Sea hare (genus of gastropods) sea hare(Aplysia), a genus of marine gastropods of the opisthobranch subclass. Body length up to 40 cm. There are 2 pairs of head tentacles, of which the rear one is shaped like a hare’s ears (hence the name). The thin lamellar shell is covered with a mantle. In the mantle cavity there are glands that secrete a toxic colored liquid. The leg has lateral blades used for swimming. About 35 species. Herbivorous; They live mainly in tropical seas. Large nerve cells M. z. - object of neurophysiological research. Rice. see Art. Gastropods.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what “Sea hare (genus of gastropod mollusks)” is in other dictionaries:
Aplysia (Aplysia) is a genus of gastropods from the order Opisthobranchiata, suborder Tectibranchata, belonging to the family M. hares (Aplysiidae). Features of the family: the internal shell is underdeveloped, or its... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron
I The bearded seal (Erignathus barbatus), a pinniped of the true seal family. Length 2.2 2.6 m, weighs 225,360 kg. The hair is grey-brown, sometimes with several light spots on the back. The fur of a newborn is dark... Great Soviet Encyclopedia
Even those living creatures that seem completely defenseless actually know how to defend themselves from predators. And here the defense methods of the Aplysia mollusk are very interesting - it can release various substances into the water that either deprive the predator of the sense of smell or create an “odor phantom” that distracts the hunter from the prey itself. But that's not all...
Life of the nudibranch mollusk Aplysia ( Aplysia californica), which is also called the sea hare, is very, very difficult. The fact is that it has many enemies, but there is absolutely no place to hide from them - after all, Aplysia, unlike its relatives, is completely devoid of a shell. At the same time, it is hunted by almost all marine predators - fish, large crayfish, octopuses, and cuttlefish. Looking at this, it becomes surprising why this cute and defenseless mollusk still exists on our planet!
However, the sea hare still has some protective devices. For example, it can, like cephalopods, throw an ink stain into the water. Scientists knew about this for a long time, but did not understand what the point of such protection was. Indeed, an octopus or cuttlefish, which can swim quickly, always manages to escape before their “smoke screen” clears. But the sea hare is a slow-moving creature, and even while the spot “hangs” in the water, it still does not have time to go far.
However, as observations show, even in this case the mollusk most often remains alive. But why? Scientists from the University of Georgia (USA) decided to solve this mystery. They analyzed the chemical composition of the Aplysia ink cloud and found that it contained a substance such as opaline. It was known that it could suppress the sense of smell of some marine inhabitants. So maybe it is he who makes the mollusk invisible to his pursuers?
The researchers decided to test their hypothesis. They took opaline from the glands of the sea hare (it should be noted that it is produced separately from the coloring pigments) and applied it to the lobster's antennae, which in this arthropod play the role of an olfactory organ. After that, an extract from shrimp was added to the aquarium with this lobster, which the predator feeds on in the wild and, therefore, knows their smell by heart.
As a result, it turned out that the lobster did not react at all to the delicious smell that was quite familiar to it. Most likely because I just didn't feel it. As scientists write in an article published in Journal of Experimental Biology, according to their research, those neurons that are responsible for chemoreception, as well as the motor nerve cells associated with them, remained completely inactive all this time. And this is very strange - usually they are immediately excited by the smell of food and excite the hunting reflexes of the crayfish.
It turns out that opaline is indeed capable of completely suppressing the sense of smell. As Professor Charles Derby, who led the study, said, this substance isolated from the glands of the sea hare literally clogs the “nose” of the predator. And opaline does this in the following way - it sticks to the receptors on the lobster’s antennae and simply physically prevents odor molecules from reaching them.
It is quite obvious that as a result of such an opaline attack, the predator completely loses its sense of smell for some time. And, what is most interesting, the appetite disappears along with it - after all, if there is no smell, then hunting behavior is not aroused. Well, while he is cleaning the antennas from the scorch sticking to them, even such a slow-moving and bumpkin as the sea hare always manages to climb into some crevice between the stones and hide.
