I've removed the body wall now from the three arms and also from the central disc and I'll just point out that um as I was cutting the surface of the central disc off I was careful to leave behind the madp porate that I showed you earlier the little round uh White structure I'll get back to that uh in a moment again but I just wanted you to note that if possible try not to remove that part of the skin simply cut around it okay so you'll note that as I mentioned the internal structures in each of the arm are identical and the first thing that we can see is this uh rough looking uh sort of spongy brownish Mass on top of each one those are called pyloric seea and they're ESS essentially analogous to um the digestive gland that we've seen in other animals okay so they function basically as as a liver they secrete digestive enzymes that the stomach then is able to use um to break down food so I'm going to actually remove the pyloric Sea from One of These Arms sort of tease that off carefully and get that out of the way so we can see what's underneath now what you'll see here um you'll notice that the color has changed slightly and the texture has changed slightly these little structures all beneath here and also on this side they're sort of roundish these are called gonads so the gonads um obviously are involved in reproduction that's where um the sex cells are produced okay so there's some gonads on this arm I'm going to remove both the gonads and the pyloric sea so we can see what's underneath and now we're getting into something completely different okay so you'll note right away this sort of bony looking Ridge here this is called The ambulacral Ridge okay on either side of the ambul Lal Ridge along this surface here and along this surface here you may be able to see some very small um round and sort of jellylike little structures and those are called ampuli okay or an ampula would be the right word so ampuli okay and Uli and this ambulacral Ridge they're also involved in the water vascular system now I'm going to come back to the madreporite so I can explain a little bit how this works water enters the madreporite which is a a porous surface and you'll note that it's attached to this there's a little tube right here okay so this little tube just broken it off there but this little tube enters a series of canals there's something called um a ring Canal which runs along basically this circumference here of the central disc on the inside and from The Ring Canal water then enters what's called a radial Canal which runs it's hidden and protected underneath this ambulacral Ridge okay so water then is able to enter from the radial Canal it fills these little Uli these little balls and they become essentially little sacks of water when the Uli are squeezed they push water out into the tube feet so you'll recall we saw these tube feet underneath here those are directly connected to the ampuli so in squeezing water into the tube feet they are um Extended or retracted if water is then also taken out and and that's what's responsible for allowing them to move so you can see how this water vascular system uh essentially acts as sort of a hydrostatic or a hydraulic system to move different body parts in case you're curious um these sort of they look almost like uh little ribs running along here those are called dermal oses okay sort of dermal bones or skin bones essentially and these form uh the skeleton of the animal and they are connected to those spines that we saw on the exterior as well so the spines and these dermal ticles they're all part of the skeletal system of this animal now uh we can look up here into the area of the central disc and um it's a little bit of a mess I'll be honest with you but there are some structures up here that that are of significance um this top part this very soft spongy Mass um was at one part uh part of the digestive system it was a stomach the stomach is actually a it's a two chambered structure there are two separate stomachs the one on top here is called the pyloric stomach okay and underneath that we may be able to see some remnants of what is called the cardiac stomach underneath and this is probably some tissue from the cardiac stomach there again a little difficult to see with this specimen but what I'd like you to know is that one thing that is interesting about the way this animal feeds is that its stomach is iable which means that it can be pushed out of its body turned inside out essentially when the starfish is feeding um for example say it's caught a by Valve and it's it's holding it with its arms right here um it's able to pry the valves open to to gain access to the viscera inside it then um ints its stomach out through the mouth so it pushes its stomach out through the mouth pushes it into uh in between the valves of its of its prey the digestive glands that we saw earlier those pyloric sea they secrete gastric juices out and enzymes to start the digestion process basically inside the clam and um so once that sort of chemical digestion takes place um the food is basically slurped back up into the stomach the stomach is brought back into the body cavity and and digestion finishes in there and there is this is a complete digestive system there is an anus as well um you won't be able to see it this this small opening for the anus um does empty out via the central disc there's a small pore there that allows waste matter to be excreted as well so that is basically the internal anatomy of a sea star