Sea saucers with garlic butter. Mollusk teeth sea saucer the most durable material in nature
BIOLOGY OF THE SEA, 2011, volume 37, no. 3, p. 229-232
Brief messages
UDC 593 EMBRYOLOGY
reproduction and larval development of the limpet
LOTTIA PERSONA (RATHKE, 1833) (GAsTRoPoDA: LoTTIIDAE)1 © 2011 K. G. Kolbin and V. A. Kulikova
Establishment of the Russian Academy of Sciences Institute of Marine Biology. A.V. Zhirmunsky FEB RAS, Vladivostok 690041 e-mail: [email protected]
The article was accepted for publication on November 25, 2010.
The reproduction and development of the limpet Lottia persona (Rathke, 1833) was studied for the first time under laboratory conditions. Mollusks breed in the second half of July, have external fertilization, pelagic lecithotrophic type of development. The larval shell is transparent, symmetrical, bag-shaped, with well-defined lateral depressions and a large rounded mouth. The sculpture of the protoconch is characterized by wide wavy lines separated by radial ribs; on the ventral side of the shell, the lines become narrow and are directed perpendicular to those of the dorsal and lateral sections. The duration of development from the moment of fertilization to settling at a water temperature of 19-20 ° C is three days.
Key words: sea limpets, reproduction, egg, trochophore, veliger, protoconch.
Reproduction and larval development of the limpet Lottia persona (Rathke, 1833) (Gastropoda: Lottiidae).
K. G. Kolbin, V. A. Kulikova (A. V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, Vladivostok 690041)
Reproduction and larval development of the limpet Lottia persona (Rathke, 1833) were first investigated in vitro for the time. The limpets breed in late July; they exhibit external fertilization and a pelagic lecithotrophic type of development. The larval shell is transparent, symmetrical, bottle-shaped, with well-marked lateral fossae and a large rounded operculum. The protoconch sculpture is characterized by broad wavy lines and radial ribs at the dorsal side. Ventrally, the lines become narrow and are directed perpendicular to those of the dorsal and lateral regions. Development from fertilization to settling lasts 3 days at a water temperature of 19-20°C. (Biologiya Morya, Vladivostok, 2011, vol. 37, no. 3, pp. 229-232).
Key words: limpets, reproduction, egg, trochophore, veliger, protoconch.
The Far Eastern seas of Russia are inhabited by 27 species of limpets, of which 21 species belong to the family Lottiidae (Chernyshev and Chernova, 2005). Currently, information on the reproductive biology of patellogastropods in this area is practically absent in the literature. There is only brief information on the reproduction and development of Erginus sybariticus (= Problacmea sybaritica) (Golikov and Kusakin, 1972; Golikov and Gulbin, 1978); Niveotectura pallida (= Acmea pallida) (Korenbaum, 1983); Iothia sp. and Erginus moskalevi (= Problacmea moskalevi) (Golikov and Gulbin, 1978; Golikov and Kusakin, 1978; Sasaki, 1998); Erginus rubella (= Problacmea rubella) and Rhodopetata rosea (Golikov and Gulbin, 1978); Erginus galkini (Chernyshev and Chernova, 2002); Lottia versicolor and Nipponacmea moskalevi (own data), Testudinalia tessellata (Golikov and Kusakin, 1978). The larval development and morphology of the Limalepeta lima protoconch have been studied in the most detail (see Kolbin, 2006).
This work contains the first information about the reproduction and larval development of the limpet Lottia persona (Rathke, 1833) from the family Lottiidae. It is a Pacific widespread boreal species. It occurs in the western and northern parts of the Sea of Japan, distributed from the coast of Korea in the south, off the coast of the Kuril Islands, in the coastal waters of the Sea of Okhotsk and the Bering Sea, off the Pacific coast of America to the bay. Monterey in California in the southeast. Predominantly littoral species, inhabiting
It occurs in the middle and lower horizons of the littoral and is rarely found in the uppermost sublittoral at a depth of up to 4 m. It lives mainly on hard and stony soils at water temperatures from negative values in winter to 20 ° C in summer with a salinity of 30-34%o ( Golikov and Kusakin, 1978).
Material and technique. Individuals of Lottia persona were collected at a depth of 0–1 m in the hall. Vostok (Peter the Great Bay) in mid-July 2009. Mollusks ready for spawning were kept in an aquarium with sea water at a temperature of 19–20°C and constant aeration. Shortly after spawning and fertilization, the embryos were transferred to 300 ml glass containers filled with sterilized sea water, which was changed after 48 hours. On the 3rd day of development, a substrate was introduced into the containers for settling of larvae. During development, the larvae were not fed.
The general morphology of the larvae was studied using an MBS-10 binocular, a Leica MZ 12.5 stereomicroscope, and a Polyvar light microscope. The sculpture of larval and juvenile shells was studied using Leo-430 and EVO-40 scanning electron microscopes. The shells were fixed in 70% ethanol, dried in increasing concentrations of alcohol and acetone, then glued onto tables and sprayed with gold or platinum.
Results and discussion. Lottia persona is a dioecious species, during the pre-spawning period the gonads of males are milky or cream in color, females are dark brown. Spawning
1 This work was supported by grants from the Russian Foundation for Basic Research (08-04-00929) and the Far Eastern Branch of the Russian Academy of Sciences (10-Sh-V-06-122).
