Radically Radial: The Sea Star
Posted on March 19th, 2019
Imagine a creature with such a radically different body plan that we, bilateral humans, can’t really fathom how they have been so successful. Sea stars, and other echinoderms, move and feed like no other animals. They are animals that followed a different evolutionary path after evolving from the same bilateral ancestors as us.
Many still call sea stars “starfish”, but they certainly aren’t fish. No head, no tail, all arms –sea stars are just that: stars. Based on five-part radial symmetry (though some sea stars have many more arms), key functions are coordinated in the center of their bodies, then passed down the arms. The sea star has no brain, but a nerve ring in its center, like a relay station that coordinates the movement of its arms. This nervous system relays impulses from light, touch and chemical sensors around its body.
Marine flatworms can dazzle with wild colors and patterns – if you’re lucky enough to see one. They live from the intertidal to tropical coral reefs to deep water. The free-living flatworms (polyclads) have thin, almost leaf-like bodies and move with a gliding motion. Their ancestors were some of the first bilateral animals, and being bilateral gives them a body plan designed for an active life style.
Where we at Shape of Life live, we know when anchovies are in the neighborhood because when we go down to the ocean, we’ll see hundreds of diving sea birds, jumping sea lions, and if we’re lucky, humpback whales. They’re all here to feed on massive schools of anchovies close to shore. As they swim through the water with their mouths open, anchovies strain out plant and animal plankton. They then are food to all of the animals we see plus so many more, including larger fish and people. In fact, these small schooling fish (@nine inches long) support a large part of the oceanic food web. Some scientists say anchovies are the most important prey—also called forage fish—in the U.S. Pacific Ocean. 
Those pin-cushion looking creatures you want to avoid touching or stepping on are sea urchins. There are about 950 species living in all oceans and depth zones, from the intertidal to 16,000 feet deep. Sea urchins are echinoderms, related to sea stars and sea cucumbers. Although that might not seem immediately obvious, sea urchins have five-part symmetry (watch our video on the body plan of these animals: 
Cephalopods (octopus, cuttlefish and squid) seem to be flourishing in our changing oceans. Their numbers are increasing worldwide according to a 
Albatrosses are amazing sea birds that spend over 80% of their lives at sea, visiting land only for breeding. An albatross can live up to 60 years and in that time it would have travelled millions of miles. To fuel their large size – they are the largest flying birds – albatrosses feed mainly on squid but also on fish eggs and crustaceans.
Believe it or not, millions of tiny delicate coral animals create the enormous coral reefs that can even be seen from outer space. The coral polyps (cnidarians related to anemones and jellies) live in a colony. Together they build a mineral skeleton from calcium carbonate, which creates a complicated reef structure with a myriad of shapes and sizes.
Imagine the oceans 530 million years ago, during the Cambrian Explosion, filled with creatures alien to us today. Anomalocaris (ah-NOM-ah-LAH-kariss), from the Greek meaning “unusual shrimp”, was a major predator of those ancient seas. Fossils from the Cambrian in the Burgess Shale in Canada, and formations in China, Greenland, Australia, and Utah show that this large, ancient shrimp was widespread during this period.