Overview of Animals - 4

by Jason Amores Sumpter
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as animal bodies develop, they start to form various types of symmetry along certain axes of the body. And what were you often will think of? His less complex organisms tend to show what's called radial symmetry, where basically the body parts are all arranged around one main axis. And you can see um, example of radial symmetry right here in this hydra. And basically the way to think of it is that, um if you put a plane in any direction through the top of this hydra, uh, it would look the same on both sides, right? Each side of the plane would mirror the other, no matter how you shifted it, right? So if we took, uh, for example, this plane and then shifted it over to this position, we'd still have more or less the same looking halves of a hydra on either side. Now, organisms that we typically think of when we think of animals are violet Terrians. And basically that means that they have a bilateral symmetry and this is ah, body plan that's divided into roughly two equal halves. So essentially, there is a, uh, in these animals bodies. You can draw a line through a particular point and you will have a mirror image on either side. But you can't shift that plane around right. We can't shift it this way or this way, because then we'll end up with uneven halves, right? The haves won't mirror each other anymore, which is not the case for these organisms that have radial symmetry. So just to be clear, this is bilateral symmetry here and here. This is actually an example of Hey, symmetry. This organism doesn't show any symmetry, its's type of sponge, and, uh, there are some organisms, some animals that don't show symmetry. However, most that we're used to thinking of are going to show bilateral symmetry. And as as we learn, that's because there was an explosion of bilateral fila during the what's called the Cambrian Explosion. All right now, there are also some important body axes to know, and that's because there's some terminology used to describe the position of things. So here we have our person. Uh, so, of course, this person has bilateral symmetry, right? And these terms are going to refer thio, uh, different directions along three axes of this person's body. So anterior anterior is things that point towards the head. That's anterior. The opposite of anterior is posterior, which is things that point toward the tail more or less. Of course, humans don't have tails. We still have a little tailbone. There you get the general direction. That's why sometimes your teacher might call your but your posterior, sort of a polite, I guess, way of saying it now. There's also ventral and dorsal and those they're going to go along those directions. They're gonna be perpendicular to anterior and posterior. So ventral is toward the belly and dorsal is toward the back. And you might recall that dolphins, for example, have what's known as a dorsal fin, right? It's a thin on their backs. That's where the term comes from. So, uh, make sure you know these terms because they will be used to describe the position of things when talking about anatomy. Alright, that let's flip the page