Can a starfish walk like that

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Anyone who has ever spent their relaxing holiday in a seaside resort will certainly find a few dried up Starfish () (Fig. 7). They are also very nice souvenirs, but they must have been thoroughly leached in fresh water before drying, otherwise they always keep sea salt in the body, so they easily absorb moisture and finally disintegrate completely.

Fig. 6. Male of the paper nautilus with free hectocotylus.

The ancient Romans considered such dried starfish to be a sign of good luck. In addition, there is not much that can be done with captured starfish, because with the best will in the world they are not edible and are even considered poisonous in many cases. Where, for example, many starfish are occasionally brought up from the sea bed with the oyster fishery, they are used to fertilize the fields, for which they are suitable because of their high calcium content.

It is extremely difficult to give the layman a really clear and comprehensible concept of the physical structure of starfish and echinoderms in general, because these animals are built so completely different from what we usually associate with our ideas of animals, namely not bilaterally, but radial. With them there is no front and back, no left and right, just an up and down. The skeleton that supports the body is not inside the body, but on its outside, but is not a calcareous excretion of the epidermis, but the dermis, i.e. still covered by a part of it and by the epithelial cells of the epidermis. That is why the movable pincers, spines and suction feet can also stand on the outside, which is why it has such a flickering appearance in living animals. The limestone framework itself is made up of a myriad of small, very differently shaped, but delicately arranged platelets. In contrast to the sea urchins, these are only more firmly connected in the center disc in the starfish, but loosely displaceable against each other in the beam arms, the gaps are only filled with soft connective tissue, which explains the great flexibility and mobility of these body parts.

Fig. 7. Starfish ().

The living starfish is by no means as hard and wooden as the dried one. Tiedemann took the trouble to determine the number of pieces of lime in the bitter orange starfish and came up with 12945, all of which can be moved and displaced against each other by tiny muscles. By way of comparison, it should be mentioned that the human skeleton, including the ossicles and 32 teeth, consists of only 245 pieces of bone. From the disc-shaped central part of the animal, five ray-shaped arms extend as a rule, which are provided with a deep longitudinal groove on their underside. The mouth opening, which leads into a closed intestinal canal, is located on the underside of the central disc itself. The echinoderms, in contrast to the coelenterates, have a real stomach, but are inferior even to the stupid oyster in that they do not have a heart straight away. The anus is only missing in the group of brittle stars. Between the spines of the mostly lively, most often red-colored upper side, there are still masses of small, pincer-like structures, the so-called. Pedicellariums. As long as animal science was still in its infancy, these little things, which look like bird's beaks and are serrated on their inner edge, have given rise to the most amusing mix-ups when they are found detached in the sea sand and examined microscopically, which is always a worthwhile thing . An English scholar proudly described it as the smallest vertebrate in the world he discovered, a fish barely 1–½ mm in length, and other researchers interpreted it as the claw thumb of a still unknown type of cancer. Much has also been argued about the biological significance of these grasping claws. Originally it was generally believed that they were there to pass small chunks of food that had been fished up at the tip of the arm, one to the other, to the mouth. In the case of the sea urchins this interpretation could not be completely dismissed, but in the case of the starfish it seems impossible, since there are also stretches between the tip of the arm and the mouth on which there are no claws at all or at least only so far away that one Passing chunks of food from one to the other is not possible. Therefore Marshall will probably be right, who regards the grasping claws as cleaning organs, destined to remove all the dirt and debris that settles on the often very dirty seabed between the spiked clothing. Indeed, it is amazing how pure and clean the starfish always look. On closer inspection we notice a small, slipper-shaped pad of a striking red color at the tip of each arm: the seat of the eyesight. This is because visual cells sit in this cushion, which have clearly separated rods at their ends protruding freely into the epithelium, but which are drawn out into a nerve fiber at their base. In some species, according to Hesse-Doflein, this system is perfected by the fact that the photoreceptor cells are not evenly distributed over the cushion, but are clustered in such a way that they delimit a thimble-shaped pit into which the rods protrude, in this way thus a pigment cup cell with increased vision is created. After all, the starfish with these primitive eyes can probably only distinguish between light and dark and shadowy outlines of objects.

