggests, if you read it from a different angle) hahaha XD.

I have a serious (and fun! who would've thought!) essay to write before Monday, and my eyes haven't gotten better, so I am taking a friend's advice and trying out working by the computer only for fifteen minutes per full hour. (I use this time to copy the information I have gathered on paper, so I can use the time in the breaks to process it.) This makes the work less efficient, but more sustainable. And I like sustainability :D

Hopefully I will be able to tell more tomorrow!

Thinking about New Year's resolution

I definitely want to make a New Year's resolution about my study situation. I need a solid framework to survive this quadrupling of my workload. I find this video with Tony Robbins greatly inspiring.



Having arrived late at night, after a wonderful pantomime performance (it's a sort of theatre, but with far more interaction with the audience, and usually peppered with lame puns and sexual innuendos), I am afraid I am not in top condition to properly summarise my thoughts about New Year's resolutions so far, but I thought I could at least introduce this video tonight, and follow up tomorrow with more musings.

I am thinking about this already because (as the video also suggests), if the resolution is to be kept, it needs to be inspiring and compelling, so I think it is useful to work up some excitement about it way before New Year! I encourage you to do the same! :)

Derposaurus

I recently picked up another daily exercise: posting a daily derp picture on Facebook. I think 'derp' really applies to any photo with a person making an unintentionally hilarious face, sometimes with the help of a little photoshop to make the eyes diverge and the nostrils bigger.

Here are some nice Derposaurus!

 

Our history in two minutes

This is an amazing slideshow of the history of our planet and our species. It is only images, but powerful ones.

Laziness... why?

Why did laziness evolve?

To conserve energy when not needed, perhaps?

But then again, you are not being lazy when you don't need to do something... so that makes no sense.

I guess it will just be one of life's great mysteries...

The doddler: cute name for a parasite plant

Doddler (Cuscuta) could not be a cuter (no pun intended!) name for a plant that lives as a parasite.

The doddler has virtually no chlorophyll, the essential pigment used to capture the energy of sunlight in photosynthesis, so it cannot produce it's own food. Mature forms lack roots, and so cannot absorb nutrients from the soil. Instead, this vicious plant winds it's thread-like stem around other plants, and somehow feeds on their nturients. It looks like the doddler is strangling the plant, which is why it is also known as 'strangleweed'.

Orange toddler stems. Image from http://www.cod.edu/people/faculty/chenpe/WOLF/2007_06_16/

This lifestyle essentially makes the toddler a heterotrophic plant! To a biologist, that sounds insane! Plants just keep surprising!

New insights into the origin of life

For the second essay – which is about the origin of life – I stumbled upon a couple of recent reviews discussing a different way of viewing life, in particular the early stages.

Scientists see life as a hugely complex chemical system, typically capable of self-replication (reproduction) and using catalysts (ingredients in a reaction that make it happen faster). They understand that this complexity – i.e. ordered structure – requires some kind of stability, or it would collapse.

The traditional school of thought is that life achieves thermodynamic stability by giving off energy. The idea is that a chemical system is more stable the less energy it has, because more energy means that the molecules will be vibrating and moving around more. We are all familiar with what happens to ice – an orderly, crystalline susbtance – when it is given energy and melts in to water, where the molecules can flow around, mostly sticking together. If more energy is added, the water molecules start to evaporate and convert into a gas – molecules floating around freely with no attachment to one another, i.e. in complete disarray. We can make skulptures of ice and snow, but as soon as they melt, that orderly structure is destroyed and it falls apart.

Imagine building a house where the wall bricks are vibrating at will...

It is thought that life forms strive for thermodynamic stability (i.e. lowest energy state) by giving away energy to their environment. As chemical reaction occur continuously in a cell, energy must also be expelled continuously. And in order to be able to give away energy forever, there needs to be some way of taking in energy that can be given away. (Indeed, I suppose that if no energy is taken in, the cell could perhaps achieve stability, but it would not be able to grow, repair eventual damage, or anything like that... it would not be much alive, I guess...)

