No one has even taken a stab at solving Puzzler A from last week. Maybe it's time I give you a clue. The location of the painting in question is a park in Spain. This puzzle is now worth 250 points.
Crustaceans vary from 100 µm to several metres in length. They are found in all habitats and at all depths. Whether they are barnacles, lobsters, pill bugs, or waterfleas all crustaceans have multiarticulate appendages, and probably the most durable exoskeleton of all the arthropods. There are five classes: remipedia, cephalocarida, branchiopoda, malacostraca, and maxillopoda. For the purposes of this particular Sunday Inverts selection, I plan to talk about them in a more generalized manner with an emphasis upon a decapods, an order of the Malacostran class. That’s the taxon that includes, lobsters, shrimps, crabs, and crayfish.
The crustacean cephalon has five pairs of appendages. The antennules and antennae are normally used for purposes of sensory perception, but in the larval form or nauplius, they are used to swim. The three other appendage pairs form the jaw: mandibles, maxillules and maxillae.
The cephalothorax is formed by tagmosis of the head and thorax,and is covered by a hard tergite (dorsal sclerite) called the carapace. That sentence might need a bit more explanation: tagmosis is the organization of arthropod body segements (somites) into tagmata. Tagmata are the compound body sections which results from embryonic fusion of two or more somites. Sclerites are skeletal plates which cover somites. Also for future reference sternites are ventral sclerites.
As you can see arthropods come with all sorts of jargon. Take thoracomere for example. It refers to a segment of the thorax. As you’ve already seen segments are also called somites, but sometimes they are also called metameres, even though most of the time metamere refers to the segments of an annelid. Anyways, if you stick thorax and metamere together you get thoracomere: thorax segment.
And there are quite a few thoracomeres, all with their own appendages. The first three appendages are called the maxillipeds and are mouthparts which assists the maxillules and maxillae. The remaining thoracomeres bear five pairs of perepods, also known as the walking legs. Walking isn’t all these legs do however, they they also swim, fight, feed, and even used in the process of gas exchange.
Now continuing down the body, past the cephalothorax is the abdomen. The abdomen, unlike the cephalothorax, is made up of numerous overlapping segments. Attached to these segments are more legs called the pleopods (swimming legs). The abdomen is the part which most people refer to as the tail. However, the tail is actually only made up of the last two pleopods (in this case called uropods) and the final abdominal segment (telson).
Confusingly crustaceans swim backwards. On one hand, they are really quick which really helps them out in case of an emergency. On the other hand, they can’t really see where they are going. When they are walking, they can pretty much go in any direction.
Feeding is quite different depending on which class you are referring to, maxillopods (barnacles) have long feathery thoracopods called cirri which they use to filter feed. Another interesting fact about barnacles is that they have the largest penises (compared to body size) in the animal kingdom.
As for decapods, their gut is divided into three sections; the foregut, the midgut and the hindgut. The foregut is quite complex and does a fair bit of the digestion. First the food is stored in the anterior cardiac stomach, then it’s moved to the gastric mill, which is still inside the cardiac stomach, only it’s the part with the teeth. Yep, that’s right, decapods have teeth inside their stomach. After the food is all chewed up it moves to the posterior pyloric stomach, where filtering setae prevent the passage of large particles from entering the midgut. The midgut is made up of the intestine as well as digestive ceca.
As for circulation, it’s the same in all arthropods. There’s a dorsal ostiate heart, arties and veins which empty into the hemocoel, and a cor frontale (anterior accessory pump). The blood is called hemolymph and contains phagocytic amebocytes, explosive cells (clotting agents) and dissolved respiratory pigments.
In the smaller crustaceans gas exchange occurs by diffusion across the cuticle. However, most species have gills. These gills are derived from thoracic epipods and are housed in branchial chambers (between the carapace and body wall). The branchial chambers protect the gills from damage and desiccation, but at the same time restrict the passive flow of water. In order to overcome this problem there are gill bailers, basically modified maxillae which create ventilating currents by moving water from the posterior to the anterior of the organism. Excretion is another function which is in part carried out by the gills. Although the nepridial excretory organs (antennal and maxillary glands) also assist in this process.
