I will no longer provide notes on the different animal phyla. It is taking too much time to convert them into note form. I may provide my last semester notes, with all their typos and mistakes, but will  concentrate instead on the ideas that connect all this together.

This post helps to explain why life on Earth was microscopic for 3 billion years and how it was able to overcome the physical constraint that imposed the size limit on life. Read these notes first:

2 Surface Area

I saved you the trouble of doing the math, however, try to understand what the math means. As much as students, typically, do not like math, it is the language of patterns and understanding some math allows us to understand why some phenomenon occurs as it does, and allows us to extend the pattern and make predictions. In this case, it explains why sponges are the way they are and could not change in the last 600 million plus years and why the evolution of organ systems allows the largest animal ever to exist on Earth, the blue whale, to exist. Which leads us to the following:

3 Homeostasis

With these two notes as background, you will have a better understanding of why the animal phyla showcased in the Shape of Life series progress as they do. I recommend you watch, or re-watch, the rest of the series with these notes in mind. The order should be, after the sponges,

https://www.shapeoflife.org/video/cnidarians-life-move

https://www.shapeoflife.org/video/flatworms-first-hunter

https://www.shapeoflife.org/video/annelids-powerful-and-capable-worms

https://www.shapeoflife.org/video/marine-arthropods-successful-design

https://www.shapeoflife.org/video/terrestrial-arthropods-conquerors

https://www.shapeoflife.org/video/molluscs-survival-game

https://www.shapeoflife.org/video/echinoderms-ultimate-animal

https://www.shapeoflife.org/video/chordates-we%E2%80%99re-all-family

The next set of notes will highlight the crustaceans and insects, sister clades, meaning they share a common ancestor. They look extremely different simply because one evolved for water and the other evolved for land. Again, life is the way it is because of the planet we live on. Just as how the planet is now is because of the life that evolved on it. We do not live on the planet, we are part of the planet and it is part of us.