However, these reviews suggest a different form of stability, which they call dynamic kinetic stability. It is based on the principle of chemical reactions going both ways – i.e. being reversible – which naturally makes chemical systems unstable, unless there is something preventing the reaction from going either way, so that only one direction is favoured. I will soon explain what a reversible reaction is, but I want you to understand that that is the very thing dynamic kinetic stability avoids. If the reaction can be controlled in a way that makes it go in one way only, then the products are less likely to disintegrate at will, which could cause the entire system to collapse.

My chemistry is rather rusty, and I have never been very good at it in the first place, but hopefully I can explain the basics well enough!

Most chemical reactions are reversible in theory. For example, consider mixing sodium chloride (NaCl) with magnesium hydroxide (Mg(OH)₂): they could separate into their constituent ions (Na⁺, Cl^-, Mg²⁺, OH^-) and reassemble as different compounts, i.e. magnesium chloride (MgCl₂) and sodium hydroxide (NaOH). In this case, the first pair of chemicals were the reactants, and the last two were the products. However, this reaction could happen the other way as well, starting out with magnesium chloride and sodium hydroxide as reactants, and end up with sodium chloride and magnesium hydroxide as products.

The entire reaction could be written as:

2NaCl + Mg(OH₂) ⇌ MgCl₂ + 2NaOH

the double arrows symbolising that it could go in either direction, in theory.

A general equation would be:

A + B ⇌ C + D

A, B, C and D symbolising different compounds. Depending on the direction, the reactants could be either A and B, or C and D, and the products would be the other pair.

I hope that is simple enough to grasp. Let us move on to the critical point.

Most biological reactions are so slow that they would not naturally occur during an organism's lifespan, so they require catalysts that accelerate the process. Now, consider what would happen if only one direction of the reaction is catalysed! The reverse would be so slow that it is unlikely to occur in the near future, and the reaction thus becomes stable.

I'm nut sure I quite understand the implications (deeper meanings) of this view on how life aims for stability. It seems the dynamic kinetic stability still requires the release of energy. However, the mechanisms and 'purpose' behind this other form of stability seems to be more selective, almost like evolution by natural selection toward a more stable state (higher complexity). But I am reading the papers as I'm writing this (just couldn't wait to share!), so I hope that by the end of it, it will be clearer what this new isnight means.

What is the relationship between the stratigraphic record and animal diversity in the fossil record?

I finished the first of the essays, which was an assignment for a tutorial session on Monday. It is not formally marked, so I doubt I would get in trouble for putting it here as well. It should be simple enough for most people to understand anyway :) 

The impact of animals on geological processes may not be intuitively appreciated, but even large-scale differences in the outlook of our modern world compared to the times where no animals were around could be attributed to animals, directly through erosion and bio­miner­alisation, and indirectly through their effects on nutrient cycles, plant distribution, and their various ecological roles.

     This essay will discuss the role of ancient animals on the stratigraphic record – the se­quen­ce of preserved rock strata – in particular the impact of their diversity. The implied focus is on animals preserved in the fossil record, but the role diverse of animals in weathering and erosion will also be considered.

     Biogenic strata consist of rocks derived from parts of organisms, typically chemically altered into rock (lithified), and comprise the clearest connection between animal remains and the rock record. Limestones and dolomites are familiar examples, their calcium carbonate component often derived from biomineralising organisms, many of which are animals that secrete calcareous shells or exoskeletons. These include corals, poriferans, bryozoans, echinoderms, brachiopods, most molluscs, and some marine arthropods (e.g. trilobites). The diversity of calcareous animals may affect the precise composition of the limestone or dolomite. Presumably, differences in precipitation rate of these diverse animals also influence the rate of carbonate rock formation. It should, however, be noted that biomineralising microbes, such as diatoms, foraminiferans and some dinoflagellates, also play a significant part in the formation of biogenic rocks.

     Some of the mentioned phyla also include forms that compose their exoskeleton of other compounds, such as chitin (e.g. some bryozoans, many arthropods, craniiform brachiopods). Chitin is a polysaccharide lacking the preservation potential of calcium carbonate, and is especially susceptible to degradation in marine settings (Stankiewicz et al. 1998) . Therefore, a high proportion of animals with chitinous exoskeletons, relative to calcareous ones, may influence the carbonate content of the derived rock. The chitinous organisms are also less likely to be preserved, which would manifest as an underrepresentation of diversity in the fossil record, possibly quantitatively proportional to the carbonate content in the rock – in other words, there may be a numerical relationship between animal diversity and the chemical composition of biogenic rocks.