However, as it turned out, that's not all. Further research showed that Aplysias also have a second level of protection. It turns out that the same ink mixture of this mollusk contains many different amino acids, which, when they reach the olfactory receptors of predators, create a very attractive smell of prey. As a result, the predator begins to hunt precisely this “scent phantom”, and not the real sea hare. Apparently, this defense works if the predator is not affected by opaline.
Experiments carried out on the sea snail Aplysia laid the foundation for modern ideas about the mechanisms of learning, the development of conditioned reflexes, and memory. Therefore, they are important in the study of such disciplines as Physiology of the nervous system, Physiology of the central nervous system, Physiology of the central nervous system, Neurophysiology, Neurobiology, Psychophysiology and Psychology.
Researcher E. Kandel studied the mechanisms of memory in snails, and discovered the mechanisms of plasticity and explained the mechanisms of learning, memory and the formation of conditioned reflexes.
Aplysia (lat. Aplysia), or sea hare is a large marine gastropod (sea snail), on which very valuable experiments for neurophysiology were carried out to study the neural mechanisms of learning (training), memory and the development of conditioned reflexes.
In these experiments, under the influence of stimuli, the strength of synaptic connections between neurons, which is what was called plasticity.
Neural mechanisms of learning and memory
Behavioral learning is the acquisition of new forms of behavior and response to a stimulus.
Neural learning is a change in the response of a neuron to incoming excitation.
“In its simplest forms, learning selects from a wide repertoire of predetermined connections and modifies the strength of a specific subset of those connections.” Source: Kandel, E. R. (2007), In Search of Memory: The Emergence of a New Science of Mind, New York: W. W. Norton & Company, ISBN 978-0-393-32937-7.
Memory can be found in different forms: 1) declarative memory is the memorization of any information, 2) procedural memory is the memorization of any actions or their sequence. In both cases, the acquired experience is fixed (consolidated), i.e. of what happened before.
"Memory" for neural memory mechanisms
Memory
- this is not a storage cabinet,
and an easy, reliable way to get excited!
Memory includes several stages:
1. Translation of sensory images or motor programs into a form accessible for storage in the nervous system, i.e. coding
2. Fixing (fixing) the received codes so that they do not change in the future during storage.
3. Preservation of the received nerve codes for a certain time.
4. Extracting stored codes, transferring them to a state available for reproduction.
5. Reconstruction from extracted codes of sensory images or motor programs.
6. Reproduction of restored sensory images and motor programs or their use.
For the first time in psychology, Ebbinghaus applied a consistent scientific approach to the study of memory. True, he did not use a statistical approach, and carried out all the experiments on himself (using many three-letter combinations that did not make sense).
In experiments on Aplysia, three phenomena were studied (learning, memory, conditioned reflexes) at three levels (behavioral, neural, molecular).
1. Behavioral (organismal)
There are three known options for simple forms of learning:
1. Habituation (habituation)
- This is a weakening of the initial response after repeated repetitions of the same irritation. In higher animals, habituation (or extinction) is characteristic of an orienting reflex that occurs in response to the novelty of a stimulus.
The response orienting reaction fades with repetitions of stimulation by the same stimulus (stimulus).
In Aplysia, Kandel received a moderate retraction of the gills after touching its siphon - the tube through which the Aplysia draws in water, directing it to the gills. But if you make several identical touches to the siphon in a row, the Aplysia begins to retract its gills less and less and eventually stops retracting them altogether. That's what it is behavioral addiction- weakening of the response when stimulation is repeated.
Here is what Kandel himself writes:
Habituation refers to the weakening of a behavioral response upon repeated repetition of a stimulus that was initially novel. When an animal is exposed to a new stimulus, it first responds with a combination of indicative and defensive reflexes. When the signal is repeated, the animal quickly learns to recognize it. If it is not followed by a reward or turns out to be harmless, the animal weakens and eventually suppresses its responses to it. Although habituation is surprisingly simple, it is perhaps the most common form of learning. Through habituation, animals, including humans, learn to ignore stimuli that have lost their novelty or meaning. Habituation frees them up to respond to stimuli that provide rewards or have survival value. Habituation is thought to be the first learning process to occur in children; it is commonly used to study the development of intellectual processes such as attention, perception, and memory.