Morphology of larvae and protoconch of Lottiapersona. A - a fertilized egg; B - trochophore; B - veliger; G - pediveliger; D - lateral side of the protoconch; E - dorsal side of the protoconch. Symbols: ap - apical bundle of cilia, vl - velum, zn - leg rudiment, lu - lateral depression, n - leg, prt - prototroch, prk - protoconch, p - ribs, tlr - telotroch. Scale, µm: A - 50; B, D - 25; B - 30; D-E - 20.
lyuskov occurs in the second half of July at a water temperature of 19-20°C. Fertilization is external. Males release sperm in the form of matte white strands, which soon disintegrate, and the spermatozoa disperse into the water column. Females spawn large, yolk-rich, light brown eggs 145 µm in diameter (see figure, A). Trochophores 145 μm in size develop 12 hours after fertilization. By this time, a powerful proto-troch had already formed, encircling the larva almost in the middle and consisting of trochoblasts and tufts of long cilia (see figure, B). On the apical plate, covered with short cilia-
mi, a bundle of long cilia is clearly visible, on the opposite side a telotroch (anal bundle of cilia) is visible. Such a larva actively swims due to the work of the prototroch. After 38 hours, veligers develop from the trochophore. L. persona veligers typical of Patellogastropoda have a simple velum not divided into lobes, equipped with long cilia, a transparent, symmetrical sac-like shell (protoconch) with well-defined lateral depressions and a large rounded mouth (see figure, C, E, F). The protoconch of the early veliger is 174 µm long and 145 µm wide. The sculpture of the larval shell is represented by
BREEDING
on the ventral side of the shell, the lines become narrow and directed perpendicular to those of the dorsal and lateral sections (see figure, E, F). On the 2nd day of development, the larvae begin to form a leg, and individual larvae are already able to attach to the substrate for a short time (see figure, D). On the 3rd day, the larvae completely settle on the substrate, the leg begins to function actively, the velum is reduced, but its cilia remain mobile for several days. Eye tentacles appear. Such larvae are able to separate from the substrate and swim for a short time, after which they again sink to the bottom and attach to the substrate. The length of the protoconch before settling of the larvae is 180 µm, and the width is 145 µm. During metamorphosis, the teleoconch (juvenile shell) grows.
The limpets are one of the most ancient and primitive groups among the living Prosobranchia. Almost all representatives of the order Patellogastropoda have a simple structure of the reproductive system and a completely pelagic lecithotrophic type of development (Fretter and Graham, 1962; Ivanova-Kazas, 1977; Sasaki, 1998). An exception is the viviparous species of the genus Erginus, in which embryonic and larval development occurs in the brood chamber (Lindberg, 1983).
Among the studied species of patellogastropods in the hall. Peter the Great, the smallest eggs (130 µm) are in Nipponacmea moskalevi (own data), and the largest (200 µm) are in Niveotecturapallida (= Acmaeapallida) (see: Korenbaum, 1983). In Limalepeta lima, the egg size coincides with that of the studied species (145 µm) (Kolbin, 2006). The duration of the development of sea limpets from spawning to settling is short and at a water temperature of 19-20°C is 3-7 days. An exception is N. pallida, in which the eggs are quite large, and the larvae develop at a water temperature of 16-19°C and settle on the ground after 2-3 weeks. after fertilization (Korenbaum, 1983). Short development (3-4 days) is typical for species with a relatively small egg diameter, however, in Lottia versicolor with a large egg cell 175 µm in diameter, development lasts 7 days. The shortest period of larval development is in Lottia persona, its duration is 3 days. The development of L. lima (Kolbin, 2006) and N. moskalevi (own data) lasts 4 days, L. versicolor - 7 days (own data). The rate of pelagic development of mollusks is determined not only by the size of the egg, but also by the ambient temperature. Thus, Lottia digitalis and L. asmi from the coastal waters of Oregon with egg diameters of 155 and 134 μm, respectively, at a temperature of 13°C complete development in 7–8 days, and at 8°C the pelagic phase increases by 2–3 days (Kay, Emlet, 2002).
Snails, or gastropods, constitute the soft-bodied class richest in species. There are about 90,000 species in this class. They inhabited both the coastal zone of the oceans and seas, and significant depths and the open sea; they settled in fresh waters and adapted to life on land, penetrating even into rocky deserts, into the subalpine belt of mountains, into caves. Some modern groups of freshwater gastropods have gone through a very difficult evolutionary path: they left sea reservoirs for land, acquired a new type of breathing in connection with this, and then again went to “permanent residence” in fresh waters, retaining there, however, this acquired on land type of breathing. One of the characteristic signs of gastropods is the presence of a whole shell in them, not divided into valves or plates and covering the back of the animal; it would be more correct to say that the shell here covers the so-called visceral sac, i.e., a sac-like protrusion on the back, inside which there are a number of organs. Another typical sign of gastropods is that most of them have lost their bilateral symmetry. The intestine in all modern gastropods forms a loop-like bend, and therefore the anus lies above the head or to the side of it, on the right side of the body. In most gastropods, the shell is twisted into a spiral, while the whorls of the spiral most often lie in different planes. Such a coil is called a turbocoil. The whorls of the shell form a whorl. In addition, they distinguish between the top and the mouth - a hole from which the head and leg of the mollusk protrude. Correspondingly with the spiral twisting of the shell, the visceral sac is also spirally twisted. In the vast majority of cases, a clockwise twist is observed, i.e., to the right, if you look at the shell from its top; in more rare cases, the shell and the visceral sac are twisted counterclockwise, that is, to the left. According to the direction of shell twisting, right-handed (dexiotropic) and left-handed (leotropic) shells are distinguished, and sometimes individuals of the same species can have both right- and left-handed shells. The shells of various snails are extremely diverse in appearance, which is determined by the number and shape of the turns of the spiral, by how steep or flat its turns are. Sometimes the whorls of the shell spiral, closely adhering to each other, fuse with their inner parts, forming an integral column (columella), sometimes they lag behind one another, due to which, instead of a continuous column, an umbilical canal is formed along the axis of the shell, which opens at the last whorl of the shell with a hole called navel. Finally, in a number of cases we see in snails a seemingly simpler shell in the form of a cap or a saucer, but, as the history of development shows, such shells in modern snails are the result of a simplification of the originally spirally twisted shell. The violation of bilateral symmetry, characteristic of most gastropods, i.e., the asymmetry of the organs of the visceral sac and the mantle cavity (one gill, one atrium, one kidney), is caused by the turbospiral shape of the shell. With this shape of the shell, with the volute directed laterally, and despite the fact that the main mass of the liver is located in the last whorls of the volute, the center of gravity of the shell is shifted away from the midline of the body. Because of this, one of the sides of the open (mouth) whorl of the shell is closer to the body than the other side, which is elevated above it. All this resembles a hat worn on one side. But such a position of the shell narrows the space of the mantle cavity on one side, which leads to the reduction of one of the gills and the associated atrium and, of course, the kidney. The correctness of such an explanation for the emergence of asymmetry in gastropods is confirmed by the fact that in modern primitive representatives all stages of its development can be observed. In some gastropods with a cap-shaped shell, the bilateral symmetry of the entire complex of mantle organs is still preserved, in others one can see the reduction of one or both ctenidia and the atrium.