     Biostratigraphy is the subdivision of the stratigraphic record into units defined by their fossil content. The definitions are made on the basis of biozones: assemblages of index fossils – which ideally (1) are common, and have (2) distinct diagnostic features and (3) rapid speciation rates. Thus, high diversity is an implied requirement for a good index fossil taxon. Animal examples include graptolites and belemnite cephalopods. Their diversity is helpful for our cataloguing (and later our understanding) of the stratigraphic record. Identical or similar fossil assemblages also play a considerable role in correlating strata chronically across their spatial distribution around the world, as many taxa provide a quick field estimate of rock age, and thus a context for interpretation of other features under study.

     In addition, a comprehensive section in the fossil record may assist in the identification of paraconformities (unconformities where the strata above and below the unconformity plane are parallel). A diverse record of fossils would improve the chances of discovering a gap in the sequence, and multiple fossils may corroborate the interpretation.

     Moreover, this relationship may be viewed from the opposite perspective: an incomplete stratigraphic record influences the apparent diversity of fossil in the rock record. Missing strata equates with missing fossils; the relationship is two-way. For example, the Late Cretaceous hiatus (paucity in the fossil record) of sauropods in North America may be attributed to preferential preservation of coastal sediments (Lucas & Hunt 1989, Mannion & Upchurch 2011), while North American sauropods of that age may have preferred inland habitats  (Mannion & Upchurch 2010). Thus, what appears as an extinction of sauropods on the North American continent may simply be due to bias in the stratigraphic record.

     The role of animals in rock weathering and sediment erosion may not be obvious, but it is nonetheless significant. For example, aeolian erosion requires sediment particles to be ejected into the air before the wind can transport them, as wind speed at the ground surface is negligible; animals can assist in this, be it by small bioturbating vertebrates and insects, or large ungulate herds stirring up dust as they migrate (Tarbuck et al. 2011).

     Animals may also be significant for chemical weathering, as they can be regarded as mobile digestive systems. Their guts maintain optimal conditions for catabolic reactions, albeit in particular of organic molecules (Beerling & Butterfield 2012), and their mobility enables animals to transport the material away from the site of ingestion before egesting the weathered products into a potentially different environment. Examples include a diversity of migratory aquatic animals, such as diadromous fish, sharks, eels and cetacean mammals.

     In addition, soil-living animals play an important role in soil formation, which involves the chemical weathering of sediment, and thus an alteration of the stratigraphic record. Their metabolic diversity determines the range of transformation processes that are possible. However, soil microbes and fungi arguably play a greater part in soil formation than animals.

     Finally, the sheer size and mobility of animals enables them to function as agents of physical weathering and transport. Benthic animals rarely break bedrock, but stir loose sediment and may leave distinct traces, burrowers in particular. Terrestrial animals, free from the ancestral bond of the water, may assert their influence over inland environments, expanding the range of bioturbation. Terrestial animals also have great potential for transport of sediment, even between aquatic and terrestrial environments. However, the likelihood of leaving noticeable marks in the stratigraphic record may be negligible.

     It should be noted once again that the role of animals as erosional agents only has one foot in the implicit scope of this essay. Fossil animals are unlikely to influence weathering or erosion, as they are long dead. However, the persistence of fossil-supported (a variant of clast-supported) strata may be determined by the resistance of the fossil material. Also, as food for thought, it is not impossible that fossilised animals may have influenced younger strata – e.g. by eroding them or assisting in soil formation – in their lifetime!

References

· Beerling, David J., Butterfield, Nicholas J. 2012. Plants and animals as geobiological agents in Fundamentals of Geobiology ed.s Knoll, Andrew J., Canfield, Don E., Konhauser, Kurt, O. Blackwell Publishing Ltd. Chapter 11. Pp. 188-204

· Lucas, Spencer G., Hunt, Adrian P. 1989. Alamosaurus and the sauropod hiatus in the Cretaceous of North American Western Interior. in Paleobiology of the Dinosaurs ed. Farlow, James O. Boulder. Colorado. Pp. 75-85