Particularly characteristic of the echinoderms is the so-called. Water vascular system (Ambulacral system), a great branching of water-filled, calcareous-walled canals, which starts from the mouth and extends into the swellable, cylindrical suction feet ( Ambulacral feet), which are in the service of locomotion. On the upper side of the central disc there is a sieve-like perforated lime plate, through which the seawater flows into a short channel and from there into a second, which surrounds the intestine in the vicinity of the mouth opening in a ring and is therefore called an annular channel. A further main channel branches off from this ring channel after each of the five arms (radial channel), which in turn emits a myriad of small side channels to both sides like a spring shaft the individual rays of the spring flag. The side channels finally run out into the suction cups, which sit in two double rows close to each other in the grooves running on the underside from the mouth to the tips of the arms. Where they merge into the canal, there is a vesicular, contractible swelling. If such a vesicle contracts through muscle power, the water contained in it drives into the little foot, which stiffens, swells, and elongates considerably, while when the vesicle expands the reverse is of course the case. We can watch the process most beautifully when we roll a starfish onto its back in the water. Annoyed by this indelible treatment, he at first fearfully withdrew all the suckers, but soon they reappear, one after the other, as if white worms were crawling out of the star animal, stretching themselves to the limit of the possible and groping for a firm hold. When they have finally found it, they suck on each other, in increasing numbers, until this is enough to bring the whole animal back into the correct position, as if pulled by hundreds of ropes. The trick is done in about ten minutes. Quite similar with the usual way of getting around. The feet stretch out, expand, attach themselves to a point as distant as possible, shorten again and thus pull the animal body forward step by step with combined forces. With all this, of course, the starfish are not fast runners; after all, the common red species can advance about 8 cm per minute in this way, and others even manage 60 cm and more, not to mention the much more nimble and agile brittle stars, which travel about 2 m per minute. Depending on the work to be done, the animal has it completely in its power whether it wants to let all feet play at the same time or many or only a few. If one sees this swarm of hundreds of suckers, how it lives, stirs and stirs and surging around one another, one must be amazed that the starfish, which only has the hint of a nervous system, can purposefully control all these similar structures and theirs Moves can lead to a specific goal. In common starfish, the little feet, which, by the way, also serve as tactile organs, are designed to suck in, and that is why these animals are good climbers and can even climb the glass panes of the aquarium, a skill that brittle stars lack.

Like most sea animals, the starfish, despite their apparent awkwardness, are vicious predators, mainly targeting the even slower mussels. If they manage to surprise an open shell, they quickly slide one of their arms into the gaping slit, whereupon the shell immediately closes its shells and squeezes the star arm miserably without the robber seeming to care much about it. Rather, it is precisely through this squeezing of the arm that the secretion of its poisonous juice is accelerated, so that after a short time the mussel is numbed and paralyzed and now falls victim to its mortal enemy without resistance. If the starfish encounters a closed shell, it embraces it, presses its toothless mouth against the edge of the shell and smears it with its poisonous juice until the passed out shell opens the castle gate and reveals its naked body to the enemy. He turns his stomach over the whole shellfish and sucks it out in order to later spit out the indigestible remains through the mouth. In this way, large starfish overpower even their spiny cousins, the sea urchins, and their immensely elastic stomach sac seems to be insensitive to the spines. So at least the species with a narrow mouth feed, while loud-mouthed species feed the whole bite directly into the mouth and intestines. With a clam 4 cm in length, a medium-sized starfish of the ordinary type will be ready in 15 to 20 minutes in this way. The animals often eat each other in their greed to such an extent that the skin of the back is humped up. According to Hesse-Doflein, a single starfish was found: 10 scallops, 6 scallops, 5 toothed and several cone snails. Unfortunately, the starfish express a pronounced preference for oysters, which are also so tasty for us humans, and with their insatiability and the abundance of their occurrence - they are so common in some parts of the ocean that they cover the entire sea floor like a carpet - they are able to do so to cause quite serious damage to the oyster banks. Since they also like to eat the bait off the fishing rods, the fisherman hates them from the bottom of his heart and tries to destroy them wherever the opportunity arises. Only, out of ignorance of the character of the starfish, he proceeds as clumsily as possible, namely by grimly tearing them into two or three pieces and then throwing them back into the sea. But that is actually the best way to start a large starfish farm, because the regenerative capacity of these animals is so amazing that every torn arm grows into a new starfish if only a small piece of the central disc stuck to it. Also otherwise very tough, the starfish die almost instantly if you throw them into fresh water. In general, they are extremely sensitive to fluctuations in the salinity of the water; certain species do not tolerate it when they are suddenly transferred from the Baltic Sea to the North Sea. Strangely enough, soft-bodied snails come first among their animal enemies; Opposite them, the star animals neither use their spiked entrenchments nor their calcium carbonate armor, because those snails have chemical means with which they dissolve the armor plates.