The shell of gastropods is covered with a thin layer of organic matter that makes up its outer layer - the periostracum. The latter sometimes forms bristle-like processes, due to which the shell looks hairy from the outside. The part of the shell covered by the periostracum is composed of thin calcareous plates, which together form the so-called porcelain layer, in which, in turn, up to three layers of calcareous plates can be distinguished. In some (relatively few) snails, the inner surface of the shell is lined with a shiny mother-of-pearl layer. The intraspecific variability of the shells of many gastropod species is very wide. This breadth of its variability shows the importance of the shell in ensuring the adaptability of individuals of the species to living in places with different combinations of environmental factors. The Black Sea mollusk researcher V. D. Chukhchin showed the existence of differences in the shape of the shell and in its thickness in males and females of the same species.
Turning to the consideration of the soft parts of the body of snails, first of all, it should be noted that they have a more or less isolated head, carrying a mouth, eyes and tentacles, and on the ventral side - a massive muscular leg with a wide lower surface called the sole. The mode of locomotion characteristic of most snails is a slow gliding along the substrate on the sole of the foot, and the movement itself is carried out due to the waves of contraction running along the sole of the foot from back to front. Abundant mucus secreted by the skin softens friction and facilitates sliding on a solid substrate. In some snails, in connection with their transition to a different type of movement, both the function and the structure of the leg change. In many snails, the back of the leg bears a special horny or calcified cap on the upper surface, and when the snail hides in the shell, the cap closes the mouth. The shell is connected to the body with the help of a powerful muscle, the contraction of which draws the snail into the shell.
Directly under the shell, dressing the visceral sac, there is a mantle, the front thickened edge of which freely hangs over the body of the animal and covers the mantle cavity formed under it, into which the anal, excretory and genital openings open; holes. Respiratory organs are also located in the mantle cavity - most often one cirrus gill, or cteninidium (a relatively small number of snails have two gills); in snails belonging to the pulmonary subclass, the gills are lost, and the arch of the mantle cavity functions as a lung. The free edge of the mantle in some snails can be extended into a more or less long tube - a siphon that fits in the siphonal outgrowth of the shell. In other cases, the free edge of the mantle can be wrapped over the edge of the shell, so that the mantle, protruding from under the shell, partially or completely covers it from above. In the latter case, the shell becomes internal, usually undergoing reduction to some extent. The mouth of snails leads into a voluminous oral cavity, in which there is a paired or unpaired jaw and an organ typical of most mollusks - a grater, or radula. The ducts of the paired salivary glands open into the oral cavity, and in some snails, the ducts of other glands, such as poisonous or acid-producing ones. A thin esophagus departs from the oral cavity, in some snails it expands into a voluminous goiter, and the latter passes into the stomach, into which the digestive gland (“liver”) opens. The intestine begins from the stomach, which is shorter in predatory gastropods and longer in herbivores. The intestine opens outward through the anus inside the mantle cavity.
The circulatory system of snails is not closed: the heart consists of one ventricle and one atrium (few forms have two atria). In the atrium, oxidized blood is collected from the gills or lung, from where it is distilled into the ventricle, and then it is carried through the body through the branching head and splanchnic aorta. The heart of snails lies inside the pericardial cavity. The excretory organs, the kidneys, in rare cases are paired, also communicate with this cavity. The nervous system of the snails consists of 5 pairs of nerve nodes, or ganglia: cerebral, foot, or pedal, pleural, visceral and parietal. Ganglia are connected by nerve cords: ganglia of the same name - the so-called commissures, opposite - by connectives. In connection with the twisting of the visceral sac, in snails belonging to the subclass of the anterior branchial, as well as in some of the lowest representatives of the other two subclasses (posterior branchial and pulmonary), a characteristic crossing of the connectives is formed between the pleural and visceral ganglia. The higher posterior branchial and pulmonary do not have this decussation. The convergence of various ganglia and the corresponding shortening of the connectives connecting them in many snails is very pronounced. In this case, all the ganglia located under the pharynx, including the pedal ones, form a compact group.