• Mannion, Philip. D., Upchurch, Paul. 2010. A quantitative analysis of environmental associations in sauropod dinosaurs. Paleobiology 36(2). Pp. 253-282

• — 2011. A re-evaluation of the ‘mid-Cretaceous sauropod hiatus’ and the impact of uneven sampling of the fossil record on patterns of regional dinosaur extinction. Palaeogeography, Palaeoclimatology, Palaeoecology 299. Pp. 529-540

· Stankiewicz, B. A., Briggs, D. E., Evershed, R. P., Miller, R. F., & Bierstedt, A. 1998. The fate of chitin in Quaternary and Tertiary strata. In ACS Symposium Series. American Chemical Society. Pp. 211-225

· Tarbuck, Edward J. Lutgens, K., Tasa, D. 2011. Earth – An Introduction to Physical Geology. 10^th ed. Pearson Education Inc. New Jersey.

Essays

I have two essays I want to get well started on tonight, and my eyes have gotten even worse these last days, so I really need to stay away from my computer more.

But the two essay tasks are paleo-related!

"Evaluate hypotheses for the origin of life. Discuss whether the origin of life is such a complicated process that it has only happened once"

and


"What is the relationship between the stratigraphic record and animal diversity in the fossil record?"

7-day challenge

The Saw films have an underlying philosophy, beyond the mesh of gore and torture, which basically is an encouragement to appreciate your life. The evil guy captures people he considers to have wasted or even disrespected the gift of life, usually by promiscuity, taking drugs, and puts them through an 'appropriate' challenge – or, as the villain calls it, a 'game' – typically involving enduring massive pain and/or physical damage, in order to gain their freedom. If they truly value their life enough, they will pull through, and are rewarded with life, and, ideally, a better appreciation for it.

Now, that almost never happens. Most of them take too long to start the task, and end up dying a gruesome death.

While the vilain's right to judge other people's lives is questionable, the message to value your life, and show it to yourself how much you appreciate it, is something we should all take in.

I just saw this picture on Facebook this afternoon, and thought to myself that it is a useful task, I think, to focus the next seven days on completing what you need to make this semester worthwhile. I want to do this, and I urge you to take on the challenge for yourself. Search yourself, find what you want to have achieved by the end of 2013, figure out what you need to do in order to get to where you want to be, and make sure you do it. Then, you will have plenty of time to relax and feel good before celebrating Christmas!

So... let the game begin!   :)

Basic groups 7: Animals IV

Now we have reached what I like to call the ‘higher invertebrates’. We will look at the arthropods – the most diverse animal phyla ever, and therefore arguably the most successful animals. Since I feel my eyes are not as recovered as I thought, I will save the echinoderms, which includes starfish and sea urchins, relatively closely related to vertebrates, for tomorrow. Sorry for that!

Arthropoda is closely related to the nematode worms (see Part 5), united by the shared process of moulting – shedding their outer protective layer as the body grows. Arthropods are well characterised by their jointed exoskeleton composed mainly of chitin (a complex sugar) and segmented body. Moreover, they are bilaterally symmetrical, triploblastic, coelomate animals (see Part 4).

Previously, arthropods were actually thought to be close relatives of annelid worms, rather than nematodes, because they are both segmented, have similar nerve cord arrangement, and hearts located in similar positions. Moreover, the velvet worms seemed to make a perfect intermediate form between annelids and arthropods. However, genetic information suggests that the common features rather are the result of convergent evolution (which I’m sure you are familiar with), and that the true ancestry of the arthropods is shared with the nematodes.

We all know what arthropods are: insects, crustaceans (shrimps, lobsters, crabs and the lot), centipedes and millipedes, and spiders and scorpions. These subgroups are very different in their details, and there is enormous diversity within them, so we should take a closer look at them.

Crustacea includes all arthropods that have two pairs of antennae and biramous limbs (branched in two). Their heads are also fused to the thorax (where most limbs come out from), forming a structure called cephalothorax.

Familiar examples are shrimps, crayfish, lobsters, crabs, etc., and less typical forms include planktonic groups (i.e. really tiny ones floating around in the water column), such as the copepods and the cladocerans.

Daphnia, a typical planktonic cladoceran crustacean. 

