What are the main food sources of starfish?
Starfish are the most representative group of echinoderms in terms of structure and physiology. Their bodies are flat, mostly with five-ray radial symmetry, and the boundary between the body disc and the arms is not obvious. There are 1600 extant species and 300 fossil species, widely distributed in sandy seabeds, soft mud seabeds, coral reefs and oceans at various depths. Let us take a look below at what starfish eat!
What do starfish eat?
Starfish are all carnivorous animals and can feed on various invertebrates, especially shellfish, crustaceans, polychaetes, and even fish. The starfish is a greedy predator. Because it cannot move as nimbly and swiftly as a shark, its prey are slower-moving marine animals, such as shellfish, sea urchins, crabs and sea anemones. When hunting, it often adopts a slow, roundabout strategy, gradually approaching its prey, grabbing the prey with the tube feet on its arms and wrapping its entire body around it, then ejecting its stomach from its mouth and using digestive enzymes to dissolve the prey outside its body and absorb it.
Classification of starfish species
1. Paxillosida: The arms have two rows of obvious marginal plates and no papulae. They live on soft seabeds. The tube feet are in 2 rows, without suckers, arranged in two rows in the ambulacral groove, which is favorable for burrowing in mud and sand or crawling. Most deep-sea starfish belong to this order, such as the maple starfish, which filter-feeds with cilia.
2. Valvatida: The marginal plates are very small, and the pedicellariae are simple or absent. There are clustered spines, and the tube feet have suckers, but pedicellariae are rare. The common goosefoot starfish is found on the stony seabeds of Europe. The northern genera Asterias and Solaster have many short arms and a relatively wide body disc. The spiny starfish has 15 arms.
3. Forcipulatida: They have bivalved pedicellariae with long stalks, and the spines serve a protective or feeding function. Among the common species that feed on bivalves in shallow water are the red starfish distributed in Northern Europe and the many-spined starfish from the Bering Sea to the Korean Peninsula. The short-spined bean starfish on the west coast of North America reaches 65 cm and is one of the largest starfish in the world, feeding on sand dollars, sea urchins and the like. The many-armed sunflower starfish from Alaska to California has 15-24 arms. The genus Pycnopodia starfish of Central America has as many as 50 arms.
How starfish prey
1. Most starfish have long, bendable arms, and the tube feet have suckers. They mostly feed on bivalves. When feeding, the body is positioned on the shell, with two arms attached to the two sides of the shell. Due to the vacuum action of the suckers at the ends of the tube feet, their pulling force is enough to pull open the shell valves of bivalves. The starfish immediately turns out its cardiac stomach and inserts it into the shell opening, and secretes digestive enzymes until the adductor muscle and part of the internal organs are digested, the shell opens completely, and then the stomach surrounds and swallows the food, which enters the mouth together.
2. Some species with short arms and no suckers on the tube feet feed on smaller animals such as small crustaceans. When feeding, they swallow the food whole, and digestion takes place in the stomach rather than outside the body.
3. Species living in the deep sea feed by ciliary filtration. Through the action of cilia, settled organic matter and the like falling onto the body surface are swept into the ambulacral groove, forming a food string, which is then sent into the mouth, for example the maple starfish. Another example is the chicken-foot starfish, whose gastric caeca contain cilia, and the movement of the cilia helps draw food into the stomach.