2. Sensitization (sensitization) - this is an increase in sensitivity and an increase in reaction to a moderate stimulus if a strong other stimulus was applied before it. It is important to note that to obtain sensitization, strong irritation is applied precisely before test irritation. It is also important to consider that sensitization nonspecific to the test stimulus, i.e. any weak stimuli against the background of sensitization will give a stronger effect.
In Aplysia Kandel, as we said earlier, usually received moderate retraction of the gills after touching its siphon.
To induce sensitization of the Aplysia nanosilly, we first gave a strong electric shock to the tail (or to the head in another series of experiments) and only then touched its siphon. In this case we received strong retraction of gills. Thus, after preliminary strong irritation of the tail, subsequent touches to the siphon no longer cause moderate, but strong retraction of gills. Those. sensitization occurs - increased sensitivity to moderate irritation of the siphon. This is sensitization at the behavioral level.
3. Association (conditioned reflex) - this is the appearance of an enhanced reaction to a stimulus, if when it is repeated after it each time a strong irritation is given. An association (linking) of two stimuli occurs and the weak stimulus begins to cause not its usual reaction, but the reaction that was caused by the strong stimulus.
Association (conditioned reflex) is a specific strengthening of the initial reaction to a stimulus similar to the response to a stronger stimulus. As a result of associations (connections) of two stimuli close in time, it turns out that a weak stimulus precedes a strong one and warns the nervous system about it.
Kandel's great merit was obtaining a conditioned reflex in Aplysia, a relatively primitive animal. In Aplysia Kandel, the siphon irritated and received moderate retraction of gills. After this, he immediately gave her an electric shock to the tail (or to the head in another series of experiments) and received strong retraction of gills. After several repetitions of such combinations of stimuli (weak and then strong), association their actions, i.e. an information connection was established between them. Now touching the siphon caused strong retraction of the gills, the same as when receiving an electric shock to the tail. Unlike sensitization, this was a strong reaction of the gills specific in relation to the conditioned stimulus, i.e. touching the siphon. Touching other parts of the body did not cause such a strong reaction of the gills (while with sensitization it did).
Thus, E. Kandel obtained in Aplysia simple behavioral analogues of complex forms of behavior characterizing learning, which are inherent in higher animals and humans.
Memory manifested itself in these experiments in the influence of previous actions on subsequent ones. This meant that Aplysia was learning and remembered your experience. Her gills acted differently depending on the previous irritation. Those. Aplysia was able to change its behavior. Kandel decided to find neural mechanisms these phenomena.
2. Neuronal (cellular) level of learning, memory and reflexes
Kandel found sensory neurons (afferent) in Aplysia in the abdominal ganglion. When the siphon was stimulated, an action potential arose in them. Then he found motor neurons. When they were irritated by an electric current, the gills were retracted. It turned out that sensory neurons are connected to motor neurons. When sensory neurons were stimulated by an electric current, an action potential was recorded in the motor neurons associated with the sensory neurons, and then the gills were retracted.
Unlike behavioral experiments, in this series of experiments the irritation was applied not to the Aplysia body, but directly to the neurons. At the same time, the electrical potentials generated in the neurons were recorded. All this was done to simplify the picture, this method of scientific approach is called reductionism (simplification). Kandel isolated neural chains consisting of sensory and motor neurons and in a number of experiments studied them separately from Aplysia. It turned out that all 3 forms of learning have neural analogues, i.e. appear even at the level of neurons alone.
1. addictive
If you repeatedly stimulate a sensory neuron with electric current, the potentials arising in the motor neuron decrease. The electrical response of the neuron is weakened. This is the neural analogue of addiction (fading of the orienting reflex).
2. Sensitization
If, before irritating a sensory neuron, an electric current is applied to the modulating neuron associated with it, then subsequent stimulation of the sensory neuron with current will lead to the appearance of increased potentials in the associated motor neuron. This is the neural analogue of sensitization. This phenomenon of increased synaptic activity is called heterosynaptic facilitation. In our case, this was an improvement in the functioning of the synapse connecting the sensory neuron with the motor one.
