Сбор, диагностика и обработка палеонтологических материалов при проведении учебных геологических практик. Учебное пособие на модульной основе

4. The system of the organic world

developed nervous system. Cephalopods appeared in the Late Cambrian. They are of the greatest importance for the dissection and correlation of Mesozoic sediments.

Currently, there are forms with an external and internal shell. Modern forms with an internal shell – squid, cuttlefish, octopus.

Modern forms with an external shell are represented by only one genus – Nautilus.

In addition to the position and structure of the shell, organisms differ in the number and structure of the arms, as well as the number of gills. Two gills and about ten long arms with suckers in organisms with an internal shell and four gills and many short arms without suckers in forms with an external shell.

Most cephalopods lead a nectonic lifestyle. All of the above distinctive features, as well as the structure of the radula, the presence or absence of an ink sac, serve to distinguish cephalopods into two subclasses: Ectocochlia (ectocochlians) and Endocochlia (endocochlians). The function of the pseudoskeleton of the endocochlians is performed by the rostrum.

Ectocochlia subclass.

The shell is bilaterally symmetrical, spirally folded. It consists of several whorls. The soft body of the animal is placed in the final part of the shell (the living chamber), occupying 1/3 or 1/2 of the last whorl.

The internal whorls are divided by concave, slightly wavy or sinuous septa partitions into numerous chambers. The sum of all the cameras is a phragmocone.

The chambers closest to the residential are called hydrostatic and filled with liquid, and the rest are air and filled withgas.

At the anterior end of the soft body there is a head section with many short tentacles that serve to capture prey and transfer it to the mouth. In males, the number of tentacles reaches 65, and in females – more than 100. The mouth is equipped with a radula and jaws. Next to the tentacles on the abdominal side of the animal there is a muscular funnel tube through which water is forcefully pushed out of the gill cavity and the animal acquires a forward movement in the opposite direction.

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The partitions are attached from the inside to the walls of the shell, the contour of which forms a partition line on the core – the line of attachment of the partition. One of the most important signs is the structure of the blade line. In ammonoids, in contrast to all other subclasses, the partition had a corrugated edge, which means that the line of its attachment to the shell had a more complex pattern (Rostovtsev, Stankevich, 1965).

The elements of the line directed backwards were called blades, and forward (in the shell) – saddles. There are four main types of blade lines: agoniatite – with rounded saddles and rounded blades; goniatite – with solid rounded saddles and solid pointed blades; ceratite – with solid rounded saddles and serrated dissected blades; ammonite – with dissected saddles and blades. In the Late Cretaceous epoch, some ammonites have a simplification of the lobed line and a return to the ceratite type (pseudoceratites).

The change in the evolution of the lobed lines of ammonoids is an example of the law of irreversibility of evolution, formulated by L. Dollo in 1893.

Currently, the division of cephalopods into ectocochlians and endocochlians is biased, since similar structural features have been found (Bondarenko et al.). There are seven independent subclasses:

1.Nautiloidea (Late Cambrian – now).

2.Orthoceratoidea (Ordovician –Triassic).

3.Endoceratoidea (Ordovician).

4.Actinoceratoidea (Ordovician-Middle Carboniferous).

5.Bactritoidea (Devonian – Permian).

6.Ammonoidea (Devonian – Carboniferous).

7.Coleoidea (Carboniferous -now).

Organisms of the fifth subclass gave rise to ammonites and belemnites, which are of great importance for biostratigraphy. It was according to the ammonoidea that the eons were distinguished – the most fractional divisions of the stratigraphic scale.

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Characteristics of the Gastropods class. Classis Gastropoda.

So, gastropods. There are about 100 thousand species of them in the seas, on land and fresh waters. Usually their representatives hide their bodies in spiral shells. Only a few have all the spirals lying in the same plane (rolled up like a clock spring). Most shells are conical (turbospiral).

A head and a foot stick out of the shell of a calmly crawling snail. The latter with a wide flat sole. Its muscles undulate from front to back and thus slowly propel the snail forward. (This is especially clearly visible if you put a snail on the glass and look at it from below).

Note briefly that in some marine swimming gastropods, the foot can be stretched down in the form of a fin. Swinging it briskly from side to side, such a finfooted, as it is called, a mollusk swims forward. In other, wing-footed mollusks, the foot has expanded to the sides, turning into wide blades like wings.