The star animals are of separate sexes and produce larvae from the eggs, which are provided with eyelash hairs, romp around freely in the water and have to go through a rather cumbersome transformation. To the Swedish Pastor Sars, who in the far north, beyond the 60th parallel, far from all technical collections, libraries and societies, had thrown himself eagerly and successfully on animal science and continually delighted the scientific world with the strangest discoveries about the lower sea animals, We owe the surprising knowledge of a maternal brood care of the star animals, as one would truly not have expected these creatures. While the star animals have numerous but small eggs without brood care, the species with brood care lay only a few, but significantly larger eggs, and the intermediate stage of the eyelash larva is completely eliminated in them. The mother bends its central disc and bends its arms so strongly inward that a closed sack is created in which the embryos are well protected from all external threats. But the mother's protective activity is also limited to this; she cannot feed her offspring, but they have to feed on the abundant yolk remains of the eggs.

Fig. 8. Snake starfish from the mouth side.

The Brittle stars (Fig. 8) have very long and thin arms that are constantly engaged in lively sinuous motion, which do not grow directly out of the strikingly small middle section, but are sharply set off from it, so to speak, are deflected. In the event of danger, they are thrown off with such ease that it is almost impossible to catch a completely intact brittle star. It is the most fragile creature of the salt flood. But its wonderful power of renewal always replaces all losses in a surprisingly short time. The brittle stars are not as bad predators as the real starfish, but live on all kinds of small animals and are often content with grazing the coral sticks.

Fig. 9. Hair star.

For their part, they make a favorite food of cod. It caused a tremendous sensation in the scientific world at the time when Thompson appeared in the one living representative of the Hair stars () (Fig. 9) discovered a link between the free-living starfish of the present day and the stalked, fixed asteria of an age that has been swept by for millions of years. Less large and more powerfully developed than its primeval relatives, it does not yet have an actual handle, but only a kind of button in its place, which is surrounded by a circle of fine, claw-reinforced tendrils. With this device, the animal clings to any object and now lets its five arms play in the water, which are covered on both sides with innumerable feathers representing the finest buttons and fork right at the bottom, so that instead of five arms, ten of them are admitted in front of you have believes.

Fig. 10. Left: Stalked hair star (). Right: glass pole sponge ().

“The hair stars,” exclaims Gustav Jäger in admiration, “have always been the most wonderful of all echinoderms for me. Imagine a fern forest, the stems and pinnate branches of which are composed of hundreds of stone limbs, and combine five such fronds, which are more than hand-long, to form a star, and you have a picture of these strange creatures. In the water it moves by striking the fronds with whip-like vibrations, with the rhythm of a giant garden spider; it doesn't swim, it doesn't sail, it doesn't work, it is a mixture of all these types of movement, as if a flower that has turned out to be great is moving through the water. If the animal has found a place where it can rest, it holds on to five short fibers that stand at the point of union of the five fronds and rolls the fronds up inwards, again presenting the image of a budding fern frond. " Later representatives of the stalked genus (Fig. 10) were found, which are even more closely related to the primeval ancestors of today's star animals, the extinct. At first only very few pieces were known that were coveted rarities for the collections, but modern deep-sea research then introduced us to a large number of the most varied of species.