Image from https://wiki.cgb.indiana.edu/display/DGC/Images+Set+2

Strictly speaking, crustacean is defined by a unique larval stage called the nauplius larva, which is… uhh… ugly…

Nauplius larva, a unique shared larval stage of the Crustacea. 

Image from http://commons.wikimedia.org/wiki/File:Fairy_shrimp_larva.jpg

Crustaceans typically have more limbs than anyone could count, many of which carry sensory structures, detecting chemicals (taste) or pressure changes (touch). They also have compound eyes, which, unlike ours, have a myriad of lenses, each producing its own image, and connected to all others in the brain to give a single picture in their head (I guess… I don’t really know how a shrimp sees, hahaha…). The two pairs of antennae are also involved in sense perception, so you can see that crustaceans have a plethora of sensory organs.

So many legs! Image from http://www.flickr.com/photos/dwysiu/434088344/

Cheliceriformes is a mouthful, and includes all eight-legged arthropods. They have six limb pairs in total, the last pair being used for feeding, either for grasping, like in scorpions, or piercing, as in spiders. Instead of antennae, they also have an extra pair sensory appendages, called pedipalps, near the mouth. Like the crustaceans, the cheliceriforms have a cephalothorax, a fused head and thorax, where the six limbs are attached; the rest of the body has relatively few appendages.

Scorpion. Image from

 http://connectnigeria.com/articles/2012/10/08/discover-nigeria-an-army-general-called-the-black-scorpion/

Cheliceriformes includes Merostomata (horseshoe crabs and king crabs, though none of them are actual crabs) and Arachnida (spiders, scorpions, plus ticks and mites… nasty creatures). The horseshoe crabs are remarkable examples of living fossils, having persisted virtually unchanged for more than 400 million years.

Horseshoe crab. Image from http://thenotsosilentspring.blogspot.co.uk/2013/07/the-10-eyed-horseshoe-crab.html

We would all know spiders and scorpions if we saw them. Ticks and mites are so tiny you will probably never (want to) see them, and if you do, just avoid them, for the good of everyone. They should not be encouraged to exist. (Just joking, not being serious!)

Spiders and merostomatans, unlike scorpions and the others, are sectorial feeders, which means that they can only take in food as a liquid. They must therefore digest the food before they suck it up. Spiders inject digestive juices into their victims, literally dissolving them from inside out. This is probably why it is handy to trap the prey in webs.

Myriapoda is the group that comprises centipedes (Chilopoda) and millipedes (Diplopoda). They are closer relatives of insects than the rest of the arthropods, having heads separate from the trunk, a single pair of antennae, and one pair of mandibles (feeding appendages). The main difference between insects and myriapods is the number of segments: whereas insects reduced their numbers to only three segments, the myriapods have too many to count.

Centipedes have one leg pair per segment, millipedes have two. This is a certain way of distinguishing between the two. However, you might want to be able to tell them apart before getting too close, because centipedes are vicious, often poisonous predators, while millipedes are harmless herbivores. Other useful characteristics are the length of the antennae – centipedes have very long ones, while the millipede antennae are stubby – and the poison fangs of the centipedes, which evolved from modified front legs.

Centipede (Chilopoda). Image from http://en.wikipedia.org/wiki/Centipede

Centipede fangs. Image from http://carnivoraforum.com/topic/9680654/3/

Millipede (Diplopoda). Image from http://topicstock.pantip.com/wahkor/topicstock/2011/11/X11358397/X11358397.html

Myriapods are restricted to moist environments, because their exoskeleton is less advanced than that of other land-based arthropods. They lack a waxy layer, which helps conserve water, so they need to be in damp areas in order to not dry out.

Insecta, as already mentioned, are distinguished by having three distinct segments: the cephalon (head), where the mouth, eyes and antennae are, the thorax, where the three leg pairs are attached, and the abdomen, where the most internal organs are concentrated, and which lacks appendages. Many insects also have wings – typically two pairs – on their thorax. Insects are the only flying arthropods, and, indeed, the only flying invertebrates.

Insecta. Image from http://www.naturephoto-cz.com/wasp-photo-4260.html

Insects are incredibly diverse, including flies, dragonflies, mosquitos, wasps, bees, bumblebees, grasshoppers, crickets, all sorts of beetles, butterflies, moths, ants… and many more that I just can’t think of right now! There’s so many of them! And they are everywhere. I wish I knew more about insects. They could probably have made up a post like these on their own!