The head is clearly separated from the body. It has a mouth on the bottom, one or two pairs of tentacles on top, which are commonly called “horns”. One pair of tentacles has one eye on each.

The body of the snail itself is placed behind the head, above the leg, and is twisted spirally in proportion to the whorls of the shell.

In some snails, the hole of the shell (mouth) is firmly closed, when necessary, with a opercle – this is a round, just the size of the mouth, a calcareous plate sitting on the foot from behind, on its upper side.

Snails usually feed on plants, but there are predators among them. There is a lot of sulfuric acid in the saliva of predatory gastropods.

The acid is so strong that when it hits the marble, it hisses and bubbles. The acidic secret serves these predators to locally dissolve the shells of other mollusks or the shells of echinoderms that they feed on.

The bite of some predatory sea snails is even poisonous. In the “cone”, for example, the teeth of the radula are so large

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that they look like teeth. Moreover, like the teeth of many snakes, they are pierced from the base to the end by an internal channel through which venom flows, which gets into the wound when bitten and causes severe inflammation even in humans (Akimushkin, 1992).

Many land snails easily tolerate both cold and intense heat. In the Sahara, when the heat is up to 70 degrees, snails, for example, of the genus Teba, do not die, they remain viable. They cover almost entirely dried grasses and branches of bushes,in some places just lie motionless on hot stones, tightly pressed together. They come to life only at night, when the heat subsides.

The ability to temporarily fade is explained by extreme examples of Gastropoda endurance, such as the revival of several Helix desertorum specimens, which had previously been glued in one of the demonstration boxes of the British Museum for 4 years (Akimushkin, 1992).

Snails resort to “temporary fading” – to dormancy: winter in the north and summer in the South – in extreme conditions. They burrow into the ground, plug the mouth with an additional plug of frozen mucus, which often does not touch the first lid tightly. The air enclosed between them is an additional heat insulator. In some snails, the shells are covered with a film, similar to a hair pile. It also protects the animal that has fallen into a dormancy from hypothermia. That is why land snails live even in the far North: in Greenland, for example, there are five species.

Gastropods have digestive, circulatory, nervous, excretory systems. Breathing is carried out either by the gills or by the lungs. Animals are diclinous.

The structure of the shell. The shell of the gastropods is externally covered with a periostracum or corneous layer. The shell itself is aragonitic, less often calcite. Some gastropods retain an inner nacreous layer.

There are two groups of shells – wrapped and mitriform. Wrapped shells are the most diverse. They can be symmetrical (less often) or asymmetrical (more often). In symmetrical shells,

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the initial coils are located in cone-shaped recesses covered by subsequent coils. Usually these are pelagic, free-floating forms. Asymmetrical shells form a whorl of different heights, consisting of separate coils. The last coil of the spiral is called the actual coil.

In many modern gastropods, the shell is reduced. Thus, in some predatory pelagic gastropods, the shell does not perform protective functions; it plays the role of a keel and facilitates swimming. Many terrestrial gastropods are also devoid of shells.

Gastropod shells have an opening (mouth or aperture) through which communication with the external environment occurs. It is diverse in size and shape. In some genera, there is a cutout for the passage of a siphon at the edges of the mouth, through which water is supplied to the gills. Sometimes the mouth is closed with a lid.

For adult individuals of gastropods, which are in strictly defined conditions, the constancy of the size of the shell is characteristic. But with the change of living conditions, the size of the shell also changes. For example, the size and thickness of the shells of limnetic gastropods living in the river heads is much smaller than the shells of gastropods living in the lower reaches. This is due to the different temperature of the water. Also, gastropods that live in shallow water are larger than deep dwelling ones. There is also age variability.

Wrapped shells are most widely developed in gastropods, with right-turned shells predominating. The general outline of the shell mainly depends on the nature of the whorls.

Reliable representatives of gastropods have been known since the Cambrian, although their more ancient origin is not excluded. Currently, they are experiencing a real flourishing, which began at the end of the Mesozoic – the beginning of the Cenozoic and was associated with the transition from the marine environment to free-salined and terrestrial.

For adults,a bottom way of life is common, in the larval stage, gastropods are suspended in water (plankton).

