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Video transcript

hi there just hanging out with some of my distant relatives here and I got to say I got a lot of respect for these guys because they are some of the most successful organisms on the earth we think we run things on this planet but we don't they do on one acre of cultivated land annelids like this earthworm process about 16,000 pounds of soil a year which makes plant life and our lives therefore possible and not only are there about a billion billion arthropods like this in the world that's 10 to the 18th power by the way but also 80% of known animal species are arthropods and don't get me wrong even though bugs and spiders and worms and shrimp totally outnumber us humans we are far more complex than them when it comes to like armwrestling and guitar playing and long division we totally school them but complexity like ours had to start somewhere and it started with a very special trait that we share with these animals can you see the resemblance austan we talked about how in the very simplest animals there are two traits that indicate an animal's relative complexity there's how many germ layers they develop when their embryos and whether or not they have a coelom or a body cavity that holds their organs so it's in the next two phyla annelida and arthropoda where we find the new big thing in animal complexity segmentation segmentation is the repetition of anatomically identical units that can be added to and modified to serve different purposes as animals evolved and evolution is the way to win it folks in fact the three biggest and most diverse groups of animals in the world are the ones that display segmentation annelida Arthropoda and Chordata which includes the vertebrate all segmented animals have a common ancestor that probably lived about 600 million years ago that's how long ago it was when one of your grandparents and one of the earthworm's grandparents and one of the beetles grandparents all played on the same softball team pretty great segmentation has proven to be unbelievably useful from an evolutionary perspective in humans you see anatomically identical pieces repeated along an axis from our butts to our heads there can be a little hard to see because they're so highly modified but think about our vertebra their segments our ribs our segments the cartilage around our Czechia those are segments even the folds in our brains are segments they're crazy evolved segments but segments just the same among today's NL file of the earliest to display segmentation is annelida which includes leeches and earthworms and lugworms see how their whole bodies look like rings fused together segments in fact the word annelida comes from the greek for little rings and when you look at an analytic mented now this segmentation is a great example of synapomorphy and analysts NAPA more fees are traits that set one group of animals apart from its ancestors and from other groups that came from the same ancestor so one like they're flat warm and neematoad cousins annelids are segmented and they've also got little bristles on their bodies called key tey that provide traction and help them move through the dirt these are both a little extra something's that annelids have that less complex relatives don't have and that their common ancestors didn't have synapomorphies literally shared derived traits are usually the defining traits of a phylum but you can also learn something about an animal's lineage by comparing please yo more fees very basic traits that are shared by animals with a common ancestry so between the platyhelminthes and the nematodes and the annelids one please Oh Murphy is that they're all worm-shaped which tells you that they have a common distant ancestor that was were me looking so as we talk about these phyla and the classes within them notice how they're similar and different from each other for instance within a Nolita there are three different classes everybody's favorite of course is the all ago Keats the earthworm's their name refers to these synapomorphy I just mentioned they have key tey or bristles but only an awl ago few of them and they're everyone's favorite because they eat soil and crap it out the other end allowing air in water to circulate in the soil plus their poo is rich in things that plants need to grow like nitrogen and calcium and magnesium and phosphorus and now I'm gonna go wash my hands sound the glass hair edenia the leeches a lot of which are parasitic and you know eat blood and other bodily fluids the synapomorphy of leeches are their powerful suckers they've got them on both ends of their bodies the posterior one being used to anchor itself while the anterior one that surrounds its mouth attaches to its host all eight species are carnivorous and they are hermaphrodites like earthworms now the poly gates are bristly worms hence a synapomorphy of this class is their poly many kita bristles almost all these are marine species and they're really diverse but the ones you've probably seen evidence of our lugworms the ones that dig holes at the beach and leave piles of castings on the sand okay I know you've had enough of worms and now we've got Arthropoda to talk about and that's very easy to do because there are a lot of them like I said they totally outnumber us just to put things into perspective there are more insects in a square mile of rural land than there are human beings on the earth one reason to scientists think arthropods do so well has to do with their you guessed it segmented bodies fossils of early arthropods show that there used to be very little variation between segments but as they evolved segments fused and became specialized for different functions which led to crazy amounts of diversity so much diversity that Arthropoda includes stuff like scorpions butterflies and lobsters which I know seems like maybe a bit of a stretch but here the synapomorphies that make them all arthropods one they have segmented bodies that in most cases are broken up into three segments head thorax and abdomen and check this out here segmentation in arthropods is a good example of please yo Murphy it's a basic ancient trait that they share with annelids and us coordinates for that matter dating back to that softball game our forebears played some 600 million years ago to all arthropods have an exoskeleton a hard outer shell made out of chitin which is a really tough carbohydrate that's chemically similar to the cellulose that you find in plants and in order to grow