Basic groups 6: Animals III

Back again with a few more lower invertebrates, before we dive into the higher invertebrates and then the vertebrates. We will look at the molluscs in some detail, as well as a couple of less common phyla that were important in the past, such as the brachiopods and bryozoans.

Brachiopoda is a group of marine, filter-feeding, shelled organisms with much resemblance to bivalves (mussels, clams, oysters, etc., which are molluscs and will be dealt with later). They are bilaterally symmetrical triploblasts (see Part 4 if that makes no sense). Brachiopods were hugely successful in the Palaeozoic era, but suffered a rapid decline in the Mesozoic era, the time of the dinosaurs, and have not recovered since. Today, there are only a few living species, the most familiar being Lingula.

Lingula, an extant brachiopod. Image from http://www.aquarium.co.jp/shell/gallery/hyouzi.php?nakama=wansoku  

Brachiopods can be sessile – like sponges and sea anemones, attaching to the substrate with their fleshy, tongue-like pedicle – buried in the sediment – like many worms – or free-lying on the sea bottom (though I think maybe only extinct brachiopods did that). 

They take in water into their shell in different ways, and filter out food particles with their coiled, ribbon-like lophophore, a special feeding organ, which they share with bryozoans and some other related phyla. The lophophore is the unifying feature of a large group of phyla called Lophophorata, which we will come across when discussing how all the animals we have gone through are related. The lophophore is made up of what could be seen as a main stalk and a myriad of tight, hair-like structures extending out at a right angle, sort of like a brush, but flat. These hairs filter out food particles from the water, and transport them to a cryptic mouth.

The lophophore (filter-feeding organ) of a brachiopod. 

Image from http://invertpaleo.blogspot.co.uk/2011/07/brachiopods-versus-bivalves.html

At first sight, the brachiopods might seem indistinguishable from bivalve molluscs, especially if you cannot see the insides (bivalves do not have a lophophore, but use modified gills to filter food from the water). However, there is one simple way of telling them apart by just looking at their shells (which is important in fossils!). Brachiopods and bivalves are both bilaterally symmetrical, but the symmetry planes are different: in brachiopods, the symmetry plane goes across the shells, whereas bivalves have the plane of symmetry between the shells. In effect, this means that the two shell halves are identical in molluscs, but not necessarily in brachiopods – in fact, brachiopod shell halves are always different, the ventral (down-facing) being larger (but they sit upside down, so the ventral appears as the top shell in life position).

Comparing the symmetry planes of brachiopods and bivalve molluscs (‘valve’ is just a fancy word for an invertebrate shell). Image from http://www.kgs.ku.edu/Publications/PIC/pic24.html

Bryozoa, moss animals, is another group that has seen its glory days in the past, but now is quite uncommon. Like brachiopods, they are marine, sessile filter-feeders (and of course bilaterally symmetrical triploblasts). They also have a lophophore, which they can extend out to the water to trap particles carried with the currents, and retract to bring the food to the mouth. Their perhaps main characteristic is a ‘crown’ of hollow tentacles.

Bryozoans. Image from http://goldfishgarage.blogspot.co.uk/2012/04/plumatella-bryozoan.html

Bryozoans are typically colonial, like many corals are, living together in tightly associated communities, helping each other out. Bryozoan colonies are mostly clones (maybe they should be said to be ‘clonial’?) stemmed from an original individual. They may have specialised on carrying out particular functions in the colony, such as taking in food, excreting waste, etc., so they work as a super-organism.

Bryozoan colony. Image from http://www.starfish.ch/c-invertebrates/bryozoans.html

The common name of bryozoans refers to them looking a bit like mosses, but being animals. So, I guess that is a good clue: if you find something in the shallow seas that looks like a moss, it is probably a bryozoan!

Now let us take a close look at Mollusca, a very diverse phylum of bilaterally symmetrical, triploblastic invertebrates. We know many molluscs from our gardens (snails and slugs – gastropods) and dinner plate (mussels, clams, oysters – bivalves – and squid and octopi – cephalopods). Some, like the alien-looking monoplacophorans and polyplacophorans are probably less familiar. Because these are generally very different-looking subgroups, with rather different ecologies, we will look at them more closely than we have for the subgroups of previous phyla.