The nervous system has a tri-lobed cerebral ganglion like in all arthropods. The ventral cords are quite different depending on the shape of the crustacean. In crabs they are a bit more primitive and ladder-like in structure. Lobsters have the more advanced single ventral nerve cord with additional ganglia. As for sensory organs, there are mechanoreceptors, chemoreceptors, proprioreceptors, and statocysts. The eyes, or photoreceptors, are present in both the form of medial ocelli and lateral compound eyes. Some species of crustaceans have the unique characteristic of having compound eyes that sit upon stalks.
Most crustaceans are dioecious and brood their eggs. In development blastomeres are formed by holoblastic cleavage. That is of course with exception to the malacostracans which undergo meroblastic cleavage. Some crustaceans have a larval form known as a Nauplius.
Well, that’s the bare bones, or should I say bare exoskeleton, on crustaceans. It’s a little dry I know. I’m just trying to get all this terminology sorted in my head. Now that we’ve gotten the basics of one arthropod subphylum out of the way, we can see how other subphyla differ. I think the next instalment on Hexapods will probably be a lot more interesting. After all those fellas can fly...
Arthropods are an extremely diverse phylum of invertebrate animals. They are found in nearly every habitat on earth and make up 85% of all known animal species. Currently there are 1,097,289 known species of arthropods, and there is estimated to be another 3 million unclassified species. There are four extant subphyla of arthropods; Crustacea, Hexapoda, Myriapoda, and the Cheliceriformes. Additionaly there is also the extinct subphyla trilobitomorpha, more commonly known to as the trilobites.
So what do crabs, centipedes, butterflies and scorpions have in common? Well, quite a few things, the first and foremost being a shared ancestry. On a anatomical level they share a number of characteristics, such as their open circulatory system which has caused a reduction in the coelom (body cavity) and created a distinct cavity known as the hemocoel. Within the hemocoel all the organs of the arthropod are directly immersed in hemolymph (the arthropod version of blood).
Arthropods are also united by their unique nervous system. While it does share similarities with other organisms, such as the annelids, the tripartite arrangement of their cerebral ganglion is one-of-a-kind. It's partitioned in such a manner because the ganglia are formed separately and then fused together, while the organism is still an embryo. The result is the gluing together of the protocerebrum, deutocerebrum, and the tritocerebrum. However it should be pointed out that it is at this point we can also see the differences between subphyla begin to emerge, for the cheliceriformes have no deutocerebrum.
Externally all arthropods have an exoskeleton, made from chitin, proteins, and calcium carbonate. This exoskeleton is what allowed insects to move from the ocean, colonizing the land and eventually the sky. It protects arthropods from predation and perhaps more importantly, it protects them from desiccation and gives their bodies the support they need to live on land.
From time to time, arthropods will outgrow their exoskeleton, at which point they will shed it and grow a new one in a process known as ecdysis or molting. Ecdysis is controlled by two organs, the X-organ and the Y-organ. The Y-organ produces a hormone called ecdysone which continually tells the animal to molt. At the same time the X-organ is continually producing a molt-inhibiting-hormone (MIH) which stops ecdysone from taking effect. When the arthropod is appropriately stimulated, either by an internal or external source, the X-organ is inhibited from producing MIH, causing the MIH levels to drop to a level where they are no longer effective. The ecdysone is then allowed to work and the process of molting is initiated.
Ecdysis works by dissolving the procuticle, which is the tough by flexible layers of chitin and proteins just beneath the harder epicuticle of the exoskeleton. In the space where the procuticle once was, a new soft cuticle begins to form and the old epicuticle is shed. At this point the arthropod is not as well protected, so many species spend this time hiding. The body then swells by taking in large amounts of water, causing the new cuticle to expand larger then the previous exoskeleton. Following this the cuticle hardens by the processes of sclerotization and mineralization. The water is then eliminated and the inner tissues are allowed to grow and fill the empty space in the exoskeleton. If you’ve ever cracked open a big lobster claw only to discover a small flimsy hunk of meat this is because the lobster just molted.
Most arthropods are dioecious, and usually engage in internal fertilization. Their eggs are centrolecithal, which means the yolk clusters around the center. Like annelids they develop by a process of teloblastic segmental growth, meaning they develop their segments from their anterior to their posterior.
Arthropods usually have one pair of lateral compound eyes on their cephalon (head) as well as light detecting photoreceptors known as ocelli between these. They also have a wide range of other sense organs, which will be examined in further detail as Sunday Inverts continues this exploration into the world of arthropods in subsequent episodes.