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Despite the fact that gastropods inhabit different parts of the sea in depth, they are extremely sensitive to the type of coast and the nature of the bottom topography. Genera, in which the peculiarity of the sculpture of the shell allows to resist the currents live on the sandy bottom; predatory gastropods settle on the muddy shores.

Gastropods, breathing through lungs, exist at a wide variety of temperatures (from Greenland to the Sahara). Moreover, the largest ones are found in tropical areas, which is explained by the fact that in the seas of this belt, the rate of precipitation of calcite, the main material for the construction of the shell, increases. A decrease in temperature leads to a decrease in the size of the shell. But on the other hand, in warm seas, gastropods are diverse in the number of genera and species, with a small number of individuals of the same species and vice versa in cold waters.

Gastropods are used to determine the age of Mesozoic and mainly Cenozoic sediments, they are also an excellent indicator of the paleogeographic stop of previous geological epochs.

Characteristics of the Bivalve class. Classis Bivalvia.

Bivalves are often called shells. They live only in the aquatic environment – seas, rivers. The class has about 20 thousand species. This class includes mollusks with a shell consisting of two symmetrical halves, or flaps. These are sedentary, sometimes completely motionless animals that live at the bottom of seas and freshwater reservoirs. Often they burrow into the ground. The head is reduced. In freshwater reservoirs, swan mussels or pearl shells are widespread. Of the marine forms, oysters are the most important. Very large species are found in tropical seas. The shell of a giant tridacna weighs up to 250 kg. Bivalves are characterized by the presence of a shell of two flaps, a wedgeshaped burrowing foot and the absence of a head. In nonmotile forms, the foot is reduced. The shape and size of the bivalve shells vary greatly.

The flaps of the shell are connected on the dorsal side by a ligament – ligament consisting of a thickenedcorneous layer

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of the shell. Most species have a lock on the flaps of the shell. These are teeth and cavities on the dorsal edge of the shell from the inner surface. The flaps of the shell of a live mollusk can open and close. For this purpose, the closing muscles serve.

At the end of the leg, most of them have an acetic gland, which emits sticky threads that harden in water. They attach them to rocks or other underwater objects. They were used in Ancient Rome to make expensive fabric – byssin (Akimushkin, 1992).

Bivalves are the only class of mollusks that does not have a lingual ribbon or radula – a special muscular tongue with chitinous teeth. The method of obtaining food is related to how and what bivalves breathe. All representatives of the class have gills that filter simultaneously with breathing.

According to the method of nutrition, this class of mollusks is a filterer. They pass water with suspended food particles through them. Some mollusks of this class are able to drill holes in rocks or wood, using either the shape of a shell or releasing acid. Bivalves are the main producer of pearls.

Project specification for the material

In accordance with the goals and objectives of paleontological research, select representatives of Mollusca-type fossils (Mollusks) from the reference collection. Phylum Mollusca.

Make reference collections: Bivalve class, Gastropod class., and Cephalopods class. Identify their main differences and similarities.

Questions for self-control

1.What determines the importance of mollusks as the most important group of fossils, even though they are inferior in number to arthropods?

2.Which of the classes of mollusks is the most numerous?

3.Can the size of the gastropod shell change when conditions change?

4.What does the radula serve for gastropods?

5.How do predators of the gastropod class (Rapana Schumacher) destroy the shell of their prey?

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6.What were the shells of the gastropod Monetaria annulus (Cowry) used for in North America before 1786?

7.What sharply distinguishes the mollusks of the cephalopods class from others?

8.What is the shell of most modern cephalopods?

9.How many hearts do cephalopods have?

10.What is the main significance of cephalopods in geology?

4.1.6. Echinoderms type Echinodermata. (Greek echinos – hedgehog; dermatos – skin)

Characteristics of Echinozoa subtype. Subphylum Echinozoa

Echinoderms are multicellular three–layered secondarydeuterostomatous animals that live in marine basins. Modern forms live mainly on the bottom, some have adapted to a pelagic lifestyle. These are starfishes, sea urchins, sea lilies, as well as holothurias and brittlestars. Distinctive features of this type are the five-beam symmetry of most representatives and the presence of an ambulacral system. The five-beam symmetry is most clearly manifested in starfish, although in exceptional cases the number of beams increases sharply, reaching 50. The ambulacral system is a system of channels that ensure the performance of various functions: movement, breathing, sense of touch.