Of the sense organs, in addition to the eyes on the front pair of tentacles of the head and a pair of head tentacles, which are important organs of touch, snails have developed organs of balance - a pair of statocysts, which are innervated from the cerebral ganglia, although they lie in close proximity to the pedal ones. Statocysts are closed vesicles, the walls of which are lined with ciliated and sensitive cells, and the cavity contains a liquid in which one large or many small grains of calcium carbonate float. The pressure exerted by calcium carbonate grains on one or another section of the bubble wall at various positions of the cochlea allows it to orient itself in space. Snails also have a chemical sense organ - osphradium, which lies at the base of the gill and serves to test the water that enters the mantle cavity. The second pair of head tentacles in land snails is the organ of smell. In addition, the skin of snails is rich in sensitive cells. Chemoreception is very well developed in gastropods. Specialized nerve cells of the tentacles, areas of skin near the mouth and osphradia provide remote recognition of food, return to a previously chosen place, a sense of the proximity of predators, such as starfish or brittle stars, by their smell.
The reproductive system of representatives of different subclasses of gastropods has a different structure. Among the snails there are both dioecious and hermaphroditic forms. In the latter, the structure of the reproductive apparatus is the most complex. Fertilization in most gastropods is internal. Spawning methods in gastropods are different. The most low-organized forms throw eggs and sperm directly into the water, where fertilization takes place. Some species wrap eggs in mucus, forming cords, cocoons, slimy shapeless masses. Such aggregations of eggs are most often attached to the substrate - algae, empty shells and to the bodies of other aquatic animals, buried in the soil of reservoirs. Terrestrial gastropods bury their eggs in moist soil or attach them to the stems and roots of plants. The development of gastropods is either carried out through the stage of the larva, which will be discussed later, or it is direct, that is, a small mollusk emerges from the egg shells with an incomplete number of shell turns and an undeveloped reproductive system. But in all groups of gastropods, along with direct development, live birth can also be found, when eggs develop in special sections of the mother's reproductive system. In other cases of direct development, the eggs, up to the hatching of juveniles, are hatched under the protection of a shell or mantle.
Let us now return to the cases of development of gastropods with the larval stage. In some, very few modern marine gastropods, a larva emerges from the egg - a trochophore, very similar to the larva of annelids. Trochophores are characteristic of the most simply organized gastropods (Patella, Gibbula). Free-swimming trochophores soon develop into the next larval stage, the veliger. In some gastropods, the trochophore stage passes inside the egg membranes and the veliger larva emerges from the egg, or, as it is called, the "sailboat". The larva received this name for moving with the help of highly developed sail-like lobes of the mantle, the edges of which are covered with cilia. In different species of gastropods, veligers spend different times in the water column and, therefore, are carried to different distances from the spawning site. The settling of larvae to the bottom is facilitated by chemicals secreted by other organisms, with which gastropods usually live, - cyanobacteria, corals, sponges, algae. These chemical signals perfectly demonstrate those complex relationships between different species, which are part of the biocenotic relationship. After the larva settles to the bottom, its metamorphosis occurs, i.e., the transformation of the larva into an adult mollusk. This is done by discarding the larval skin with cilia, and in other cases by discarding other parts of the body of the larva. By this time, the body of an adult mollusk has already been formed under the larval covers. There is evidence that metamorphosis is also stimulated by chemicals released by those organisms that are most characteristic in the habitual habitats of this type of mollusk.
Many marine species of gastropods are eaten by fish - herring, sardines, mackerel. As Lebour points out, these fishes especially strongly eat planktonic gastropod larvae. Other fish, such as gobies, kill adult benthic gastropods. Birds are also not averse to eating gastropods, especially various waders that live on sea beaches and near fresh water bodies are especially active. Terrestrial gastropods are eaten by thrushes and some other birds, from mammals - hedgehogs and moles, as well as reptiles. Often, gastropods are attacked by predatory beetles, tahini flies, and fireflies. The empty shells of terrestrial molluscs are used by flies and wasps to lay eggs. Sponges, bryozoans, sea acorns, hydroid polyps and other animals often use the shells of marine gastropods as a substrate on which their larvae settle. To date, there are different views on the taxonomy of the class of gastropods. The most natural groups of gastropods can be considered the following: subclass anterior branchial (Prosobranchia), subclass posterior branchial (Opisthobrauchia), subclass pulmonary (Pulmonata).
It is hardly possible to list all the anterior gills that are eaten by the population of the coastal regions of the countries of Southeast Asia, Africa, and South America. Many species, such as Littorina, Buccinum, Patella, etc., are still in great demand. Variegated graceful snail shells are used in the form of jewelry - beads, pendants. Cameos are cut out of them, moreover. colored hypostracum, dark brown in Cassis cameo, yellow in C. rufa, pink-red in Strombus gigas, stands out very effectively against the white background of the ostracum. Finally, Thochus shells are used as raw material for button production. All this, unfortunately, is associated with the destruction of a significant number of mollusks and leads to the destruction of natural communities.