1. Association
If you repeatedly stimulate first a sensory neuron and then a modulating neuron, then when a separate sensory neuron is stimulated separately, stronger response potentials will now arise in the motor neuron. This is the neural analogue of a conditioned reflex.
conclusions E. Kandel and his colleagues, based on experiments on Aplysia:
“The cellular mechanisms of learning and memory lie not in the special properties of the neuron itself, but in the connections that it forms with other cells of the neural circuit of which it is a part.”
Let's start our acquaintance with the smallest representative in the sea hare family (Aplysiidae) - the dwarf sea hare (Aplysia parvula). It lives at depths from 5 to 24 meters. Its size does not exceed 70 mm. This small gastropod with rabbit-like ears (actually sensory appendages) is brown, maroon or olive green, and can also be spotted. Dark colors are widespread in the Red Sea and western Indian Ocean, and are also found in the western Pacific, although not frequently. Pale specimens have a cream-colored body with black edges on the oral tentacles, legs, and parapodia.
Both color forms are small. Although, pale individuals of the dwarf sea hare grow up to 120 mm. There is also a black form: the body is dark brown or black, sometimes with white speckles, and with a pale pink or purple edge on the parapodia and tentacles. The pale form is found in shallow intertidal areas with seagrass, while the dark form is found on coral reefs in more exposed areas. Aplysia feeds on various types of algae. Dwarf sea hare eggs are masses of tangled, sticky strings of orange, green or brown that can be found in rocks or among seaweed.
Aplysia californica or California sea hare is one of the largest opisthobranch gastropods in this family. This species lives in the Pacific coast of North America (in California) and Northern Mexico, but can also be found near Florida. These sea slugs prefer to inhabit light areas where algae grows vigorously, at depths of up to 20 meters. The maximum size documented for the California sea hare was 75 cm, although most individuals are typically half that length. Adult animals can weigh up to 7 kg. Only a closely related species, the black sea hare (Aplysia vaccaria), can grow even larger. There are not so many people who want to eat a sea hare. These include the giant green anemone (Anthopleura xanthogrammica), starfish and lobsters. For protection, the sea hare acts almost the same as the cuttlefish, using reddish-purple ink, which it releases from the mantle cavity.
Like all sea hares, Aplysia Californian is a hermaphrodite, and for mating it forms chains, in which there are sometimes up to 20 animals, so each animal can act as a female or a male. Fertilized and laid eggs are yellow-green in color, and after 8-9 days they turn brown. Mating occurs in the summer months as soon as the water temperature rises to 17 degrees Celsius. The clam reaches reproductive maturity 85 days after hatching (or 133 days after laying fertilized eggs, the planktonic stage). Development of the nervous system lasts a total of 140 days. The full life cycle is about a year, but can be extended due to low temperatures.
And a few more words about the California black sea hare (Aplysia vaccaria), an incredibly large sea slug. This gastropod is not only the largest in the family Aplysiidae, but also the largest of all known sea slug species. The maximum size that was officially recorded for the black sea hare was 99 cm and weighed almost 14 kg. So far, today it remains the world's largest mollusk among living gastropods. Unlike other members of this family, the black hare is not capable of producing ink. It feeds on brown algae, which, apparently, is what gives it its dark color.
Aplysia(lat. Aplysia) - one of the largest representatives of opisthobranch mollusks, also called sea hare.
Aplysia is characterized by the position of the gills on the right side of the body under the fold of the mantle (in the mantle cavity). The sea hare has a pair of sensitive appendages on its head. On the sides, the Aplysia's body is covered with a pair of massive blades, which straighten out and, contracting in waves, allow the Aplysia to swim for quite a long time. The coloring of aplysias is very beautiful and varied: it can be dark purple with white spots scattered over it, then these spots are scattered over an ocher-yellow background, or dirty gray and yellowish tones without sharply defined spots predominate. The genus Aplysia is widely distributed throughout the warm seas of the globe; it includes a fairly large number of species.
Sea hares are hermaphrodites and usually mate in a chain. So the individuals in the middle of the chain perform alternately male and female functions with those in front or behind.
Aplysia as model organisms
The nervous system of the sea hare consists of only 20,000 nerve cells. They are so large (can reach up to 1 mm in diameter) that they are visible to the naked eye. Aplysia nerve cells are clearly distinguishable visually: they are painted in different colors. It was these advantages that the Nobel laureate used
