The Strange Story of a Sea Star’s Suppertime

sea star

Sea stars use an unusual method to digest their meals. (Photo credit: Photodisc/Getty Images)

Have you ever ridden a rollercoaster? If so, you probably well remember the feeling of that first, big drop. Many describe the sensation as feeling like my stomach fell out of my body.

Of course, its only an illusion caused by the sudden shifting of the forces acting on the body. Indeed, while after a big meal we may wish our stomachs could be taken out of our bodies, were stuck with them and that bloated feeling for as long as it takes to digest the food. For a certain group of sea creatures, however, this isn’t the case. Sea stars (often referred to as starfish) literally spew their guts out in the process of having a meal. This curious method of digestion allows them to get at food sources that otherwise would be impossible, if not quite painful, to eat with a regular old mouth and set of teeth.

Sea stars are marine invertebrates that belong to the class Asteroidea. They get their name, obviously, from their curious anatomy, which in most species consists of a central disc with five protruding arms, although some species can have up to 40 arms. They live on the sea floor and can be found in oceans from the tropics to the arctic, not to mention in some home aquariums. Most likely, the sea stars that most of us have seen are only the dried-out remains of once living animals. These are popular curiosities for both children and adults because of their unique shape. But, don’t let the seemingly benign appearance fool you. Sea stars may seem harmless, but in ecological terms they are considered to be a keystone species, that is, a species which has a disproportionately large effect on its environment. In many instances, sea stars can have a decisive influence on what other species can live in a particular environment. Some sea stars prey on coral, and others, if unknowingly introduced into a new region, can begin attacking already endangered species and so upset the ecologic balance in that region. While no species of sea star is exceptionally large or ferocious when compared to some other denizens of the deep, a large part of the why they’re able to exert such a great influence on all those around them is the way they eat.

Sea stars have two stomachs: the cardiac stomach and the pyloric stomach. The stomachs get their names from their positions in the body, the cardiac stomach being the one closer to the sea stars mouth. When the sea star encounters a potential meal, it pushes its cardiac stomach outside its mouth and literally engulfs the food whole to start digesting it. After a while, it brings the stomach back into its body, passes the partially digested food into its pyloric stomach, and continues digestion. Many sea stars eat clams by using their powerful vascular water systems to blow a tiny opening in the clams shell through which it can insert its stomach and start digesting the insides. Of course it eventually will need to retract its stomach, but it can do this after the clams insides are a much smaller, already partially digested chum. Thus, while the shell may be a good defense for the clam against many predators, its no match for the sea star when it decides to spill its guts.

Researchers at Queen Mary University of London and Warwick University are hoping to lend a hand to clams and other bivalves in their defense against the home invasion of the sea stars stomach. They believe they’ve identified the neuropeptide that regulates stomach contraction and retraction in the sea star. If so, they feel this can lead to chemically-designed strategies to combat sea star predation and its adverse ecologic and economic consequences. Maurice Elphick, Professor of Physiology and Neuroscience at Queen Mary’s School of Biological and Chemical Sciences, the leader of the research team, adds that “Interestingly, we have also found that the neuropeptide behind the stomach retraction is evolutionarily related to a neuropeptide that regulates anxiety and arousal in humans.” Put another way, perhaps much of the problem from sea stars arises from the fact that they are the ultimate nervous eaters.

More to Explore
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Watch This: A Starfish Digesting Its Prey, From the Dinner’s Point of View (video)


  1. Certainly a satisfying story which satiated my salivation for substantive stories sensitive to the situations in which sea stars struggle successfully to survive.

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