SUBCLASS OPISTHOBRANCHIA The posterior branchial molluscs are significantly inferior to the anterobranch molluscs in a variety of forms, but still make up a group of gastropods that is quite rich in species. The most primitive representatives of this subclass retained in some respects their resemblance to the anterior gills. This similarity is expressed not only in purely external signs of the shape of the body or in the presence of a spirally twisted shell with a more or less elevated curl, but also in the anatomical features of the structure of the nervous system, gill apparatus, and other features. However, most of the posterior branchial species in the process of evolution deviated quite far from the original ancestral forms, which, as can be assumed, had typical features of the posterior branchial. The mantle cavity in posterior branchials, if present, is comparatively small and located on the right side of the body. The atrium lies behind the ventricle, while the ctenidium lies behind the heart (hence the name "posterior gills"). In very many posterior gills, the shell is overgrown with a mantle and undergoes reduction to one degree or another. In some forms, it is reduced to a small plate of irregular shape lying under the mantle, in others it disappears altogether. Only a very few, more primitive species have an operculum that closes the mouth. It is interesting to note that among testate posterior gills, the percentage of species with a left-curled (leotropic) shell is very high. The leg of many representatives of the subclass is modified very much. A number of forms are known in which the leg is extremely poorly developed, and in some it is reduced altogether. In others, on the contrary, the sides of the legs grow into wide pterygoid lobes, the so-called parapodia, which serve for swimming. The structure of the respiratory organs also undergoes drastic changes. Most often, skin outgrowths are located in various pestles of the body of the posterior gills - secondary gills that develop in place of the lost real ctenidia. Secondary gills are usually located symmetrically either around the anus, or on the sides of the back, or on the underside of a special thickening of the mantle on the back of the animal. In the posterior branchials, a common characteristic in the external shape of their body can be noted - some tendency to return to bilateral symmetry. This feature appears not only in pelagic forms, but also in forms that live on the sea floor and move by crawling, like other molluscs. The anus of some posterior gills is located on the midline of the back. In some species, the body is strongly elongated in length and laterally compressed, while in others, on the contrary, it is flattened in the dorsal-ventral direction and acquires a general external resemblance to the shape of the body of turbellarian flatworms. Some return to bilateral symmetry is also manifested in the structure of the nervous system: if in the primitive representatives of the subclass, closer to the anterior branchial, we still meet the crossover of the pleurovisceral nerve trunks typical of the latter, then in other posterior branchials this feature is hardly noticeable.
Of the sensory organs typical of mollusks, as a rule, there are balance organs (statocysts); the osphradium associated with the gill is found in representatives of the order of the angiobranchs, to which the more primitive forms of the subclass belong. Characteristic for posterior gills are areas of skin located on the head on the sides of the mouth with accumulations of sensitive cells, which apparently serve as organs of smell or taste. In a number of forms, the same functions are performed by sensory cells located on the posterior pair of head tentacles (rhinophores). As organs of touch, some posterior gills develop tentacle-like appendages on the sides of the mouth. As for the eyes, although they are developed in most posterior gills, they are of secondary importance in these mollusks and are usually covered by skin. The heart in posterior branchials consists of one ventricle and one atrium and lies in the pericardium. Only in one genus (Rodope) the heart is reduced. The unpaired kidney connects to the pericardial cavity, and its external excretory opening opens on the right side of the body or at the base of the gill. The sex glands are hermaphroditic, and the reproductive apparatus is more complex than that of the anterior gills. Sexual maturity usually occurs during the second year of life, and after reproduction, the posterior gills quickly die. Among the posterior gills, we meet both herbivorous forms and predators. Most animals have a well-developed radula, and in some, in addition, the mouth is armed with a ring of spines or numerous hooks. There are salivary glands and a digestive gland, the so-called liver, which in some posterior gills breaks up into many separate lobules. This organ serves to digest and assimilate food, the particles of which are captured by cells (intracellular digestion). In some posterior gills, the muscular stomach has hard, calcified plates on the inner surface, which serve to better crush food. Most of the posterior gills live on the sea floor, on sandy or muddy ground, and many are at the very edge of the water, so that at low tide they can be easily found among kelp beds or accumulations of hydroids. Species that usually stay on the bottom can, with the help of developed skin folds, rise above the ground and swim short distances. The posterior gills, which are part of the Pteropod order, are typical planktonic animals. Representatives of the posterior branchial subclass are widespread in the seas, with most species living in warm seas and temperate seas, but many of them are also found in cold zones, and several species have adapted to life in estuaries (Palau and Flores islands in Micronesia).
SUBCLASS PULMONATA Pulmonary snails are the group most deviated in the process of evolution from the common trunk of gastropods. All lung snails have adapted to life either on land or in fresh waters, and if some of their representatives are sometimes found in the seas, then only in highly desalinated areas. The shells of lung mollusks are most often spirally twisted and very diverse in shape - from tower-shaped or valky to disc-shaped. In a relatively small number of species, the shell has taken the form of a cap covering the whole body from above, like in snails living in fast-flowing rivers. In other species, this cap covers only a small part of the body and is a vestigial shell, as we see in many land snails. Finally, in terrestrial snails, we encounter cases of complete overgrowth of the shell by the mantle, sometimes accompanied by the complete disappearance of the shell. In species with a well-developed shell, it shows a clear spiral twist and is usually twisted to the right; however, there are groups of lung snails in which the shells are twisted to the left, and specimens with a right-handed shell are an exception. The shell opening usually remains open, since the operculum is preserved only in members of the family Amphibolidae. In a small ancient group of terrestrial lung snails of the Glausiliidae family, the mouth is closed by a special shell valve, the clausilium, which relies on a complex system of plates. Clausilium outwardly resembles the operculum of the anterior gills, but it is of a completely different origin. Another way to protect against adverse environmental conditions, for example, from drought or cold, is the tightening of the shell opening with a film of mucus that hardens in air containing calcium, the so-called epiphragmon. Between the film and the body of the snail, which is deeply drawn into the shell, there is usually a layer of air. The degree of reliability of the protection created in this way can be judged from the data of experiments during which garden snails were exposed to low temperatures. Under the protection of the epiphragm, the snails endured temperatures of 110 and 120°C below zero for several years, except for those specimens in which this fragment was cracked. In addition, there are known examples of land snails transferring free heat and drought due to this adaptation. Abundant and rapid secretion of mucus necessary for the formation of the epiphragm is facilitated by the so-called "teeth" of the mouth, especially characteristic of species living in arid conditions. In some species, the teeth are very numerous strong protuberances on the inner wall of the mouth, in others they look like thin and sharp plates extending along the inner wall of the whorl far into the depths of the shell. All these formations, when the body of the snail is drawn into the shell, press on the soft tissues and squeeze out the mucous secret that forms the epiphragm. When unfavorable conditions occur, aquatic pulmonary snails resort to clogging the mouth of the shell, which also close the shell opening with a layer of mucus with an air gap between it and the body; in such a way they sometimes even freeze into the ice and survive the winter without harm to themselves. Shellless land snails, the so-called slugs, are much worse protected in this regard. Severe drought, bright sunlight in the summer heat, and sharp cold make slugs seek shelter under various covers, for example, under a layer of fallen leaves, in cracks under the bark in rotting stumps, or hide between clods of soil, sometimes climbing quite deep into the ground; moisture is retained there and temperature fluctuations are less sharp. All pulmonary snails are characterized by smooth sliding movement on the soles of the feet in the front part of which there is a highly developed gland that secretes mucus. The latter wets the sole and protects its skin from damage, reducing friction on the hard surface of the substrate. The movement of the cochlea forward occurs due to the wave-like contractions running along the soles from behind to the front, due to the interaction of the longitudinal and transverse muscles. Moving forward, the mollusk usually extends its tentacles, using them as a sense of touch. In freshwater forms, the head is a gift of such tentacles, at the base of which, a pair of eyes is located. Land snails often have two pairs of tentacles, and some forms also have a third pair - tentacle-like appendages located at the edges of the mouth. The eyes of terrestrial are located differently than those of freshwater at the ends of the tentacles. Of the other sense organs, there are developed organs of balance - statocysts. Aquatic forms also have a poorly developed osphradium.