bigger they actually have to shed it and be glad that you don't have to do that because it looks like kind of a traumatic experience for them finally they've all got paired and jointed appendages which is actually where their name comes from arthropod means jointed feet but it's not just their legs that are jointed some of them have claws and jointed antennae and they all have these external mouth parts that are also jointed so that's what arthropods have in common but they are grouped into four sub phyla based on how they differ from each other first and perhaps most terrifying you have your Chalisa reform ease which includes spiders and scorpions but also horseshoe crabs which are kind of nice antics which aren't and mites which don't bother you at all probably they might chalo so reform use comes from the Greek for arm lips which whatever Greeks refer to their long fang-like pinchers unlike a lot of arthropods they have simple eyes with just one lens not compound eyes like flies and they lack antennae most Chile's are reformed use our landlubbers but the fossil record tells us that a lot of them were marine back in the olden days sea spiders and horseshoe crabs are the only ones left now the largest class of chiloé so for me are the arachnids the group that includes spiders at scorpions and ticks and mites and they have what's called a cephalothorax which is a head segment and a thorax segment fused together with eight legs and an abdomen behind most directin sar carnivorous or parasitic and they're very skittery just Sam next myriapoda or many feet includes what you would expect the millipedes and scent beads these are where the author pods were like let's see how far we can take the segmentation thing shall we all myriapods are terrestrial and have an 10a and sort of scary jaw like mandibles millipedes are vegetarians and they may have been some of the very first animals to live on land where there were mosses and primitive vascular plants for them to munch also although millipedes have a crap-ton of legs they don't have as many as a thousand as their name implies they've actually got anywhere between 94 and 394 legs depending on the species centipedes whose name is a little more Aptus they generally have between 20 and 350 legs are carnivores and have poisoned claws to paralyze their prey so if you're looking to cuddle with a myriapod I'm going to advise you to go with the millipede but please save some love for the hexapod of meaning 6 feet most of which are insects the synapomorphies day share our 3-part bodies consisting of a head a thorax and an abdomen three pairs of jointed legs that come off the thorax compound eyes and two and 10a now think of any random way you could put these characteristics together and you probably come with something that exists because you guys there are so many damn insects out there you have no idea there are more species of insects then there are all other animal species combined which is why I'm taking this opportunity to do a biography the insects Edition very little is understood about the evolution of insects but scientists think that they probably split off from their crustacean cousins about 410 million years ago and for tens of millions of years insects and some little skittery and vertebrates were about the only land dwelling animals about 320 million years ago thanks to the high oxygen levels of the Carboniferous period some insects grew to be terrifyingly big like the mega Nora which looked like a dragonfly with a two-foot wingspan but since an insect size is restrained by its respiratory system as oxygen levels went down these massive insects couldn't circulate enough oxygen to keep their gigantic bodies going and they died off the next major milestone of insect history occurred from 120 million years ago which is when most flowering plants evolved and with it the sweet spirit of cooperation that insects and flowering plants still share to this day in fact some insects and flowering plants have co-evolved really neat pollination strategies so that they basically evolved together which i think is really sweet and as a result of insect pollination flowering plants are now the overlords of the plant world and thus everything smells nicer it looks prettier thanks insects insects are the only arthropods that have developed the ability to fly and it has served them well insects wings are just extensions of the cuticle of the thorax so unlike birds and bats which have to sacrifice walking legs in order to evolve wings insects are just as graceful on the ground as they are in the air but in order to be so awesome insects had to develop this crazy thing called metamorphosis in partial metamorphosis the young called nymphs look exactly like the adult of the species and undergo a series of multiples allows them to get bigger and bigger but they look basically the same the whole time most of the types of arthropods do this and some insects including grasshoppers and cockroaches however complete metamorphosis is a process unique to some insects that lets them completely change shape maggots turn into flies mule worms turn into beetles caterpillars turn into butterflies the baby insect called a larva I have one right here this is a rhinoceros beetle larva hangs out and eats until it's time to build a little case around self called a pupa this is the rhinoceros beetle pupa which is exceptionally creepy oh and then when it comes out of the pupa it's fully grown rhinoceros bed it's like soft at first and then it's chitin hardens up and it becomes it the adult so insects basically wizards but not as delicious as Crustacea the insects of the sea crustaceans include crabs lobsters shrimp and barnacles and like insect they have three body segments head thorax and abdomen although some have a cephalothorax like spiders do well most other arthropods have learned to love the land very few crustaceans have they have decided to put their energy into developing other amazing characteristics for instance lobsters and crayfish are like walking multi-tools they have 19 pairs of appendages some of which are claws some are mouth parts some are regular old walking legs some shrimp have evolved bioluminescence which is pretty much the most amazing thing any animal can do as far as I can tell and this Yeti crab looks like a Yeti and we've covered most of the types of animals on the earth and what ten minutes hopefully now you can see the resemblance between these guys I love my caterpillar
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