Category: Invertebrates
Also known as starfish, these echinoderms are found on the sea floors of all the world’s oceans from the equatorial tropics to frigid polar zones. There are around 1500 species of sea stars, some being able to survive at abyssal depths of 20,000 feet below the surface of the ocean. They usually have a central disc with five arms, though some exceptions have more. Their tube feet, which help them move, maneuver food, breathe, and also attach themselves firmly to rocks and other underwater structures, are operated by their “water vascular system,” a hydraulic system of interconnected fluid-filled canals. Their digestive system or “gut” occupies most of their central disc and also extend into their arms.
https://en.wikipedia.org/wiki/Starfish
The world’s first Animals
Invertebrates were the first animals to evolve. While their soft bodies left precious few records behind, there are fossils of sponge-like animals that are 665 million years old, as well as traces of tracks and burros from worm-like animals going back 1 billion years. By comparison, the earliest birds appeared only 150 million years ago! And not only were invertebrates first, they are the most plentiful of animals - it is estimated that 97% of all animals living on the Earth today are invertebrates, with several groups containing more species than all vertebrates combined!
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