The episode discusses the evolution and unique characteristics of sea stars and their relatives. It begins with the evolution of sea stars from a bilateral baby to a round baby, which eventually forms a body cavity filled with advanced hydraulic systems. The skeletons of echinoderms, including sea stars, are made of ossicles, which are like 3D printers that create a porous honeycomb mesh of magnesium calcite. This structure is flexible and can form a solid dome or test in sea urchins.
The episode also discusses the unique walking style of sea stars, which involves using their arms in a sort of breaststroke. They can change direction quickly without turning, leading with a different arm.
Sea stars have a distributed nervous system, with individual parts of the arms sensing and reacting to stimuli on their own. They have a compound eye on each arm, which allows them to have a near 360-degree simultaneous field of vision.
The episode also discusses the feeding habits of sea stars, which can vary greatly depending on the species. Some species feed by suspension, using their arms to trap floating particles. Others feed by using their pedestal larvae to catch prey.
Sea stars can regenerate lost limbs, a process that involves using special collagenous tissue throughout their bodies. This tissue can harden or soften quickly, allowing the sea stars to crawl into cracks when they're limp and then stiffen up to be wedged in there.
The episode concludes with a discussion on the reproduction of sea stars. Some species reproduce by splitting in two, while others release their baby-making bits into the water.
The episode is sponsored by Brilliant, an interactive stem learning platform that helps users understand concepts in science, math, and computer science.
1. Sea stars and other echinoderms evolved from an ancestor that wanted to be a circle.
2. The ancestor's descendants often start their lives as two-sided bilateral babies.
3. As these larvae grow, a second baby starts to develop inside them, which eventually bursts out into the world.
4. The new body plan of echinoderms has radial symmetry.
5. The skeletons of echinoderms are made out of ossicles, which are porous honeycomb mesh of magnesium calcite.
6. These ossicles allow tissue to grow inside them and to connect them to other ossicles in a kind of 3D jigsaw puzzle.
7. Sea stars have a series of canals connected to rows of tube-like nubbins, which are controlled by a valve called the madraporite.
8. Sea stars use their tube feet for various functions, including breathing, absorbing oxygen, walking, and even eating.
9. Sea stars have a distributed nervous system, with sensory tubes and little eyes on their arms.
10. Some sea star species have modified tubed feet that act like sunglasses, allowing them to search around for things to eat.
11. Sea stars have a unique way of feeding known as suspension feeding, using their arms to trap floating prey.
12. Sea urchins have evolved a unique feeding mechanism, using their pedestalari to inject toxins into anything they touch.
13. Crinoids, a type of sea star, have evolved a unique feeding mechanism that involves using their arms to scrape algae off rocks.
14. Some sea lilies have evolved a daring escape plan, where they can weaken and break their stalks when threatened, allowing them to escape by crawling away.
15. Sea stars can regenerate lost limbs by using a special collagenous tissue throughout their body.
16. Some sea stars can even regenerate their entire bodies by splitting into two and growing a whole new starfish from the remaining part.
17. Sea stars reproduce through a unique process where males and females release their baby-making bits into the water, cross their little tube feeds, and hope for the best.