But first: what makes molluscs molluscs? They all have a mantle, which usually forms a mantle cavity, where important organs and stuff happen, and a muscular ‘foot’ that is typically used for movement – or for staying put, in the case of bivalves. Another shared feature is the radula, a rasping tongue, full of chitinous teeth on one side, typically used to scrape various foods off a substrate; however, the radula has been lost (evolved away) in the bivalves, which have no use for it, being filter-feeders. Moreover, molluscs usually have shells, which are secreted by the mantle; cephalopods are a notable exception.

Monoplacophorans and polyplacophorans (chitons) are not very familiar, but not very abundant either, so I will just show you some pictures for you to behold.

Drawing of a monoplacophoran mollusc. From the underside (ventral view) just looks like a gluttonous, fat blob monster. Image from http://www.ucmp.berkeley.edu/taxa/inverts/mollusca/monoplacophora.php

Drawing of a polyplacophoran mollusc. I strongly recommend you to google some images of live polyplacohporans: some are really pretty, others rather frightening… Image from http://www.marlin.ac.uk/taxonomydescriptions.php

Gastropoda comprises our familiar slugs and snails, the latter being the ones with shells (though neither are formal groupings; shells have appeared and disappeared here and there throughout gastropod evolution). They have a well-developed foot, used for locomotion, sometimes aided by slime and/or cilia (hair-like structures).

Gastropod shells are coiled, as opposed to the convex shells of mono- and polyplacophorans, and the bilaterally symmetrical two-part shells of bivalves. This reflects a process called torsion, which is unique to gastropods. As they mature, the bulk of the internal organs, including hearts, lungs/gills and intestines, is turned 180° inside the body. This also causes nerve threads to cross over, so the brain needs to compensate. In addition, this means that the anus points forward, and is located above the head, in mature individuals. Torsion occurs in slugs as well, but is not as conspicuous, as it is not mirrored by shell shape.

Drawing of a gastropod mollusc. Image from http://bio1151.nicerweb.com/Locked/media/ch33/gastropod-torsion.html

Bivalvia is probably the most specialised mollusc group. As already mentioned, they have lost their radula, otherwise so characteristic of molluscs, and their head is reduced to virtually nothing, including the loss of eyes and other sensory organs. None of that is needed, though, because they are filter-feeders. They use modified gills to filter food (instead of oxygen) out of the water, and bring it to the mouth. Like brachiopods, they keep their filtering organ inside the shell, and take in water through tubes called siphons. Their foot is used to either attach to a substrate, or bore into the sediment.

Drawing of a bivalve mollusc, with one shell half removed.

 Image from http://kids.britannica.com/elementary/art-66016/Internal-structure-of-a-clam

Finally, we have Cephalopoda, the squids and octopi. They are the most advanced molluscs, some with brain capacities matching mammals! Cephalopods are also notable for having evolved complex eyes independently of vertebrates!

Cephalopods are adapted for swimming rather than lumbering across a surface, making them the fastest among the molluscs. The foot is modified into tentacles, used for swimming, and the siphon can expel water explosively, giving a speed burst if the animal needs to escape quickly.

 

Cephalopod mollusc. Image from http://bogleech.com/bio-ceph.html

The mouth, containing a radula, has a sharp beak, looking pretty much like that of a bird. Most cephalopods today have no shells, but the now-extinct ammonoids and nautiloids (represented by a single living genus: Nautilus) exhibited elaborate shells in ancient times. A final epic thing about cephalopods is that they basically have three hearts!!

...aaand another one

Okay, this time I'm making it a bit more complex, but hopefully it should still be fun and engaging!

Figure out which five key events in the evolutionary history of life you think are the most important. Write two paragraphs for each, the first explaining the event, the second analysing the results and why these are so important. Finally, pick three other key events that are not so important, and write down what they were and why they were not as significant as the first five. 

Next thing

Think about why some animal groups have remained virtually unchanged through their evolutionary history. Consider as many examples as you can come up with, and look for a common trend. 

Some examples to get you started:

Sharks
Turtles
Spiders
Scorpions
...

(and it's not "they all start with 's'" :p )