In Italy or Spain, some wandering German craftspeople have washed up on the beach at low tide sea ​​urchin () learned to appreciate it as food and by eating these animals appeased the worst hunger.Indeed, the sea urchin is a delicacy even for the spoiled gourmet, admittedly not the whole animal, but only the large, appetizingly orange-red colored sexual tubes, which are eaten raw after opening the animal from the mouth like an egg and opening the entrails along with the chewing device. To date, however, sea urchins seem to have been used on a larger scale for human cuisine only in Corfu and on the southern French coast; In Marseille alone, according to Marshall, about 1-1 / 4 million pieces are put on the weekly market each year at a price of 2-5 centimes. The sea urchins do not provide any other use, but on the other hand they do not cause any damage, because with their pronounced indolence they are mostly not predators and are usually content with algae and seaweed and the small animals sitting on them. English fishermen believe that they are good weather prophets because they should seek out the depths as soon as a storm is imminent. There are no sea urchins in our Baltic Sea, but there are in the North Sea.

We can best get an idea of ​​the intricate physique of an apple-shaped sea urchin (Fig. 11) of the common species if we picture it as a starfish whose arms are tapered upwards so that their edges touch each other and the End tips come together around the top of the anus opening. Then the close relationship between the two apparently so different animal groups becomes clear to us at a stroke. As a result, even the red eye-spots are right at the top of the head, although they can be of very little use to the animal here. But the Sarasin's cousins ​​have also found beautiful blue hints of faceted eyes in other parts of the body of Indian species, which may reveal the shadowy outlines of an approaching enemy to the sea urchin, because he immediately pointed his long spines menacingly in the direction from which the hand was coming of the observer hit him.

Fig. 11, Sea urchin, freed from the spines on the left half of the body

The main peculiarities of the starfish are also found in the sea urchin, especially the grasping claws, the spines and the widely ramified water vessel system with madrepora plate and suction feet. Probably everyone has seen the dainty but solid lime casing of a sea urchin, which is a true masterpiece of mosaic in a 20-fold radial arrangement composed of hundreds of pentagonal plates and a large number of its small holes as passage openings for the suction feet and wart-shaped buttons as points of view for which has spines. These are not only more numerous, but in their very different formation often also much stronger, more pointed and longer than the starfish, so that they can not only serve as a threatening repellent, but often also as stilts when walking. Then, of course, the suction feet must also be able to be extended accordingly, up to 5 cm and more. The numerous limestone plates of the armor cannot be moved as in the case of the starfish (with the exception of one genus in which they are stored in the shape of roof tiles), but are firmly and rigidly joined together. But the epidermis that covers the entire armor sinks into the seams between the individual plates, and this is absolutely necessary, because it is this epidermis that excretes the lime as the animal grows to form new plates that are inserted between the old ones and so must create the necessary space. The innumerable fine muscles also run in the skin, lifting the spines, lowering them and turning them in various directions or guiding the constantly snapping claws. The whole machine is moved by around 1400 suction cups. So actually the little sea urchin is a real monster that just stares in spite of its harmlessness of weapons. “Just imagine,” says Marshall, “a sea urchin puffed up the size of an elephant, what a terrible beast it must be. A true walking fortress, staring all around with long lances, provided with thousands of trunks that constantly snap around in all directions. One is literally appalled by such an idea! «In the wonderfully colorful coral forests of tropical seas, there are huge, violet-black sea urchins whose thin, needle-sharp spines are supposed to reach 20 cm in length, so they are very effective weapons. According to Morin, if one is hit by such a sting, one feels severe pain because a caustic dye follows the breaking point, and the natives therefore fearfully avoid such sea urchins. These well-fortified animals are even supposed to act aggressively by advancing from all times and aiming their bayonets purposefully at the troublemaker. While the starfish have a toothless mouth, the sea urchins are distinguished by the possession of an extensive and very intricately built chewing device, which has been named the "Lantern of Aristotle" (Fig. 12). Five strong teeth protrude from the mouth to grab small prey or to graze on the algae. Together with 15 other pieces of bone, they form a pyramid-shaped structure that is connected by strong ligaments and muscles. These are used to move the whole masterpiece, bring the jaws closer to each other or move them up and down, so that the most skilled mechanic could hardly invent a better crushing tool and a more thorough grinding device. Just that Heart hedgehog are toothless, but they don't need to chew either, since they live in sand holes in the seabed and, like sea cucumbers, swallow nothing but sand, the organic admixtures of which have to be sufficient for their nutrition. The species that live in the deep sea have very fragile carapaces that collapse into a flat disk when the animals are brought into the air. The amazing strength of the sea urchin shell is mainly due to its high arched shape. Where this is missing, as with the flattened ones Shield hedgehogs (), support and buttresses are necessary, which penetrate the interior and connect the belly and back of the body wall with each other.If you put a sea urchin in fresh water, after a few days the connection between the armor plates loosens and the whole housing falls into its individual components apart. The Stone hedgehog are strange because they inhabit hollows in the rock that exactly match their size. This suggests that they make these cavities themselves; it is indeed so, but we are still quite unclear about the "how?" Perhaps the animals can make the rock brittle by a sharp secretion, so that the strong teeth then have easier work and the spines finally rub the wall smoothly. In these seats they hold so tight with their suction cups that they can hardly be loosened, especially since one cannot use the full force of the hand because of the pointed spikes and the suction cups often tear rather than let go. On the English chalk coast you can see many thousands of such sea urchins buried in the limestone cliffs, their purple spines form a beautiful contrast to their bright white.