The skeleton of modern echinoderms is internal, it has a mesodermic origin and is covered with skin on top. This is either a solid shell (sea urchins) or a calyx (sea lilies), often equipped with a stem and arms (brachioles); in starfish, the skeleton consists of separate scattered elements, in holothurias – of formations similar to spicules. Often there are additional spikes and needles, especially characteristic of sea urchins. The composition of the skeleton is calcareous with an admixture of magnesium carbonate and calcium phosphate. All elements of the skeleton (plates, needles, segments of the stem, arms) have the same crystallographic properties. They, like a calcite single crystal, usually split along a rhombohedron – a hexahedron with beveled parallel planes.

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Further, a feature inherent in all echinoderms is the radial plan of the structure, usually a multiple of five. Both the ambulacral system, and the nervous, and circulatory, and some other organs have a many-fold five-beam plan of structure.

Finally, the skeleton. Unlike all other invertebrates, it is internal (calcareous) in origin and arises from a tiny, “barely noticeable under the microscope, a grain of calcium carbonate” that lies inside the skin cell. This grain grows over time, comes out of the cell that gave birth to it and now lies in the intercellular space in the form of a three-beam plate. Its rays ramify, connect with other similar branches, the edges of the overgrown plates merge and form a sufficiently strong shell or “a more or less loose or dense network, or connect to each other like vertebrae”. However, the holothurians have a different skeleton: separate small plates scattered in the skin.

As the name shows, the skin of echinoderms is armed with needles and tubercles of different lengths. And starfish and urchins on its surface have something that none of the other animals also have – pedicellaria formed from a needle. These are a kind of small pliers or tweezers, driven by special muscles. They sit on movable legs (in sea urchins) and are able to grab some small creature, alternately leaning towards each other, transfer it from one pedicellaria to another, located closer to the mouth, and thus, as a relay, deliver the caught prey directly into the mouth of the urchin. In some urchins, they also work for defense: they are endowed with a poisonous gland, and then the “bite” of these tweezers is unsafe for not very large enemies (Akimushkin, 1992).

The sizes of echinoderms vary considerably: from minimal (about 1 cm) in brittlestars, starfish and “microscopic” sea lilies to giant (about 1 m) in starfish, and the maximum sizes of echinoderms (up to 20 m) are known in some Mesozoic fossil sea lilies, which had a very long stem and long ramified arms.

Usually, the characteristics of echinoderms are illustrated by the example of starfish. But for paleontologists and geologists,

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sea lilies and sea urchins are more important, since they have a dense skeleton and therefore are preserved in a fossil state.

Ambulacral (Latin ambulacrum – a place for walking, walking) system consists of a rocky, annular and five radial channels, from the latter ambulacrums with small ampoules at the base grow away in two directions. In the intervals – the interradii – polian vesicles are attached to the annular channel, serving as a container for the reserve liquid. They are capable of greatly stretching and contracting.

Unlike the digestive system, which has an inlet (mouth) and outlet (anus) openings, the ambulacral system is blind and communication with the external environment occurs through the madreporic plate, or madreporite. This plate is sieve-shaped, it is located on the upper side of the sea urchin near the anal opening. Through the madreporite, water enters a vertically positioned channel with calcified walls (a rocky channel). This is followed by an annular channel, radial channels radiate from it along the radii, and polian vesicles radiate along the interradii.

The ambulacrums are tubes capable of significant stretching (and extension), compression (and shortening) and suction. Stretching or compression of the foot is coordinated with the help of additional small “reservoirs” – ampoules, and suction cups are often present at the outer end of the foot. The total number of ambulacrums may exceed a thousand.

The circulatory and nervous systems also have a radial plan of structure. Echinoderms live in marine pools, reacting sensitively to changes in salinity. Therefore, they are diverse and numerous only in our northern and eastern seas, whereas only small relict forms are rarely found in the Black Sea, only one species is generally known in the Baltic Sea, and there are no echinoderms in the Caspian Sea. As an exception, there are forms that have adapted to exist at both low and high salinity.

The depth of habitat varies from littoral to abyssal, previously echinoderms inhabited mainly the bottom of reservoirs, currently they are one of the main elements of the bottom fauna. At the

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