One of the characteristic features of lung molluscs, which determined the name of the subclass, is the respiratory organs and the transformation of the cavity into a lung. This occurs by fusion of the free edge of the hanging mantle with the cover of the anterior part of the body so that a small respiratory opening remains - the cneumostum, through which the mantle cavity communicates with the external environment; the walls of the cneumostome can close. The fusion of the mantle with the integument occurs at the early stages of embryogenesis, which indicates the ancient origin of pulmonary mollusks. On the arch of the mantle cavity, on the inside, a dense plexus of vessels is developed, into which oxygen enters by diffusion. The gill in lung snails is found only as an exception. Thus, terrestrial and freshwater pulmonary mollusks breathe atmospheric air, and therefore freshwater forms must from time to time rise to the surface of the water and take in air into the mantle cavity. The heart of pulmonary snails consists of one ventricle and atrium. The nerve ganglia are more or less clearly concentrated and form a ring around the pharynx. Among lung snails, we meet herbivorous, omnivorous, and predatory species. Predatory lung molluscs feed on other snails, sometimes worms. Pulmonary snails have a well-developed radula, while herbivorous snails also have an unpaired horseshoe-shaped jaw. The teeth on the plates of the radula are especially long and pointed, resembling the fangs of vertebrates in shape. The pharynx is well developed. The ducts of the salivary glands open into it. The digestive gland, the liver, flows into the muscular stomach. The intestine forms a loop, and the anus is usually placed near the inhalation opening on the right side of the body. Next to the anus is usually the external opening of the only kidney, which is connected to the pericardial sac (pericardium). Particular complexity in lung snails reaches the reproductive apparatus. The gonad is hermaphroditic. The common duct departing from it is then divided into male and female parts, both of which have a number of adnexal formations. The protein and shell glands, the seminal receptacle, and sometimes a number of other glandular appendages belong to the female part. The most highly organized representatives of the subclass have developed a complex male copulatory organ. Some species are characterized by the formation of spermatophores, i.e., special receptacles for the seed. When mating, both partners mutually fertilize each other, and the mating itself is usually preceded by a "love game". In some forms, during mating, special calcareous needles penetrate into the partner's body - "love arrows" that serve for sexual arousal. They are formed in special sections of the reproductive system - bags of "love arrows". Lung snail eggs are laid either in a common gelatinous cocoon of one form or another (freshwater species), or separately, although in a common clutch (terrestrial species). Each egg is surrounded by a significant supply of nutrient material, and in some forms the ratio of the mass of the egg to the mass of the protein surrounding it is 1: 8000 (in Limax variegatus). Development proceeds without the stage of a free-floating larva; an almost formed snail emerges from the egg. Lung snails are divided into two orders.
The sea limpet is a typical inhabitant of the surf zone of the Far Eastern seas. It is found on coastal stones and rocks, sticking tightly to their surface, usually in shallow recesses and crevices.The shell of the sea limpet consists of one leaf, spirally curled to the right or left side, and on its surface, also spirally wrapping around, there are clearly distinguishable growth lines. As a rule, their number does not exceed twenty, according to which one can judge the probable age of the mollusk. The shape of the shell can be very diverse: slightly flattened, with the tip shifted to the side, or, conversely, towering regular pyramid...
In general, this mollusk is characterized precisely by a simplified symmetrical shell, having the shape of a cap or a saucer turned upside down, which is why it got its name. True, it is a stretch to call such a shell a saucer, well, if only it served in this capacity some tiny sea bird, for example, a storm-petrel. Despite its apparent fragility, the shell of the sea limpet is very strong and is able to withstand the incessantly oncoming stubborn waves, not being afraid of the strongest surf.
Of course, the shape of the shell of the sea limpet is rather primitive, and yet these mollusks attract attention precisely by the simplicity of their house, which seems very charming and secluded. Stubborn waves are unable to knock these shells off the coastal stones, sea water, as if angry at the recalcitrant inhabitants of the coastal strip, flows freely from their smooth conical walls, and the tops of the shells are sharply pointed, despite everything, always set to grow. It makes you want to tear off the sea saucer from the rock and look - what is inside it?