Fig. 12 Sea urchin teeth

Since the ejection opening of the sea urchin is extremely impractical on top of the apex of the apple-shaped carapace, the shed feces will mostly slide along the outer wall of the carapace and get caught between the many spikes, which is why the prongs of these animals evidently play the role of sweeping brooms have to play. In addition, they also serve to capture prey, and in some species their effect is enhanced by the fact that they are connected at the bottom with poison glands, the duct of which opens through the tips of the forceps. Horngold has made very beautiful observations about the activity of these poison forceps. B. a small annelid worm to such a sea urchin, so its spines drove apart, the hidden claws came to light, opened greedily and moved towards the worm. When they got close enough, one after the other grabbed their hands and beat their way into the flesh of the victim, a red liquid flowing freely from the tips of the tongs, which was obviously a violent poison, for the worm only made a few convulsive movements and died then within a few minutes. The claws break off from the sea urchin at a precisely prepared place, as the microscopic examination has shown, but are soon replaced by regeneration. The breaking off can also be induced artificially by nerve stimulation, for example by teasing the animal with a needle or spraying it with a jet of fresh water. In some species, the suction feet are also used to catch prey. If any edible animal comes near, some suckers stretch out until they reach it, and the poor creature is lost if it does not notice this insidious approach in time and gets out of the way, for more suckers follow quickly, and so the victim is soon wrapped in hundreds of small but tough shackles, like Gulliver once did by the Lilliputians, and in a completely defenseless state is brought close and closer to the toothy mouth.

The free-swimming larvae of the sea urchins are very peculiar creatures, which do not have the slightest resemblance to their creators and which later turn into a finished animal in a very strange way. Marshall does not compare her figure badly with a Prussian spiked bonnet, the shield of which is drawn out a little long and ends in two points, as well as two points on the opposite side of the lower edge. On the inner side of the shield, the mouth opens and leads through a short esophagus to the conical stomach, which then again leads through a simple intestine to the anal opening on the opposite side. The cavity between the abdominal wall and the stomach is initially only filled with liquid, but the future sea urchin is created in it as an initially circular system. As it grows around the larva, its covering body wall disappears, until finally the young sea urchin rises from it like a bud, closing its stomach in itself. Soon the larva is only an insignificant appendage of the young sea urchin, and as soon as it has a mouth opening and is able to take in food independently, these last remnants of youth also fall off it and disappear in the sea.

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