As you may have gleaned from past blog posts I'm a fan of debates, and in particular those in which Christopher Hitchens is involved. Yesterday, the BBC aired one such debate on it's program Intelligence Squared which pitted Hitchens and Stephen Fry against Archbishop John Onaiyekan and Anne Widdecombe MP. The question: The Catholic Church is a force for good in the world?
Hitchens and Fry devastated the the other side. It almost seemed unfair two pit such a pair against Onaiyekan and Widdecombe. Interestingly the BBC conducted opinion polls of the audience before and after the event.
From The Telegraph:
The voting gives a good idea of how it went. Before the debate, for the motion: 678. Against: 1102. Don't know: 346. This is how it changed after the debate. For: 268. Against: 1876. Don't know: 34. In other words, after hearing the speakers, the number of people in the audience who opposed the motion increased by 774.
Also recently released in the new film Collision. Collision follows Hitchens and Douglas Wilson on a debating tour after the publication of their book: Is Christianity Good for the World?
Hitchens is of course, CON where Wilson is PRO. This film is for the most part a loose assortment of different clips from various debates, but it goes a little further to explore the relationship between these two men. Wilson and Hitchens believe the other to hold a morally indefensible position, a position which has major consequences for the fate of the world.
If you're interested in watching a regular debate than Collision isn't the answer. You can however find lots of Hitchens vs. Wilson debates all over the interwebz. Collision is a little different, and if you're inclined to find these topics interesting, worth a watch.
Today is the first official Carl Sagan Day. Sagan was an astronomer, astrochemist, skeptic, and a pioneer in the field of exobiology. If you are unfamiliar with Sagan I'd suggest getting your grubby mitts on a copy of Cosmos: A Personal Voyage. I know it's been released on DVD with a few updates, and it appears on PBS from time to time. There's also the more malevolent option of torrents as well. Ssshhh.
Sagan was probably best known as popularizer of science. In the early part of his career gained him flack from the more self-congratulatory members of the scientific community. But this didn't slow Sagan down, in fact it probably had the opposite effect of striving even hard to acheive his goal was of making science more accessible to everyone. His argument was that the scientific method is the best tool we have for understanding the world, and everyone should be provided with the basic toolkit which can allow them to view the world in more enlightened way.
This is one of the major premises of Sagan's book the Demon Haunted World, in which he presented the baloney detection kit. Below I have presented the abridged version of the baloney detection kit brought to you via Operation clambake.
The following are suggested as tools for testing arguments and detecting fallacious or fraudulent arguments:
This week's Saturday Morning Cartoon is The Real Ghostbusters: The Collect Call of Cthulu (Season 1 - Episode 41). Written by Michael Reaves. 1987.
Sometimes simple questions do not have simple answers.
Q: What is light?
A: It's a particle and a wave.
Q: What? is it a particle or wave?
A: Both.
Q: How can it be both?
A: 
Q: What does that mean?
A: Well...
Sometimes there are events which are not just hard to understand, but also scary, and ultimately beyond our control. Such befuddlement can become the breeding ground for conspiracy theories.
The terrorist attacks of September 11th, 2001 was one of those events. Before that day Osama Bin Laden, al-Qaeda, and the Taliban, were not household names, at least in North America. In order to understand the series of political events which lead up to the attacks, one needs to gain a deep understanding of the history of the Middle East, the growth of fundamentalist death cults throughout that area of the world, American foreign policy, and other very often complicated topics.
Even those that do have a good understanding of issues, like Noam Chomsky and Christopher Hitchens, disagree profusely over what the next reasonable course of action should be. What is not argued over, by anyone who has a basic grasp on reality, is who actually flew those planes into the buildings.
Yet to those who may be unfamiliar with the complexities of American-Middle East relations there is a vastly more simplistic answer: It was an inside job, the American Government did themselves. Why? They are evil.
Conspiracy theories can at first seem very intricate, but this pseudo-complexity is a false veneer. By the end of any of the recent conspiracy videos produced by the likes of Alex Jones, Dylan Avery(the Loose Change kid), or David "reptile overload" Icke, everything is summed up nicely into a tight little explanation.
This is always an erroneously simplified explanation. But if you seek to place order into a disordered world, such explanations will become more appealing. However, reality is not simple. Like the wave-particle duality nature of light, it takes time and hard work in order to understand complicated answers, even if the questions themselves may sound easy.
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