Whether the tide is approaching, whether the tide is ebbing, outwardly the saucers do not react in any way to what is happening and from the side they look completely indifferent to everything beings, even lazy. This is their original habitat, where they live, firmly attached to the coastal rocks, it seems, from time immemorial. Cone-shaped shells with bluish-gray, beige and cream tops are pressed against the stones so tightly that it is impossible to squeeze a knife blade between them. Even when the rocky surface turns out to be rough and uneven, the edges of the shell also become uneven and jagged, following all the irregularities of the stone, which gives the mollusk the opportunity to cuddle tightly.
When a mollusk is disturbed, it clings to the stone on which it sits with great force, and in order to overcome the suction force of this ordinary small shell, it is necessary to drive a sharp iron object between the shell and the stone. Then, acting as a lever, one should try to separate the mollusk from the stone, from which it most often breaks: the stuck foot remains on the stone, and the shell with the mantle and entrails comes off. But if the mollusk sits with its shell raised so that its head and lateral parts of the body remain open, then a light blow is enough for the saucer to separate from its place of attachment.
For a long time it was considered incomprehensible how the limpet is attached: whether it is glued by the secretion of special glands, or is held solely by the shell muscle. Now it is already known that at first, indeed, mucus is secreted from the many skin glands of the sole of the foot, which serves to fill small gaps between the sole and the stone, and after that the shell muscle begins to act with all its strength, the annular shape of which is only disturbed in front by a small notch, thanks to to which it resembles a horseshoe. The muscle tenses with each wave of the surf, and also at all the time of low tide, while the mollusk is exposed to sunlight.
Previously, there was an erroneous judgment that, due to the very strong attachment to the rock, the sea saucer allegedly never changes its place. However, it turned out that the mollusk still travels, however, only at night. It is remarkable that, moving in a certain way always to the left, he eventually returns to the starting point of his path and strengthens himself in the old place in the same way as he sat there before. The mollusk is helped by a uniform deviation from a straight line when moving, and its orientation in the boundless sea space is limited to just a meter!
The sea limpet is very attached to its place of residence. It turns out that only if the place where the mollusk lives has undergone fundamental changes during his absence, he decides to look for a new one and in no case settles anywhere. When choosing a more convenient place, the mollusk is guided by the need for air sufficiently saturated with water vapor, and therefore prefers crevices in stones, especially their shady side. But what forces the sea saucer to travel, and even at night?
Night wanderings of the sea limpet serve mainly to satisfy hunger, and it is less safe to do this at night. During its movement, the mollusk eats the surface of the rock, and the gnawed strip betrays its path, because all the time while the animal is crawling, its radula, which is thick, strong blades - an excellent scraping tool, is constantly in action. The mollusk feeds on various microorganisms that grow on rocks, and along the way, small plants, such as ulva and fucus, but he does not look for them on purpose, eating mainly everything that he can shave along the way from the surface of the stone with his radula. Its strong teeth are quite suitable for their purpose in the surf rocky zone, but this work, however, leads to extremely rapid wear of the tool, and when it is completely erased, the mollusk dies from the inability to feed, after which its shell falls off, replenishing the empty shell rock near the surf, where imperceptibly frayed by waves in the sand.
But along the shores of the Sea of Japan and the Sea of Okhotsk there are so many saucers, and scientists have found at least 11 species of them here, that you can not be afraid: this mollusk will never be transferred. The largest of the sea limpets, the pale acmea, is found off South Sakhalin and the South Kuril Islands. Its strong, thick-walled, almost snow-white shell reaches 6-8 centimeters in length.
When such a shell, already without a mollusk and carefully licked by the sea, falls into your hands, you want to weigh it in the palm of your hand, run your finger along the smooth inner walls, in the end not knowing what to do with it next? But you can’t immediately get rid of the shell, and again you begin to turn it in your hands, examining and admiring it, until you take it away as a keepsake, in order to then give it to some person you know well. I remember that I collected a great many of these saucers, because they all attracted with their shape or color, and I stopped in my hobby only when I realized that the shells began to repeat each other. Many of them are now in my closet, behind glass, and sometimes for some reason I touch their cool sides or even pick them up, regretfully returning them back. You won’t believe it, the saucers still quietly emit a light hum of the rolling surf, and it seems to me that they don’t worry at all that I deprived them of their beloved Sakhalin coast ...
And again, the indented island shores with deep ravines and black rocks, sandy spits and underwater ridges, densely covered with sea saucers are recalled ... For some reason, small conical shells made of fragile limestone always made me timidly want to smile. Maybe because they staunchly resist the stubborn surf, and also resemble the so-called “Chinese hats” made of straw, with the help of which Chinese and Japanese fishermen usually save themselves from the sun while working, and shellfish from numerous enemies. Thanks to the akmei, tightly clinging to wet stones, industrious Asian inhabitants arise in your memory, but when you see the Japanese or Chinese in straw hats, graceful shells of sea saucers that live near the sea appear before your eyes. The reason for this is probably the surprisingly similar forms, and the fragile charm of the lines, containing a sensitive laconicism of ordinary natural truth, which does not seek to embellish itself, but only wants to defend itself. In a word, something very touching is contained in sea saucers, which cannot be explained.
Other acmea shells are so expressive in their color that at first you even mistake them for sea snails or littorinas: in the very middle, at the top, they have bluish specks-shimmers, bordered by delicate greenery, reminiscent of algae thrown out after a storm. Surprisingly discreet and affectionate combination of these colors seems to even enlarge the shell, making it more alive. The mollusk itself is not visible, but its house is distinguished by grace, and therefore the owner of this house is also perceived as graceful and sweet. A small, pea-sized mollusk, judging by its habitat, lives in it quite reliably and joyfully, like a magical pearl.
