If you are lucky and once you find yourself on the shore of the ocean, you will see sea stars. They come in a variety of sizes and colors, but have you ever wondered how this multi-armed or multi-legged creature manages to live in the oceans, remaining so unlike other animals? The other day PRSB published a study that not only stressed that the starfish have eyes, but also revealed what it can see in the dark. A starfish may seem rather inanimate, like a clam seated on the ocean floor and absorbing nutrients from the water. But in reality this is not so.
See and glow in the dark
Most sea stars have a rough eye on the tip of each arrow. These compound eyes contain several lenses (ommatidia), each of which creates one pixel of the total image that this creature sees. Tropical starfish can see with their own eyes rough images that allow animals to stay closer to home.
The scientists found that some species of deep-sea starfish, found at a depth of 1 km below the surface of the water, where sunlight does not penetrate, can see, despite the darkness. Most species that can see in the dark depths of the ocean have more sensitive eyes, but see coarser images. These same starfish seem to distinguish objects more distinctly than their tropical counterparts living on the bright shallows.
Scientists offer different explanations for this. Some species apparently clearly see in the horizontal direction, but less clearly in the vertical direction, which is absolutely true for the organism that lies on the seabed. Other species, apparently, have less opportunity to detect changes in what they see over time.
Two of these species are also bioluminescent, that is able to produce short flashes of light on the surface of their body. The combination of these light flashes and the ability to see clearly allows these deep sea stars to communicate with potential partners.
Hungry predators, crabs or fish, can bite off the starfish to sea stars. If a fight is launched, some types of sea stars voluntarily lose their limbs so that the rest of the body can escape. Moreover, they can regenerate an entire limb. If you find a starfish, which has one arrow less than the rest, it is likely that this is a new limb.
On sea water
Marine stars do not have the usual set of muscles. Instead, they move with the help of sea water, which is under pressure in the vascular system of their bodies. They draw seawater through the pores, then it passes through the internal channels to the limbs, and they already set in motion thousands of tubular “legs.”
The muscles and valves inside each tube squeeze the water, which allows them to stretch and retract, creating movements as when walking with their feet, but multiplied by hundreds of times. At the end of each tubular leg is a tiny sucker that can stick to the surfaces and helps the stars to accelerate.
Starfishes are extremely effective predators of the seabed, feeding on a wide range of products – mussels, mollusks, oysters. They creep up to their prey and use the legs to simultaneously capture the prey and press it to the seabed.
If the production is small enough, the starfish swallows the entire animal, inflating its stomach located in the center. Keeping the position of a mortal grasp, the starfish will gradually dissolve the edible soft tissues, using enzymes inside the stomach, and then throw out the inedible solid parts of the shell.
But if the victim is too large to put it in the stomach, the starfish will first try to open the shell doors, and then push her stomach into the gap so that he can destroy the soft tissue inside the victim and digest it right in her house, as if sucking through a straw.