The gentle name of the shell is acmea, and its neat appearance, decorated by nature, evokes a no less touching phrase - cameo ... Decoration made of stone with artistic carving and a convex image, more often it is onyx or agate ... And sometimes, oddly enough, an elegant cameo evokes memories about the sea, at the sight of the acmea itself, sensitively attached to a wet stone, one recalls an exquisite jewel, without which it is impossible to imagine a reverent attitude to any beauty. The beauty of the sea carries many priceless surprises, and all of them make up its mysterious, enchanting bliss. The sea itself is an unsurpassed blue pearl framed by red, black and grayish-green coastal granite.
More often, however, acmea remains unobtrusive, completely invisible, well, if only you pay attention to it at low tide, when shells and stones that have not yet dried out shine with their true colors. Having in its very middle, at the top, a bluish-smoky coating, which also appears as a radiant lake surrounded by dark rocky shores, acmea, in miniature, resembles the sea that gave birth to it. But then a light breeze from an unknown land will fly in, dry the shell, and it will close again, becoming completely inconspicuous. Who will pay attention to this low-key beauty now?
I always liked to note for myself these inconspicuous manifestations of marine life, to look at them and remember them. So I once met Acmea, at first not knowing what this neat, elegant shell is called, and when I heard its unusual, even for the sea, name, I rejoiced even more from the overwhelming joy of being close to the sea world. What is not hidden in it, and here, please, such an inconspicuous and touching reality - akmeya! Something airy, but also strong, inseparable from the gloomy stone shores, in a word, subtle and strict. Akmeya… Enchanting underwater dreams, the dream of an unknown mollusk lulled by sea waves, its unchanging commitment to unbending rocks…
Although the acmea shell is fragile and elegant, it is not easy to separate it from these unyielding, gloomy and wave-beaten boulders. Acmea itself resembles a sea pebble, nestled comfortably in some crevice, and I never had a desire to deprive the shell of its habitat. Only once I tried to separate with an underwater knife one of the shells with a blue top that I liked, but I almost broke the tip of the blade while I tore off several mollusks, a good half of which I simply crumbled: the shells were firmly attached to the stones, and it was better to pick up the already detached, empty ones, than disturb the living. True, the old limestone houses already looked unattractive, they were mostly dirty gray in color, and only after a long time the sea had run in became snow-white, and the shape of the shells still remained conical, elevated, as if rushing, no matter what, to something unattainable and beautiful.
In general, in the sea I constantly had the feeling that it knows everything about me, knows that I will never forget about it, and someday I will write about its currents, fogs and winds that live in the depths of animals and mysterious thickets of algae, I will mention , of course, and about stones, especially about shells. The shells and stones in some unimaginable way felt me, did everything so that I would find them at any suitable moment, and even if I didn’t take them with me, I would definitely consider them, picking them up, then carefully returning them to their place. Everything that surrounded me in the sea and next to it was alive, it radiated its invisible energy, which I guessed with an inexplicable instinct, and from this mutual understanding with your native element, life became even more joyful.
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Sea saucer
marine gastropod molluscs with cap-shaped shells and the ability to stick with their feet to a solid substrate, which combines them into a special life form. To M. b. include representatives of the family Patellidae, Tecturidae (subclass of anterior gills, more precisely roundbranchs), Siphonariidae (subclass of pulmonary), etc.
Wikipedia
Sea saucer
Sea saucer- a common name for various salt and fresh water snails (aquatic gastropods). It refers to snails with a simple shell, usually conical, not coiled.
Sea limpets are most commonly referred to as members of the clade, true sea limpets found in sea basins; however, conical shells arose during the evolution of gastropods several times in various clades with gill and pulmonary respiration. The name is associated with the characteristic "saucer-shaped" shape of the shell. Many mollusks that have such a shell belong to different taxa:
- Heterobranchia, a group of Opisthobranchia for example
- Heterobranchia, Pulmonata group e.g. Siphonariidae, Latiidae,
For example
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A study of limpet teeth has revealed that they are the most durable biological structure known.
Teeth common type of mollusk sea limpet (Patella vulgata) stronger than Kevlar and stronger than spider silk, scientists report in the February 18 issue of The Royal Society Journal.
Saucers are hardy little molluscs that are ubiquitous in our planet's oceans. Their conical shells protect the leg, with which they are attached with incredible force to underwater rocks. Saucers feed on algae, releasing a long tongue studded with hundreds of sharp teeth that scrape food particles from rocks.
A research team from the University of Southampton, England, led by professor of mechanical engineering Asa Barber, studied microscopic fragments of the teeth of this mollusk. Each curved tooth is about 1 millimeter long and about 100 times thinner than a human hair.
The secret to these teeth's strength lies in the size of the fiber structures that form them, Barber says. As long as the dimensions of these fibers are below a certain critical length, their strength remains unchanged, even if their material contains defects. They themselves are a biological composite of goethite (mineral iron oxide) and chitin, which plays the role of natural plastic.
As a result of this combination, teeth made of this material withstand a load equivalent to 1,500 kilograms, suspended on a thread as thick as spaghetti.
The scientists' next task will be to reproduce the mechanism by which the saucers create these unique materials. And while spider silk has proven incredibly difficult to mimic in artificial conditions, the researchers believe that the fibers of the limpet teeth can be 3D printed.
Spider silk is one of the most durable natural materials. Its fibers have a specific strength five times that of the best steels, and yet they are free to stretch. The strongest known silk is produced by Darwin's tree spiders, which are found in Madagascar - their silk is 10 times stronger than Kevlar. To put things in perspective, the mineral teeth of the saucer are about 10 percent stronger than this silk.